Renishaw touch-trigger probing technology

Renishaw touch-trigger probing technology
The presentation explains how Renishaw designs its touch-trigger probing systems, providing comparisons between various Renishaw’s solutions. Rugged and flexible solutions for discrete point measurement on CMMs Issue 2

Questions to ask your metrology system supplier
Are my measurement applications best inspected with discrete points? if so, should I use a scanning probe or a touch-trigger probe? Will I benefit from the flexibility of an articulating head access to the component sensor and stylus changing What are the lifetime costs? purchase price what are the likely failure modes and what protection is provided? repair / replacement costs and speed of service These questions were the conclusion of the CMM inspection fundamentals presentation. These should be considerations for any potential user of a touch-trigger probing system. Throughout the rest of this presentation, touch-trigger probing solutions should be considered in light of these fundamental business needs.

Renishaw touch-trigger probing - our objectives
robustness compact and rugged crash protection extended operating life flexibility probe changing stylus changing articulation cost effectiveness innovative hardware simple programming for lower running costs robust designs and responsive service for lower lifetime costs Renishaw provides an unrivalled range of touch-trigger probing solutions based on innovative design of each element of the system: Sensors - Renishaw touch-trigger probes are compact and rugged, enabling them to be applied to any discrete point measurement task. Many include solid-state switching for greater operating life, whilst all include features to help protect them from damage in the case of mis- programming or mis-handling. All Renishaw probes provide repeatable point measurement. Articulating heads - provide flexibility and automation, whilst reducing measurement cycle time, since indexing is quicker than stylus changing. Due to the lightweight sensor design, heads can themselves be compact and light, thus minimising dynamic loads on the CMM. Probe and stylus changing - providing flexibility and optimisation of sensor choice for each measurement task, reducing the need for clumsy stylus clusters. This improves measurement accuracy and allows components to be measured on smaller, and hence less expensive, CMMs.

Renishaw touch-trigger probing systems
Touch-trigger probe applications Metrology of trigger probes Trigger probe design The main topics in this presentation are: Touch-trigger probe applications - where touch-trigger probes are most appropriate and the characteristics of Renishaw touch-trigger probes that make them well suited to industrial measurement applications. Metrology of trigger probes - key factors that govern the performance of touch-trigger probes. Trigger probe design - a closer look at key features of Renishaw touch-trigger probes, explaining how these benefit measurement performance. Each of the main kinematic trigger probe technologies - resistive, strain-gauge and piezo - are reviewed. Articulating heads - indexing and servo solutions for trigger probing on CMMs that provide flexible access to the part, focussing on key design features. Probe and stylus changing - solutions that increase probing flexibility - key features that ensure a reliable and cost-effective product. Articulating heads Probe and stylus changing

Probing applications - factors
Manufacturers need a range of measurement solutions. Why? machining processes have different levels of stability: stable form : therefore control size and position discrete point measurement form variation significant : therefore form must be measured and controlled scanning How stable are your manufacturing processes? In general, you should measure your components only as often as required to ensure the stability of your manufacturing processes. In reality, this involves focussing on key features on your components - those that are critical to its function - to work out the best process control strategy. Your choice of manufacturing technique for these features will be a critical factor in the choice of process control method: If, for example, you machine a critical bore with a process that reliably produces features with good form, it's size or position may vary. In this case, control of the size and position will be important, but not control of the roundness or cylindricity. By contrast, if you use a machining process that produces features with significant form variation (i.e. the variability of the form is a significant proportion of the form tolerance), then understanding form errors will become important.

Probing applications - factors
Manufacturers need a range of measurement solutions. Why? Features have different functions: for clearance or location form is not important Discrete point measurement for functional fits form is critical and must be controlled Scanning Features that have functional fits Some features on your components will need to mate with other parts for your product to work correctly. In many cases, the form or profile of these features will be critical to the functional fit. This is where scanning is the ideal measurement technology Other features Most of the features on your parts will not have such exacting tolerances. Many will be clearance holes, location features or drilled holes. In these cases, measuring discrete points might be the best approach, since it can be faster and simpler than scanning such features, and it avoids excess stylus wear The pragmatic approach Typically you will want to use a combination of scanning and discrete point measurement to control your production processes. On most parts, there will be some features that you want to scan, whilst many others can be controlled by discrete point measurement This practical approach will give you the right amount of information for control, without incurring unnecessary measurement time and expense. Measured values Best fit circle Maximum inscribed (functional fit) circle

Discrete point measurement
Ideal for controlling the position or size of clearance and location features Data capture rates of 1 or 2 points per second Avoids stylus wear Touch-trigger probes are ideal lower cost, small size and great versatility Scanning probes can also be used passive probes can probe quickly active probes are slower because the probe must settle at a target force to take the reading The majority of features on a part are likely not to require tight tolerances for the proper function of the component. Where a feature has a clearance fit or where it is used just to locate the part, then only simple parameters such as size or position need to be controlled Typical features that fall into this category are drilled or tapped holes, holes that carry fluids (e.g. coolant holes), clearance holes and non-mating surfaces Discrete point measurement is an effective way to measure these types of features. This involves locating a small number of surface points quickly, which define each feature (typically four points for a bore, for instance). It is fast, simple and flexible, and provides an accurate assessment of feature size and location Taking discrete points also minimises stylus wear, since the stylus usually approaches the surface on a normal vector, rather than being dragged over the surface during scanning Both of the two main types of CMM probes can be used to measure discrete points: Touch-trigger probes are the simplest form of sensor for CMMs. They are ideally suited for discrete point measurements and have the advantages of low cost, small size and great versatility. However, they are not the best choice for high point density scanning or digitising applications. Scanning probes can also be used to acquire discrete points at a similar rate to touch-trigger probes if extrapolate to zero routines are used. Furthermore, scanning sensors provide the extra flexibility of scanning and digitising. If a high proportion of the features will be measured with discrete points, then the speed of single point data capture is critical.

Discrete point measurement
Speed comparison The movie clips show discrete point measurement using both touch-trigger and scanning probes. With appropriate discrete point measurement routines, scanning probes can measure points at a similar rate to touch-trigger probes, governed mainly by the dynamic capabilities of the CMM. Active sensors tend to be slower at discrete point measurement since they have to settle at the calibrated force and ‘static-average’ to take the reading. Of course, scanning probes can provide far higher data capture rates than touch-trigger probes when scanning. Touch-trigger probes are ideal for high speed discrete point measurement Scanning probes can also measure discrete points quickly, and provide higher data capture rates when scanning

Touch-trigger probing operation
Trigger probes measure discrete points... a trigger probe is in one of two states: seated when the stylus is not in contact with the part unseated when the stylus is touching the part a trigger signal is generated when the probe changes from seated to unseated the trigger signal latches the machine position to record the location of the surface feature geometry is computed from a best fit of discrete surface points The trigger probe is a switch Trigger probes use a mechanism that generates a trigger when the stylus is deflected away from its fixed seated position. They are effectively a digital device - either seated or unseated. Integral electronics process the voltages and currents in the sensor circuit and generate a trigger signal when contact with the surface is detected. This trigger signal, which is generated in real time by the probe, is used to freeze or latch the machine position at that point in time. The location in each axis of motion is recorded at the point of contact, after which the machine decelerates to a halt and then backs off the surface. The compliance of the probe mechanism allows the stylus to deflect relative to the CMM quill without damage to the probe or the component. As the CMM backs off the surface, the stylus returns to its seated position and is ready to measure the next point. Once several discrete points have been captured, a representation of the feature can be computed using ‘best fit’ algorithms. For most features the results will be size and position, whilst some information about the form of the feature can also be derived.

