Considerations on using capacitance proximity sensing (CPS) to protect machine maintenance workers.
Maint Manage Int 1985 Nov; 5(4):261-268
The use of capacitance proximity sensing (CPS) to protect individuals who work near of maintain machines such as metal stamping presses, pipe bending machines, or robot machining cells is discussed. CPS devices are designed to output a machine control command (apply brake, remove power, stop machinery, sound alarm) when a person or hand gets too close to a machine hazard. The components of a CPS device are discussed. Measuring safety separation distance with CPS and cross sensitivity as a factor in CPS performance are considered. A method for observing cross sensitivity effects was described. The method incorporates a model of the human hand and arm as part of a triangular pendulum which can be released so that the test object penetrates the sensing field at a speed of 2.5 meters/second. Tests were performed in a structure built to model the environment of grounded surfaces which would be near a CPS application. The sensing antenna was placed 19 centimeters from the vertical ground plane. The results showed that the effective sensing position indicated by CPS could be reduced by by moving grounded metal objects near the sensor. The author points out that movements of workers and machine parts, and the introduction of different materials under the workers' feet may lead to changes in CPS performance. Computer and microprocessor based methods are recommended for mapping and monitoring CPS fields to insure that hazards are recognized in spite of cross sensitivities.
Industrial-hazards; Hand-injuries; Accident-potential; Accident-prevention; Detectors; Electromagnetic-fields; Safety-engineering; Safety-equipment; Equipment-reliability
Maintenance Management International