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Precision Sub-Fractional Motor Technologies:
How to Match the Best Technology for Your Application Day 2: DC (Brush) PM & Piezo Motors, Advantages/Disadvantages, Examining Selected Precision Application Examples for Sub-Fractional Motors
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Motor Technology in Precision Applications Using Small Motors
Day 1- Brushless PM Day 2- Brush DC PM Day 3- Stepper (focus on PM) You are here
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Brush DC PM Technology Review Outline
Introduction History: Concept to Commercialization Motor Technology Advantages Motor Technology Disadvantages Expected Enhancements, Changes, etc. Suppliers of Note Application List and/or Examples
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History: Concept to Commercialization
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The First DC Motor Built by Thomas Davenport in his shop in Vermont in 1837. He used magnetized railroad track spikes secured to a wooden drum for the rotor. He purchased an electromagnet for the stator winding. His wife sacrificed a silk dress for the wire insulation. The electric source was a 3 cell Grove battery. The invention was a technical success but a dismal commercial failure.
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Brush DC motors have evolved into high-performance energy converters with the advent of permanent magnets.
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Evolution of PM Brush DC Motors and Piezo Actuators
1950s – Alnico Torque Motor Invention of the self-supporting motor coil, without need for an iron core (slotless) by Dr. Faulhaber 1960s – Ceramic Motor and Tachometer 1970s – Rare Earth Motor (SaCo) 1980s – Rare Earth Motor (NeoFe) 1990s – Bonded Rare Earth Motors in Higher Volume Applications 2000s- First piezo actuator developed by PiezoMotor AB, supported by Faulhaber and later in the decade introduced to MICROMO customers
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Brush DC PM Basics: Advantages and Disadvantages
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Brush DC PM Advantages
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Brush DC PM Advantages Getting a motor moving requires the proper timing of current in the motor windings. This function is called “motor commutation.” The simplest commutation system is a mechanical one in the form of a metal ring electrically divided in segments, where each segment is connected to part of the motor windings. As the commutator ring and windings rotate together, the timing of the current in the windings depends on which “commutator” segments are in contact with the metal brushes.
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Brush DC PM Commutation: Simple, Inexpensive
DC Volts to winding current to winding Commutator and Windings Rotate Together Brush Is stationary DC Volts
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Brush DC PM Advantages Simple linear relationship between voltage and speed. Easy to control. Low cost approach to variable speed drives and positioning. Well down the manufacturing cost curve.
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Brush Motor Cross-section
Drive, Control Circuitry Rotating Windings Stationary Magnets
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Next two slides show relative simplicity of Brush control compared to Brushless DC motor control <Toggle back and forth to illustrate>
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Brushless DC PM Motor, Drive, Feedback Connections
Rotating Magnets Sponsored by:
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Brush DC PM Motor, Drive, Feedback Connections
Rotating Windings Drive Circuitry
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Brush DC PM Motor Exploded View
DC Voltage Applied to Brushes ‘Armature’ coils on iron core rotates Brushes ride on ‘commutator,’ a segmented copper ring rotating with armature Brushes provide current to rotating windings through the ‘commutator’
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Dewalt Drill brush DC PM Motor Exploded View
Sponsored by:
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Faulhaber Coreless DC Motor
Rotating coils (armature) special winding (‘floating,’ no core) Very low inductance Very high speed Challenge to wind stator coils
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Faulhaber Flat Coreless DC Motor
Stator, Flat No Iron Core Commutation Board - Brushes Rotor Magnets Planetary Gears MICROMO 1512-SR Motor Sponsored by:
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Faulhaber Coreless DC Motor
Stator Windings Basket Style, No Slots or Stator Iron Graphite Brushes and Holders Rotor Core MICROMO 3890 BDC PM High Power Rotor Magnets High strength Neo Sponsored by:
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Linear Device: Easier To Control, More Predictable
The linear nature of the operating curve compared with AC induction Technology makes it easier to control Speed Increases Linearly with Voltage Sponsored by:
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Linear Device: Easier To Control, More Predictable
Stall Current Torque Increases Linearly with Current Sponsored by:
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Trade-offs Are Inevitable
Note that max power and max efficiency and operating point rarely coincide Sponsored by:
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Brush PM Motor Torque/Speed Curve
No Load Speed CONTINUOUS TORQUE ZONE Intermittent Torque Zone Peak Torque
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Brush DC PM Disadvantages
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Negative Impact on Environment
Brush DC PM Disadvantages Negative Impact on Environment Brush-to-commutator (metal-on-metal) sparking presents potential hazard. Brush-to-commutator (metal-on-metal) also creates excessive EMI/RFI electrical noise/interference. Brush wear creates particle contamination. Limited speed range due to mechanical brush-commutator resistance as brushes ‘ride’ on the metal commutator.