Touch-trigger probing characteristics
Versatile wide range of probes sensors that range in size from the small, industry-standard TP20, to larger, high accuracy sensors like the TP7M probes suitable for use on manual and motorised heads and for quill mounting Quill mounted TP800 Versatility Renishaw provides a range of touch-trigger probes that covers all discrete point measurement needs: Ultra-compact sensors, for example the TP20 and TP200, enable flexible access to the component and mounting on extension bars. Solid-state switching is provided by the TP200 and TP7M, yielding greater measurement accuracy with long styli, better repeatability and extended operating life. Piezo sensing in the TP800 enables ultra-high precision measurement, plus the use of very long styli. Most Renishaw trigger probes can be mounted to an articulating head and on the end of probe extension bars, greatly increasing the flexibility of access to the component. High accuracy TP7M Ultra-compact TP20

Versatile stylus changing fast and automated stylus changing without re-qualification sensor changing allows for a range of probes on your CMM, each suited to a specific measurement task Stylus and probe changing A single configuration of probe and stylus is rarely sufficient to measure all the features on your parts (although articulating heads can reduce the number of complex stylus clusters that you would otherwise need). Stylus changing, which can be fully automated on DCC CMMs, ensures that you are using the best stylus for each measurement task. A highly repeatable joint between the removable stylus modules and the probe ensures that styli can be changed and re-used without having to re-qualify the stylus, saving you time. In some cases it will be advantageous to use more than one probe, including other trigger probes and other types of sensor like scanning and optical probes. Renishaw’s unique Autojoint enables rapid and repeatable inter-changing between a wide range of sensors, increasing your flexibility and enabling automated inspection of even the most complex components. Sensor changing Stylus changing

Flexible part access articulating heads flexible reorientation of inspection sensors for better part access extensions compact sensors can be mounted on long extension bars for access to deep features Flexible part access Articulating heads enable a probe to be re-orientated such that it can access features on all faces of the part. The compact nature of most touch-trigger probes allows them to be mounted on extensions, keeping stylus lengths short and measurement accuracy high, even whilst accessing features deep in the component. This combination of qualities avoids the need for large and complex stylus clusters, which reduce measurement performance and increase the space required to move around the component. Articulation allows a single probe and stylus combination to measure many different features, thus reducing stylus changes and keeping inspection cycle times short.

Robust and crash resistant rugged design simple and robust mechanism crash protection magnetic kinematic mount allows stylus module to detach when over travelled Kinematic mechanism The kinematic touch-trigger probe mechanism is simple and robust, allowing the stylus to be deflected at a low force, yielding significant travel in all directions before any damage is likely to be done to the probe or the component. Ultra-hard contacts provide a rugged and repeatable seat for the stylus, ensuring reliable operation throughout the probe’s operating life. Crash protection Many touch-trigger probes feature stylus changing, which provides an excellent safety feature as well as increased flexibility. The magnetic coupling allows the stylus to detach in a crash situation, minimising damage to the probe and the part. Robust kinematic mechanism Magnetic mount for stylus module

Cost effective simple and affordable low lifetime costs advance replacement service at discounted price Low lifetime costs Touch-trigger probes are the simplest form of sensor and so are generally more affordable than more complex technologies like scanning and optical probes. Over the lifetime of a CMM, probes will typically need replacement with repeated use. Renishaw lifetime costs are low by providing a cost-effective replacement service: Existing probe users can return sensors that are at the end of their operating lives to Renishaw’s local offices and receive a replacement probe, built to factory specifications at a substantial discount off the list price. Renishaw also offers an advance replacement service where a replacement unit is shipped to you on the same day that you call us, enabling you to keep your CMMs running. Service Centre Renishaw Inc

Touch-trigger probe applications Metrology of trigger probes Trigger probe design The main topics in this presentation are: Touch-trigger probe applications - where touch-trigger probes are most appropriate and the characteristics of Renishaw touch-trigger probes that make them well suited to industrial measurement applications. Metrology of trigger probes - key factors that govern the performance of touch-trigger probes. Trigger probe design - a closer look at key features of Renishaw touch-trigger probes, explaining how these benefit measurement performance. Each of the main kinematic trigger probe technologies - resistive, strain-gauge and piezo - are reviewed. Articulating heads - indexing and servo solutions for trigger probing on CMMs that provide flexible access to the part, focussing on key design features. Probe and stylus changing - solutions that increase probing flexibility - key features that ensure a reliable and cost-effective product. Articulating heads Probe and stylus changing

Touch-trigger probe technologies
All Renishaw probes use a kinematic mechanism to retain the stylus and to provide overtravel. However, the method of trigger sensing varies from model to model. Three main sensing technologies: Resistive - the original design of touch-trigger probe, in which a kinematic mechanism also provides the trigger sensing. These probes are simple, cost-effective, very compact and rugged. Strain-gauge - silicon gauges measure the contact force and trigger once a threshold is breached. This provides a consistent and highly repeatable trigger characteristic, eliminating the ‘lobing’ effects of resistive probes. Solid-state switching is inherently more reliable than electro-mechanical switching, mean that strain-gauge probes have much longer operational lives. Piezo - measuring the tiny shock that is transmitted up the stylus when the tip strikes the component, these probes provide a near-perfect trigger characteristic and can support very long styli and large stylus clusters without loss of accuracy. However, there are significant application restrictions to take into account. Resistive simple compact rugged Strain-gauge solid-state switching high accuracy and repeatability long operating life Piezo three sensing methods in one probe ultra-high accuracy quill mounted

Kinematic resistive probe operation
In a kinematic resistive probe, the stylus is located such that all degrees of freedom are constrained by 6 points of contact between a set of spheres and cylinders. The diagram shows a typical kinematic mechanism A spring holds the stylus carrier against a ball plate that is fitted to the probe housing. The ultra- hard contacts ensure that there is little deformation of the surfaces under the retaining spring force. An electrical circuit runs through the six contacts and the electrical resistance is monitored When the probe stylus contacts the surface, this force acts against the retaining spring and causes one or two pairs of the contacts to move apart. As the force between the kinematic contacts reduces, the contact patch between the elements gets smaller. As a result, the electrical resistance around the circuit increases. It is this change that is sensed by the probe electronics The elegance of the kinematic resistive sensor is that it combines a mechanically repeatable location and electrical sensing in a simple mechanism. Kinematic trigger probes can be very compact, whilst their robust design makes them suitable for most measurement applications. The arrangement of contacts means that the force required to trigger the probe in the XY plane varies depending on the direction of contact. This varying force causes the stylus to deflect by a different amount when the trigger occurs. This characteristic - called ‘lobing’ or pre-travel variation (PTV) - can be easily compensated through probe calibration. The PTV effect is more severe during 3D contacts - i.e. where the probe meets the surface along a compound vector in all three axes. This makes kinematic resistive probe unsuitable for complex digitising applications.

