DIY Stepper function

Hello everyone.

I have been in the electrical trade for close to forty years. I have done basic programming but now have a need to go further.

I would like to control a trolley over an aquarium so as to move my lighting fixture from one side to the other in stepped order. There is a need to keep it simple. My thought would be to have a drive pulley in the middle with two idlers at each end.

The drive pulley would either have holes or some kind of pickup for the proximity switch. This would count the revolutions and then stop the trolley at the next position. There would also be a need for an over travel function prox and a home location prox.

The biggest thing is when a power loss happens the 'on power loss' position would need to be called on.

You can think of this as a DIY very slow encoder setup.

I am not well versed in the drum sequencer but would this be the option I would look for?

Any help would be greatly appreciated.

Regards,
mrhappyzapp

I could see using a DC motor and control. Direction and speed selection can be done via relays that connect to the motor controller.

You would likely be using a PLC maybe an Automation Direct Click.

I have done a similar thing on an overhead crane for a gigantic pick and place. I used several photoeyes on the trolley with reflectors stationary on the rails to provide major positions binary indication and a photoeye looking at reflectors on the trolley wheel to provide finer incremental info.

On power loss you could simply home the device then return to the previous position.

One pulley is motor. No middle pulley. Use Posi-Drive belt.
Use stepper motor.
One prox at home. Home after power fail.
You would not use Drum for this. Use up/down counter for position. Reset counter with prox.

Thank you for the replies.

Yes, I am using a Click.

Ok, so I will have a pulley with pickup points for the prox switch.

Yes this will allow an up counter which will enable timer functions until the next move forward. This I will play with. No doubt this will be a rudimentary way of moving the trolley along as long as the power stays on.

Question is how to get the trolley to move to the proper position after homing out on power up.

The only thing I can think of is having some kind of register to save the counts in each position forward, overwriting the last and have this register value somehow be saved on power outage.

The only time this register would totally clear is when the trolley has done a full run and would home at that time automatically anyway awaiting the next pull sequence.

Hope I am making some sense.

Yes a stepper motor would simplify things using the Click but I would like to make this work for my own education.

Thanks all,
mrhappyzapp

A stepper motor is perfect for this.

www.linengineering.com is a great source for steppers. Call and speak with an application engineer. They can help you size the motor and the drive based on the needed torque and the available supply voltage.

+1 on the mechanical config suggested by keithkyll.

Drive the stepper with this drive, the R710:

http://www.linengineering.com/Drivers-Controllers/R701-R710.aspx

You can control the motor with an AutomationDirect DL-05 PLC.

http://www.automationdirect.com/adc...ogic_05_(Micro_Brick_PLC)/PLC_Units/D0-05DD-D

Those AD PLCs have a built-in stepper "motion controller" function.

Come back with questions. This is a cool project.


-rpoet

Yes, will keep you posted as I progress.

Thanks for the additional info.

Regards,
mrhappyzapp

mrhappyzapp said:

... The only thing I can think of is having some kind of register to save the counts in each position forward, overwriting the last and have this register value somehow be saved on power outage.

Click to expand...

Home - drive slow in reverse until prox.
Clear up/down counter. Counter is now your position register. Every time you send a forward pulse, pulse the counter "up" input. For reverse...

PLC's can save values. With the Click, you can select it for every variable.
Saves for a few days with a supercap. Years with a battery.

Thanks keithkyll.

Your suggestion is with a stepper motor, no?

I am trying to do this with DC motor, gear reduction and prox switches.

Yes you may think me a little off but it is a project and no doubt the final version will be with a stepper.

Thanks for the links rpoet. I will be using them.

For now I need to get this to work as I said for my own education.

When power fails I will have no need to count down, just go back to the home position. What I need to figure out is the register thing. I think I will add to the register instead of updating with new count each time. Hopefully when power outage occurs, trolley homes, count on PF in register remains with RTC time stamp and then the sequence can go to the proper location after looking at RTC so as to complete the sequence.

Would using the RTC for each move be a better timing function and have the accumulated count refer to each time stamp. This way on a PF reset the program would look at RTC and determine which count to go to.

Thanks,
mrhappyzapp

RTC's (Real Time Clock) are used with microprocessor systems. You don't have that kind of high speed access to a time stamp with a PLC. You need an encoder, or some way to generate pulses as you rotate. Low cost encoder from AD.
Cheapest method is to use a screw with a large head on a pulley and use a prox to sense it. Again, use the pulse to increment/decrement a counter.

OK. Having worked with older gantry style robotic machines every time there was a power outage you would need to home out the gantry. Old incremental encoders. Same as I am trying to build with pulley, pickups on pulley and proximity switch for counts. There was no counter down scenario for homing with the old machine. Just slow travel back to home.

Then you would need to take it back close to where it left off, (step in the program), and the machine would complete it's program.

Prox switches and homing limit switches were used.

Worked there and I guess I am trying to build an old machine.

I am just trying to mimic the scenario but I would like an Auto restart so when I am not around the lighting system will always be correctly aligned.

Will have to begin the experiment.

Regards,
mrhappyzapp

Sounds like a perfect application for an Arduino (or even Raspberry PI). Cheaper than a Click PLC. Arduinos start at around 25 bucks.

You can probably do it for less with a DC motor and a string pot for feedback. The string pot is an inexpensive absolute position sensor. You won't loose position due to a power off condition, allowing you to dispense with end of travel limit switches and a homing operation.

Arduino. That word gives me a bit of a scare. My C++ is very rusty, as in rusted out.

Will have to look into it though.

Thanks,
mrhappyzapp

K and B Electronics has many DC controls for low $$$. I have used them many times.

http://www.kbelectronics.com/Variable_Speed_DC_Drives.html

TConnolly, thanks for the tip.

@danatomega, thanks for the link.

Began sourcing out these string pots and least expensive one I could find was 42.00 bucks but by the time shipping and taxes were tacked on came in over 90.00 bucks.

Sooo DIY brain kicked in.

Will be making my own with a retractable key ring holder, 2 4 inch plastic pulleys and one 10K 3 turn pot. This will give me my 32 inches of travel. Maybe 40.00 bucks into it.

With this feedback from the pot and 2 capacitive prox switches for overtravel the system will be functional and simple.

Ya', just needed to use those emotos!

Thanks,
mrhappyzapp

With a click it is possible:
for each direction you will need a small relay to switch the motor current each way.
now for the encoder two inputs are enough, with two small microswitches you can build your own encoder. on the shaft comes a square with rounded corners, the switches should be one on the edge and one on the rib.

and one home switch.
move forward until encoder has made 100 steps forward.