Problem with TCST2103 sensor

[Neena Desai]

tcst2103

Hi all..

In my project, i need accuracy of stepper motor position. I have used transmissive optical sensor TCST2103. I used this sensor to recognize motor home position and the all the other process is done in reference to this home position. I get same home position for my whole day testing but when i turn off machine for whole night and next day morning when i turn on the machine i get error in home position. The error is in micron but it is too much for my application.

Can anybody please suggest me what can i do?

Thanks in advance

 

[FvM]

tcst 2103

TCST2103 has an aperture of 1 mm and a specified resolution of 0.6 mm. It sounds unlikely to achieve more than 100 um repeatability without special optics. You basically are using the wrong position detector. Furthermore, there may be other sources of position error in your application. We can't know, cause you didn't give any details.

 

[Neena Desai]

sensor home position repeatability

Thanks for reply.

I get 35 micron(approx) error in motor position when i turn on the machine in the morning but after 2-3 hours i get back actual position. Is there any temperature effect or somthing else?

 

[FvM]

tcst2103

There's surely a temperature effect in TCST2103 sensor. You should use a better sensor or add an additional aperture to increase the sensor repeatability and long-term stability. Then you'll see, if the sensor is the dominant source of position error. Photo-interruptors with apertures down to 0.1 mm are standard products, available from several manufacturers, BTW. To provide some more application background, what's your step resolution? What's the gear backlash amount (if any)?

 

[kspalla]

It may be stupid suggestion that
you should try with two sensors may be in differntial mode.

 

[Neena Desai]

I am using IMS Mdrive17plus motor. Step resolution is 51200.

Added after 3 hours 35 minutes:

I run the motor with motion controller card which is very accurate. Is there any other logic circuit?

 

[FvM]

Do you have a specification for absolute position accuracy/repeatability of the drive? I see, that it provides the resolution through 256:1 micro stepping. Micro stepping can be expected to achieve a monotone positioning, but not necessarily a long-term stable position in a micro-step scale, cause the motor magnetic properties are temperature dependant.

But I would try with a more accurate reference position sensor first, as previously discussed.

 

[Neena Desai]

I don't have exact idea about absolute postion abd due to some mechanical limitations i can not change sensor in my current machine. Only electronic circuit i can edit. So please give me some ore guidence.

 

[FvM]

No way, cause it's most likely not an electronic problem. BTW, I also suggested adding an additional aperture. That should be possible somehow, at least as a temporary means of test.

 

[Neena Desai]

Can you suggest me any other sensor?

Added after 1 minutes:

I don't have any clear idea how to add an aditional aperature. Please explain me more about this.

 

[FvM]

You can browse the catalogs of e.g. Vishay or Sharp and choose a transmissive sensor (photo interruptor) with a smaller slit or aperture. They may have one with a form factor identical to TCST2103. Possibly the output current is lower, the load resistor has to be adjusted in this case. You can try to reduce the aperture of TCST2103 by partially covering the existing one. A possible solution would be a laser printed transparency film, that can be attached to the part.

However, after I know about the micro-stepping ratio of your drive, I fear, there may be rather a problem of drive position temperature drift and repeatability. The difference can be checked by performing repeatability tests with and without re-zeroing the position, I think.

 

[Neena Desai]

Thanks FvM,

I will try to reduce the aperture of sensor and check the result.