Kinematic resistive probe operation
machine backs off surface and probe reseats stylus makes contact with component contact force resisted by reactive force in probe mechanism resulting in bending of the stylus Reactive force Contact force stylus assembly pivots about kinematic contacts, resulting in one or two contacts moving apart trigger generated before contacts separate Contacts separate Pivots about these contacts All kinematics in contact probe in seated position Motion of machine This slide shows the actions of the probe mechanism during a trigger. The probe is in free space and the mechanism is seated. Once the stylus touches the component, contact forces start to build. At first, the spring in the probe mechanism holds the kinematic contacts together. The contacts remain seated until the point where the spring force reaches a threshold level where the moment generated by the contact force match the resistive moment generated by the spring. Before this point of equilibrium is reached, the contact force causes the stylus to bend by a small amount (depending on the probe spring rate, the stylus stiffness and the stylus length). When the contact moment exceeds the resistive moment, the kinematic contacts start to separate. An increase in resistance across the contacts causes a trigger signal to be generated, and the current to be cut off, before the contacts separate. The machine then stars to decelerate, with the probe mechanism continuing to deflect to accommodate this movement. Finally, the machine backs off the part, allowing the mechanism to reseat and the stylus to return to its repeatable location.

Kinematics bonded to (and insulated from) probe body
Kinematic resistive probe operation Electrical switching electrical circuit through contacts resistance measured contact patches reduce in size as stylus forces build Kinematic attached to stylus Section through kinematics: Current flows through kinematics Kinematics bonded to (and insulated from) probe body Close-up view of kinematics: Resistance rises as area reduces (R = /A) The probe control circuit continuously monitors the resistance through the kinematic contacts. At rest, the kinematics are pressed together by the retaining spring, causing a small amount of elastic deformation where the contacts meet. The resistance of the circuit is controlled by the size of these contact patches between the kinematics and the resistivity of the material from which they are made (R = /A). When the stylus strikes the surface, the force of contact starts to acts against the spring force. Before the stylus starts to pivot, this has the effect of reducing the elastic deformation of some of the contacts. Reducing the contact area increases the resistance. Elastic deformation Contact patch shrinks as stylus force balances spring force

Force on kinematics when stylus is in free space
Kinematic resistive probe operation Electrical switching resistance breaches threshold and probe triggers kinematics are still in contact when probe triggers stylus in defined position current cut before kinematics separate to avoid arcing Resistance Force on kinematics when stylus is in free space Trigger threshold The probe control circuit generates a trigger signal once the resistance exceeds a resistance threshold. It is important to note that the probe triggers whilst the kinematics are still in contact (i.e. the is still a force holding all the sets of kinematics together) and before any pivoting occurs. This means that the stylus is in a defined location at the point of trigger. Once the contacts separate, the stylus is unconstrained. The probe control circuit cuts the current through the kinematics as soon as a trigger is generated. This means that there is no potential across the contacts when they separate. This avoids arcing across the small air gap immediately after the contacts separate, ensuring a longer operating life for the sensor. Trigger signal generated Force on kinematics

FC is proportional to R
Factors in measurement performance Pre-travel stylus bending under contact loads before trigger threshold is reached pre-travel depends on FC and L trigger is generated a short distance after the stylus first touches the component This slide highlights the forces that are in action during the trigger process. The contact force FC generates a moment about the kinematics, resisted by the spring force FS. The point of equilibrium is reached when the moment generated by FC x L matches that generated by FS x R. The load FC causes the stylus to bend. The amount of bending prior to the point that a trigger occurs depends of the magnitude of FC needed to overcome the spring force, plus the length and stiffness of the stylus. The amount of stylus bending at the point that a trigger occurs is known as the pre-travel. The pre-travel is direction-dependent, since it depends on the lever arm over which the spring force acts (R). As will be seen on the next slide, R changes depending on which direction the contact force acts relative to the probe mechanism, meaning the the magnitude of the contact force needed to trigger the probe also varies with probing direction. FC x L = FS x R L and FS are constant FC is proportional to R

Factors in measurement performance
Pre-travel variation - ‘lobing’ trigger force depends on probing direction, since pivot point varies FC is proportional to R therefore, pre-travel varies around the XY plane Top view Low force direction: Pivot point High force direction: Pivot point The diagram (top right) shows a plan view of the kinematics. The direction of the contact force relative to this triangular arrangement of contacts will determine about which points the mechanism pivots. In the high force direction, the mechanism must pivot about a single contact. In the low force direction, the mechanism pivots around two contact pairs. The value of R1 is twice that of R2, meaning that the spring has greater mechanical advantage in the high force direction and therefore demands a higher contact force to trigger the probe. A higher contact force results in greater pre-travel in the high force direction. The range of pre- travel as the contact direction varies in the XY plane is known as the XY pre-travel variation (XY PTV). R1 > R2 FC1 > FC2

Pre-travel variation - ‘lobing’ trigger force in Z direction is higher than in XY plane no mechanical advantage over spring FC = FS kinematic resistive probes exhibit 3D (XYZ) pre-travel variation combination of Z and XY trigger effects low XYZ PTV useful for contoured part inspection Probes are also triggered axially when measuring a flat surface, for instance. In this instance, the contact force must match the spring force to trigger the probe since there is no leverage to exploit. Trigger forces on kinematic resistive probes are much higher in the Z direction than in the XY plane. Another difference is the greater stiffness in this direction, since the stylus is in compression rather than bending. This means that, despite the higher forces, pre-travel in the Z direction tends to be small. The 3D or XYZ pre-travel variation is a measure of the sphericity of the probe’s trigger performance, measured by trigger the probe in many directions in both planes. This is an important measure for inspection of contoured parts, where it is not always possible to calibrate the probe is each probing direction. The high Z trigger force can affect measurement performance on glancing contacts, where the stylus can slide along the surface bending laterally without triggering, A low trigger force and low XYZ PTV characteristic is helpful for inspecting contoured parts. Test data: ISO D form TP20 with 50 mm stylus: 4.0 m ( in)

Probe calibration pre-travel can be compensated by probe calibration a datum feature (of known size and position) is measured to establish the average pre-travel key performance factor is repeatability Limitations on complex parts, many probing directions may be needed low PTV means simple calibration can be used for complex measurements if PTV is significant compared to allowable measurement error, may need to qualify the probe / stylus in each probing direction Even though pre-travel can be quite large, it’s effects can be eliminated through calibration. By measuring the pre-travel characteristic, compensations can be applied to measured data to get true surface data. Calibration is needed for each stylus arrangement, since the stiffness and length of the stylus is a critical factor in PTV, as well as the performance and design of the probe itself. Fast and simple calibration routines are therefore desirable, since probe calibration is a regular task on a CMM. Most calibration routines compensate for an average pre-travel value for the probe / stylus assembly. Pre-travel variation (PTV) will therefore result in small measurment errors either side of the mean pre-travel value. Once PTV is removed, the key performance factor is repeatability (see next slide). Calibration is performed on all probes, but there are limitations to trigger probe calibration. If PTV is low, then a few calibration measurements are all that is needed to compensate for the characteristics of each stylus. Probe designs that feature low PTV are therefore useful for complex part inspection. If a probe has PTV that is significant compared to the allowable measurement error, then it may be necessary to calibrate in each probing directions. For simple routines this is not a problem, but for inspection of complex parts this can itself become complex.

Typical pre-travel variation XY plane The diagram shows a pre-travel plot for a typical kinematic resistive probe, showing the triangular ‘lobing’ effect around the XY plane. A typical calibration cycle will determine the average pre-travel, meaning that any variation in pre- travel will result in measurement errors. In this case, the pre-travel variation is 3.3 microns, whilst the maximum measurement error likely to be encountered through using a single ball radius in all directions will be less than 2 microns. More sophisticated compensation, where multiple local ball radii are determined and applied depending on the contact vector, is rarely used. Hence probes with low PTV (e.g. strain-gauge sensors) are best suited to complex part inspection.

