Page 29 - MetalForming July 2010

The described setup, by simulating the actual application on the test bench, verifies that the sensors are fast enough in terms of their response times to detect the target. It is quite possible to have a relatively slow-running die with a very fast internal assembly operation. It is paramount that the sensor have a response time that can keep up with the process that it is supposed to monitor. If you have any doubts about this being so, then the bench-test simulation is a must.
Another way to perform the simula- tion is to activate the air cylinder with a signal generator capable of outputs that match the press speeds on the shop floor. The generator’s output would trig- ger a solid-state relay that in turn would activate the air cylinder’s solenoid.
If such a signal generator is not avail- able, then another possibility would be to use a cam attached to a variable speed motor. The lobe of the cam would be monitored by a proximity sensor, which in turn would activate the solid-state relay. The outputs of the two sensors monitoring the air cylinder’s extending and retracting rod would be connected to an oscilloscope. This scope would display the on/off activities of the sen- sors and make their responses obvious to the experimenter. In a later column we will explore the oscilloscope in detail and its applications to in-die sensing.
Basically, when timing is critical and doubts arise as to the ability of a given sensor to detect a moving target, a bench test is warranted. The extra time that such a bench experiment requires is nothing compared to discovering that one’s assumptions about the response time of a sensor are incorrect.
There is nothing more tragic than a sensor buried deep within a die, blind to a target that is in motion. This is par- ticularly true if such a discovery is made when the die is ready for its first pro- duction run. MF
Yeah—it’s that good.
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