best practices for motion control: stepper motor and encoder selection
Post on 22-Jun-2015
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• Selec%ng a step motor • Common step motor enhancements
• Case History • Benefits of an encoder • Encoder selec%on
1. Maximum Efficiency Torque at Speed
2. Power Available Voltage & Current
3. Common Issues Resonance
Accuracy
• Vary the voltage or the current
• Find an opera%ng speed
• Motor supplier will back calculate required torque
5
80
70
60
50
40
30
20
10
0
200 400 600 800 1000 1200
Speed (pps, 1 pulse = 1.8 degree)
NEW Opera%ng Speed
Lin Motor ExisOng Motor
Pullo
ut Torqu
e (oz-‐in)
Maximizing Torque @ OperaOng Speed
OLD Opera%ng Speed
24VDC, 2.0 Amps/Phase, Full Stepping
6
(Varied by motor winding and power)
8 16 0 4 12 2 6 10 14
80
70
60
50
40
30
20
10
0
We design motor’s max. efficiency at your opera%ng speed
Speed (RPS)
Efficien
cy (%
)
Tips to reduce resonance • Change Voltage and Current • Change Iner%a of the load • Change microstepping
• Change to a different motor
3709 vs.
Vibr
atio
n A
mpl
itude
Vibr
atio
n A
mpl
itude
Standard 0.9
• Vary Current or Voltage to find torque
• Every motor can be maximized for best performance for max efficiency
• Reduce resonance by changing voltage, current, microstepping or load.
• Lower Speeds and/or Higher Torque-‐ Gearboxes
• Reduce Resonance-‐ Dampers
• Posi%on Verifica%on and Correc%on-‐ Encoders
• When posi:on of motor must always be maintained
• If a motor stall detec:on and ac%on is required
• Typical Industries: • Medical • Solar • Semiconductor
Background:
• Medical device used to remove mucus from pa%ent airways
Requirements: • High holding torque • Accurate posi%oning • Posi%on feedback
• Mechanical • Resolu%on • Index • Differen%al vs. Single Ended Output
• Frame Size • Shac Diameter • Moun%ng Bolt Circle • Environmental Considera%ons
One Cycle
1 2 4 3
Quadrature States
• CPR -‐ Cycles Per Revolu%on • PPR -‐ Pulses Per Revolu%on • Example -‐ 100 CPR = 400 PPR
Output A
Output B
A Leads B
Output A
Output B
B Leads A
• Provide Direc%on of Shac Rota%on Informa%on
• Enable 4x Resolu%on Increase Over Disk CPR • Standard Signals Regardless of Encoder Mechanical Package
Output A
Output B
Index
Index Paeern
• Once per 360 Degree Rota%on • Gives a Single Absolute Loca%on • Typically Used for Home or Zero Loca%on
A
A’
B
B’
A
A’
Index
Index’
• High Electrical Noise Immunity • Transmijng Encoder Signals Over a Long Distance
• Requires Differen%al Receiver
Output A
Output B
Index
• Simple Interface Requirements • Most Common Form of Encoder Output
• Short Distance Signal Transmission
• Mechanical • Resolu%on • Index • Differen%al vs. Single Ended Output • Final Step -‐ Decision
• Short Lead Times • Personal Customer Service
• Great Value • Reliability • Custom Mo%on Control Solu%ons
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