Repeatability the ability of a probe to trigger at the same point each time a random error with a Normal distribution for a given probe and probing condition, repeatability is equal to twice the standard deviation (2) of the Normal distribution 95% confidence level that all readings taken in this mode will repeat within +/- 2  from a mean value Hysteresis error arising from the direction of the preceding probing move maximum hysteresis occurs when a measurement follows a probing moves in opposite directions to each other in the probe’s XY plane hysteresis errors increases linearly with trigger force and stylus length kinematic mechanism minimises hysteresis Once calibration has been performed, repeatability is the critical factor that governs measurement performance. Repeatability is a measure of the range of readings taken by the same probe on the same feature. It arises due to the small variations in mechanical and electrical reseating of the probe mechanism, and is measured in terms of the standard deviation of a Normal distribution. Renishaw quotes repeatability as 2 sigma values - i.e. 95% of the readings can be expected to fall within the quoted repeatability value of a mean. Repeatability tends to increase linearly with trigger force and stylus length. Whilst repeatability is a random phenomenon, hysteresis is a systematic variation that depends on the previous measurement activity. As the probe reseats, its resting position depends on the direction in which it was deflected - the mechanism ‘favours’ the direction in which it was last triggered. This means that another trigger in the same direction will require a little less force than one in a different direction. This effect is superimposed on top of the predictable pre-travle variation that arises due to the design of the mechanism. Hysteresis is at its highest when a trigger follows a measurement in the opposite direction. In practice, hysteresis manifests itself as a very small measurement error. The amount of hysteresis for most probes tends to be significantly smaller than the repeatability. The kinematic mechanism ensures a repeatable reseat position with very low hysteresis.

Ranked in terms of importance repeatability key requirement of any trigger probe fundamental limit on system measurement performance hysteresis contributes to measurement repeatability pre-travel variation can be calibrated, provided all probing directions are known measurement accuracy will be reduced if probe used in un-qualified direction and PTV is high increases rapidly with stylus length hysteresis small error factor for probes with kinematic mechanisms Two factors are vital when selecting in trigger probe: Repeatability is the ultimate limit for measurement performance. Pre-travel variation can be compensated, but low PTV is good for measurement of complex parts. PTV increases exponentially with stylus length, so good performance with long styli demands a probe with consistent pre-travel. Hysteresis manifests itself as a small measurement error and is generally a far smaller value than the other factors. Kinematic stylus seats ensure low hysteresis.

Touch-trigger probe applications Metrology of trigger probes Trigger probe design The main topics in this presentation are: Touch-trigger probe applications - where touch-trigger probes are most appropriate and the characteristics of Renishaw touch-trigger probes that make them well suited to industrial measurement applications. Metrology of trigger probes - key factors in assessing the performance of touch-trigger probes. Trigger probe design - a closer look at key features of Renishaw touch-trigger probes, explaining how these benefit measurement performance. Each of the main kinematic trigger probe technologies - resistive, strain-gauge and piezo - are reviewed. Articulating heads - indexing and servo solutions for trigger probing on CMMs that provide flexible access to the part, focussing on key design features. Probe and stylus changing - solutions that increase probing flexibility - key features that ensure a reliable and cost-effective product. Articulating heads Probe and stylus changing

Kinematic resistive probe technology
Simple electro-mechanical switching resistive probes use the probe kinematics as an electrical trigger circuit pre-travel variation is significant due to the arrangement of the kinematics The kinematic resistive probe mechanism has already been examined in some detail. It is a simple and robust mechanism, that uses electro-mechanical contacts to affect switching. A consequence of the triangular arrangement of contacts is significant pre-travel variation. Although trigger forces can be low, these tend to be higher than for strain and shock sensing probes. These two factors - PTV and higher contact forces - result in limited performance with long styli.

Kinematic resistive probe characteristics
Extremely robust Compact good part access suitable for long extensions Good repeatability excellent performance with shorter styli low contact and overtravel forces minimise stylus bending and part deflection Universal fitment simple interfacing Cost-effective Finite operating life electro-mechanical switching Qualities of kinematic resistive probes: Robust- the kinematic mechanism is simple and rugged, able to cope with shock and vibration. Compact - small and lightweight probes can be mounted on articulating heads for flexible reorientation, and on long extensions (up to 750 mm), enabling access to deep features. Repeatability - good mechanical and electrical repeatability is achieved, although repeatability spans are related to the square of stylus length. This means that performance on the smaller trigger probes is compromised with longer styli. However, excellent part access can still be achieved through mounting on extension bars, thus limiting the need for long styli. Universal fitment - a well established technology, with simple mechanical and electrical installation. Power and signals are carried on just two wires. Cost-effective - resistive probes feature the simplest technology and are therefore affordable, with low running and replacement costs. Operating life - the electro-mechanical switch does suffer from wear over time, thus limiting the life of this type of probe. Kinematic resistive probes are therefore not well suited to very high intensity probing applications like ‘peck’ or ‘stitch’ digitising. Such applications are better served by scanning probes or strain gauge touch-trigger sensors.

TP20 stylus changing probe
Concept direct replacement for TP2 ultra-compact probe at just Ø13.2 mm TP20 features fast and highly repeatable stylus changing manual or automatic enhanced functionality through extended force and extension modules The new industry standard The TP20 directly replaces the TP2, the previous industry standard touch-trigger probe. The TP20 is fit, form and function compatible, making upgrades simple. Comparison with TP2: Same length (37 mm) and diameter (13.2 mm) TP20 has a wider trigger force range (0.055 N to 0.35 N) to allow for longer styli and probing of soft materials Same stylus attachment (M2) Same probe mount (M8) The principal advantage of TP20 is repeatable stylus changing, which broadens the range of measurement applications that can be supported by such a compact probe.

Benefits reduced cycle times achieved by fast stylus changing without re-qualification optimised probe and stylus performance with seven specialised probe modules easily retrofitted to all Renishaw standard probe heads (M8 or Autojoint coupling) compatible with existing touch-trigger probe interfaces metrology performance equivalent to industry proven TP2 system but with greater flexibility of operation Stylus changing benefits On complex parts, different styli are often needed to inspect specific features. Stylus changing using magnetic modules can be done in seconds, whilst a manual change can take minutes. There is then the further advantage that the new TP20 stylus need not be qualified if it has already been datumed. This greatly reduces measurement cycle times on complex parts. Stylus modules 7 different modules mean that you can always select the best one for each measurement task, resulting in better measurement accuracy. Upgrades If you currently use a TP2, you can use a TP20 immediately. Full compatibility with existing installations means that you can use existing inspection programmes at once. Flexibility Stylus changing brings no loss of measurement performance - only increased flexibility. The TP20 can measure deeper features than a TP2, or softer materials, or undercuts that require 6-way capability.

