Not only in biological ecosystems (bio)diversity is benefitial but also in industrial factory automation. Diversity helps to limit effects of unpredictable events.
Diversity in factory automation
Typically in factory automation a control unit collects data of sensors, analyzes these data and, according to it’s programmed instruction, triggers actuators to a defined operation. In most cases a single-channel structure consisting of sensor, logic and output perfectly fulfils the application requirements. Yet in some cases two-channel structures are preferred to increase the reliability of the control concept.
Clamping control at machine tool spindles
To monitor clamping positions of tools in machine tool spindles several options are possible: Sensors with binary output (e.g. PNP normally open) or sensors with continous output (e.g. 0..10V or IO-Link) may be installed. The clamping process in many spindles is controlled with hydrauilic actuators.This means the clamping force can be controlled by using pressure sensors which control the applied hydraulic pressure in the clamping cylinder.
The combined usage of both position and pressure sensors controls the clamping status in a better manner rather than just using one sensor principle. Typically there are 3 clamping situations: 1) unclamped 2) clamped without object 3) clamped with object. In tooling spindles mostly the clamped position is achieved by using springs which force the mechanics to hold and clamp the object when no pressure is applied. A pneumatic or hydraulic actuator allows to unclamp the object by providing force to overcome the spring load. Without hydraulic or pneumatic pressure therefore the clamped position should be detected by the position sensor. When enough pressure is being built up, after a short delay the unclamped position should be achieved. Otherwise something must be wrong….
The advantage of diversity
By using two different sensor principles (in this case pressure sensing and position sensing) the risk of so called common cause failures is reduced. The probability of concurrent effects of envrironmental impact on the different sensors is diminished, This increases the detection rate of failures. The machine control can immediately react if the signals of pressure and position sensors do not match, which simplifies monitoring of the clamping process.
Diversity makes life easier in industry.
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