ELEC 3105 Basic EM and Power Engineering Stepping Motors

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ELEC 3105 Basic EM and Power Engineering Stepping Motors

Stepping Motor Step motors (SMs) are electric motors that have no rotating windings, mechanical commutators, brushes or slip-rings. All the windings are part of the stator, and the rotor is usually a permanent magnet. Unlike traditional motors, all the commutation is done externally by a (digital) controller. The SM and its controller are designed so that the shaft can be set to a specific angular orientation, or driven quasi-continuously forwards or backwards as desired.

Stepping Motor Unipolar Motors Variable Reluctance Motors Step motors (SMs) are electric motors that have no rotating windings, mechanical commutators, brushes or slip-rings. All the windings are part of the stator, and the rotor is usually a permanent magnet. Unlike traditional motors, all the commutation is done externally by a (digital) controller. The SM and its controller are designed so that the shaft can be set to a specific angular orientation, or driven quasi-continuously forwards or backwards as desired. Unipolar Motors Variable Reluctance Motors Bipolar Motors

Stepping Motor The idea is to produce a discrete quantum of angular rotation in response to an applied pulse. To produce quasi-continuous rotation, you need to apply a coded pulse train to the stator windings (using digital electronics) that will create an incrementally rotating magnetic pattern. Variable Reluctance Motors Winding 1 1001001001001001001001001 Winding 2 0100100100100100100100100 Winding 3 0010010010010010010010010

Stepping Motor Disadvantages Resonance effects and long settling times Low cost Ruggedness Simplicity of construction High reliability No maintenance Wide acceptance No tweaking to stabilize No feedback components are needed Inherently more fail-safe than other types of motors. Disadvantages Resonance effects and long settling times Rough performance at slow speeds unless micro-stepping is used Position loss Run hot due to current required in drive for all load conditions Noisy

Stepping Motor Types Permanent magnet (PM) step motors Contain a permanent magnet in the rotor. Sequenced stator coil energizing provides rotation Variable reluctance (VR) step motors Have no permanent magnets Rotor is a unmagnetized soft magnetic material Special drive circuits a re required Hybrid step motors Combined PM and VR step motor They are the most common design They usually operate in 2-phase mode 5-phase versions also available.

Stepping Motor Unipolar In use, the central taps of the windings are typically wired to the positive supply, and the two ends of each winding are alternately grounded to reverse the direction of the field provided by that winding. Interleaving the two sequences will cause the motor to half-step Step Coil 4 Coil 3 Coil 2 Coil 1 ==== ====== ====== ====== a1 on off off off b1 on on off off a2 off on off off b2 off on on off a3 off off on off b3 off off on on a4 off off off on b4 on off off on This gives twice as many stationary positions between steps Single-Coil Excitation Each successive coil is energized in turn. Step Coil 4 Coil 3 Coil 2 Coil 1 ==== ====== ====== ====== ====== a1 on off off off a2 off on off off a3 off off on off a4 off off off on This sequence produces the smoothest movement and consumes least power. Two-Coil Excitation Each successive pair of adjacent coils is energized in turn. Step Coil 4 Coil 3 Coil 2 Coil 1 ==== ====== ====== ====== ====== b1 on on off off b2 off on on off b3 off off on on b4 on off off on This is not as smooth and uses more power but produces greater torque.

Stepping Motor How to generate sequence electronically ? The idea is to produce a discrete quantum of angular rotation in response to an applied pulse. To produce quasi-continuous rotation, you need to apply a coded pulse train to the stator windings (using digital electronics) that will create an incrementally rotating TM pattern. Winding 1a 1000100010001000100010001 Winding 1b 0010001000100010001000100 Winding 2a 0100010001000100010001000 Winding 2b 0001000100010001000100010 time ---> Winding 1a 1100110011001100110011001 Winding 1b 0011001100110011001100110 Winding 2a 0110011001100110011001100 Winding 2b 1001100110011001100110011 Unipolar Motors How to generate sequence electronically ?

Stepping Motor How to generate sequence? Unipolar Motors Sequence to generate Unipolar Motors Winding 1a 1000100010001000100010001 Winding 1b 0010001000100010001000100 Winding 2a 0100010001000100010001000 Winding 2b 0001000100010001000100010 time ---> Winding 1a 1100110011001100110011001 Winding 1b 0011001100110011001100110 Winding 2a 0110011001100110011001100 Winding 2b 1001100110011001100110011 Digital sequential machine based on flip-flops, ...

Stepping Motor Bipolar Motors Single phase wiring diagram These motors are wired exactly the same way as unipolar step motors, but the two windings are wired more simply, with no center tap. Thus the motor itself is simpler but the drive circuitry needed to reverse the polarity of each pair of motor poles is more complex. Bipolar Motors Single phase wiring diagram

Stepping Motor Variable Reluctance Motors The idea is to produce a discrete quantum of angular rotation in response to an applied pulse. To produce quasi-continuous rotation, you need to apply a coded pulse train to the stator windings (using digital electronics) that will create an incrementally rotating TM pattern. Variable Reluctance Motors Winding 1 1001001001001001001001001 Winding 2 0100100100100100100100100 Winding 3 0010010010010010010010010

Stepping Motor Stator: Can be energized in various ways has 4 poles pieces, each extending the length of the motor. We will assume at the moment that coils 1A and 1B are connected in series, and that coils 2A and 2B are separately connected in series. Rotor: Is magnetized along its axis so that one end is north (N) and the other end is south (S). In this design each end of the rotor has three teeth for a total of 6. The N and S teeth are offset. 12 Step per revolution Hybrid Motor