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Brush DC PM Disadvantages
Electrical Wear of Brushes and Commutator Ring Is Not Predictable Wear characteristics non-linear and depend on current, motor inductance, temperature, and other environmental conditions. Wear varies from 2nd power to 4th power.
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Brush DC PM Disadvantages
Mechanical Wear Is Not Easily Predicted Brush DC motors have been used for over 120 years, and we still do not know how to predict brush wear with any mathematical certainty. It is operating life uncertainty that has plagued the brush DC motor. Stiction creates initial resistance to motion.
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Enhancements, Improvements, etc., to Brush DC PM Technology
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Brush DC PM Better Brushes Better Materials Motor Consistent Manufacturing Processes
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Brush DC PM Material improvements in magnets (stronger, more rugged), iron (better steels), and insulation (magnet wire, potting, slot liners, separators) will continue to evolve, raising motor performance characteristics. Application of new, higher performing plastics and other materials to replace aluminum and metal parts will help lower manufacturing costs.
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Brush DC PM Suppliers of Note
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Major Supplier Brush DC Motors
Brush Motor Supplier Affiliate Company or HQ Country Alcatel Germany Allied Motion USA Astromec Baldor Electric ABB Barber-Colman Baumueller Bison Gear Bodine Electric Bosch Buehler Motors Canon Japan CE India China Dragon China Chongsha Copal Electric Crouzet France DCM Dumore ElectroCraft EAD Sponsored by:
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Major Supplier Brush DC Motors
Brush Motor Supplier Affiliate Company or HQ Country Foster Danaher Fufa Motor China General Industrial USA Globe Motors Groschopp Germany GSK Harowe Servo Heidenhein Hitachi Japan IMC Hansen Emerson Johnson Electric King Clean Leeson Electric Regal Beloit Lexel Mabuchi Mabuchi Motors Mamco Maxon Motors Switzerland MICROMO (FAULHABER Group) USA, Germany Moog Motion Components Group Motor Products Sponsored by:
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Major Supplier Brush DC Motors
Brush Motor Supplier Affiliate Company or HQ Country MTI SLI Muirhead Vactric UK Pan Air Taiwan Panasonic Japan Parvex France Pittman Motors Ametek PMI Danaher/Kollmorgen Portescap Danaher RAE USA Saggu India Sanyo Denki Sawamura Denki SEM Shaanxi Beyond China Siemens Energy & Automation Germany Tamagawa Seiki Telco Tiebaq Torque Systems ITT Toshiba Tyoki Sponsored by:
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Applications for Brush DC PM Motors
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Application Characteristics Favorable to Brush DC Motors
Speed control with low cost. Speeds under 2000 rpm for larger motors but capable of 20,000 rpm in micro motor sizes. Lower duty cycle applications. Fractional horsepower needs. Power Source: Battery powered.
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The Universe of Application Segments
Brush DC PM technology is broadly used in many major application segments: Transportation Personal Vehicles Commercial Vehicles Off-Road Vehicles
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motors in a car are Brush DC PM
About 80% of electric motors in a car are Brush DC PM
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Sample of Automotive Applications
Door Locks Window Lifts Seat Adjust Engine Fan Climate Control Fuel and Exhaust
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The Universe of Application Segments
Brush DC PM technology is broadly used in many major application segments: Factory Automation Conveyor Systems General Industrial Equipment Material Handling Packaging Semiconductor Processing Equipment Special Industrial Equipment
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The Universe of Application Segments
Brush DM PM technology…more application segments with broad penetration: Medical Equipment Air moving (Sleep Apnea, Ventilators, Respirators, etc.) Diagnostic Equipment (Centrifuges, Scanning Machines, etc.) Tools, Hand Helds, Surgery and Dental Mobility Equipment Medical: Pump and Ventilator Motors Sponsored by:
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The Universe of Application Segments
Brush DC PM technology application segments with moderate penetration: Aerospace Commercial Aviation Military Aviation Missiles/Drones/UAVs Military/Defense Vehicles UAVs and UGVs Autonomous Vehicles in Commercial, Security, Farming Applications
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The Universe of Application Segments
Brush DC PM technology application segments in home and commercial uses: Home Appliances Hand Tools Commercial and Industrial HVAC Sponsored by:
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Precision Applications Using Small Motors
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Remote Presence Robot Challenge?
