Clock query

Thread Starter

NeilIves

Joined Aug 10, 2020
9
Hi. Sorry if this is not the right place for my question.

I have been given an ancient card clocking-in machine. It, and presumably others around a factory were once controlled by a central master pulse sent twice a minute. Some clever person, before my ownership, designed a pulse sender to fit inside the clock case. The clock works but when the pulse is sent, the mechanism, (a pair of large electromagnets acting on a lever) make a rather loud CADONK!
Here's my question. Can you give me advice on how to make that electromagnet pull-down slower and hence quieter?
I was wondering about a large value capacitor across the coils.

If this idea will not work, I was wondering about using a cam on a stepper motor with a 30-second revolution to push the lever instead of the pulse sender. The engineering for that might be beyond my abilities though.

Many thanks to anybody who replies!

Neil
 

Attachments

Papabravo

Joined Feb 24, 2006
14,244
The circuit you are dealing with is called an RL-circuit
https://en.wikipedia.org/wiki/RL_circuit

It is modeled by an ideal inductor in series with an ideal resistor. The characteristic of this circuit which is relevant to your problem is the L/R time constant. The magnitude of the current is what makes the solenoid move. To slow it down means increasing the value of L/R. The way you do that is to reduce the value of R. Do you have a shot at determining the present value of R?

BTW - I don't think a capacitor will help you very much, especially in parallel with the inductor. You can solve that ODE and see for yourself.
 

Thread Starter

NeilIves

Joined Aug 10, 2020
9
The piston idea sounds like fun! I could probably make that with plumbing bits. Do you think it would need a damping fluid, or would air suffice?
 

Thread Starter

NeilIves

Joined Aug 10, 2020
9
MInd you, there is not very much movement; probably only 2mm between the face of the electromagnet and the lever it attracts. I could get a bit more movement by extending the operating lever
I wonder if a strongish spring might be enough to tame the beast.
 

andrewmm

Joined Feb 25, 2011
532
lump of foam rubber at the end thats making the clunk.
lump of sound deadening around end that making the clunk
isolate on springs the clunking thing from the case that could be acting as a sound board.
 

Thread Starter

NeilIves

Joined Aug 10, 2020
9
lump of foam rubber at the end thats making the clunk.
lump of sound deadening around end that making the clunk
isolate on springs the clunking thing from the case that could be acting as a sound board.
I placed a piece of cardboard between the core and the lever. It quietened the sound but prevented the clock escapement from fully engaging.

The clock mechanism is bolted into a nice soundboard of a wooden case!
 

Thread Starter

NeilIves

Joined Aug 10, 2020
9
Just let you know what I did with my clock:
To recap; I needed to operate the escapement of this Gledhill Clocking-in machine twice a minute.
Using the pulse generator that someone had designed and made for it was really too noisy to be used indoors, (it wouldn't have mattered in a factory environment)

I bought a 12v 2rpm geared motor unit, (cost £13 from Amazon). I made a cam for the motor shaft. I added a piece of stainless steel to the existing aluminium lever. I knocked up a bracket to hold the motor. I already had a good quality 12v PSU to use.

It worked straight away but the clock ran too fast. I've added a PWM DC Motor speed control module to regulate the speed.

Ok, I know that that little motor was not designed to run constantly. It doesn't get warm to the touch but I don't think it will be running in 10 years time! Ok, I know the accuracy is not going to be very good.

The clock is now almost silent. Wifey is pleased!

https://www.dropbox.com/s/01sotlih5ohi5fm/VID_20200815_184733.mp4?dl=0
and
https://www.dropbox.com/s/mxdkcgj1nb72d6z/IMG_20200815_184805.jpg?dl=0
 

Thread Starter

NeilIves

Joined Aug 10, 2020
9
The motor driving a cam was not accurate. I've now bought an Arduino Uno clone, modified one of the code examples and fitted a servo to my clock. The servo turns slowly back and forth every 30 seconds, as required by the clock design. The servo arm presses on an extended lever that shifts the escapement mechanism. At the moment, the only servo I had at home is too puny to operate the clock escapement reliably so I've ordered a more gutsy one.
These Arduino boards have great potential; I'm pondering what else they can do around the place!
 
Top