Detecting Motor Rotation When Motor Is Not Energized

We had essentially the same problem with trucks that moved along long horizontal cheese drain tables in the food industry. The answer was to have the power cords pay out from spring powered cord reels.

IN the dairy industry, when hooking up centrifugal pumps, we had the same issue on making sure the motor runs in the correct direction... one can really destroy the impeller shaft in no time just by testing the rotation...

Your 250m requirement is a long way. My cord reel idea would be hard pressed to handle that length.

Well for a 3Cx50 sq mm cable the spring powered cord reels for a length of 250mtrs is not feasible.

Thank you

Thank you very much for your patient reply.

Firstly, the CRD motor is a Demag make Torque motor (SRIM with conical rotor and shaft mounted brake, the motor is vertically mounted) which works on DOL and no VFD.

Secondly, the tension gets maintained with a feedback from pendulum limit switches and when command is given, by picking up the rotor contactor of CRD motor.

But as can be seen from the figure, the loop formed after some length of cable is not detected by the CRD motor when travel motor is not energized.

When the travel motor rotates without command towards CRD (due to many reasons) the cable needs to get retracted. The logic takes care if the slackness in cable extends till the pendulum switch and none of them (left or right) are in action and no command is given.

So I need to know the rotation in the travel motor when it is not energized so that it can be used to pick up the rotor contactor of CRD motor to pull the cable taut and thus avoid loop and cable cuts.

Stop the transfer car from moving when not commanded, that will fix the CRD reel problem.

When the VSD for the car was changed from DC to AC, and not installing a line voltage mechanical set brake, that appears to be the start of your trouble. Now, add dc injection brake to your transfer car drive, and the motor will not move unless commanded.

Your comment is marked off topic, but it is not, you should change that...

Magnets and hall sensors....

http://archives.sensorsmag.com/articles/0397/mar_mag/

Why not add other position sensors, like an encoder or camera to this transfer car.

If the cord reel is not working, why is that? Seems an obvious solution to me.

NVE makes all manner of rotation sensors using Hall effect, one that measures angles down to about 0.3 degrees. All you may need, though is a number of magnets and a switch sensor (the GMR ones can have some real separation between magnet and sensor), and a counter. If it counts after power is down, then it requires an interlock override from a human operator that has checked the cable reel up, or not.

An elegant answer and solution my digging friend.

I need to know how can i detect the rotation of motor (placed in the car) when it is not energized, so that if it rotates a signal can be given to the CRD motor to retract the cable so that loop formation and subsequent cutting of cables be avoided.

Why not battery powered sensors in the cars to detect motor rotation? Batteries could be recharged by power to the VFD motors if necessary.

Option 1 : If new Electromechanical brake is possible to mount on mechanical assembly to prevent the motor shaft rotation when not Energized. Solidstate relay can be use to control the brake On-Off. Option 2 : If Bosch Rexroth servo drive can be use to replace the vfd. Sothat motor shaft will be in servo hold condition when not Energized.This will prevent motor shaft rotation when not Energized. But before this use, you must ensure that you have full technical data sheet of your motor, which is needed at the time of Bosch Rexroth servo drive programming.

How do i control the brake? The CRD cable used is 4Cx50 sq mm.

Why are your cables vulnerable to being cut by this transfer car or anything else? Put these cables into a flexible cable tray.

The fact that it rolls with out power should be the major concern. Accident waiting for a place to happen. Put a brake on it. Which would solve the cable issue.

You failed to specify how much rotation is tolerable (if any), and at what rotation you need to activate the CRD motor. Also you failed to point out the general lay-out in your steel mill of the trolley and the cable.

As indicated by redfred, what prevents you from placing the cable on overhead flex tray?

I've used a tachometer that is basically a magnet wrapped with a coil that is mounted near a gear on a shaft. If the gear rotates, the teeth interact with the magnetic field from the magnet and generate a pulse in the coil. I was using that signal to determine speed of the shaft and also as a zero speed sensor, similar to what you are trying to do.

Absolute encoder

I assume you want the car to be able to move if pushed by other car or whatever. A hundred years ago (before VFD's, encoders etc.) in blast furnaces they used "tri-rods" to determine level of burden in blast furnaces. A weight rested on burden and a DC electric motor (Driving a "winch") kept cable (a wire rope then) taught. The motor (because of low applied voltage) was unable to lift weight but kept cable taught. When time to add material (replace burden) full voltage was applied to motor and weight came up. After addition went back to reduced voltage and weight rested on burden. If burden raised (It never did.) "winch" would reel in cable and keep it taught. We still use these in plant I work in although there are other burden level indicators as well.