TP20 stylus modules Optimal measuring performance
seven specialised probe modules allow optimisation of stylus arrangement for best accuracy and feature access in all user applications module attaches to probe body via a quick release, highly repeatable kinematic coupling module range covers all forces supported by TP2 6-way module replaces TP2-6W Stylus module changing A range of modules, each with a fixed trigger force, can support a wide range of styli and extensions. A fixed spring force means that, unlike the TP2, you do not need to adjust the force to suit the application (thus voiding your previous stylus qualification results). Your results will be more repeatable, and cycle times will be shorter. The probe body contains a magnet which retains the stylus module against a set of kinematic contacts. This ensures repeatability, whilst allowing the stylus to detach in the event of a crash. The low force TP20 stylus module provides a lower trigger force than a TP2 with its spring rate set at the minimum end of its range. The extended force module provides a higher spring rate than the maximum TP2 value, enabling it to carry heavier styli. A 6-way TP20 module replaces the discontinued TP2-6W probe, and is suited to measurement of grooves and undercuts. TP20 probe body

Comparative module and stylus lengths
Soft materials General use Longer or heavier styli Grooves and undercuts Stylus modules The range of modules also allows a greater reach into deep features - up to 125 mm with the EM2 standard force module. The extension modules allow the probe sensor to be positioned closer to the workpiece, improving the measurement performance compared to a conventional probe with a longer stylus. Reach up to 125 mm (5 in)

Strain-gauge probe technology
Solid state switching silicon strain gauges measure contact forces transmitted through the stylus trigger signal generated once a threshold force is reached consistent, low trigger force in all directions kinematics retain the stylus / not used for triggering Strain gauge technology Strain gauge probes use a different sensing technology to resistive probes, whilst still using the kinematic mechanism to mechanically retain the stylus and to provide overtravel. Inside the probe sensor are micro silicon strain gauges that sense the contact force in three directions. The outputs from these three gauges are combined by electronics in the probe, which look for the total force vector to exceed a threshold value. When this threshold is reached, a trigger signal is generated. Strain gauge probes trigger at a much lower force than resistive probes, meaning that there is less stylus bending or pre-travel. Because they measure the force vector in all three axes at once and combine the results, strain gauge probes are much better suited than resistive sensors to measuring surfaces at compound angles. Unlike resistive probes, they have a consistent trigger force in all directions (resistive probes tend to have much higher trigger forces in Z than in the XY plane). The signal processing electronics are contained within the probe body, with a trigger signal generated to latch the machine position. Due to the high sensitivity of the sensor, filtering must be applied to the output to prevent machine vibrations causing the probe to trigger when it is not in contact with the part. This filtering introduces a small, fixed delay in the trigger signal whilst the circuit checks to see if the contact is real rather than a transient shock. This delay, typically a few milliseconds, is highly repeatable, ensuring that measurement repeatability is maintained. It is important that the probing speed is constant since the machine motion during the sensing delay forms part of the probe’s trigger characteristic.

Strain-gauge probe operation
Force sensing four strain gauges are mounted on webs inside the probe body X, Y and Z directions, plus one control gauge to counter thermal drift low contact forces from the stylus tip is transmitted via the kinematics, which remain seated at these low forces gauges measure force in each direction and trigger once force threshold is breached (before kinematics are unseated) Silicon strain gauges mounted on webs (1 out of 4 shown) Kinematics remain seated at low FC The diagram shows how the strain gauges are mounted above the kinematics, which are still used to provide overtravel and mechanical repeatability for the stylus. The strain gauges are aligned to directly sense force in any direction that the stylus makes contact. The gauges are mounted on thin webs of the probe structure to allow them to sense the strains. A fourth gauge is used as a master to eliminate thermal drift from the three measuring gauges. The strain gauges are very sensitive and can trigger at forces which do not unseat the kinematics. At these forces, the kinematic mechanism is effectively solid. A key advantage of strain-gauge sensing is the ability to combine the forces in each direction and trigger at a constant force, whichever direction the contact occurs. This largely eliminates the pre- travel variation effects of resistive probes, since the triangular kinematics are not part of the trigger circuit.

Low lobing measurement trigger force is uniform in all directions very low pre-travel variation A key advantage of strain-gauge technology is the low and uniform pre-travel in all probing directions. Strain-gauge sensing effectively eliminates the lobing characteristics of resistive probes, making them ideal for precision measurements on complex parts where measurements must be taken in many different directions. The plot shows the pre-travel in the XY plane for a typical strain-gauge probe. Note that the scale of this plot is very different to the previous plot for TP6.

Lobing comparison plots at same scale These two plots highlight the difference in performance between a strain-gauge probe and a kinematic resistive probe. The strain-gauge probe delivers a lower and much more consistent pre- travel characteristic. Strain-gauge XY PTV = 0.34 m Kinematic resistive XY PTV = 3.28 m

Strain-gauge probe characteristics
High accuracy and repeatability probe accuracy even better than standard kinematic probes minimal lobing (very low pre-travel variation) Reliable operation no reseat failures suitable for intensive "peck" or "stitch” scanning life greater than 10 Million triggers Flexibility long stylus reach suitable for mounting on articulating heads and extension bars stylus changing available on some models Benefits of solid state switching Strain gauge sensors are more sensitive and trigger at lower forces than resistive probes, making them more repeatable, especially at longer stylus lengths. Strain gauge probes have the same trigger force in all directions. This force is also low. This means that the level of stylus bending under contact loads is both smaller and more consistent than resistive probes. This manifests itself in smaller pre-travel variation (PTV): TP7M = 0.25 microns (strain gauge) 50 mm stylus TP6 = 1 micron (resistive) 22 mm stylus Resistive probes can suffer from reseat failures, where the resistance around the contact circuit fails to fall below the threshold after a trigger. Reseat failures tend to increase in frequency during the life of the probe. By contrast, strain gauge probes do not use the kinematics for trigger sensing. The trigger circuit does not suffer from electro-mechanical wear. This reliability makes strain gauge probes suited to high intensity applications like peck scanning. An operating life in excess of 10 million triggers can be expected. Resistive probes see PTV values that increase with the square of stylus length, meaning that they are best suited to applications with shorter styli. Strain gauge probes can support much longer styli since the PTV value does not increase so rapidly with stylus length.

TP7M strain-gauge probe
Concept 25 mm (1 in) diameter probe Autojoint mounted for use with PH10M multi-wire probe output Benefits highest accuracy, even when used with long styli - up to 180mm long ("GF" range) compatible with full range of multi-wired probe heads and extension bars for flexible part access plus general strain-gauge benefits: non-lobing no reseat failures extended operating life 6-way measuring capability TP7M The TP7M was the first strain-gauge probe to be introduced, and is the most repeatable and accurate touch-trigger probe in widespread use. Mounted on an Autojoint, the TP7M can be fitted to PH10M series heads for flexible reorientation, and can be used with PAA series extension bars for greater reach. Long and star stylus configurations can be used with excellent measurement performance. Graphite fibre styli of up to 180 mm (7.1 in) can be fitted.

TP7M performance Specification Test results from 5 probes
Repeatability The graphs show test results from 5 TP7M probes, tested on a high accuracy calibration rig. The probes have been triggered up to 20 million times, and still provide measurement repeatability well within the specification. This illustrates the longevity of probes with solid state switching.

TP7M performance Specification Test results from 5 probes
Pre-travel variation This graph shows the measured form error in the XY plane (which results from variation in the pre-travel of the probe). Once again, this shows that the trigger characteristic of the probe remains well within specification throughout a very long operating life.

Concept TP2-sized probe, with strain gauge accuracy stylus changing for greater flexibility and measurement automation 2-wire probe output (like TP2) Benefits long stylus reach - up to 100mm long ("GF" range) match stylus to the workpiece using high speed stylus changing improve accuracy for each feature no re-qualification manual or automatic changing with SCR200 compatible with full range of heads and extension bars TP200 The TP200 is the most widely used strain gauge probe, providing ultra-compact size and stylus changing capability. Whilst the TP200 cannot quite match the measurement performance of the larger TP7M, it’s convenience and size make it ideal for general inspection applications where accuracy and longevity are critical requirements. Power and signals are carried on two wires, meaning that the TP200 can be fitted to articulating heads that do not have an Autojoint. The TP200 is the same size as the TP20 kinematic resistive probe, and offers similar benefits in terms of part access and flexibility. It exceeds the TP20’s performance in terms of measurement performance with long styli and operating life (> 10 million triggers).

