Closed-Loop Feedback / Degradation
The consistency of the desired optical output is an important factor in establishing and maintaining a high yield manufacturing process. It is an inescapable fact that mercury arc lamps degrade with use, standard mercury arc lamp efficiency declines slowly.
This decline is primarily caused by the deterioration in UV transparency of the quartz jacket, and depends on a number of factors: - Lamp cooling efficiency, Power rating, Current rating of the electrodes, electrode cooling efficiency, contamination of the Quartz reflector and switching frequency. Typically Mercury lamps can lose 10 to 15 percent of its initial output during the first three hundred hours of operation.
Improved engineering methods for driving the lamp can extend the half-life point significantly; this has a favourable impact on process economics, because material and labor costs in addition to process downtime are substantially reduced.
Consistent and repeatable curing of an adhesive requires repeatable light exposure. While the rate of change in output from the arc lamp can be reduced, additional controls are needed to provide consistent output through the life of the lamp. Conventional systems eliminate this variation by manually increasing intensity to offset this degradation. However this is best implemented through a feedback system that monitors bulb output and automatically makes appropriate equipment adjustments to control the light delivery, thereby saving considerable time required to validate the required light output.
Some High end systems have a patented approach to solving this problem which employs a beam splitter in the optical path, coupled to electronics that control a variable aperture. As lamp output begins to decline, this is detected and the aperture is opened slightly to maintain the desired optical power. At some future point, when the aperture cannot be opened further, the system will trigger an alarm signal to indicate that lamp replacement is required.
Why is this important to you?
- Ensures constant light output guaranteeing process repeatability
- Automatically compensates for lamp degradation
- Increases yields and quality of assembly
- Minimizes labor and eliminates chance of operator error
- Internal intensity monitor opens the iris to automatically correct light output within +/-5%
- The lamp can be used until the end of its lifetime, with less work of checking lamp intensity
