Servo Positioning - AB - HSCE / NO4V

Ramil

Guest
R
Dear All,
I am upgrading the PLC of an old machine which came with Omron PLC to AB SLC 500 for servo positioning.

Machine operatoin: Punch and shearing.

Servo drive and motor are from Indramat. (model: DKS1.1-W100A-D)

I have used the below for servo:

1. 1746-HSCE (high speed counter encoder card)
2. 1746-NO4V (Analog(voltage) output card)

Problem faced:

1.SLC analog output:
In SLC - i used 0 to 32764 for 0 to 10Volt DC.
When i write 0 to the analog output channel and measure the output voltage at the analog output channel i get voltage from 0 to 0.25 and it varies. it does not remain 0.
Because of this the motor is moving very minutely.
To avoid that we removed the drive enable command so that the brake holds the motor. Is there a way to make the SLC analog output card to output only 0 volts when i move 0 to output file so that i donot have to make and break drive enable command.

2. The indramat drive has two analog input. All single ended. One single ended analog input for forward and another single ended analog input for reverse. But they donot have any point for return signal.
I have wired Analog output channel 0 positive signal to forward point and wired the negative or return signal to a 24V common on the drive.
Also i have wired the analog output channel 1 positive signal to reverse point in drive and wired the negative or return signal of channel 1 to 24V common found on the drive.
Becuase the drive does not have any common point in the analog input card. Is this o.k. Should i have to connect my user 24Vdc power supply common or return wire, which is fed to SLC analog output card to the drive 24V common point.

In SLC analog output card i have kept the jumper to External 24Vdc power supply and i am feeding 24Vdc from external source. Should this external 24Vdc return and servo drive 24 return be joined together and then brought to ground.

Encoder:
we are using Omron make encoder (1000 PPR), 24vdc. This encoder is mounted to one of the pinch roll of 150mm dia.
Servo motor is directly mounted to other pinch roll.

Positioning error:
I have used a fast output from High speed counter card to enable and disable the servo drive. The open collector output from HSCE card is wired to a relay and the contact of the relay is wired to Enable/disable of drive.

i am using range function in the High speed counter card to enable and disable.

Now suppose i need to stop at 100 mm: i do the below:

Analog output of 2vdc is given to the forward point. the drive is enabled. once i reach 100mm i disable the drive enable output.
But i can actually see that it stops only at 107 mm or 108 mm.
also suppose for 100mm i should get 212 pulse. now suppose i compare for 212 pulse and stop or disable the drive. I actually stop only at 224 pulse.
How to stop exactly at the required pulse or distance (mm).

I tried with compare instruction in ladder logic and also the range function directly in the HSCE to control the output but getting the same result.

How can i exactly stop at the required position.

Thanks for all your inputs.
 
Ramp

Dear all,

Also i increase / decrese speed in steps by moving to the analog output file.

suppose the total length required is 200 mm.
I move 2 volts from 0 to 50mm and then from 50 to 150 mm at 10vdc and then from 150 to 200mm i move 2 volts again.

Instead i thought of using the ramp function to have smooth speed instead of steps.

The ramp function does all the job in terms of time. ramp up or rampdown in so and so time.

but i wanted the same ramp to work as per distance. ie from 0 to 50mm reach 10votls and then run with 10V command till 150mm and then ramp down from 150mm to 200mm to 0 volts. For this i cannot use a ramp instruction as i donot know how much time it takes to move from 0 to 50mm. Is there any other way of getting that done.

If is suceed with this ramp instruction will i be able to stop correctly at the required position?

thanks
 
Ramil said:

Analog output of 2vdc is given to the forward point. the drive is enabled. once i reach 100mm i disable the drive enable output.
But i can actually see that it stops only at 107 mm or 108 mm.
also suppose for 100mm i should get 212 pulse. now suppose i compare for 212 pulse and stop or disable the drive. I actually stop only at 224 pulse.
How to stop exactly at the required pulse or distance (mm).


The motor does not stop instantaneously. It ramps to a stop. That ramp is changable based on servo parameters. The only thing that you can do is disable the drive early and hope it stops.

The product you should be using is the 1746-HSRV card in the SLC rack, it is actually meant for servos and closing the position loop. You have this expensive servo and are not going to even come close to it's potential with the setup that you have.

It has been a while since I used a DKS, but your two inputs- one for forward and one for reverse seems fishy to me. There should be a single -10V to +10V interface available.
 

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