Need expertise located remotely with a patient in immediate need? Need remote control to move about, see, hear, and be seen and be heard? Need to be able to operate on batteries; quiet; reliable? Motor Need? Highly reliable, efficient, lighter weight, small, higher power per volume. Motion Solution? Coreless brush motor, geared (planetary, low backlash, precise) to translate higher speed to higher torque. Electronics for precision camera positioning; mitigation of EMI/RFI emissions. Innovative feedback combining potentiometers and magnetic encoders to achieve absolute and relative positioning inexpensively.
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Autonomous All Terrain Vehicle
Challenge? How do you go where it may be unsafe or difficult for humans to assess a problem; rescue miners or earthquake victims; inspect or analyze farm land; inspect nuclear plants; inspect construction in progress or hazardous industrial areas? All in extremely varied and at times difficult terrain? Motor Need? Operate at very low voltages (battery, solar powered); high torque per weight; easy to control. Motion Solution? Coreless brush motor, geared (planetary, low backlash, precise) with precious metal commutator for minimum size and ability to operate at lower voltages. Small and light weight are also important in mobile applications.
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Rosetta Comet Exploring Space Probe
Challenge? Ever land on a comet orbiting the Sun for exploration? No one has! So…you need to be ready for almost any situation with motorized sub-systems for controlled landing, anchoring, orienting the landing probe. Landing Probe Motor Need? Reliability of the highest order; simple controls; space ready. Small, lightweight. High torque per volume. Motion Solution? 14 brush DC motors and controls, geared (planetary, low backlash, precise) to translate higher speed to higher torque. Motor functions include: precision camera positioning to search for good landing site; act as motors and generators to capture precious power from kinetic motion; draw anchor lines taught; actuating analytical instruments. Anchoring Actuator
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Piezo Actuators Overview
Piezo technology, while not electromagnetic in nature, is an interesting and alternative approach to actuation where physical contact (like brushes in a DC PM motor) help convey the energy needed for motion. Like a DC motor, piezo technology is energized by applying a voltage to the mechanism and that electrical energy is converted to mechanical energy in the form of vibrations. By controlling the application of the energy and the structure of the stationary and moving elements, linear or rotary motion is initiated. Many camera auto-focuses use piezo rotating motors. Metrology applications (small movements) are also an important area of use.
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Piezo Advantages/Disadvantages
Capable of very small moves (nano motion). Very high holding torque with almost no power consumed. Fast response (micro-seconds) compared to electromagnetic devices (high milli-seconds). Operate in harsh environments such as vacuums, extreme cold, high magnetic fields, high energy radiation where typical electro-magnetic and PM actuators require special designs or materials. Disadvantages (compared to electromagnetic devices) Operate primarily at very slow speeds. Travel is limited. Limited at high temperature levels (200 deg C). Made of brittle material. High hysteresis (does not return to original position) and creep, but both controllable.
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Surgical Robot Inside An MRI
Challenge? If you can position a surgical probe remotely, while you view an active MRI image you can increase the accuracy of the surgical procedure and reduce surgery time. But the extremely strong magnetic field of the MRI creates significant challenges for standard electric motor-driven robots. Screws, gears, motors become hazards within the MRI unit. Motor Need? Unaffected by the strong magnetic field of the MRI machine. Accurate, micro positioning. Audibly and electrically quiet. Motion Solution? Piezo-electric ceramic actuator. Creates motion when a voltage is applied. No magnetic/metal parts. Special design to increase speed. Inherently safe as loss of power brings the motion to a stop.
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