Automated Parking Lot

[bigoldblack]

Hi all,

My names Ben and I'm new to this forum. I'm currently a college student so is pretty new to the electronic/electrical world.

I'm currently working on a school project that is due in about 5months. Its a automated parking lot controlled by a plc (Micrologix 1000 L32BWA) using a 3 axis system. The motor I am using are these :
**broken link removed**

This is the design I have made and is currently building.
**broken link removed**

This is what I have currently done so far. I'm actually done building the structure, working on the axis now.
Flickrhotostream

My question is this. I need to be pretty accurate on the location of each section when programming and putting together axis. Any idea on how can achieve this as I am using dc motor with no braking system. I've already spent alot on this project and am not planning to spend more than $300.

Thanks, any help/suggestions would help.
Just ask if anymore information is needed.

Ben.

 

[Diver300]

You need a servo system.

Servo motors have a potentiometer that measures the position of the motor, in your case the height of the lift or whatever. The position is compared with what it is supposed to be, and the difference is used to control the motor current. A brake isn't important.

However, I would suggest a stepper motor system instead.

 

[jpanhalt]

However, I would suggest a stepper motor system instead.

Maybe a word was left out?

I concur that a servo would work. A viable alternative would be stepper with feedback, such as a sensor when the lift is at the correct floor. Considering the number of rotations needed for the leadscrew, a stepper may be a simpler solution, particularly because you will probably have to have a location sensor anyway for the transfer function.

You will need a way to transition from the elevator floor to your lift. For that, consider a continuous belt on each floor and on the lift. I suspect a stepper with position feedback would be the best choice for that as it would need to compensate for slippage between the car and the moving track.

It looks really fun, and it is great to see a question like this where progress is demonstrated by the OP.

John

 

[blueroomelectronics]

How would a servo with about 180degrees of movement be used to run an elevator?

Limit switches are how real elevators work.

 

[bigoldblack]

In the very beginning when I decided to build this, I wanted to use steppers but I found it to be really difficult hooking it up to my plc which I had before hand.

I just recently got these dc motors off Ebay and wanted to give it shot to see how it goes. I know I will have no precision at all but I'm wondering if there is a way to control the DC motor to make it as precise as possible. Would limit switches or photo sensors work?
I plan to use the timer in the plc with a sensor as an input to located each position, would that be possible?

I want to know if these combinations work before purchasing the sensors.
If it doesn't work I may need to sell the DC motors and purchase Steppers but I really don't want to.

Ben.

 

[jpanhalt]

Continuous rotation servos can be made from standard servos. Perhaps most important, they are now being sold commercially by at least one vendor for the robotics trade (Hitec).

One could also envision a series of gears or levers too, but that approach would be complex and more demanding from a design and construction standpoint.

John

Edit: Steppers are only one way to do it. There are plenty of DIY CNC with ready made applications using them, which made them attractive. Continuous-run motors, as long as you have feedback, will work fine. If you use a worm gear, they are self holding, and with DC power, overrun would be quite minimal, which might negate the need for a brake.

 

[Diver300]

How would a servo with about 180degrees of movement be used to run an elevator?

I wasn't suggesting an RC servo motor. The 180 degree movement would be useless.

I should have explained better. You need a potentiometer connected to the movement so that the potentiometer it moved over its range as the lift goes from bottom to top. That will give feedback so that the motor can be controlled.

With DC motors and a PLC, you could also use microswitches at each level. You would need to program the PLC to stop the DC motor when the lift gets to the right level,

 

[Boncuk]

Just one more hint:

Penny & Giles (UK) produce linear pots of different lengths. (Normally 200mm). They are pretty precise, too.

Connected to a reduction gear they would give information about the location of the lift.

Using two SPDT relays you can force the DC motor to stop hard by shorting the motor.

BTW: Commonly CNC machines don't use feedback for the stepper motors. Initial zero/zero positioning is used for almost every machine. You could use any motor if a stepper motor wouldn't have the necessary accuracy.

Boncuk

 

[Mr RB]

I would use DC geared motors connected to a simple threaded rod (1mm pitch) for the elevators. If you pull apart some old printers you can get slide rods and bearings for the elevator mechanism. You can also buy stainless steel 1/2" tube from the hardware store (towel railing) which is good enough for slide mechanisms.

Then something as easy as a microswitch on each level (as Blueroom said) to tell the controller the elevator has reached that level.

 

[bigoldblack]

Thanks for the replys, I have finished with my X and Y axis of my project and have decided to use the microswitch idea. My last axis is almost complete now.

I have a question regarding my load platform (the middle part in the diagram)

**broken link removed**


I'm going to need rotate this 90 degrees at a really slow speed. Any device anyone could recommend I could do this with. I will be controlling it with a PLC (micrologix 1000) so a servo would be quite difficult. Would stepper motors be possible? I know the 90vdc motors I have now would be impossible to use.

Any suggestions would be great.

Thanks,

Ben