TP200 stylus modules Optimal sensor performance
6-way operation ±X, ±Y and ±Z two types of module: SF (standard force) LF (low force) provides lower overtravel force option for use with small ball styli and for probing soft materials detachable from probe sensor via a highly repeatable magnetic coupling provides overtravel capability suitable for both automatic and manual stylus changing module life of >10 million triggers TP200 stylus modules The body of the TP200 contains the strain gauges and signal processing electronics. The magnetically attached stylus module acts simply as an overtravel mechanism with high mechanical repeatability. Two module types are available with different spring rates. The lower force version is designed to minimise forces on the component after the trigger has been recorded. However, he trigger force is set by the probe electronics, and is the same for both modules. Strain gauge sensors can detect forces in all six probing axes, including -Z, making the TP200 suitable for measuring grooves and undercuts.

Piezo shock sensing Shock sensing
piezo sensors generate a voltage when subjected to pressure piezos can detect the mechanical shock signal generated when the stylus ball impacts the workpiece they can respond to frequencies higher than those detected by many other sensors the result is that piezo probes "hear" the stylus ball touch the surface Piezo ceramic sensor detects shock of impact Stylus changing kinematics A piezo probe uses one or more piezo ceramic elements as the sensor. The advantage of piezos is that they are able to detect the mechanical shock signal generated when the stylus ball impacts the workpiece. This is due to their ability to respond to frequencies higher than those detected by many other sensors. The result is that piezo probes "hear" the stylus ball touch the surface. When the stylus meets the surface, it ‘rings as the shock waves passes up the stylus and into the probe body. These signals are at very high frequencies and travel very quickly, meaning that a shock sensor can respond to a surface contact more quickly than other types of probe.’ Similarly to strain-gauge probes, at the frequencies and forces concerned, the kinematic elements act as a solid, transmitting the shock waves from the stylus further into the probe structure. Shock wave travels up stylus and is transmitted through kinematics

Piezo shock sensing Ultra-sensitivity
shock travels at speed of sound through the stylus and probe 800 m per second (2,600 ft/sec) response time is 1.25 sec / mm High performance pre-travel depends on stylus length and probing speed pre-travel is the same in all directions since mechanical signal path is constant lobing effect limited to ball sphericity! Piezo ceramic sensor detects shock of impact Stylus changing kinematics The shock waves travel at the speed of sound through the metal and ceramics of the stylus and probe mechanism. This is typically at 800 m/sec or 2,600 ft/sec. This means a response time of around 1.25 micro seconds per mm of mechanical signal path. For a 100 mm (4 in) stylus and a probing speed of 8 mm/sec, this means a pre-travel of around 1 micron. At this deflection, the contact forces are still very low - typically less than 1 gf. Pre-travel variation is very low since the signal transmission path is the same, irrespective of the direction of contact. PTV is governed only by the sphericity of the stylus ball. Shock wave travels up stylus and is transmitted through kinematics

Multi-sensor operation
Kinematic and strain sensing shock sensing is not 100% reliable speed sensitive surface contamination workpiece hardness small stylus ball diameters are not reliable shock can be backed by kinematic and strain sensing to confirm triggers generated by shock sensor life of piezo probes are limited by electro-mechanical elements Despite this key benefit of ultra-sensitive performance, there are limitations. Shock sensing is not as reliable a trigger mechanism as strain or resistive sensing. Key factors: Speed sensitivity - pre-travel is dependent on probing speed. Therefore it is vital that probing moves are conducted at the calibrated speed or errors will arise. Surface contamination - if a soft substance is on the surface of the part (such as coolant or dirt) this will hamper a clean trigger signal. Workpiece hardness - softer materials do not generate a ‘ring’ in the stylus - metals are better than plastics. Small stylus balls do not generate a reliable shock signal. Some of these factors can be alleviated through the use of multi-sensor technology. Piezo sensors can also be used to measure strain, which can act as a confirmation signal to back up contacts that were first identified by trigger signals. The downside of this approach is the need for complex, high speed electronic circuitry inside the probe. In Renishaw piezo probes, the shock sensor is backed up by a kinematic resistive sensor that acts as the trigger signal confirmation. Whilst this improves robustness of the trigger circuit, it introduces electro-mechanical wear as a factor in the life of the system as a whole.

TP800 piezo probe Unprecedented performance
quill mounted probe featuring unique multi-sensor design ultra-high accuracy repeatability specification: 0.25 m with 50 mm stylus 1 m with 250 mm stylus low trigger force < 1 gf pre-travel variation << 0.5 m typical values for 150 mm stylus: 0.15 m repeatability 0.25 m PTV support for very large stylus clusters 350 mm straight 200 mm star Piezo technology The TP800 is unique in that it provides piezo shock and piezo strain sensing in a single probe, combined with a resistive mechanism for overtravel protection and trigger signal confirmation. This sensing technology provides the highest measurement performance of all touch-trigger probes. The product is specified to provide repeatability of 1 micron with a 250 mm (10 in) stylus, although typical performance is superior to this. The trigger force is also very low at less than 1 gf. Since the piezo sensor is not using transmitted force to generate the trigger signal, the pre-travel variation of the TP800 is limited only by the sphericity of the ball. PTV values as low as 0.25 microns can be achieved even with long styli. The extreme sensitivity of the TP800 enables it to support very long styli (up to 350 mm) with excellent metrology performance. The major disadvantage of the TP800 is its size (80 mm diameter, 127 mm length, 850g mass), which means it must be quill mounted. It therefore lacks the flexibility of a smaller probe mounted to an articulating head.

TP800 piezo probe Application limitations cannot measure small bores
probe works best with larger stylus balls (e.g. 6 mm) machine may not reach calibrated probing speed without sufficient clearance surface condition is critical dirt on the surface can reduce shock and prevent a clean trigger soft surfaces such as plastics do not generate sufficient shock probing speed must be controlled to within 1 mms-1 large probe size prevents use with articulating heads or extension bars Piezo technology application limitations The TP800 provides the best performance of all trigger probes under the correct conditions. However, limitations of the piezo design mean it is not suited to some applications: Small bores cannot be accessed due to the need to use larger stylus balls for reliable performance. Probing speed is critical. Sufficient clearance is needed to attain the calibrated probing speed if measurement errors are to be minimised. Parts must be clean and free from coolant or dirt. Piezo probes are not suited to measuring soft materials At 80 mm diameter, 127 mm length, 850g mass, the TP800 cannot be mounted on articulating heads or extension bars, limiting its application to some complex parts. Overall ,the TP800 is a specialist probe suitable for limited applications. For most applications, resistive or strain-gauge probes, mounted to an articulating head, tend to provide the best all round performance.

Trigger probe measurement performance comparison
These charts show relative performance of four trigger probes, covering the major performance factors of repeatability and PTV. Repeatability All probes provide good repeatability with short styli, but strain-gauge and piezo probes perform better at long stylus lengths. ISO D form This chart shows comparative measurement performance in 2D, using the ISO Part 2 test. The results show the deviation from a circular trigger characteristic (i.e. one in which the same stylus deflection is seen in all directions in the XY plane). The TP200 and TP7M strain-gauge probes show lower form errors than theTP20 resistive probe. Under the correct conditions, the TP800 can provide exceptionally low PTV at very long stylus lengths.

