Transport of high-sheen sport rims “seen” as a sporting challenge
TRAPO AG: Automated depalletizing with servo-pneumatic gripper
Light alloy wheels are becoming more elegant - and with glossy wheels, exciting contrasts are created between bare metal and painted surface. In the production process, these are first painted black, then a portion of varnish and material will be removed; the high-sheen wheel is formed, which is subsequently protected with an additional clear lacquer.
On the way to this additive painting process, it must not be contaminated in any way by hands or external influences. As a pioneer, the development team at TRAPO AG faced the special challenge of reliably depalletizing either standing or horizontally-placed palletized wheels with a machine.
The servo-pneumatic gripper from TRAPO AG depalletizes sensitive wheels with the assistance of ultra modern laser technology.
The scratch-sensitive, high-sheen wheels are transported standing, handled with white gloves and hooked into the lacquer chain. This process was automated by TRAPO. The goal is the humanization of the workplace, in addition, contamination by workers is to be avoided.
A specially-developed gripper with three plastic fingers gently grasps the tire seat behind the rim flange and places it on the conveyor belt - without touching the sensitive design side, scratches are precluded. This gripper can grip both standing and horizontally-placed palletized wheels.
The gripper being developed had to be absolutely flexible as it has to adjust itself automatically to the different center distances of the palletized wheels as well as to the different diameters. This was realized employing a combination of servo technology and pneumatics. The result is a highly flexible servo-pneumatic gripper, which has been integrated as an additional axis into the control of the manipulator.
The special gripper developed for this challenging task unites all tasks which arise – a complicated gripper change-over system can be dispensed with. This in turn saves costs in the project and brings additional advantages with spare parts, maintenance, space requirements and operation of the plant.
Dietary program for storage and services
Since only a small space of engagement is available through the workpieces, the gripper is characterized by its optical slenderness, simplicity and, since it contains only a few wear parts, pronounced maintenance-friendliness.
Due to the development of this gripper, a complicated gripper change-over system could be dispensed with. This in turn saved costs in the project and brings additional advantages with spare parts, maintenance, space requirements and operation of the plant.
The wheels are placed on pallets/frames at the depalletizing station via conveyor belts. Standing wheels are delivered on a frame of eight to 12 individual wheels per position, lying according to the EWPS* system. The frames for the high-sheen wheels were developed especially for this task by the customer.
Greatest importance was attached to durability, avoidance of additional packaging materials, such as film and contamination of the rim flange. Furthermore, the distances and dimensions of the carrier frame were communicated in close cooperation with the development team of TRAPO AG.
In order to preclude damage and contamination on the rim flange during the automatic pick-up of the wheel by a depalletizing robot, it is necessary to precisely determine the wheel in its position in the space.
**European Wheel Pallet System (EWPS)
Laser scanner opens its eyes
Two laser scanners are used to precisely determine the position of the wheel in the room.
The wheels, which are manually placed on the transport frame after the high-sheen process, are indeterminate in their position relative to the edge of the frame, also by manually placing the wheels an angle offset to the base of the frame results. Two laser scanners are used to precisely determine the position of the wheel in the room. A laser scanner travels horizontally over the position, then a further laser scanner scans the position vertically. By scanning horizontally, the wheels are determined per position, relative to the reference edge, as well as the number and diameter of the wheels in the position. Due to the data of the scan, incorrectly stored wheels are detected. Thus, potential damage to the gripper and further to the paint line can be ruled out by an incorrect wheel size in the batch.
If such a wheel - designated as a cuckoo wheel - is detected by the scanner on the pallet, this pallet is not depalletized, but rejected for removal by a worker.
After removing the wheel not belonging to the batch, the pallet can be fed and returned to the depalletizing process.
By vertical scanning, the wheel is recorded in its position relative to the base area. The collected 3D coordinates of the scanners are transmitted to the robot controls. Thanks to the determined coordinates, the wheel is approached precisely by a permanent set/actual value adjustment so that it can be picked up precisely by the gripper.
A high-speed connection between the robot control system and the scanning system enables the gripper to be brought to the wheel in a timely and ergonomic manner.
During the scanning process, a laser beam is guided over the wheel position - the running time of the laser beam determines the distance to the object. A software program combines the individual pixels into a surface profile image.
Space there! Wheels safely parked
In the course of the onward transport, the depalletized wheels are fed to individual receival locations by a further robot. It was important to note that the sensitive wheels should not come into contact with one another during a stop. This is ensured by the proven single-station positioning technology. An accumulating conveyor buffers wheels at times during pallet and/or batch changes and avoids downtimes at the paint line.
A manual task, for example, completes the holistic concept for refinished wheels. This is connected to the feed for handling and attaching to the pre-lacquer chain.
The wheels, which are manually fed to the pre-lacquer chain, pass through a measuring station in which they are measured in height and diameter. This is used for a comparison with the expected wheel data in order to identify incorrectly fed wheels in the size and to exclude them from entering the subsequent process.
The depalletised pallets or frames are finally stacked in palletizing magazines each with 15 EWPS pallets or 30 frames and are ready for new transport tasks.
Also the stacking of the pallets is monitored with a sensor. If damaged pallets cause skewed stacking, the stacking process is not continued, but the existing stack is removed.
In order for the EWPS frames to be accommodated at the stack removal station, a basic pallet is moved under the stack after reaching the stacking height, and the covers are deposited on this carrier pallet.
Visionary strategies between time and space
Only one of numerous, individual solutions from TRAPO AG, which designs, develops and installs modular conveying and robot systems. As a specialist in CONVEYING TECHNOLOGY, ROBOTICS and AUTOMATION, TRAPO AG assumes the lead role - its visions and production strategies characterize sectors. Solutions that have already proven their worth in everyday life can be adapted to all sectors and products.
The special, intelligent components of the conveying and handling systems - including special applications in the clean room - are manufactured exclusively in the workshops in Gescher-Hochmoor/Germany.