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Forum Index : Microcontroller and PC projects : Question for Computerized motion gurus
| Author | Message | ||||
| matherp Guru  Joined: 11/12/2012 Location: United KingdomPosts: 11094 |
Probably no correct answer but... If I get an estop condition should I remove the enable on the motion drivers? For: guarantees power is removed Against: axis momentum could cause more issues |
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| PhenixRising Guru Joined: 07/11/2023 Location: United KingdomPosts: 1791 |
In the context of closed loop servo motors: A regular e-stop, I change the current decel ramp to as fast as is reasonable. Use the motor power to bring the motor to a controlled stop and then disable. Coasting can be catastrophic. If the e-stop is caused by a servo loop going awry (servo-amp, feedback, etc.) then disable immediately. In some applications, my motors feature an integral brake (fail-to-safe). Don't know about open loop steppers, though. |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 8681 |
It's a case of which is the lesser of two evils - let the thing come to a natural stop or use some sort of braking to prevent damage from inertia. Industrial approaches often use the latter, with mechanical brakes held off by a control supply. If that supply fails the brakes come on. If the device is still being powered then it will probably trip it's overcurrent protection. Pumps and medium size fans are usually just left to freewheel to a stop. A motion drive module may be configurable to use electrical braking if disabled (e.g. both top or bottom devices in a H bridge turned on to short circuit the motor). Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| PhenixRising Guru Joined: 07/11/2023 Location: United KingdomPosts: 1791 |
Mick, yeah I had to ask ChatGPT it dynamic braking worked for steppers  |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 3084 |
If the E-stop needs to cater for controller failure a DPDT relay for each motor could supply dynamic braking without short-circuiting the driver. The contact Commons go to one end of the stepper phases, the NCs to the other ends and the NOs to the driver. Cutting power to the relay shorts the motor. |
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| mozzie Senior Member  Joined: 15/06/2020 Location: AustraliaPosts: 235 |
G'day, Not claiming to be a guru by any means  This is going to depend as much on the way the motors drive the machine as the motor type. With single/dual start (fine pitch) leadscrews the motor+leadscrew inertia is going to be the main factor determining how quickly the machine comes to rest. With multistart / broad pitch leadscrews or rack+pinion / chain / toothed belt drive the actual machine inertia will be the main factor. Stepper motors also have a fairly high detent torque and this plays a major role, regardless of the driver state. Also some motor drivers handle the inhibit / enable signal differently so more variables. My suggestion would be making it a parameter in STEPPER INIT so the integrator can decide what will work best on a given machine. Also throws the onus back on them to make the correct choice. Regards, Lyle. Edited 2026-03-20 16:51 by mozzie |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 8681 |
There are many ways of braking. Another is by DC injection onto the windings of an AC motor. I suspect this would stop a stepper immediately by locking the rotor solid. You only need to inject across 2 of the wires. In all cases though, stopping the prime mover of a system will always stop the rest of the drive chain, although it's possible for something to get damaged in some cases. In an emergency stop that doesn't matter as the machine can be repaired. The important thing is that it stops. As ChatGPT says though, sometimes you don't want a sudden stop, you want a controlled deceleration. This would be typical for a crane, where a sudden brake could snap the cable with even worse consequences as the load is suddenly removed. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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