Articulation or fixed sensors?
Articulating heads are a standard feature of most computer- controlled CMMs heads are the most cost-effective way to measure complex parts Fixed probes are best suited to small machines on which simple parts are to be measured ideal for flat parts where a single stylus can access all features Articulating heads allow users to reorientate the probe without the need to re-qualify the stylus. This alone increases flexibility and saves time that fixed probe spend changing styli. Fixed probes are only the optimum choice when the range of parts to be measured is small and the parts themselves are simple.

Renishaw articulating heads
Increased flexibility… easy access to all features on the part repeatable re-orientation of the probe reduced need for stylus changing optimise stylus stiffness for better metrology Reduced costs… indexing is faster than stylus changing less expensive than active scanning systems reduced stylus costs simpler programming Flexibility Articulation brings the key benefit of simpler stylus arrangements that can be used to probe features in almost any orientation. In many cases, one stylus is all you need to inspect a whole component By contrast, fixed probe systems typically require several styli to inspect a part, particularly where features can not be accessed by a straight stylus mounted vertically. This need for multiple styli makes fixed sensors slower to use than probes mounted on articulating heads - since indexing is faster than stylus changing. Reduced costs and higher throughput Articulating heads allow you to measure more features with the same stylus, reducing the need for stylus changes. This means that you can spend more time inspecting and less time getting ready to measure.

Renishaw articulating heads for trigger probing
PH10T The PH10T is the basic articulating head, providing repeatable indexing and interfacing for 2 wire probes such as TP20 and TP200. Probes are attached via an M8 threaded connection. PH10M / MQ Similar to the PH10T, except that these heads are fitted with an Autojoint for automatic probe changing. 2 wire and multi-wire probes (such as the TP7M) can be fitted and stored in probe change racks. Machines fitted with a PH10M can use different types of sensor like scanning or optical probes, as well as touch-trigger probes. The PH10MQ is an in-quill version of the PH10 in which the upper axis is embedded in the CMM quill, thus occupying less of the machine’s operating volume. PHS1 A servo positioning head that is able to position at any orientation in two axes for total flexibility. The PHS1 is larger than the PH10 family and can support heavier sensors and longer extension bars. PH10T indexing head 2-wire probes TP20 TP200 PH10M / MQ indexing head Autojoint connector (multi-wire) TP7M & 2-wire probes with PAA adaptors PHS1 servo positioning head infinite range of orientations longer extension bars

Articulating head applications
Flexible probe orientation PH10M offers 7.5° increments in 2 axes - is this enough? prismatic parts generally few features at irregular angles use a custom stylus to suit the angle required fixed scanning probes also need customer styli for such features Knuckle joint needed to access features at irregular angles The PH10 family of indexing heads provide sufficient flexibility of probe positioning for all but the most specialised inspection tasks. With 7.5° increments in each axis, PH10 heads allow the probe to be orientated at the optimum angle for most features. Whilst it is possible to provide smaller increments, this provides little real world advantage and serves to increase the complexity and mass of the articulating head. Where features are orientated at an irregular angle on a prismatic part, then the best course of action is to configure a custom stylus to suit that feature. Renishaw provides a range of knuckle joints and stylus accessories to build up such special configurations. Note that a fixed probe also needs to use custom styli to measure the same feature.

Articulating head applications
Flexible probe orientation PH10M offers 7.5° increments in 2 axes - is this enough? sheet metal / contoured parts many features at different irregular angles stylus must be perfectly aligned with surface in each case no indexing head is suitable fixed probes also unsuitable due to need for many stylus orientations need continuously variable head (PHS1) Cylindrical stylus must be perfectly aligned with hole In the case of sheet metal or contoured parts, where there are numerous surfaces and features at irregular angles, then using custom styli is not a cost-effective solution. In sheet metal work inspection (e.g. body-in-white) it is essential to have perfect alignment between the stylus and the part. This is where an infinitely variable servo head such as the Renishaw PHS1 is useful. Whilst such a head could be used for all measurements on all features, the PHS1's extra size and mass compared to the PH10 family makes it best suited to larger CMMs. Sheet metal

PH10M indexing head - design characteristics
Head repeatability test results: Method: 50 measurements of calibration sphere at {A45,B45}, then 50 with an index of the PH10M head to {A0,B0} between each reading TP200 trigger probe with 10mm stylus Results: Comment: indexing head repeatability has a similar effect on measurement accuracy to stylus changing repeatability Result Span fixed Span index  [Span]  [Repeatability] X ± Y ± Z ± Test spec: Machine Specification: U1 = L / 1000 U3 = L / 1000 Controller: Renishaw UCC-1 Controller. Head: PH10MQ. Extension Bar: None. Probe: TP200. Stylus: 10x4mm Stainless Steel Software: Virtual DMIS V3.8.5 Test method: Machine underwent a 90 minute warm-up cycle. 50 measurements were made on a calibration sphere (13 points per measurement) with the head fixed at angle A45, B45. This establishes a baseline repeatability for the machine. Another set of measurements were made, with an index to A0, B0 and back again between each. The same qualification data was used throughout. Spans and standard deviations for the sphere centre position were established for both set of readings. Increases in span and standard deviation can be attributed to head index repeatability. Repeatability is defined as a 2 sigma value (i.e. 95% of readings will fall within this amount of the mean). Increases in repeatability were less than 0.4 microns in each direction (increase in 3D repeatability was approx 0.5 microns) - typically not a significant part of allowable measurement error.

Indexing repeatability affects the measured position of features Size and form are unaffected Most features relationships are measured ‘in a plane’ Feature positions are defined relative to datum features in the same plane (i.e. the same index position) Datum feature used to establish a part co-ordinate system Therefore indexing typically has no negative impact on measurement results, but many benefits Although indexing repeatability is very small, it is sometimes argued that it will have a detrimental effect on measurement accuracy. This can be demonstrated to be untrue in almost all instances. The repeatability of indexing will affect the position of the stylus tip. It will not, of course, affect the size and shape of the tip, nor the measurement characteristics of the CMM. Consequently, indexing repeatability has no impact on the measured size or form of component features. In the case of measured position, this effect is also zero in most cases. Complex parts with features in many different orientations are generally toleranced relative to datum features in the same plane. Thus it is a simple matter to inspect the datum feature and establish a part co- ordinate system (PCS), thus eliminating the small effect of indexing repeatability. All the features in that plane can then be measured relative to the PCS with the articulating head locked in that orientation.

PH10 series indexing head - design characteristics
Light weight 650 g (1.4 lbs) lightest indexing head available total weight of < 1 kg including scanning probe Fast indexing typical indexing time is 2 to 3 seconds indexes can occur during positioning moves no impact on measurement cycle time Using a single probe and simple stylus combination to measure features in several orientations saves time. Re-orientating the sensor takes bout 2 to 3 seconds - and can be performed during positioning moves - thus having no impact on cycle times By contrast, using a quill mounted probe could require a clumsy stylus cluster or demand multiple stylus arrangements. To change styli, the quill must be moved to a docking position at the stylus rack, a change operation must occur, and the probe must then be positioned back to the part. If a complex stylus is used, time is wasted on longer clearance moves around the part With Renishaw's kinematic stylus changing system, this time is minimised. Conventional stylus changing systems are slower. Indexing can be up to 10 times faster than stylus changing, with the extra benefit on proven programs of combining indexing with positioning moves.

