timbo_uk
Member
Hi all,
Slightly off topic question.
I have a web postioning unit that moves a web, in a printing press, sideways (to 0.05mm accuracy) to correct register. This is moved by a DC servo motor controlled by a custom made PCB.
Basically the DC servo motor (20 years old and obsolete!)is in good condition, other than a slightly reduced torque output due to (I assume) reduced power in the permanent magnets. The problem is the DC Tacho, it has a low output.
The tacho is supposed to give 20mV/rpm, but it is actually producing 16.5mV. The (non adjustable) control pcb is therefore overspeeding the motor when it's trying to postion. The controller is looking for 20V when moving at full speed; this equates to 1000RPM. With the reduced output from the tacho the motor actually runs at 1240 rpm.
This is causing overshoot and then a correction. The register then never "locks on" to the correct position and constantly wanders back and forward.
The OEM has quoted us around £12,000 for a replacement motor and tacho; BUT they need to send an engineer with it to modify the frame to make it fit. Only another £3,000!
I had an idea that if we could "amplify" the voltage from the tacho to the correct level, then I could see if it cured the problem we are having. For example if I get 16.5V out from the tacho I want to scale it to 20.0V
I have googled around but cannot find anything. Has anyone come across something that could potentially do the job?
Or have I just found a product that many would buy if I made one!!!
Cheers
Slightly off topic question.
I have a web postioning unit that moves a web, in a printing press, sideways (to 0.05mm accuracy) to correct register. This is moved by a DC servo motor controlled by a custom made PCB.
Basically the DC servo motor (20 years old and obsolete!)is in good condition, other than a slightly reduced torque output due to (I assume) reduced power in the permanent magnets. The problem is the DC Tacho, it has a low output.
The tacho is supposed to give 20mV/rpm, but it is actually producing 16.5mV. The (non adjustable) control pcb is therefore overspeeding the motor when it's trying to postion. The controller is looking for 20V when moving at full speed; this equates to 1000RPM. With the reduced output from the tacho the motor actually runs at 1240 rpm.
This is causing overshoot and then a correction. The register then never "locks on" to the correct position and constantly wanders back and forward.
The OEM has quoted us around £12,000 for a replacement motor and tacho; BUT they need to send an engineer with it to modify the frame to make it fit. Only another £3,000!
I had an idea that if we could "amplify" the voltage from the tacho to the correct level, then I could see if it cured the problem we are having. For example if I get 16.5V out from the tacho I want to scale it to 20.0V
I have googled around but cannot find anything. Has anyone come across something that could potentially do the job?
Or have I just found a product that many would buy if I made one!!!
Cheers