Problem with TCST2103 sensor

[Neena]

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

 

[Neena]

Please help anybody

 

[bassnut]

If its only micron errors there are lots of things that could affect it. Is the 24v supply rock solid?, ambient light getting in the sensor slot?, ambient temp changes?. By the look of the datasheet, are you sure this device is designed for repeatable accurracy to microns?.

 

[mneary]

The ambient light is coming from a different direction, and the temperature is colder. You could just wait till it stabilizes.

But really, the circuit just sucks. Start by regulating the 24V to a very clean 12V. Drive the LED with a 2.7k resistor from 12V. The sensor's collector resistor would be 47K to maintain the existing bias. Replace the floating base junction of the SK100 with an honest comparator set to 3V. (Operating at a higher collector voltage gives a better CTR and a better curve.) A cheap LM393 will do as a comparator, with the reference set by resistors at (12/4) volts.

The TCST2103 is marginal for this job. You shouldn't expect micron precision from a 0.6mm aperture. You could change the TCST2103 to a TCST2300 which would get your aperture down to 200 microns. The operating current would need to be adjusted because the CTR is 2.5% instead of 20%, and some mechanical parts might change because the opening is thinner.