Unraveling The Mystery of Stepper Motor Technology

1
Unraveling The Mystery of Stepper Motor Technology
Jeramé Chamberlain Nippon Pulse America, Inc.,
USA
2
What is a Open LoopStepper Motor System?

• What Are Stepper Motors?
• How Do Stepper Motors Work?
• Troubleshoot Test Stepper Motors

3
Basic Stepper Application
4
Stepper Motor Coil
5
PHASE A
PHASE A
One PhaseStep Sequence
S
N S
S
N
?
PHASE B
PHASE B
PHASE B
PHASE B
N
STEP 1
STEP 2
PHASE A
PHASE A
Two PhaseStepper Motor
PHASE A
PHASE A
N
N
S
PHASE B
PHASE B
PHASE B
PHASE B
S
STEP 4
STEP 3
PHASE A
PHASE A
6
Types of Stepper Motors

• Permanent-Magnet (PM)
• PM rotor electromagnetic coil
• Variable Reluctance (VR)
• No PM, no residual torque
• Hybrid NEMA Sizing
• Combined PM VR Technology

7
Cross Section of A TwoPhase Hybrid Motor
8
PM Hybrid Stepper Motors
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Bipolar Coil Winding

• Each phase is a single winding

• Current flow and electromagnetic polarity is
  reverses in the windings

10
Unipolar Coil Winding

• Sometimes calledfour-phase steppers

• Current flow and electromagnetic polarity is NOT
  reversed in the windings. Polarity comes from
  alternately energized windings

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Motors Need MaintenanceSteppers Not So Much

• Stalled motors burn up
• Steppers operate in stall condition
• Most brushes go bad
• Steppers are brushless
• All bearings go bad
• Quality Stepper bearings are rated from 90-100K
  hours
• People break them
• Hammers dont fix Steppers

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Ohmmeter Test With Steppers

• Bipolar
• Always 4 leads
• Resistance is the same in both windings and both
  directions

• Some 8 lead motors can be connected as bipolar

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Ohmmeter Test With Steppers

• Unipolar
• 5 or 6 leads
• Resistance from each phase to Common is the same
  in both directions

• If 5 leads, two commons connected
• Some 8 lead motors can be Unipolar

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Unipolar Windings Wire Colors
15
Bipolar Windings Wire Colors
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Stepper Motor Electronic System

• CPU, Controller, Sequencer, Driver
• One or more parts can be combined, based on
  motion complexity

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Controller Receives Coordinates

• A dedicated controller generates motion profiles
  that produce smoother motor operation than just
  with a CPU.

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Controller Manages Interpolates

• Some controllers provide interpolation between
  motors to produce smooth XYZ motions CNC
  Machines

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Two Outputs Types to Sequencer

• Pulse Direction Speed Rotation
• CW/CCW Speed Rotation

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One Controller Two Output Types

• Pulse Direction Speed Rotation
• CW/CCW Speed Rotation

• Pulse Direction is the most common format used
  in the USA
• PCL6045B can output both formats

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Stepper Motor Sequencers

• Sequencers read speed and direction from
  controller and deliver excitation sequence to the
  driver

22
Bipolar Stepper Drivers

• When Q1a and Q4a (green) are on, current flows in
  one direction
• When Q2a and Q3a (red) are turned on, current
  flow is reversed

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Unipolar Stepper Drivers

• Half the drive electronics of bipolar, and 30
  less torque
• However, unipolar coils allow a higher pulse rate
  than bipolar, before becoming saturated.

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Constant Current - Constant Voltage
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Current Lags Voltage in an Inductor

• Torque from stepper motors is generated by
  current, not voltage
• PWM or Chopper drive manages current through a
  switch, applied at higher voltages to induce more
  winding current
• Chopper delivers more torque at higher speeds

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Half Stepping A Stepper Motor

• Easiest way to accomplish half stepping is by
  using 1-2 phase excitation
• Divides a steppers full step angle by two 7.5/2
  3.25 per half step
• 30 loss of torque depending on step rate when
  compared to full step
• Winding is not energized during each alternating
  half step

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PHASE A
PHASE A
Half SteppingSequence
S
N S
S
N
?
PHASE B
PHASE B
PHASE B
PHASE B
N
STEP 1
STEP 3
PHASE A
PHASE A
Two PhaseStepper Motor
PHASE A
PHASE A
N
N
N
N
S
S
PHASE B
PHASE B
PHASE B
PHASE B
S
S
STEP 4
STEP 2
PHASE A
PHASE A
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Microstepping A Stepper Motor

• Full step can be broken into as many as 512 parts
• Current is limited through each winding.
• Unequal pull on the magnet means it moves toward
  the weaker winding
• Torque falls rapidly as speed increases
• Steps are not constant for positioning
• Microstepping should only be used for smooth
  movement.

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Combined Sequencer Translator