OT Pallet transfer shuttle car Siemens

Hi guys,

I have a scenario on a project and would like your thoughts.

We have a shuttle car that transfers empty and full pallets between loading and offloading station. The product weight i'm unsure at the moment but i know it is 16 20liter containers. so max load at about 500kg (roughly esimated and exagurated)

We are using a Siemens S7-300, and i intend using a SEW Movidrive inverter and communicate over profibus. The process department have a concern that when they size the drive under full load conditions, the wheels would spin under empty pallet load conditions. I'm thinking of playing with the torque parameters on the drive to make sure that this does not happen and accessing these parameters via the profibus interface.

Although i believe the weight of the shuttle should seat it sufficiently on the shuttle rail.

Has anyone seen or been involved with a simular situation.

Any feedback will be apreciated.

Rheinhardt said:

The process department have a concern that when they size the drive under full load conditions, the wheels would spin under empty pallet load conditions.

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No, they wont spin. The motor slip will drop meaning the motor speed will increase slightly.

Rheinhardt said:

Although i believe the weight of the shuttle should seat it sufficiently on the shuttle rail.

Click to expand...

I have had a similar problem where the entire shuttle was so stiff that there was no flexibility. The smallest variation in the rails that the shuttle was moving on would mean that some wheels would loose grip.
That didnt mean that the wheels would spin at a high speed. It meant that the traction became uneven, and sometimes insufficient to move the shuttle. Especially at very low speeds, there is less force available, so if one or more wheels lose grip, it may become a problem.
So I recommend that some kind of flexibility or suspension is built into the design. Pneumatic tires in stead of steel wheels f.ex.

Hi Rheinhardt

I have a little experience using SEW Movidrive with Profibus. Just did my first system with them in Port Elizabeth.

You can adjust the Torque limit parameter via the Profibus parameter channel, but that involves some advanced programming.

I would suggest you get a Movidrive Application Version. That gives the drive the power to think for itself. Non application drives can be upgraded. Then also get your motor from SEW with a build in encoder. Using a SEW motor with it's included simplifies setup and allows extra functionality. You then input the drive wheel diameter and gearbox ratio and you get positioning down to 0.01 (depending on max distance). You then run the "Positioning via Bus" application. You then set the speed and target position via profibus and the drive will ramp up and down and stop at target position. If you use the "Extended Positioning via Bus" you can also set the Ramp up and down values"

I don't think you will have a problem with wheels spinning. I have a 4 wheel trolley that is about 1500kg driving on 2 300mm dia wheels on one side - metal on metal rails. We load a 3000kg tank on it. There is no difference in the moving between loaded and unloaded.

My trolley has a 0.75kW motor on gearbox with 181:1 ratio. I do positioning at max speed (1400 rpm and 2s ramp) and on a 3m run it runs about 1mm more than the setpoint. It will probably be more accurate if I make it go a bit slower and lenghten the ramp down.

You will also need the USB-RS485 interface to program the drive.

Hope this helps.
Bestbier

Hi guys, thank you for you replies.

Bestbier, i like the idea that you mentioned will do some homework and reply back on the forum, till then.Many thanks

Rheinhardt

I don't think you will have a problem with wheel slip at steady speed, loaded or unloaded. But, you may well have wheel slip under accel and decel, unloaded.

You may be able to tune the slippage out of your system by lengthening the accel and decel time under unloaded conditions. That same accel/decel time would then apply to loaded conditions as well.

If the extra time for longer accel/decel when loaded is unacceptable, you will need to develop an input to the system that represents the load/unload conditions and modify the accel/decel ramps accordingly.

Usually, you can select two different accel/decel ramp sets in the drive with a single digital input which is a lot simpler than trying to do it via fieldbus.