Created Date: February 26,2019

Created by: psvail

Hi,

We have a 90VDC clutch coupling a motor and a chain-driven winding drum. Right now its a simple on/off circuit, but I need to make it shut down softly so that the tension in the drive chain doesn't allow the drum dog to get slammed when the clutch is released.

Initially I thought to use an analog output and ramp the voltage down over a short time, allowing the clutch to slip a little, thereby releasing tension.

My question is: Whats the cheapest circuit or control I can add that would reliably provide this? The clutch draws about 3-4 Amps.

Thx!

Created Date: February 26,2019

Created by: RogerR

I have some circuits similar using a 90vdc magnetic particle clutch.

To vary the voltage, I use a PWM with a DC-DC SSR.

Pulsing the SSR at different On-Off times will make a varied amount of power.

This allows for a ramp up/down.

Requires a PLC or some kind of pulse for the SSR.

Alternately a power resistor(s) placed in series with the clutch coil via relay contacts may drop its power slow enough.

This may be done without a PLC if the relay(s) can be turned on with existing logic.

The relay contacts may not last that long depending on the frequency of the machine cycle.

Created Date: February 26,2019

Created by: psvail

Thanks for the thoughts, Roger. Great answer, and I think that may be my clutch as well (it's magnetic, anyway). I wasn't very clear, sorry, I do have the system on a BRX and is now simply on a coil-based relay. I was looking how to convert the 0-5v 'WY ' output to drive the clutch. I like the idea of the PWM/SSR solution, I'll look into that. I would have never thought to pulse an SSR, but duh! So I would use the TIMEPROP function of DMD? I should be able to use a RAMPSOAK instead of a PID, right? Thx again!

Sorry, I since have done some reading and youtubing. I have been using the simulator, so didnt know about PWM Outputs modes. All set, thanks for your help!

Created Date: February 28,2019

Created by: psvail

Thanks Alexandru, that does help me understand some of the physics involved, and I appreciate your concerns.

Some background:

The application is a pre-existing church tower clock winder. 30 years ago a fellow parishioner had designed and built a robust system that uses two clutches and a good sized A/C motor using chain drives to transfer power to from the motor to the clutches to the 2 winding drums (one for the clock, the other for the bell strikes). As implemented, opto-detectors and reflectors on either winding drum would keep track of the rotations. If either drum ran out its count, it would request for power. The two clutches are independent, and if either is energized, the motor is energized. Once either drum satisfied its winding count, it would de-energize its clutch. When no clutches were active, the motor would shut off. Also, a clutch could engage while the motor is already on servicing the other drum.

Long story short, this system got struck by lightning and fried/fused the bulk of the control wires/components, hence my rebuilding it using a PLC.

The issue is that the drums are under tension due to the weights on each drum cable. When the clutch releases, it may be that there is 1/2 inch or so of backlash until the ratchet catches the pawl (not sure of terminology here). I am trying to reduce the shock of this, hence the slip. I dont really want to slow the motor, as it is still driving the other drum, potentially. Not sure how the A/C motor would take to being throttled, either - I'd have to check that.

It has been a fun project, and I'm almost there...

Thanks for the advice!

Created Date: March 01,2019

Created by: Alexandru

I wish you good luck on your amazing project. You may find a solution more practical and less intuitive than I could ever think from afar. If you ever need to implement a two-drum alternate mechanism to allow one drum to always drive the clock while the other winds up; or you decide to implement some soft brake which allows the drum to slip back slowly after clutch disengaged; or if you decide to implement both these ideas or other even more interesting, please keep us posted.

Created Date: March 01,2019

Created by: OkiePC

It's been many years since I worked with magnetic particle clutches and brakes, but we used a special power supply that allowed us to control the torque with a PLC analog signal. The supply also had a feature that momentarily would reverse the field polarity for applications that need a quick release. Magnetic brakes and clutches have a residual magnetism that can be dissipated most effectively with a brief reversal of the DC voltage applied to them.

The company we dealt with the most was MagPowr. It appears they have been bought or sold at least once since I last looked. I recall their reps being pretty good at helping us with trouble or new applications. I think we even did a trial using their power supply to operate an electromagnet for some product conveyance machinery (rubber coated steel fabric in tire industry).

http://www.maxcessintl.com/magnetic-...wer-amplifiers

Created Date: March 04,2019

Created by: RogerR

The particle clutches that I work with are always slipping some amount to provide the torque control to a spindle.

The program was a click plc and had two timers set up.

One was at 100ms and the second was at the duty cycle time required.

For each 100ms, the output of the second timer would activate the clutch for its fraction of 100ms.

The time base could have been made lower with the click, but resolution was lost due to scan time.

If a BRX was used, the PWM function could be used at a much higher rate.

The relay specs are max turn on time 300us and max turn off time 1ms.

I would think the unit could use up to a 1khz PWM signal.