Page 28 - MetalForming July 2010

George Keremedjiev has been writing this column for more than 20 years. He regularly consults with metalforming companies worldwide and provides metal- formers with training on the appli- cation and implementation of sen- sors for die protection. For more information on his seminars and consultancies, contact:
Tecknow Education Services, Inc. P.O. Box 6448
Bozeman, MT 59771
phone: 406/587-4751
fax: 406/587-9620
www.mfgadvice.com E-mail: gk@mfgadvice.com
Moving targets can be ideal candi- dates for sensing, but at a price. One has to carefully test the effects of a target’s motion on a sensor’s abili- ty to detect. Examples of moving targets include the detection of die-exiting parts, broken punches and early feed where one looks for the starting motion of a strip during the early portion of its feed cycle. Even if the press strokes at a slow speed, it is possible for the target motion to be very fast. For example, consider a returning rod in an air cylin- der that is buried deep within a die. It is paramount that,
process where the hardware being weld- ed is placed in position. Obviously it would be important to verify that the air cylinder extends and retracts within a given timing window.
The simulation would involve setting up the actual air cylinder on the test bench and activating it with the pro- grammable cam portion of the die-pro- tection controller and perhaps a solid- state relay to handle the necessary voltage and current for the air cylinder’s solenoid. Two sensors would be fix- tured to create two signals—one for
METALFORMING ELECTRONICS GEORGE KEREMEDJIEV
Sensor Fundamentals, Part 2—Motion
whenever possible, a bench test be per- formed to verify that the sensor can actually detect a given moving target.
It is paramount that,
whenever possible, a bench test be performed to verify that the sensor can actually detect a given moving target.
the proper exten- sion of the air cylin- der’s rod and the other for its retrac- tion. These two sen- sors would connect to two die-protec- tion inputs on the controller and the appropriate timing windows for each input will have been programmed. These
One way to do
this is by having a
functioning die-
protection con-
troller available on
a test bench. The
resolver of this system is attached to a variable-speed motor so that all of the shop’s press speeds can be simulated. Several companies have such a setup so that their sensor-applications spe- cialist can test the response time of the sensor and controller with a moving target. For example, you may have an application where the die will run at 40 strokes/min. with an assembly opera- tion. Let’s say that at 100 deg. of the press crankshaft an air cylinder needs to extend and present a tool in the assem- bly area and then withdraw it after the die bottoms out and is open. Perhaps this is a hardware-insertion operation, or maybe a portion of an in-die welding
angles would represent the actual expected timing for the extension and retraction of the rod. The variable- speed motor attached to the controller’s resolver would be gradually increased in speed until it reaches the actual speed that the die will be running, in strokes/min. If all works as planned, one should see the air cylinder’s rod extending and retracting and the display on the die-protection controller, clear- ly showing the cycling of the sensors and the actual crank angles at which the events are taking place.
In terms of the sensor itself, the critical number is its response time. This is clearly stated in the specifications for the sensor.
This CD-ROM presents dozens of George’s columns as well as papers and exclusive new presentations covering all aspects of die protection and part-quality inspection, starting and maintaining sensor programs, the role of controls in in-die sensing, and the benefits of a sound sensor program. Order it online at www.metalformingmagazine.com.
26 METALFORMING / JULY 2010
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