Need help with MC_JOG and MC_HOME

Hi everyone. 

I have this project where i use motion control to control the velocity where a piece of metal is moving up and down, with and AC motor, an encoder and a inductive sensor to know the position zero (simulating the 0 to 360 degrees).

Everything works fine, i can do MC_JOG and MC_HOME every time the machine needs it, BUT here is the problem: when i put the MC_JOG off, the load moves by itself for a short period of time, and the MC.Position is not following this position at all. I need the motion control to still follows the position even when the load is not controlled with MC_JOG, how can i do this?.

Eventually, the load goes down to position zero due to the weight, so i was wondering, is ok to do mc_home every time the load goes to position zero? even when the mc_jog is working? or there is a way the motion control can follow the position even when no command is controlling the load?

Hi,

Can you please expand on this a bit more:

I have this project where i use motion control to control the velocity where a piece of metal is moving up and down, with and AC motor, an encoder and a inductive sensor to know the position zero (simulating the 0 to 360 degrees).

Specifically:

1. What is the CPU?  What is the technology object(s) you are using?
2. What type of drive and how is it controlled from the PLC (via a telegram or analogue)?
3. What type of "AC" motor?  Induction, servo or other?
4. What type of encoder?  Is it on the motor, or external? 
5. What do you mean by a inductive sensor to know the position zero (simulating the 0 to 360 degrees)?  Is this the 'encoder' you refer to?
6. What do you mean by control the velocity where a piece of metal is moving up and down?

Additional to Mr. Pennalligen's post:

    7. Does the hoist motor have an electro-mechanical brake?
    8. Which motor drive is used?

 sorry for not being clear about it.

the CPU is s7-1200 1214C dc/dc/dc with A/O (0-10VDC) expansion to control a AC induction motor (with its corresponding inverter). External encoder in the AC induction motor. 

OK so, the load of the AC induction motor is a piece of metal that goes up all the way to the top and then goes down to the lowest point, and then the cicle repeats itself (the zero point has this inductive sensor sensing the load every time it goes to the bottom, this way i can measure the mc_home of the load), the AC motor just needs to rotate in one direction all the time.

Since the load is moving like this, i can simulate it as a load moving from 0 all the way to 360 and then automatically goes to 0 again. So the load goes from 0 degrees which is the zero point to 360 degrees which is the zero point again. 

So at last, the AC motor is moving with a constant speed so the load goes up and down at a constant speed wich is what i desire. Also i need to read the position of the load constantly, since the machine must do some work between 0 degrees to 360 degrees. 

The problem is, when i put off the mc_movejog, the load has inertia and potential energy soit goes to the bottom in a period of thime. The only thing i need is that the Motion control keep reading the position of the load even when i stop the mc_movejog, so when i start the AC motor again i dont need to do MC_HOME again to point out the zero position as 0 degrees.

i hope i am clear enough this time.

Hi,

Can you please expand on this a bit more:

I have this project where i use motion control to control the velocity where a piece of metal is moving up and down, with and AC motor, an encoder and a inductive sensor to know the position zero (simulating the 0 to 360 degrees).

Specifically:

1. What is the CPU?  What is the technology object(s) you are using?
2. What type of drive and how is it controlled from the PLC (via a telegram or analogue)?
3. What type of "AC" motor?  Induction, servo or other?
4. What type of encoder?  Is it on the motor, or external? 
5. What do you mean by a inductive sensor to know the position zero (simulating the 0 to 360 degrees)?  Is this the 'encoder' you refer to?
6. What do you mean by control the velocity where a piece of metal is moving up and down?

From your description it seems as if the HSC linked to the motion control is disabled when the motion is requested to stop. This catches me by surprise.

Moving up/down at constant speed does not need motion control -- does it?
Or do you need to make a controlled stop at particular positions?

Consider using a high speed counter to track movement of the load. Having the HSC active the whole time, will ensure that you are always sure of the position. 

Without a counter weight, the motor sees the full weight of the load. The distance to come to a stop looks different for stopping up movement vs stopping down movement. Having a break resistor helps to rid of the access generation power.. else the drive compensates by making the deceleration longer (see drive documentation). Having a mechanical brake is also another essential.

Walter Jacquet

<snip>i ask is if i can perform MC_HOME with the MC_MOVEVELOCITY on every time the load touches the sensor, </snip>

Yes it is possible to do what you ask. Execute homing in mode 2. See the attached document extract. The configuration for how passive homing is done, is the last 'page' in the wizard where the motion control is configured.

Be sure to test the accuracy though. Expect drift as the speed increases.