Controler. Elevator

Thread Starter

ProWeldWorx

Joined Oct 19, 2022
2
I have a project that I need help with. It’s a book shelf on tracks behind a wall that will go up and down to only expose one of the three shelves at a time. What I have is a 24v DC motor that runs a winding drum. Also a brake that is held machanicly closed but will open with a 110v coil.
The plan is kinda like this unless I find a better way.
Push the up button-brake release-motor runs up one shelf hits limit switch-motor stops- brake engages.
Push the up button again-same as above.
Push down button- brake release-goes down one shelf-hits limit-brake engages.
So I need a controller or some sort relay logic board or a PLC. Thanks
 

MisterBill2

Joined Jan 23, 2018
18,962
he sequence is good but the safety portions are missing. There needs to be a way to prevent motion if hands are reaching into the shelf, and also to stop motion if there is a jam-up and binding. Certainly this can be done with relay logic, but using a small PLC will be simpler and more reliable. Reliability is very important when safety is part of the requirement. So a small PLC with included programming software will allow programming in relay ladder logic, which is a form of boolean logic with symbolic reresentation that makes it much simpler to understand. I suggest a PLC from "Automation Direct" as a reliable, low cost and ready to use solution.
 

Thread Starter

ProWeldWorx

Joined Oct 19, 2022
2
he sequence is good but the safety portions are missing. There needs to be a way to prevent motion if hands are reaching into the shelf, and also to stop motion if there is a jam-up and binding. Certainly this can be done with relay logic, but using a small PLC will be simpler and more reliable. Reliability is very important when safety is part of the requirement. So a small PLC with included programming software will allow programming in relay ladder logic, which is a form of boolean logic with symbolic reresentation that makes it much simpler to understand. I suggest a PLC from "Automation Direct" as a reliable, low cost and ready to use solution.
How do I chose the PLC?
 
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MisterBill2

Joined Jan 23, 2018
18,962
Free programming software is one reason to use the brand that I suggested. For some brands the programming software costs more than the PLC.
The selection depends on the number and type of inputs and outputs and the size of the program,and what communication with the outside you need. In your case the inputs will all be switches, and the ouputs will control the motor direction and some indicator lights, so the I/O should be simple. The program will be short, and no data needs to be saved, so eve a "smart relay" package might be applicable.
 

Jerry-Hat-Trick

Joined Aug 31, 2022
574
For safety, I'd recommend a door hinged along the bottom with pegs either side at the top which push into holes behind which there are microswitches connected in series with each other and the motor drive. It could be glass fronted in a wooden frame. This would prevent the motor from running when the door is opened.

Maybe use a DPDT (Double Pole Double Throw) Momentary Rocker Switch so you can’t press the up and down buttons at the same time. I think the following might work:
1666275598485.png

Sx is the switch which opens when the shelf is in one of the three positions. S1a is the momentary rocker which brings power to the system when the shelf switch is open. The two "door closed" safety switches also need to be closed. The second pole of the momentary switch turns on either the UP or DOWN relay(s) in the H Bridge. Once the motor pulls the shelf away from Sx the transistor holds the relay on (when the momentary switch is released) until Sx is triggered off again. S2 and S3 are switches which stop the shelf going up when it's at the top and down when it's at the bottom.

In case the momentary switch is pressed whilst the shelf is moving in the other direction it also grounds the base of the transistor holding the present direction on. A resistor instead of two diodes might be okay. Probably best to have a delay turning on the relays with S1 to make sure the other direction has time to turn off properly.

Grateful if someone could check my logic and maybe improve on this?
 
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