Author Topic: High Speed Leadscrew Protection Circuit  (Read 421 times)

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Offline jonovid

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High Speed Leadscrew Protection Circuit
« on: November 08, 2020, 07:48:24 am »
will this H-bridge motor runaway protection circuit work?

investigation is required prior to the circuit being reset. if triped off by a malfunction!

if I have a Double BTS7960 43A H-bridge High-power Motor Driver module that will drive a 8000rpm 4 amp DC Motor with pulse width modulation
can I get your opinion
problem- I need a way to stop a 40watt dc motor from running the shuttle off the end of the leadscrew  in the event of a malfunction.
a runaway shuttle can cause major damage to the machine. as the Motor direct drives the leadscrew from one end.
the protection circuit must bypass ALL H-bridge logic and be fast acting without damaging the BTS7960 H-bridge.
the resistor is to minimize any EMF surge meanwhile stopping the motor.
use of two 10 amp micro switch's as leadscrew end stops.  independent of any logic end stop re-set micro switch's used by the Arduino / logic control
a malfunction can be for any reason whatsoever  bad code or human coding error or overheating logic circuits esc.
the circuit. is a manual reset  as the leadscrew needs to be  manually moved off the end stop before re-starting the run.
.shuttle control feedback is independent of this circuit by way of a rotary encoder not shown here!
will this runaway protection circuit work without damaging the BTS7960 H-bridge.?
it is a manual reset / hand reset.

the motor gear ratio is 1 to 1  with the lead screw.
most stepper drivers are too slow for this application.  so no belts are used .
actuator requirement is to slide a shuttle 35cm end to end in just 1.5 seconds. with a 3mm positional accuracy over that same 35cm .
by way of pulse width modulation.  sometimes under high contact resistance if steel wire is contact clamped , steel guitar mode.
to emulate the speed of a human arm / hand. over 35cm.  guitar neck
« Last Edit: November 08, 2020, 07:54:53 am by jonovid »
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Offline Doctorandus_P

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Re: High Speed Leadscrew Protection Circuit
« Reply #1 on: November 08, 2020, 11:51:18 am »
INH = Inhibit pin.
Just pull them all to GND when you want to disable the motor.
Add a bit of logic so your safety switches override what the microcontroller is doing.

One of the many possible variants is to use strong pull down resistors (Few hundred Ohm) and then simply keep the microcontroller in reset as long as the safety switches are activated.

Long wires on standard logic signals is not a good idea though. Add some RC filtering and a transistor as an input filter.
 
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Offline jonovid

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Re: High Speed Leadscrew Protection Circuit
« Reply #2 on: November 08, 2020, 05:08:09 pm »
INH = Inhibit pin.
Just pull them all to GND when you want to disable the motor.
Add a bit of logic so your safety switches override what the microcontroller is doing.

One of the many possible variants is to use strong pull down resistors (Few hundred Ohm) and then simply keep the microcontroller in reset as long as the safety switches are activated.

Long wires on standard logic signals is not a good idea though. Add some RC filtering and a transistor as an input filter.

thank you.  I will try this,   may also try adding a 2cm bit of rubber hose coupler as a slip clutch. 
still waiting for a parcel to arrive with the BTS7960 H-bridges,  as the other L298 H-bridges are too underpowered for this job.

way the cheap motors-  if you're interested
I have borrowed ideas from bubble jet printer designs by keeping costs to a minimum & avoiding complex powertrain designs,  toothed belts, pulleys esc.
« Last Edit: November 08, 2020, 05:26:53 pm by jonovid »
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Online nctnico

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Re: High Speed Leadscrew Protection Circuit
« Reply #3 on: November 15, 2020, 10:19:27 pm »
INH = Inhibit pin.
Just pull them all to GND when you want to disable the motor.
Add a bit of logic so your safety switches override what the microcontroller is doing.

One of the many possible variants is to use strong pull down resistors (Few hundred Ohm) and then simply keep the microcontroller in reset as long as the safety switches are activated.

Long wires on standard logic signals is not a good idea though. Add some RC filtering and a transistor as an input filter.

thank you.  I will try this,   may also try adding a 2cm bit of rubber hose coupler as a slip clutch. 
still waiting for a parcel to arrive with the BTS7960 H-bridges,  as the other L298 H-bridges are too underpowered for this job.
This doesn't add up to me. You want to use a slip clutch but at the same time you need a beefy motor driver. A 4A motor doesn't draw 4A. Brushed DC motor theory says that RPM is dictated by voltage and torque by current. So if you add a current limit to the PWM driver so that the torque doesn't exceed the mechanical safe limits then you are all set.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 


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