commanded position

[MIYAM]

i have a big problem... when i start my program my robot do unexpected movements then it hold and appear an error 1012 that said commanded position of JT4 suddenly change what can i do??? and why this happen???   

[roboperson]

In actuality, your problem statement is pretty vague. This error means that the current value calculated in repeat mode and the following value was exceeded. What you have in your favor is it was only JT4. Depending on the movement and what it is suppose to do you could have a variety of issues. For starters, is the movement a strong jerky movement? is it in singularity where JT 4,5 and 6 are all at a zero postion and the robot can choose several different paths of movement? Does this only happen in repeat or in teach also?
If this robot was operating normally, then you quite possibly could have a motor or an encoder problem. This is an encoder error, but the speed errors many time refer to the fact that the breaks are slipping, or there is a motor failure. The encoder is tracking properly, but the motor movement is excessive. Can you move the JT4 by hand when it is not in operation or if JT4 drifts when it is sitting with with no motor power, but if you give it motor power, does is hold? Then you probably have a motor problem. There are gearing issues, electiral issues, and so forth that can cause this also, but this is where I would start.