Stepper Motors: Performance Curve
Lower duty cycle operation allows a higher load torque.
Duty cycle of 40% permits a torque increase by about 40% (assuming that stator iron doesn’t get into saturation).
However, motor to be designed with a special winding (wire diameter increase, smaller number of turns).
Motor speed results from step clock. Speed, as well as current level, is not effected by load torque. Hence load can’t be sensed by current measurement. However, special feature in driver circuitry can be able to detect an end stop hit by measuring and evaluting the current shape. If the Torque load exceeds the Max.torque Tmax, the stepper motor can’t start or will stop running. Motor must be designed for a rated torque considering a safety margin to Tmax. Additionally, torque decreases at higher ambient temperature and with warmer winding after longer time of operation. |
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JE specifies Tmax for normal room ambient temperature and cool motor winding. Motor torque depends on clock (step frequency). The higher the clock, the lower the torque. This curve is called “Performance Chart”. There are two different Charts, showing performance for two different clock commanding methods: |
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Pull-in rangeDriver circuitry switches on/off full clock at once. fA is max. permissible clock. |
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Pull-out range (slew range)The motor starts at no load and is loaded after having accelerated. Or the Driver circuitry electronics provides an acceleration and deceleration ramp. Current controlled Chopper driver operation allows a higher clock rate. |
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Lower duty cycle operation allows a higher load torque. Duty cycle of 40% permits a torque increase by about 40% (assuming that stator iron doesn’t get into saturation). However, motor to be designed with a special winding (wire diameter increase, smaller number of turns). |
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The performance is effected by operating conditions: It decreases with higher temperature and with lower supply voltage. |
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Holding torqueStepper motors have a Holding torque: Stepper motors also have a Detent torque (Cogging torque): |
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Example: Stepper motor UCD1 |
Holding torque 1.9 cNm |