My name is Jon and I'm an applications engineer at Teknic. I came across your post and it's clear you've done your homework. I wanted to reach out to help answer your questions regarding machine safety and clarify how the “position recovery†feature functions in ClearPath.
In order for OEM machine makers to meet many industrial safety standards, two things are usually required when an e-stop is pressed:
- Disable the motor from the controller. If you disable any ClearPath-SD or -MC series motor (i.e. de-assert the Enable input), the motor will stop spinning and prohibit any future movement until it is re-enabled. With that said, de-asserting the enable input is usually combined with the next step for optimal safety practices.
- Interrupt the AC input power to the DC bus power supply (e.g. Teknic's IPC-5, 75VDC power supply) usually through the use of a safety-rated relay.
NOTE: Check the requirements of your specific safety standard.
The reason for incorporating both of these steps is that if bus voltage is still present at the motor (e.g. 75VDC), and the controller accidentally re-enables the motor, the motor can start spinning. By removing AC voltage and disabling the motor, you create a redundant safety system that prevents motion even if the controller re-enables the motor.
Once the e-stop is cleared, you can re-apply AC voltage to the 75V power supply, and your controller can then re-enable the motor. At this point, most applications have historically chosen to re-home their entire system to re-establish a known reference point.
With that said, you can avoid re-homing by using a low voltage 24VDC power supply to keep the motor’s logic (processor and encoder circuitry) alive during the e-stop. This logic power backup is fed to the Teknic POWER4-HUB. This hub seamlessly transitions the motor(s) to logic power backup upon detecting a loss of main 75V bus power. The hub also lowers the backup voltage to roughly 15V which is high enough to keep the motor's DSP alive but low enough to stay below the 24V operational threshold.
When a logic power backup event such as an e-stop occurs, two things are true:
- The ClearPath motor knows exactly where it is (its current encoder position).
- The ClearPath motor knows exactly where it is supposed to be (based on its last commanded position).
We can take advantage of this data and enable a “position recovery†feature in ClearPath. When this feature is turned on and the ClearPath motor is re-enabled, the motor will automatically move to its last commanded location, effectively syncing up the actual position with the commanded position. The motor will make this move at a user-definable (generally slow and safe) speed without any additional commands from the controller.
This means that as long as your controller keeps track of where it last commanded the motor, you’ll be able to recover to that position without re-homing your machine. If your controller takes advantage of this feature, you could even send a new command to the motor to go to a new “safe†position while the motor is disabled. Using this method, the motor will go to this new safe location automatically when the motor is re-enabled.
Teknic recently released a new video which details the ClearPath SD accessories. At the 7:40 mark in that video, we display the position recovery feature in action. If you’re interested in taking a look, you can find that video here:
https://www.teknic.com/accessories-guide-sd/
If you have any additional questions, you can reach us at support@teknic.com.
Thanks,
Jon K.