RELATIVE POSITIONING (problem Lenze)

Hi,

I have 15 drives on our new machine. The absolute positioning is no problem and works great. The relative positioning works fine too, but...

There are several ways for doing a relative positioning. This can be from the point where we are at the moment, but also via a touch probe (sensor).

The problem I have is for a touch probe.

I look on a negative edge from the touch probe (connected directly on the drive). It passes the sensor at a speed around 300mm/s, not slow...

It's a chain with tubeholders, so the relative positioning has to be correct.

Problem is, after the drives sees the negative edge, it does a relative position that isn't allways right. At low speeds the relative fault is smaller...

How can this be, the sensor ??
Or can I not do relative positioning starting from a sensor detection at higher speeds ?

Any ideas would be great !!!

Thanks in forward...

Combo said:

Hi,

I have 15 drives on our new machine. The absolute positioning is no problem and works great. The relative positioning works fine too, but...

There are several ways for doing a relative positioning. This can be from the point where we are at the moment, but also via a touch probe (sensor).

The problem I have is for a touch probe.

I look on a negative edge from the touch probe (connected directly on the drive). It passes the sensor at a speed around 300mm/s, not slow...

It's a chain with tubeholders, so the relative positioning has to be correct.

Problem is, after the drives sees the negative edge, it does a relative position that isn't allways right. At low speeds the relative fault is smaller...

How can this be, the sensor ??
Or can I not do relative positioning starting from a sensor detection at higher speeds ?

Any ideas would be great !!!

Thanks in forward...

Click to expand...

Read the actual position in the lenze drive and record it when the positioning is finished. Then you can see if the positioning is OK, if the drive really worked like supposed.

Maybe you are having a problem with your encoder/resolver?

I know too little about your application, but I mean, if the positioning is started, you don´t have a problem with your touch probe sensor?
No negative edge, no positioning is started?

Few years ago I had similar problem with a touch probe application with a SEW drive.
There were a few parameters needed to be adjusted carefully in the drive before it was working good, but this application was with various friction during the positioning, that was my big problem.

Good luck!

Combo said:

Problem is, after the drives sees the negative edge, it does a relative position that isn't allways right. At low speeds the relative fault is smaller...

Click to expand...

The encoder counts and position should be latched on the falling edge. This should be done in hardware. We use an FPGA so the delay is based on the rise time of the sensor and about 25 micro seconds for the signal to get through the opto couplers. You should be able to see this position in the setup software and check it for consistency. I know you can on ours.
If this signal is not consistent then you need a better sensor. You should be able to verify that the distance the VFD moves after the falling edge is consistent. On our controller we would read the latched encoder counts and add an offset to it and then do a go to that position. This method is not time dependent on the controller scan but sometimes another offset is added to account for the delay of the sensor and the opto couplers as a function of speed. The problem with a relative move is that relative to what position when? If you wait for the motion controller scan a lot of time ( microseconds ) and distance can go by. In your case 0.3 micorns per micro second.




How can this be, the sensor ??
Or can I not do relative positioning starting from a sensor detection at higher speeds ?

Any ideas would be great !!!

Thanks in forward...[/quote]

check the setup of the program.
When running cyclic check timing of cycle
Your sensor should interupt everything the plc does and get the position immediatly. Then you can go on with rest but interupts are a cause realtime is not working proper.

The Sensor is directly connected on The Lenze, not via a PLC.

I tried positive edge, because then there is no object in between, it works like this, as long as I am away of the object. So I did, on FP do relative +400mm, then I am over the object. The sensor sees it's reflector again, like this it works. On the object the sensor can see thrue it at some moments, so I guess that this has to be the problem. The only thing I can't understand is that I must be away of the object.

Found the error

Found the error.

I was braking the actual positioning motion off while it wasn't in target or dwelltime not released. Both had to be high. I was waiting for the target in a window of 20mm. I've setted it on 1mm. And the dwelltime was something I didn't check, so I resetted the positioning command too soon, therefor it wasn't positioning right.