position of linear motor

[sima]

hi.
i need to have a reciprocating motion for my project.
i have a PM tubular linear dc motor and i want to use of photodiode to control the position of my motor. please help me.

[Ttelmah]

You need to do a lot more work/thinking.

Start with defining your project. Begin with what range of movement, and resolution you want.
Then work out how you are going to detect 'where' the motor is. A photo-diode won't do this. The best you can do with a photo-diode/LED, is detect a 'zero' point, which then means your system has to go to this point whenever it is powered back on, and from this make a 'good guess' of where you are (limited if the motor gets overloaded, and also by the cogging effects that these display). To actually allow accurate positioning, you need something like an optical position sensor.
So does your hardware allow you to achieve what you need?.
If not, start again.
If it potentially does, then you need to design the drive electronics to move the motor, and the input from the detector. Look at the application notes from Microchip, on driving BLDC motors. The tubular motor, is akin to one of these 'opened out' into a linear structure (the slotted versions are closer to steppers, the slotless designs closer to BLDC's)
Once you have these, you can start trying to drive the motor from the PIC. You have the same problems as for a BLDC/stepper motor, with needing to limit the acceleration, and speed. If you get this far, and have problems with the code, then we can help, provided you are working in CCS C. Understand that this is a forum to help in programming using this language, not in general electronic design, and though we 'stretch' this quite a lot, we are not a 'solve a project for you' forum. You need to actually have some physical hardware and code which we can then help with.

[temtronic]

PM tubular linear dc motor, hmmm. Can you post the mfr/make/specs or a link to the datasheet?

To me a 'linear actuator' could be the same thing..so more information is needed.
I would use quadrature encoder to provide feedback. Depending on the required speed, distance and CPR, it might be better to use an external 'chip' to due the actual counting and not the PIC.

Jay

[Ttelmah]

I've used versions that had linear encoders built in. Not a quadrature encoder, but a full position sensor. Problem with a quadrature encoder is you are back to having to move to a zero position before starting.

The ones I've used came from LinMot:

<http://www.linmot.com/products/linear-motors/>

It's worth reading this overview:

<http://www.engineerlive.com/content/22466>

There are two fundamentally different types internally. The commonest is effectively just a synchronous motor 'unwound'. There are also versions closer to a stepper. He seems to be talking about a 'bare' motor (without built in control electronics), but giving us no details at all of the type involved, power levels, motion distances, and resolution. Not exactly helpful....

[temtronic]

I've got a bunch of 'linear actuators' that have a built in resistor to provide 'feedback' as to the position of the ram. Actually quite good as a sensor, though only about 1% accurate.

have to agree we need a LOT more info to help though !

Jay