2012 Texas Instruments Motor Control Training Vth Stepper

2012 Texas Instruments Motor Control Training -Vth

Stepper Motors Popularized in the early 60 s as an economical replacement to closed-loop DC servo systems. Found immediate acceptance in the emerging computer peripheral industry. Although open-loop stepper control is conceptually easy, complex motor dynamics are often underestimated. Available in many topologies and step sizes. Dave Wilson TI Spins Motors…Smarter, Safer, Greener.

Exploded View of Stepper Motor N S Dave Wilson TI Spins Motors…Smarter, Safer, Greener.

Stator-Rotor Teeth Alignment A Whole Step B 48 Stator Teeth Unalign B 50 Rotor Teeth (1. 8 o Rotor Movement) Half Step (0. 9 o Rotor Movement) ed S A A B North Pole South Pole Aligned B A Dave Wilson TI Spins Motors…Smarter, Safer, Greener.

Stepper Excitation Modes One Phase Two Phase One-Two Phase A A B B Waveform period is 4 steps (Full Stepping) Dave Wilson B A B Waveform period is 4 steps (Full Stepping) A Waveform period is 8 steps (Half-stepping) TI Spins Motors…Smarter, Safer, Greener.

Current Vectors for Various Stepper Excitation Modes Source: Monolithic, Programmable, Full-Bridge Motor Driver Integrates PWM Current Control and ‘Mixed-Mode’ Microstepping, Paul Emerald, Roger Peppiette, and Anatol Seliversto, , Allegro Micro. Systems, Inc. Technical Paper STP 97 -5 A Dave Wilson TI Spins Motors…Smarter, Safer, Greener.

Microstepped Current Waveforms B A A B Dave Wilson TI Spins Motors…Smarter, Safer, Greener.

Static Torque Curves The torque generated can be thought of as coming from a mechanical spring, where the “K” factor of the spring is proportional to this slope. Source: Making Stepper Motors Behave, Timothy J. Harned, Eastern Air Devices, Dover, NH, Reprinted from Machine Design, 1985 Dave Wilson TI Spins Motors…Smarter, Safer, Greener.

All Steppers are NOT Created Equal! High cyclic errors resulting from winding impedance mismatch and poor tolerances on spacing of teeth. Higher precision device used for microstepping applications. Source: Monolithic, Programmable, Full-Bridge Motor Driver Integrates PWM Current Control and ‘Mixed-Mode’ Microstepping, Paul Emerald, Roger Peppiette, and Anatol Seliversto, , Allegro Micro. Systems, Inc. Technical Paper STP 97 -5 A Dave Wilson TI Spins Motors…Smarter, Safer, Greener.

Stepper Resonance Source: Technical Information on Stepping Motors, Oriental Motor Ways to reduce resonance A. Damping 1. Use voltage drive instead of current drive 2. For L/n. R drives, lower the value of n 3. Interphase capacitors (unipolar drive only) B. Excitation mode 1. Half-stepping 2. Micro-stepping (next slide…) Dave Wilson TI Spins Motors…Smarter, Safer, Greener.

That’s One Small Step for Man… Phase B Phase A Microstepped Phase Currents Step Response Source: Compumotor Microstepping Linear Motor Systems, 1986, Parker Hannifin Corporation Dave Wilson TI Spins Motors…Smarter, Safer, Greener.

Unipolar Drive Topology Used primarily for simple stepped mode operation (Commutation diodes not shown) Dave Wilson Source: Airpax Stepper Motor Handbook, 1989 TI Spins Motors…Smarter, Safer, Greener.

Bipolar Drive Topology Compatible with more sophisticated control techniques (Commutation diodes not shown) Dave Wilson Source: Airpax Stepper Motor Handbook, 1989 TI Spins Motors…Smarter, Safer, Greener.

Closed-loop Current Mode Control +24 V MSP 430 + Gain PWM 1 PWM 2 - ADC 1 0. 015 Wavetable Coil A Texas Instigants Dave’s Control Center Coil B +24 V + Gain - PWM 3 PWM 4 ADC 2 0. 015 Dave Wilson TI Spins Motors…Smarter, Safer, Greener. Ia Ib

Stepper Model Dave Wilson TI Spins Motors…Smarter, Safer, Greener.

Stepper Model Results Open Coil Voltage (Moving Motor) -V(bemf_A) 0. 6 V 0. 4 V 0. 2 V 0. 0 V -0. 2 V -0. 4 V -0. 6 V -0. 8 V -1. 0 V -1. 2 V 125 ms 175 ms 225 ms 275 ms Green waveform: Spice model prediction Blue waveform: Actual measured back-EMF Dave Wilson TI Spins Motors…Smarter, Safer, Greener. 325 ms 375 ms

DRV 88 xx Motor Drivers - Gate Drivers - Power FETs - Protection - indexer / Control Logic Dave Wilson TI Spins Motors…Smarter, Safer, Greener.

Stepper Motors MSP 430 Dave Wilson TI Spins Motors…Smarter, Safer, Greener.

Stepper Motors Stellaris Dave Wilson TI Spins Motors…Smarter, Safer, Greener.