Stepper motor that can stop and start at given torque 1

[DirtyHarry84]

Hello,

I am new to this forum and I tried searching for an answer before posting here. If this is already covered I am sorry.

We need to close and open a needle valve using a motor. However, we do not want the motor to keep running when the valve has closed/opened fully at given torque. We will be using a PLC to operate this. My question is: How can I ensure that the motor stops at given torque when opening/closing.

Will be really grateful for any help and tip about this.

 

[MikeHalloran]

Steppers don't work like other motors. In your case you might use position sensors to tell the PLC to turn off the motor or just count steps and bang it against a stop many times to zero the position. If you intend to use a current sensor to detect end of travel you might use a DC motor.

Mike Halloran
Pembroke Pines, FL, USA

 

[tygerdawg]

It seems you could use a stepper motor for this. The motor would need to be sized so that the dynamic torque for moving the needle in/out is sufficient for that. For a needle-valve, should be no problem. You also need to select motor of proper size to provide you the static torque or holding torque to meet your needs. These torque values are all available in the motor torque-RPM curves and specs.

In static condition, the stepper motor is energized but not moving. In this way the motor shaft is held constant due to holding torque.

If your holding torque is not sufficient or if you must absolutely power-off the motor, then you could amplify it by incorporating a lead screw of some sort. Screw pitch should be high enough for no backdriving. Or simply incorporate a brake.

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[OperaHouse]

Many commercial stepper drivers have provision to reduce motor current when not moving to just what is needed to hold it in position. They do it by PWM but you can do it by adding a resistor to common motor power. When movement is needed your PLC can just short out the resistor with a relay prior to any movement.

 

[NCTHAI]

A simple way is to use limit switch and / or torque switch. All motor operated valves use Limit switch and torque switch to stop the motor once operation is done. It is assumed that you are using on / off valve. If you want middle position, you need to use command from PLC to run the motor for desired position. Thus use position feedback or any process parameter you are trying to control to stop the motor once desired position is achieved.