Lift height sensor makes forklift trucks safer

Some companies are optimising their logistics and material flows using draw-wire displacement sensors. On forklift trucks, for example, when raising and lowering loads, safety margins usually have to be adhered to, so that when rounding a corner, braking or accelerating, the truck is not placed in a dangerous, tilted position. If the lift height of the load can be measured accurately, the optimum 'safe' driving speed can then be determined. Still-Wagner, a manufacturer of innovative fork lift trucks based in Reutlingen, Germany, is using a special draw-wire displacement sensor from Micro-Epsilon, to measure the lift height on its fork lift trucks. The system, which uses a custom-designed Micro-Epsilon P600 series sensor, is completely failsafe, so that truck operators cannot deliberately or accidentally cause 'critical' driving conditions. The system optimises the speed of the truck and improves the safety by automatically bringing the load to the correct lift height, to speed up the movement of materials to the appropriate shelf height in the warehouse. The P600 sensor is a custom designed draw-wire sensor which has a much slimmer construction (87mm width) than the firm's standard P60 draw-wire sensor so that it could be fitted into the tight installation space on the truck. Thomas Birchinger, product manager draw-wire sensors at Micro-Epsilon explained: "If the truck operator has to raise the forks 15 metres to reach the racking where the goods are stored, the temptation for the driver may then be to accelerate away quickly with the forks still high, which can be dangerous. Our P600 sensor simultaneously measures absolute precision using a potentiometer and an encoder reading. If there is a difference between the two output signals, the truck is then automatically placed in a safe mode." The P600 is designed to operate redundantly. Two electrically-independent signals - a potentiometer output and an encoder output - ensure that a high level of safety is achieved. The high accuracy sensor has a potentiometer output that achieves a repetitive accuracy of <0.05% and a linearity of < ±0.1%. The encoder output has a resolution of <0.05% and a linearity of < ±0.05%. The operating temperature range for the P600 is from 0°C up to 50°C but there is also a special cold store version for temperatures down to -20°C. The P600 also has a sensing range of up to 15,000mm, ten times further than the standard P60 sensor.