Siemens removes eye strain from ABS manufacturing
Components of various models of anti-lock braking systems (ABSs) look almost alike. The human eye can easily miss these subtle differences. Machine vision is a vital technology for removing eyestrain and assuring quality assemblies.
MK20 is one of the highest volume ABS units at Continental/Teves (Morganton, N.C.) with over 10,000 units manufactured per day. Two critical stations involve machine vision to assure completeness and accuracy of the assemblies.
Blocks are inspected for proper boring and correct part identification in the first stage. The first system inspects a pattern representing bit positions of an 8-bit part number on the block to confirm product identity, identifies the part, and confirms that it is correct. Once the blocks have been inspected and confirmed, they are delivered in trays to a second part of the line.
Assembly begins with robot insertion of solenoid valves into proper slots of the aluminum blocks. Valves in each slot are similar, but not identical. The assembly is moved to a conveyor by the robot. The second vision system now inspects for proper valve placement, missing parts, and assembly identification.
Both machine vision stations on the MK20 line use a monochrome camera with a Siemens Videomat IV rack-mounted processing unit. The system has a 32-bit processor (faster than standard 16-bit processors) to process more images at different brightness levels in a given unit of time. Inconsistency of valve finishes causes varying levels of light reflection. The faster processor allows bracketing images with different aperture settings to obtain a more accurate image.
Gray-level evaluation is performed looking at contours, dimensions, shapes, and pattern recognition. The processing unit is connected to a Siemens S5-135U programmable logic controller. The control program reads block data transfers from the vision systems and makes a pass/fail decision. A diverter gate allows good assemblies to proceed for further assembly while diverting failed parts to a rework station.
The PLCs communicate over Ethernet, allowing data logging into the mainframe. A Centronics port is used for periodic hard copy printouts during testing and configuration.
Configuration software directs the user through six function block setups. Five function blocks stay the same in most cases, with the 'inspection/identification' function block the only one that must change with valve model.
PLC configuration setup accesses block data from Videomat processor memory through Videomat's I/O port. One of the six function block setups facilitates data exchange between the PLC and vision-processing unit. A 'camera triggering' setup block in the Videomat system allows the PLC to trigger the camera.