Advice on a Motor Application

I'm looking for some advice on a motor application. To keep it simple, I'll use the following description. I have a 20 lb weight that I want to raise and lower according to a time schedule. When the process starts, there is an initial delay and then the motor will pick up the weight say 12 inches. Next there is another delay and the motor will lower the weight back to its original position. This may repeat several times with the weight being picked up different heights each time.

I want to use a PLC to control the system. The speed of the application is relatively slow. Let's say it takes 1 second to raise or lower the weight 12 inches. Since I need to hold the weight for a few seconds, I'm thinking I need a stepper motor. 20 lbs is pretty heavy for a stepper motor so I'll need a high torque motor. I'll also need a controller for the stepper motor. The way I see it, the PLC will need to send pulses to the controller to raise and lower the weight. It is an open loop system, so I don't need feedback.

Questions:

  1. Should I consider some other type of motor and if so, what kind?
  2. Any recommendations on high torque, low cost steppers and stepper controllers?
  3. What kind of power requirements will this application have? AC, DC etc.
  4. I'm trying to keep the whole system down to a minimal size, any suggestions?
  5. I'm trying to keep the cost of the whole system down, but I don't want to have to build my on controller. Any suggestions?

Thanks in advance for your feedback.

Reply to
CCE
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The weight is not a big issue since you stated that the speed is slow. You could use a stepper motor and a speed reduction system. Steppers are open loop and can loose their set point. PLCs are now inexpensive and are easy to interface to stepper motors.

If your design requires a feedback system, you can still use a PLC.

Reply to
Charles Schuler

Gearing is potentially problematic; have you considered hydraulic solutions? A few simple solenoid valves and a compressed-air power source is all it takes to move a piston.

Also, a reel of fishing line and some block/tackle can interface a stepper to a 20 lb load pretty easily.

Reply to
whit3rd

How many different heights?

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Reply to
Homer J Simpson

I have some experience with PLC's. The benefit I see is the 4 line display that can be used as an operator interface. This type of interface can be used to reset the stepper if it looses its set point. What I don't have any experience with is the stepper controller. I've been looking at the Superior Electric KM series of high torque steppers and the SS2000D3 series controller

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It looks simple enough but it also looks expensive. Can you suggest a less expensive solution?

Reply to
CCE

Two or three. The cycle time would be less than one minute. This is not an application that would run continuously either.

Reply to
CCE

Maybe this will do you?

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-> "LA-29"

A.F.A.I.K. these products all use a normal motor driving a lead screw with a Reed-switch counting spindle revolutions.

They are used in furniture - like my ergonomic desk here - for raising beds under fat blokes, opening windows e.t.c. so there is some volume to push prices down!

Reply to
Frithiof Andreas Jensen

prices

PS: There are industrial versions too off the main site:

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Reply to
Frithiof Andreas Jensen

Thanks for the suggestion. I'm using a linear actuator now, but it is too slow and has limited stroke.

Reply to
CCE

Just use limit switches then. Enable the right limit switch as needed. It'll be a lot more accurate and repeatable.

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Reply to
Homer J Simpson

If you use a worm-gear gearbox, you can arrange it so that the weight cannot drive the motor shaft, but the motor can easily drive the weight. (This seems counterintuitive to me, but it works.) That would greatly simplify holding the weight --- just shut off the motor, which could then be a simple dc type.

Raising 20 lb at 12 in/sec is about 30 watts before you take any inefficiencies into account.

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   Wim Lewis , Seattle, WA, USA. PGP keyID 27F772C1
Reply to
Wim Lewis

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