You can feel the detent torque when you rotate the motor by hand. Stepping Motor No current: There is a minimum reluctance condition when N and S poles of the rotor are aligned with the two stator poles. There is a small detent torque. You can feel the detent torque when you rotate the motor by hand. 12 Step per revolution Hybrid Motor

Stepping Motor Current in 1A and 1B: N pole on top in stator, S pole at the bottom of stator. There are now three stable positions for the rotor with respect to the energized stator coil 1. The torque needed to move the rotor irrevocably away from a stable position is now much larger and is called the holding torque. When both halves of the coil are energized at the same time, this is called bipolar drive. 12 Step per revolution Hybrid Motor

Stepping Motor Full step, one phase on Full step mode: The idea is to provide currents in coils 1 and 2 such that the rotor is induced to rotate, in steps, in one direction. (a) Coil 1 --> N and S --> attract rotor teeth of opposite polarity. (b) Coil 2 --> N and S --> The stator field rotates through 90 degrees and attracts rotor teeth of opposite polarity and the rotor shaft rotates 30 degrees in one step. (c) Coil 1 --> S and N --> The stator field rotates through 90 degrees in the same direction as (b) and attracts rotor teeth of opposite polarity and the rotor shaft rotates 30 degrees in one step. (d) Coil 2 --> S and N --> The stator field rotates through 90 degrees in the same direction as (b)(c)and attracts rotor teeth of opposite polarity and the rotor shaft rotates 30 degrees in one step. (d) same as (a) except rotated by 90 degrees 3 steps = 1/4 turn: 12 steps = one full revolution of shaft

Stepping Motor Full step, one phase on Step 1 2 3 4 5 6 7 Full step mode: The idea is to provide currents in coils 1 and 2 such that the rotor is induced to rotate, in steps, in one direction. Step 1 2 3 4 5 6 7 (a) (b) (c) (d) (a) (b) (c) 3 steps = 1/4 turn: 12 steps = one full revolution of shaft

Stepping Motor Full step, two phases on Step 1 2 3 4 5 6 7 Full step mode: The idea is to provide currents in coils 1 and 2 such that the rotor is induced to rotate, in steps, in one direction. Step 1 2 3 4 5 6 7 (a) (b) (c) (d) (a) (b) (c)

Stepping Motor Half step mode Full step mode: The idea is to provide currents in coils 1 and 2 such that the rotor is induced to rotate, in steps, in one direction. Finer angular resolution in shaft angular position is possible using the half step mode. Provides uneven torque due to (1 coil-2 coil) energizing sequence.

Stepping Motor Half step profiled mode Full step mode: The idea is to provide currents in coils 1 and 2 such that the rotor is induced to rotate, in steps, in one direction. Finer angular resolution in shaft angular position is possible using the half step mode. Provides even torque due to double current when only one coil is energized.

Stepping Motor Microstep mode Finer angular resolution in shaft angular position is possible using the microstep mode. Two 90 degree out of phase sine waves can perform the same microstep fine control of the rotor position.

ELEC 3105 Basic EM and Power Engineering MEMS Motors Linear

Previous slide extracted from “Principle of virtual work”

Previous slide extracted from “Principle of virtual work”

ELEC 3105 Basic EM and Power Engineering MEMS Motors Rotation

ELEC 3105 Basic EM and Power Engineering Laser Driven Motors

Cylinder orientation in focused laser beam

Torque versus orientation angle Cylinder in focused laser beam

Torque versus orientation angle Cylinder in focused laser beam

Step motor operation of cylinder in laser beams Equations of motion

Smooth Rotating motor operation of cylinder in laser beams.

ELEC 3105 Basic EM and Power Engineering MEMS Laser Driven Motors

Robert C. Gauthier, R. Niall Tait, Mike Ubriaco Activation of micro-components using light for MEMS and MOEMS applications   Robert C. Gauthier, R. Niall Tait, Mike Ubriaco Department of Electronics, Carleton University, Ottawa, Ontario Canada K1S 5B6    Department of Physics and Astronomy, Laurentian University, Sudbury, Ontario, Canada, P3E 2C6 We examine the light activation properties of micron sized gear structures fabricated using polysilicon surface micromachining techniques. The gears are held in place on a substrate through a capped anchor post and are free to rotate about the post. The light activation technique is modeled based on photon radiation pressure and the equation of motion of the gear is solved for this activation technique. Experimental measurements of torque and damping are found to be consistent with expected results for micrometer scale devices. Design optimization for optically actuated microstructures is discussed.

Micro-motor design Z Y T L W Incident Laser Beam  b Gear Plane r Wo X   b

Laser Objective Lens Substrate Gear on Post CCD Filter Light Source

X L W T Y Z Incident Laser Beam Gear Plane r Wo   b

Laser Objective Lens Substrate Gear on Post CCD Filter Light Source

Experimentally measured data points From the X axis intercept the stiction torque is determined to be 200 pNm. From the slope of the line, the damping factor is determined to be b = 3.14x10-14 Nms.

Test chip layout

Other aspects of the micro-gear work Meshed gears Micro-pumps

Slides not used in lecture

ELEC 3105 Basic EM and Power Engineering Selecting a Motors

MOTOR SELECTION CHART