cant find home

[Jim Fink 0]

I have a AB Ultra 3000i drive controlling a turn table. The machine is fairly new to this company you can view it on U-tube as TMI Robot. It is designed to have 18 stations and 3 were held back so there is a balance problem. When it gets to a specific station it will rock back and forth searching for home. Part of the problem may be in the drive design as it has two large sprockets and chains attached to two tires that push along the outer edge. And the chain may force it to overshoot? Support for the machine is out of the country. I have ordered the Ultraware software to work with the parameters in the drive, but I was wondering if anyone out there has experienced similar problems? I believe that I may be able to stop this by slowing the acceleration and adding more decel time. Jim Edited 26 May 2011 by Jim Fink

[drforsythe 15]

Is this a true 'homing' problem? Meaning is it only happening at one spot in the rotation during a drive's home routine? Or does it happen at multiple stations / locations? If it is a homing issue, you may want to look at just the homing settings in the drive. You should be able to adjust the type of homing (switch, switch + marker, switch+reverse, etc.) or you can adjust the acceleration / deceleration & velocity settings. If you could shoot a video of normal operation showing when the problem does and does not occur and let us know if it is in an actual homing routine, we might be able to help better. If not homing related, it might be worth checking the tuning. If there is a large inertial mismatch, you could also get oscillation. Lastly, is there any chance of slippage of the drive wheels?

[Jim Fink 0]

From what I understand HOME is at station #1 out of 18. the problem does not occur at station # 1. It always happens in the same location ( #6 ) and will move to other locations depending on what variables we change as in adding weight to the open area. And / or changing the velocity, the acceleration and the deceleration.( The software arrived yesterday and our IT guy attempted several changes recommended by the machine builders. Also adding air to the tires affects how it acts. I think that having two large sprocket & chain driven tires driving this is likely part of the problem as the chain may push or pull the other one past its mark. Another suspicion is that there may be excessive force on the encoder at certain locations. I will try to attach some video files and the link to U-Tube. Jim

[Jim Fink 0]

About the slippage, we have tried to over inflate the tires & that caused more problems. I attempted to under inflate one of the tires and that actually helped as the problem was consistent. Always happening at station # 6.

[Shiner 2]

Is position solely based on electronics, or do you have a hardwired device that confirms it. If you have say a prox and it meets/detects each station it could be that the sensing point at station 6 is further away from the prox minimizing the contact area and allowing overshoot issues can't decel to stop before reaching far side of sensor area).

[Jim Fink 0]

[Jim Fink 0]

Underneath the machine is a circular piece of flat stock that has a plastic gear riveted on. It meets up with a gear that is attached to the encoder.There are some blue die springs that are maintaining contact between the encoder gear and the large circular gear.Blue die springs are fairly heavy, perhaps too heavy for the encoder application. We did put on the final three missing stations. That puts us closer to a balanced machine but the problem persist. Jim

[JRoss 84]

Sounds like the machine builder should be out doing some warranty service work, instead of asking you to fix their brand-new machine. I would guess that the servo isn't inertia matched properly, and that the weight of the turntable is pulling the servo out of position causing it to back up and do the same thing in the other direction. Station #6 is probably the most poorly weighted station. Decreasing the air in the tires would cause more drag, which would decrease the inertia in the load and make the inertia ratio smaller, while increasing the air would to the opposite. The best fix would be to resize the servo motor and gearbox combination so get the inertia ratio down below 10:1. You might eliminate hunting at slower speeds and longer decels, but at the cost of cycle time.