|
Solution:
The general task of this application is to separate and adjust the orientation of bulk material. The capability of handling bulk material is a big contribution for cost savings in a manufacturing process, because each preprocessing (e.g. handling, logistic and other) is very expensive and time consuming.
An Epson Scara robot is used to pick up small parts of a gear from a conveyor band and put them well oriented onto a palette of a rotary table. These parts come from a reservoir over a reciprocation feeder to a separating unit to a conveyor band. The Scara robot has the task to grip those parts and put them, correctly adjusted, into palettes of a rotary table. Subsequently they are carried with a linear module to a die casting machine, which encapsulates it with a certain form.
The recognition and position of the parts are determined using a vision system. The tracing of the products of the conveyor is done using an angular momentum reader. All information, position and orientation of the part, are given to the robot controller, which uses those data to control the movement of the robot.
The required cycle time is clearly beyond 1 second, this means, within a period of 2 seconds the machine has to pick up 2 parts and lay them down correctly oriented into the palette. The achieved cycle time of this machine is about the half, a complete gripping cycle, which works for two parts, is around 1 second – much faster than required.
Due to the small dimensions of the parts, the area of taking those units up is very small. This requires a high precision from robot and controller, while the speed must not go down significantly. Further on there must be a reliable differentiation between several parts, as there are more than one type coming along the conveyor.
The tolerances when picking up one part is very small as the units are rather tiny and light, even the faintest deviation of the optimal position of the gripper may result in a blunder and will there for prolong the cycle time. On top the grip must be synchronously to the position on the conveyor, as each shaking may slip the parts aside.
The synchronization between robot and rotary table is done by easy and reliable I/O handshake protocol. Only when the robot has filled all of the 16 places on the palettes and has left the area of risk, the palettes can be moved on from the rotary table.
The control of the whole robot system as well as the control of the rotary table is done using a SPC controller.
As an additional security device there is a ‘on-thy-fly’ Vacuum control unit. If it comes out, during the gripping, that a gripper has failed to get a piece, a second grip will be riggered. The repository place only will be approached, when the gripper has two parts secured.
Using the user interface it is possible to leave single repository places blank. The return of pieces is due to the high precision and speed of the robot including controller almost zero in normal handling procedure.
The machine has been designed under the condition of easy expandability and flexibility. The teaching of a new part is as easy as possible. Just lay down a new part onto the conveyor and be sure, that it is correct oriented. Then all the user has to do is pressing a button on his user interface to define this new, recognized model as a new part to handle.
| 
