Encoder

[Agostinho Macedo]

I´m preparing my first use of encoder to control the position of one elevator with 10 floor. My idea is to reduce costs and improve effecience and flexebility. I´m using a incremental ABZ 1000 ppr and the idea is to control the motor with a frequency variator controlled by the incoder.
I have experience on plc programming but this is my first time with encoder. If someone could give me any idea to improve the program or the main problems I could find I appreciate very mutch.

Thanks

 

[iant]

Consider the speed of the pulses to the PLC input and the maximum input speed allowable.

eg.
1000ppr x 100rpm = 100000 pulses per min.
CAN THE PLC HANDLE THIS??????

 

[J.S.PARTHASARATHI]

ENCODERS

dEAR sir,

On paper you should calibrate at what pulse each floor comes.

when it is at bootom , load the counter with 0000.

One more tip:

You should select pulse card which is bipolar. A and B pulse shall be connected to Pulse card.

When you are programming never use "EQUAL TO" block as it will not exactly stop the motor.

use Range say 650-660 pulses to stop on floor 1
use Range say 750-755 pulse for floor 2.

Also note that you should be aware of how many revolution motor makes between ground to the top.

During site trial, adjust. Once it is proven only , allow people.

Regards,
J.S.Parthasarathi.
Senior Manager , BHEL
Bangalore , INDIA.
e-mail : [email protected]

 

[Alan Case]

Can you post which building this lift is in. If I am ever in that building I will know not to use that lift. Regards Alan Case

 

[Pierre]

Alan, can you forward the answer to me if you ever get it... just in case!

 

[Goody]

Alan, I am glad you said it first; I laughed at your post as I had thought exactly the same thing. With us all being under orders to get along, I was reticent to post anything negative. But a beginner programming a ten floor lift ooooH.

 

[Peter Nachtwey]

Ditto, the above and....

The following information is for informational purposes only and should not be considered encouragement to continue with this project.

Use an absolute encoder using gray code. Can the PLC quickly convert gray code to binary? No one wants to be in the elevator when the encoder looses position/registration.

There must be a way of detecting the whether the encoder has failed or is disconnected, INSTANTLY. I would look into a synchronous serial interface instead of parallel data lines. SSI provides a way of detecting whether the absolute encoder is connected.

Use S-curves for the acceleration and deceleration. Trapezoidal ramps are jerky.

Reconsider this project and the approach.
Just because you ( think you and the PLC ) can, doesn't mean you should.

 

[Agostinho Macedo]

encoder

Is not an elevator to transport people, it´s to move materials, kceramic materials in fact, so you don´t have to wory. Of course I will never use an encoder in my first time in that condition. I´m not crasy, yet ??

If you have more issues , I thank you.

By the way , the plc is a Modicon Momentum 171CCC98030. I think one of the best to work in hard conditions.

Thank you for the tips.

 

[Alan Case]

I apologise for the misconception. A materials hoist is a different proposition altogether. Regards Alan Case

 

[Jiri Toman]

encoder issues

I am surprised that so far only one person has even touched on the
issue of reliability and safety as it obviously applies to an elevator
control.
First of all suggest that you try to use an absolute position encoder
as opposed to using an incremental one. Yes, the pulses can be lost.
Secondly the encoder alone should not be used as means of identifying the floor level. You need to verify the floor level at every floor with a prox switch. Use the encoder to provide you with the info
for accel and decel rates. In case the encoder fails you should have a safety feature that would put the motor in a safe mode (slow mode).
Do some reading with regards to safety of the elevator control.
Of course I don't know if this is a people elevator?
Good luck.

 

[Pierre]

Agostinho, using an encoder for a lifting device is just a bad (if not silly) idea. Encdoers gives you some data which cannot be given by limits switches alone, you can adjust on the fly a target position when it move(the target of course). So you can have different "recipes" and you can mix and match various axes by there relative position to one another...

So, are the floor changing position?

Beside the money involved, I can see only on reason why you should be using an encoder for lifting devices and it's a physical one.

Can you tell us why you want to use this...

For your first question, I usually work with Zones. Acceleration Zone, Deceleration # 1,Deceleration # 2 and finally Target Position zone

 

[Agostinho Macedo]

Encoders

Pierre. I don´t understand what you mean by "phisical one".
If is a 10 floor elevator I don´t have to use 10 switchs detecter more 2 for emergency, 12 in total.
Another reason to use encoder is the adjustment made by the operator in terms of distance to stop. As you maybe know the break of the motor will be different over time and besides the weight of the material changes time to time.
The distance between floors is allways the same and the middle one is the main stage where the elevator recives the material by another machine , so the elevator will have to move to the middle stage every time.

Find me ?

 

[Pierre]

Agostinho wrote:
"Pierre. I don´t understand what you mean by "phisical one".
If is a 10 floor elevator I don´t have to use 10 switchs detecter more 2 for emergency, 12 in total. "

You reasonning is perfect. I have done the same thing in the past... A physical limitation would be... space.

We where transferring tobaco boxes from ground floor to various other floors. We called this one "Elevating Conveyor" (directly translate from french), but it was an elevator...

Those boxes, when they came back down, where empty. So the encoder system was a great device to program different accel / speeds, etc.

I recommend you use a variable speed drive on this one.

The break could then be use only at very low speed and the wear would be minimal.

The bizarre answers came from the fact that you didnot state the natur of the system.

As you see, for most of us in this forum...

SECURITY is numero uno

So the comments where an healthy sign.

 

[ganutenator]

I recommend using a servo drive and a tach.

This way, if you lose the tach input, the elevator will travel up faster than freefall. Thus giving the user, a feeling of weightlessness. Much like the power tower at cedar point.

wheeeee..........fun

- just kidding, I'm out of line.

P.S. don't forget the brakes that set on loss of power.


commercial:
quack, quack, Aflac

 

[kalle]

I see no problem using a incremental encoder in this project (material elevator), but I would have used more than 1 init switch/position.

Consider that the init-switch is at the 1.floor and the elevator is at the 10th when it loose its count (power loss or someting)
The elevator has to go in slow? speed the whole way to the 1. floor to find its init-position and reload the counter with the preset value.

The go-to-init-speed would depend on the distance from the init switch to the physical end. If the go-to-init-speed is too high, then you shouldn't do the init on the positive edge of the switch, but reverse in slow speed and make the init on the neg edge

And of course: you must be able to count both up and down...

There is also a low-cost solution we often use for movement with a few fixed positions.
Instead of encoder + count-card + analog interface to inverter, there are only need for some inductive sensors and a digital speed connection (2 speed) to the inverter

At each position, there is a binary pattern of flag/metal and a slow speed flag that is longer than the position flag.

                Pos1    Pos2    Pos3    Pos4    Pos5  etc
PosSwitch 1      -               -               -
PosSwitch 2              -       -
PosSwitch 3                              -       -
PosSwitch 4
SlowSpeedSw     ---     ---     ---     ---     ---

The drawback is of course that the sensors have to be located on the mobile part, that is, the elevator. (Cable chain/reel etc..)