Automatic system tightens-up on EMS production

Citation

(1998), "Automatic system tightens-up on EMS production", Assembly Automation, Vol. 18 No. 1. https://doi.org/10.1108/aa.1998.03318aaf.006

Automatic system tightens-up on EMS production

Automatic system tightens-up on EMS production

A special-purpose automatic assembly system has been designed and developed by Tamworth-based Concentric Production Research Ltd (CPR Automation) as an essential part of an electronic management system (EMS) production plant, installed at Lucas Electronics. The overall plant produces a wide range of EMSs designed to fit vehicles from a variety of manufacturers, including Volvo and Ford, and the CPR system is located directly at the end of a hybrid printed circuit board production line.

The system came on stream in early 1997 at Lucas Electronics with the prime purpose of assembling EMSs at a rate of 1,200 units/week for use on Volvo trucks. However, CPR engineers have ensured that it can be readily programmed to suit units from other manufacturers within the automotive industry. To this end, the mechanical design of the EMS is kept relatively uncomplicated and is based on a pressure diecast aluminium housing to contain the electronics circuitry, covered by a simple steel lid. The assembly method has also been kept as simple as possible through the use of M4 thread forming screws of either taptite or plastite types, which are used throughout, to secure the circuit boards and the lid.

The complete system has several built-in processes. These include: an assembly station to locate the PCB into the housing and fasten the lid; a large indexing tunnel oven to apply a heat-soak treatment to the assembled EMSs for testing; and a final automatic testing station for passing each unit. Apart from loading the components into a fixture at the front end and labelling "passed" EMSs with a barcode at the back end, the whole process is automatically controlled by a Mitsubishi programmable controller.

The assembly station is built around a two-position indexing rotary table fitted with two identical component fixtures into which the operator locates the housing (pre-loaded with an unfastened PCB) and the lid. The PCB is automatically attached to the housing by two self-feeding screwdrivers which are used in conjunction with a separate control unit. These controllers apply the correct tightening torque to each screw and monitor the seating position of the head to ensure that it has been driven home properly.

Fastening station of assembly and test machine designed and built by CPR Automation for Lucas Electronics' Engine management Systems

One screwdriver is fitted in a horizontal position on the frame of the machine and moves via slideways operating at right-angles. It is used for fitting the plastite screws which secure the electrical connectors, mounted on the PCB, to a wall of the housing. The other is fitted to the arm of a Yamaha SCARA robot for securing the PCB inside the housing using Taptite screws and, subsequently, for fitting the lid.

The SCARA robot also has a vacuum gripper attached to the end of its arm and is used for putting the lid into position on the housing and for removing the assembled EMSs to one of the two conveyors. The units are then indexed through a 5m long tunnel oven where they are heated to 85°C ±3°C. When they emerge, the hot units are picked up individually by another vacuum gripper system, this time mounted on a 3m long robotic gantry. Each is transferred to one of two test fixtures where a Lucas-designed 72-probe automatic test head is presented to the EMS circuitry by the CPR machine. At the end of the process, "passed" EMS's are redirected to another operator who fits anti-vibration mounts into the vehicle mounting holes and applies a barcode label as a final verification under statistical process control (SPC). EMS's that fail on the automatic test equipment are transferred to a separate re-work area and recycled after rectification.

Address for enquiries: John Fowkes, Managing Director, Concentric Production Research Ltd, Concentric Park, 7 Apollo, Lichfield Road Industrial Estate, Tamworth, Staffordshire. Tel: 01827 57475; Fax: 01827 62354.