Problem with Single Phase AC variable speed induction Motor

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Problem with Single Phase AC variable speed induction Motor

Post by » Mon Mar 10, 2014 4:17 am


I am facing problem with Single Phase AC variable speed induction Motor (60w <-> 25 gear ratio).Please find the model name of the motor which am using,
1. 51k60RGU - CWE-Motor- Single Phase, 60W
2. 5GU25KB - Gear Box
3. MSC1 - Speed Controller Card.

I am using the above said motor in one of the Die and Punching application, where our machine has to cut 1.2 thickness Velcro/ribbon according to the die shape. The 60w is not able to punch the 1.2 thickness sheet, and its strange to see that sometimes it will cut, sometime it will jam and sometime it will run in bidirectional, note that the motor is unidirectional induction motor. I have verified that the torque and inertia is according to the specification.
I have attached the behavior of the motor.

Tried out the below stuffs:
1. Checked the capacitor connection also changed the capacitor
2. Forced the relay continuous "ON" which is controlling the motor on/off.
3. Change the gear box ratio from 25 to 15.

Kindly someone tell me what is this problem regard

Suman M
Please find the behavior of the motor driven shaft.
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Re: Problem with Single Phase AC variable speed induction Motor

Post by om_tech_support_JT » Mon Mar 10, 2014 6:14 pm


My first thought after watching the video is that the motor doesn't have enough torque to provide the cutting force. I believe that everytime the motor goes back and forth, the motor cuts a little bit. That would explain why the machine would cut after the motor goes back and forth a few times. The reason is because when the motor stalls, the motor will sometimes be be in the negative torque region of its speed-torque curve. When it is in the negative torque region, the motor could rotate CW or CCW depending on the external force acting upon it. Please see below.
Induction, Reversible Motor Speed-Torque Curves, negative torque region.jpg
NOTE: the motor is commanded to rotate in the CW direction in this graph. Stalling or backdriving the motor would cause the motor to be in the 0 or CCW region.

There are a few ways to increase torque: bigger motor (or different motor), larger gear ratio for the gearhead, increase capacitance for the capacitor, or reduce the weight of your load. I would say a bigger motor is the best option because it would provide the same speed range with more torque. A different motor may achieve the same performance needed. Changing the gear ratio would lower the max speed. Increasing capacitance would increase your starting torque, but it would also create overheating (depends on duty cycle).

Let me know how you would like to proceed.

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