Flexible part access This video shows scanning features in three different orientations, using a single, simple stylus. The probe is fitted to a PH10M indexing head, which allows rapid reorientation of the probe to allow access to the three features. In this instance, the head reorientations are programmed to occur during positioning moves, meaning that they have no impact on the measurement cycle time. By contrast, a fixed sensor would need either a large, complex stylus arrangement or a time-consuming stylus change to measure these features. Rapid indexing during CMM positioning moves give flexible access with no impact on cycle times

Autojoint programmable sensor changing with no manual intervention required use scanning and touch-trigger probes in the same measurement cycle Sensor changing Having access to a range of different types of probe can be invaluable if you have many different types of parts to inspect. For some parts, a touch-trigger probe will be ideal, whilst others will need a scanning sensor (to inspect complex forms, for instance), and yet others may need an optical sensor (where the material to be inspected is soft). In some cases you may need an extension bar to offset the probe from the quill to allow access to a deep feature A probe changing rack allows you to store different sensors and automatically change between them. This increases your flexibility and allows you to pick the best extension / probe / stylus combination for each key feature on your components. Autojoint features kinematic connection for high repeatability

PHS1 servo head - design characteristics
Servo positioning for total flexibility full 360° rotation in two axes for total flexibility of part access resolution of 0.2 arc sec equivalent to 0.1µm at 100mm radius servo control of both axes for infinitely variable positioning and full velocity control speeds of up to 150° per second 5-axis control required The PHS1 is a servo head, rather than an indexing head like the PH10 family. This means that the probe can be positioned at any angle, rather than a finite number of indexing positions. This can be advantageous in some sheet metal applications where features are orientated at many different angles. For prismatic parts with normal precision geometric features, the PHS1 provides no significant advantage over indexing heads. The greater size and mass of the PHS1 servo head makes it suited to larger CMMs, whereas the PH10 is ideal for small to medium measuring machines.

High torque for long reach extension bars of up to 750 mm (30 in) ideal for auto body inspection touch-trigger probes only Autojoint for use with SP600M and TP7M Powerful motors generate 2 Nm torque 4 times more than a PH10 carry probes and extension bars of up to 1 kg (2.2 lbs) The PHS1 is ideally suited to specialist inspection applications like auto body measurement. It is here that the ultimate positioning flexibility is required, whilst the PHS1's extra reach (up to mm) is also valuable. The PHS1 can support a SP600M scanning probe.

Infinitely variable positioning This video shows how an infinitely variable positioning head can be used to control precisely the position of the probe stylus throughout a measurement routine. In this case, the motion of the PHS1 head is coordinated with the motion of the CMM to keep the probe tip close to the calibration sphere, whilst accessing the sphere from several different orientations. PHS1’s motion can be combined with the CMM motion to generate blended 5 axis moves

ACR3 probe changer for use with PH10M
4 or 8 changer ports store a range of sensors, extensions and stylus configurations Passive mechanism CMM motion used to lock and unlock the Autojoint for secure and fully automatic sensor changes Sensor changing Having access to a range of different types of probe can be invaluable if you have many different types of parts to inspect. For some parts, a touch-trigger probe will be ideal, whilst others will need a scanning sensor (to inspect complex forms, for instance), and yet others may need an optical sensor (where the material to be inspected is soft). In some cases you may need an extension bar to offset the probe from the quill to allow access to a deep feature The ACR3 probe changing rack allows you to store up to 8 different sensors and automatically change between them. This increases your flexibility and allows you to pick the best extension / probe / stylus combination for each key feature on your components.

New ACR3 probe changer for use with PH10M
Probe changing Video commentary new ACR3 sensor changer no motors or separate control change is controlled by motion of the CMM The ACR3 is a simple, passive device that uses the machine motion to affect the unlocking and locking actions needed to change sensors. The lateral movement of the rack causes the Autojoint to lock or unlock, disconnecting the old sensor and connecting the new one. In this instance, a scanning sensor is swapped for a touch-trigger probe, highlighting how different types of sensor can be integrated into a single probing routine. Quick and repeatable sensor changing for maximum flexibility

ACR2 probe changer for use with PHS1
Probe module changing flexible storage of probes and extension bars The ACR2 changer rack can hold up to 6 different PHS probe modules. These are attached using kinematic mounts to the lower rotary axis of the PHS1 head. Modules can support touch- trigger probes on extension bars up to 750 mm (30 in) long, the SP600M scanning probe and non-contact probes.

TP20 stylus changing MCR20 - passive rack
simple design for rapid stylus changes under program control storage for up to 6 stylus modules kinematic stylus changing mechanism highly repeatable connection between stylus and probe styli can be stored and re-used without the need for qualification collision protection MSR1 manual rack stores and protects up to 6 modules on manual CMMs MCR20 rack for DCC CMMs Stylus changing Unless you are measuring a simple component, you will need to change your stylus configuration to suit different measurement tasks. This can be done manually using a threaded connection, but probe systems are now available with a repeatable, automated means to switch styli This greatly increases your flexibility by allowing you to access features that demand long or complex styli, as well as using different tips (sphere, disc, cylinder) needed for different surface configurations. With automated stylus changing, all of this can be achieved automatically, reducing operator intervention and increasing measurement throughput. MSR1 manual rack

TP200 stylus changing SCR200 - active rack
automated changing for up to 6 stylus modules active rack, but no communications are needed with the CMM controller operation handled by the PI200 interface 2 operating modes: TAMPER PROOF ON - protects against accidentally inhibiting probe operation TAMPER PROOF OFF - for automatic loading or high speed operation full collision protection Stylus changing Unless you are measuring a simple component, you will need to change your stylus configuration to suit different measurement tasks. This can be done manually using a threaded connection, but probe systems are now available with a repeatable, automated means to switch styli This greatly increases your flexibility by allowing you to access features that demand long or complex styli, as well as using different tips (sphere, disc, cylinder) needed for different surface configurations. With automated stylus changing, all of this can be achieved automatically, reducing operator intervention and increasing measurement throughput.

TP800 stylus changing SCR800 - passive rack
automated changing for up to 3 or 4 stylus modules passive rack, operated by motion of the CMM adjustable to suit long styli and large star configurations Stylus changing Unless you are measuring a simple component, you will need to change your stylus configuration to suit different measurement tasks. This can be done manually using a threaded connection, but probe systems are now available with a repeatable, automated means to switch styli This greatly increases your flexibility by allowing you to access features that demand long or complex styli, as well as using different tips (sphere, disc, cylinder) needed for different surface configurations. With automated stylus changing, all of this can be achieved automatically, reducing operator intervention and increasing measurement throughput.

Renishaw touch-trigger probing - our offering
Robust solutions compact and rugged sensors crash protection to avoid damage extended operating life with solid-state switching The most flexible and productive solution probe changing stylus changing articulation The lowest ownership costs innovative and affordable hardware responsive service for lower lifetime costs Renishaw’s approach to touch-trigger system design delivers robust and highly flexible solutions at an affordable cost.

Responsive service and expert support
Application and product support wherever you are Renishaw has offices in over 20 countries responsive service to keep you running optional advance RBE (repair by exchange) service on many products we ship a replacement on the day you call trouble-shooting and FAQs on Service facility at Renishaw Inc, USA

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