Torque sensor used in dc motor drive

[MedievalMan]

This isn't exactly motors related, but thought you guys might have some insight.

I'm trying to run some experiments on fault tolerant control for a dc motor torque control system with a torque sensor used as input for the current (torque) loop. Basically, this is an electric power steering system.

I have a Delphi Electric power steering system used in the Fiat vehicle; I have a working dc motor servo drive here in the lab.

So far, I've taken it apart enough to see the torque sensor connections near the gearbox -- but I don't have a part # or anything.

So, all I have is the knowledge the sensor data is sent to the controller via 7 wires. I have access to these 7 wires.

Since the torque sensor is essentially 2 position encoders, I'm guessing 1 of those is ground, the other power (to power the photodiodes, for example), but the rest is anyone's guess. I've tried looking on the internet, to no avail.

I figured I could rotate the shaft the torque sensor is on, and see if the signals on any of the lines made sense if viewed seperately, or even together (ie channel 2- channel 1) -- but the sensor would need to be powered for that.

The cables are colored, red, black, white, blue, green, etc. Black / red isn't power by standard, is it?

Any advice? I'd really like to use this torque sensor.

Thanks,

Matt Lawson

 

[MikeHalloran]

There's no standard for color coding stuff like encoders.

Maybe you can glean info from the system docs or the shop manual for the car.

You could probe the sensor with an ohmmeter and look for diodes, then apply a little power with a series resistor. If you have access to the optical path, a digital camera can 'see' IR leds.







Mike Halloran
Pembroke Pines, FL, USA

 

[BobM3]

How do you get torque from encoder signals?

 

[MedievalMan]

A Torsion bar torque sensor is just a torsion bar, with a means of measuring the angles on each side of the bar. The "twist" of the bar is then measured:

Torque from torque sensor= K*( input angle - output angle )

where k is a known stiffness constant.

So you just need to measure the input and output angles.

More often then not, the input and output angles are available from the sensor as well.

-Matt