Literature Survey on Sensors and Actuators Topic: Stepper Motor Prepared by: Michael Wood 3/4/2009

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Outline Reference list To explore further When to use Stepper vs Servo Applications Advantages and Disadvantages How stepper motors work Types of Stepper Motors Winding Arrangements Controlling How to pick Where to buy 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators To explore further Handbook of Small Electric Motors William H. Yeadon and Alan W, Yeadon, eds. McGraw-Hill, c2001. LC number: TK2537 .H34 2001 Stepping motors: a guide to modern theory and practice Acarnley, P. P. P. Peregrinus on behalf of the IEE, 1984, c1982. LC number: TK2537 .A28 1984 Stepping motors and their microprocessor controls Kenjo, Takashi Oxford University Press, c1984. LC number: TK2785 .K4 1984 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators When to Use Whenever discrete steps are required High torque at low speeds When precision positioning is required If torque needs to be held To eliminate closed loop control (stepper motors can operate in open loop) 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Stepper Vs Servo Motion Characteristics Servo Motors Stepper Motors High Torque, Low Speed Can be considered if cost/ complexity is not an issue. Continuous duty applications requiring high torque and low speed. High Torque and high speed (>2000 rpm) A DC servomotor can deliver greater continuous shaft power at high speeds compared to steppers. High speed up to 12000 rpm is possible. If speeds are less than 2000 rpm stepper may be economical. Stepper becomes bulky at high torque. Short, Rapid Repetitive Moves Use servo if you need high dynamic requirements. Stepper will offer more economic solution when requirements are more modest. Positioning Applications Servo can handle effectively when load is mostly inertia instead of friction. The ability to overdrive servo motor in intermittent duty allows a smaller motor to be used. If positioning is critical in micron level use servo. Use stepper motor if torque is lower than 500 oz-in, less 2000 rpm, low to medium acceleration rates. Applications in Hazardous Environments Use brushless servo motor. Use step motor. Low Speed, High Smoothness Use DC servo. Use microstepping. Control Method Closed loop. Preferred to be used in open loop applications. www.netmotion.com 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Example Applications Machine Tools X-Y and X-Y-Z Positioning Process Control Main Conveyor Drive Assembly Line parts positioning Business Machines Copy Machine- lens positioning and paper feed Computer Peripherals Printer- positioning the matrix print head 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Advantages Rotation angle is proportional to input pulse Motor has full torque at standstill Precise positioning and repeatability of movement Excellent response start/stop/reverse Open loop control possible Achieve low speed with a directly couple load Realize a wide range of speeds Inexpensive relative to other motion control systems Easy to set up and use Overload safe. Motor cannot be damaged by mechanical overload 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Disadvantages Low efficiency. Motor draws substantial power regarldess of load. Torque drops rapidly with speed (torque is the inverse of speed). Low accuracy. 1:200 at full load, 1:2000 at light loads. Prone to resonances. Requires microstepping to move smoothly. No feedback to indicate missed steps. Low torque to inertia ratio. Cannot accelerate loads very rapidly Motor gets very hot in high performance configurations. Motor will not “pick up” after momentary overload Motor is audibly very noisy at moderate to high speeds. Low output power for size and weight. 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

How stepper motors work Current flows through the coil creating a magnetic field A metallic core channels the field perpendicular to the rotor Depending on the polarity of the field an attraction or repulsion drives the rotor 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

How stepper motors work Current pulses are applied to the motor, and this generates discrete rotation of the motor shaft By controlling the pulses the rotation speed can be controlled 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

How stepper motors work If a coil is energized the closes rotor edges will be attracted to that coil. As long as the coils remain energized the rotor will remain stagnant. By energizing coils the correct sequence the motor will discretely rotate 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

Types of stepper motors Variable-reluctance Permanent-magnet Hybrid 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

Variable-reluctance (VR) Variable-reluctance motors are not very common but easy to understand Rotor – made of soft iron and has multiple teeth Stator – wound type stator If the stators are energized with DC current the poles are magnetized and the rotor is attracted to the stator 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

Permanent-magnet (PM) Rotor – magnetized with alternating north and south poles situated in a straight line parallel to the shaft Stator – wound type stator Characteristics Low Cost Low Precision High Torque 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Hybrid Like the name implies the hybrid motor is a combination of VR and PM motors. The rotor has teeth and axially concentric magnets around its shaft. More Expensive Better step resolution Better torque Better speed 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

Unipolar Winding Arrangement Has two windings for each phase (one for each direction of current). Each winding has one common wire and two coil-end wires Current does not need to be reversed to change the magnetic pole Easily controlled with a Stepper motor controller 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

Bipolar Winding Arrangement Has only one winding per phase Current must be reversed to change the magnetic pole More difficult to control than the unipolar winding Each phase has two leads (there is no common) 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

Controlling a two phase Stepper Motor Half Stepping there are 8 stages Assume two coils are A and B Coil A is set high Both coils A and B are high Only B is high B is high A is low Only A is low Both A and B are low Only B is low A is high B is low 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

Controlling a Stepper Motor With a HCS12 Microcontroller Microcontrollers are often used to control stepper motors because: Compatible with the discrete movements of steppers Fast Can easily be programmed to work with steppers of other types Can produce the waveform used to drive small stepper motors 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators How to pick Determine the resolution needed - "step angle”(number of degrees the shaft turns per input signal) Choose a winding scheme - unipolar or bipolar stator winding Determine the torque required for your application 4. Factor in the size, weight and power requirements 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Where to buy www.newark.com (search stepper motor) www.digikey.com (search stepper motor) http://www.anaheimautomation.com/ 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators Cost The cost of Stepper motors varies greatly depending on the required specifications. Lower end hobby stepper motors are under $2 while larger high end motor can be hundreds of dollars. For a better feel for the costs of different stepper motors go to www.digikey.com. 8/30/2018 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators