Everything different than planned, but better

A good automation and engineering partner is also characterised by the fact that he questions a concept specified by the customer, contributes his know-how and thus, under certain circumstances, rejects the originally planned concept and designs a new one. If this allows the required cycle times to be met, less floor space to be used and the investment costs to be reduced, then he has done everything right.

In this specific case, Hirata Engineering Europe GmbH in Mainz received the order to set up an automated assembly for electrical connectors for precisely this reason. The task is to assemble a part of an electrical connector (rear housing part plus clamping roller including spring, clamping roller pick-up, latch and grommet). This connector is manufactured in two variants, as a normal and low-cost connector, and in three sizes each. The customer's original plan was to manufacture these parts in two separate units, an assembly island for the strain relief (pinch rollers, springs, pinch roller pick-up) and an assembly line for the rear part of the connector housing. Both assembly areas were to be connected by a buffer area.

Concept change saves space and money

The experts at Hirata revised this concept and combined the two originally planned assembly units into one production/assembly island. Buffering was also not necessary in the work flow, and so the installation space, which was always tight anyway, could be significantly reduced and the costs lowered by using Hirata's own components such as SCARA robots and palletising. Another requirement of the customer was to design an assembly system that is as flexible as possible so that all connector sizes and both variants can be assembled on the same system with as little or no changeover effort as possible. It  also have to be possible to guarantee traceability. All containers with bulk and set material are therefore equipped with RFID tags and are recorded and checked before they are brought into the system.

Flexible due to freely programmable units

The assembly island realised by Hirata contains four SCARA robots and two palletising systems from Hirata, a turning unit, a small and a larger freely programmable rotary indexing table as well as five bowl feeders and several servo axes on an area of approx. 8 x 8 m. To ensure the flexibility of the system, all infeed, assembly and handling movements are freely programmable and the corresponding units are equipped with quick-change grippers. The entire system is controlled by a PLC, which is separated into two areas on the software side. One area is responsible for the pre-assembly of the strain relief, the other for the more complex control of the housing assembly for the normal connector and the low-cost variant. A Hirata-owned controller is used as motion control for all four SCARA robots. All robot positions are stored here, which are then approached by the commands of the PLC. The possibility of controlling up to four robot systems or up to 16 servo axes with one robot controller is not possible with many manufacturers, but ensures a high cost-saving potential. The pneumatics are also divided up. Each side of the system has its own valve terminal, so that the paths are short and fast switching cycles are possible. An employee can set up the system or call up data via a mobile operating panel and move around the system relatively freely. There are holders on the four sides of the system in which the control panel can also be stored.

On the left the clamping roller, on the right the connector housing

The assembly of the normal plug version starts at two points of the system at the same time. On the left-hand side, the strain relief (clamp roller with spring and clamp roller sensor) is mounted, on the right-hand side, the assembly of the connector housing with latch and grommet starts. In the centre of the system, these two pre-assembled units are then brought together and mounted. When assembling the low-cost variant, only the right-hand part of the assembly island works, as this connector is manufactured without strain relief and only two components (latch and grommet) have to be assembled in the connector housing.

The assembly of the clamping roller starts at the small rotary indexing table in Pos. 1 with the feeding of the clamping rollers via a spiral conveyor. A linear axis always removes a pinch roller and places it in a workpiece nest on the rotary indexing table. At Pos. 2, the springs are also fed via a spiral conveyor, picked up with a mandrel, brought into position and pressed onto the pinch rollers. At Pos. 3, a vision sensor checks the correct position of the springs. A SCARA robot AR-F 650 picks up the components in Pos. 4 and brings them to a turning unit for mounting the pinch roller transducer. Here the pinch roller transducers are fed by a spiral conveyor, removed by another SCARA robot (AR-F 500) and placed in the assembly position. Now the pinch rollers are pressed into the side of the transducer by two pneumatic cylinders and then the correct fit is checked by a vision sensor. The SCARA robot AR-F 500 removes the parts joined in this way and brings them to the large rotary indexing table (pos. 9) on the right side of the system.

Palletisers feed the connector housings

In the meantime, the connector housing was assembled on this large rotary indexing table. For this purpose, assembly starts with the feeding of the injection-moulded connector housings. These are provided in trays, which are stacked on a floor roller and pushed from behind into a palletiser. Here the trays are separated, an AR-F 650 SCARA robot removes the parts and transfers them to a vertical linear axis. This vertical linear axis is necessary to bridge the height difference of approx. 450 mm between the working level of the palletiser and the large rotary indexing table. The working height of the palletiser results from the height of the tray stack plus the height of the floor roller. The rotary indexing table is at a height of approx. 1,000 mm, so that any maintenance work that may be necessary can also be carried out without any problems. The vertical linear axis used also has a second task. It is equipped with a turning unit and turns the connector housing by 180° so that the main assembly side of the component faces upwards. The linear axis then places the component in Pos. 1 of the rotary indexing table. Pos. 2 is currently without function; another component may be mounted here later. At Pos. 3, the latch is fed by a spiral conveyor and mounted by a second SCARA robot AR-F 500. The robot is equipped with a special joining tool for this purpose. The correct fit of the latch is then checked by a vision sensor (Pos. 4). In the next position (pos. 5), the grommet of the connector is mounted. A two-axis system grips the grommet from the end position of the spiral conveyor and places it on a servo cylinder, which now inserts and latches the grommet onto the connector housing from below. In the next step (pos. 6), this assembly is also checked again. Three tactile sensors move to the grommet from below and check whether it is seated straight. Pos. 7 and 8 on the rotary indexing table remain without function with the normal connector variant.

Clamp roller transducer and housing are combined

In Pos. 9, the SCARA robot inserts the preassembled pinch roller sensor into the connector housing and tensions the spring of the pinch roller. This assembly step is also checked immediately by a laser sensor. The last position of the large rotary indexing table (Pos. 10) is the removal position, where there is also a vertical axis with a turning unit that moves the now completely assembled component (IO part) upwards, turns it and transfers it to the SCARA robot. The robot places the components back into trays, which are stacked again in a second palletiser, conveyed to the rear and moved out of the palletiser by a floor roller. NIO parts that have not passed one of the many test steps are sorted out at this removal position via a chute.

When assembling the low-cost variant, the left-hand section of the system is not in operation, as this variant does not require any additional strain relief. The assembly also starts here at Pos. 1 and the placement of the connector housing in the workpiece nest on the large rotary indexing table. In Pos. 3 the latch is mounted and then checked (Pos. 4). Then in pos. 7 the low-cost grommet is fed via a spiral conveyor, joined from below via a two-axis system and a servo cylinder as with the normal plug version and tested in pos. 8. Pos. 9 runs empty and in pos. 10 the finished low-cost connector is removed, turned and placed in the trays.

Low conversion effort

The large rotary indexing table is equipped with three different workpiece nests for the three possible connector sizes at all positions. These are designed in such a way that no changeover is necessary even between type changes (normal plug to low-cost plug). Together with the freely programmable infeed, assembly and handling movements, some assembly positions that are still free and the quick-change gripper systems used, the entire assembly island is very flexible and can also be expanded for some subsequent assembly steps.

Show overview Show home page

Additional information

Categories:
  • Professional article