Difference between revisions of "Stepper Motors"
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[http://www.probotix.com/stepper_motors/unipolar_bipolar/ Probotixs Explaination] | [http://www.probotix.com/stepper_motors/unipolar_bipolar/ Probotixs Explaination] | ||
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Revision as of 10:03, 12 December 2011
Intro
Stepper motors are constant power motors. Unlike DC motors which rotate by create a reversing magnetic field stepper motors work by attracting a rotor core with magnetic coils aligned in a stator using discrete intervals called steps.
Advantages
- Open loop, meaning there is no secondary sensor monitoring the position. In some cases this makes it cheaper to implement a digital controller.
- The errors associated with steppers are non cumulative so even running it in open loop will usually yield accurate positions.
- Full Torque Standing Still
- reliable, contactless
Disadavantages
- low torque
- high vibration
- limited speed
- Resolution is limited to a multiple of it's step intervals.
- Continuous Power Device
Bipolar vs Unipolar
- Unipolar
- Bipolar (series)
- Bipolar (Parallel)
- Bipolar (series)
Drivers
- Constant Voltage (L/R)
- Constant Current (Chopper)
Stepping Schemes
- Wave Stepping - (1 Phase on) This is the most power efficient method for stepper but supplies the least torque. this also makes it the least stable at higher speeds
| Phase | A | B | C | D |
|---|---|---|---|---|
| State1 | 1 | 0 | 0 | 0 |
| State2 | 0 | 1 | 0 | 0 |
| State3 | 0 | 0 | 1 | 0 |
| State4 | 0 | 0 | 0 | 1 |
- Full Stepping - (2 Phases on) offers half the resolution of wave stepping, but has a higher holding torque
| Phase | A | B | C | D |
|---|---|---|---|---|
| State1 | 1 | 1 | 0 | 0 |
| State2 | 0 | 1 | 1 | 0 |
| State3 | 0 | 0 | 1 | 1 |
| State4 | 1 | 0 | 0 | 1 |
- Half Stepping - (1 or 2 Phases on) a hybrid of wave and full stepping this offers higher resolution torque and speed.
| Phase | A | B | C | D |
|---|---|---|---|---|
| State1 | 1 | 0 | 0 | 0 |
| State2 | 1 | 1 | 0 | 0 |
| State3 | 0 | 1 | 0 | 0 |
| State4 | 0 | 1 | 1 | 0 |
| State5 | 0 | 0 | 1 | 0 |
| State6 | 0 | 0 | 1 | 1 |
| State7 | 0 | 0 | 0 | 1 |
| State8 | 1 | 0 | 0 | 1 |
- Micro Stepping - (continually varying currents)
Wiring
- 4 wire - Bipolar
- 8 wire - Unipolar or Bipolar
Steps per revolution
Common Step angle 1.8 deg (200 steps per rev)
NEMA Sizes
NEMA 17
NEMA 23
NEMA 35
Reprap explaination of NEMA nameing convention
Vendor List
Japan Servo KH42HM2-951
References
Formulas
Step Angle = 360/S (S = steps)
