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Laser/Electro-Optic Monitoring- System for Process Monitoring On-Line

A new approach to process monitoring for door assembly

By Dr. W.J. (Walt) Pastorius

Maintaining acceptable quality of vehicle doors has been recognized as a necessity to eliminate wind noise, water leaks, and other customer complaints. Traditionally, process monitoring for panels has been carried out with conventional offline sampling techniques, such as a co-ordinate measuring machine (CMM) and check fixtures.

CMMs are often used to monitor a number of points on doors, and have the advantage of providing large numbers of data points. The programmable nature of the CMM provides flexibility to inspect a variety of different parts. However, the CMM is relatively slow in operation, and requires a fixture for each part, which must be properly set up. Because of the time required for CMM inspection, typically only one, or two companies per shift are monitored, and delays of hours from the time a part is selected for inspection to the time data is available are common. The CMM typically is remotely located from the production area in its own room, adding to delays in providing feedback to the plant floor.

Check features have also frequently been applied to process monitoring, with selected panels being removed from the end of the line and inspected with manual probes in the fixture. Cost of check fixtures are required for any new models. Use of the check fixture is labor intensive, operators can influence data, and delays in data availability are inevitable. Typically, no more than a few panels per shift are inspected on a check fixture.

Both CMMs and check fixtures can only sample a few parts per shift and do not provide statistically significant amounts of data for proper process monitoring. Random errors can easily go undetected and process shifts can occur long before they can be detected to take corrective action. Both methods are only generally applicable to inspection of the finished component, making process correction difficult, since the location of a cause of a variation in the line is generally not easily to identify. Neither CMMs or check fixtures provide true in-process information.

Another alternative, large end-of-line vision systems, provide 100% data, but only at the end of the line. When problems are detected, information regarding where problems occurred in the process if often difficult to determine, and detection of a problem is delayed until parts arrive at the end of the line.

To address the needs for cost effective in-process monitoring capability for doors and other panels, Sensor Adaptive Machines Inc. has developed the patented SmartProx laser/electro-optic monitoring system for process monitoring in-line. SmartProx sensors are small and designed to be easy to mount in both existing and new lines. They have been applied to a number of applications for door monitoring, and can be applied to both in-process and end-of-line inspection stations for closure panels. Ideally, sensors are distributed at select operations throughout the line as well as at key locations at the end of the line, with all stations networked to display information at convenient locations in the plant.

The SmartProx sensor family includes laser triangulation sensors for surface monitoring, laser line sensors for edge and surface monitoring, and imaging sensors for hole and slot location monitoring. Combined laser line and imaging sensors provide 3D monitoring capability. Different styles of sensors can be integrated in a single application. Sensor accuracy is +/-0.05 mm 3 sigma or better for standard field of view sensors under normal test procedures.

The sensors have small standoff (the distance rom the sensor to the part), typically of 50 to 300 mm. Small standoff implies small size, which allows the sensors to be built into existing stations or lines, fixed between weld guns (left photo) and other components. The sensors have been designed to survive in close proximity to weld guns. This requires sealed sensor construction and protective shields mounted on the front of the sensors. These shields protect the sensor windows and require only infrequent changing when they have been pitted by weld splatter.

These sensors also operate from a Pentium PC platform. Complete controller packages, including the PC, sensor interface cards and SmartProx software for sensor operation control and data display, all packaged for the plant floor, can be supplied. Also supplied are multiplexers to sequentially monitor a number of sensors in one or more stations. Up to 10 multiplexers, each with up to 16 sensors, can be connected to a single controller. A PLC interface is provided to interface the sensors with the line controller to synchronize data collection with the assembly line.

The monitoring systems have been implemented with a Windows 95/NT-based operator interface to display data and control system operation. The utilization of Windows simplifies operator training, and provides maximum acceptance by users on the plant floor.

A series of Windows screens are used for sensor setup, data display and data reporting. Each sensor has a thermometer display of deviation from nominal. The thermometer is color coded in green, yellow or red, based on user programmable soft and hard limits. The user can modify this screen if sensors are added to the station, or if sensors are repositioned. A second display screen shows the actual deviation for each sensor. Data is stored in the system controller and can be reported in various formats such as accept/reject counters, statistical reports and graphical process deviation reports.

Data can also be exported over a network to plant information systems, statistical analysis systems, or to other PCS for custom report generation or other special analysis.

Sensors can also be mounted at a hemming station and provide 100% monitoring of the door header movement at each stage of the multi-step hemming operation. Two sensors are utilized to monitor both translation and rotation of the header.

Data taken from this station illustrates generally a controlled process, but with random errors occurring in location of the header. The ability to provide 100% monitoring in-process allows detection of these random defective parts, which would not be achieved by sampling techniques. In addition, a series of door end-of-line 100% stations have been implemented, typically using 10 to 12 sensors the hemmed edges and on the header.

Since the SmartProx sensors are optical-based, have no moving parts, and do not contact the surface being monitored, they have long lifetime - long beyond the usual life of a typical body style. The sensors can easily be reconfigured to a new style, without major cost of acquiring a whole new system for model change.

The author is director of marketing at Sensor Adaptive Machines Inc. (SAMI)

Reprinted with permission from DESIGN PRODUCT NEWS


		Created: 2003-12-16 Updated: 2005-04-25	Top of Page	Important Notices