A draw-wire encoder, also known as a string potentiometer, pull wire position sensor, cable extension displacement sensor, or yo-yo potentiometer. It is a cable driven position or displacement sensor for linear position measurement and velocity using a flexible cable (wire) and a spring loaded spool.
The string pot or cable extension sensor is composed of four main components in the shell: 1. High strength stainless steel cable (rope or steel wire rope); 2. Equal diameter spool (drum); 3. Power spring with high torque and long service life; 4. Rotary potential precision sensor.
In the shell of the sensor, a soft high-strength stainless steel cable is tightly wound on a precision machined cylindrical drum (or spool) with constant diameter, which rotates with the winding and unfolding of the measuring cable. In order to maintain the tension and retraction of the steel wire, the spring is connected to the drum. Then connect the spool to the shaft of the rotary potential precision sensor (or encoder). When the sensor string extends linearly with the moving object, it will cause the roller and sensor shaft to rotate.
For displacement or position measurement, the main body of the sensor is installed on the fixed surface, and the end of the flexible cable is connected to the moving object. When the object changes its position, the cable unfolds and reels and the rotating spool drive the shaft of the sensing device, generating an electrical signal proportional to the linear extension or displacement of the cable. For speed measurement, a tachometer is required.
The power spring is mainly used in the equipment of the rewind device. According to its relaxed shape, the power spring is divided into natural power spring and pre force power spring. In contrast, pre tensioned power springs can store 25% to 55% more torque and provide more effective turns. If the power spring in the equipment does not meet the standard, the sensor will be wrongly arranged and disorderly arranged in the process of wiring, and make a large noise in the process of use. Therefore, when choosing spring manufacturers, we must choose professional spring manufacturers.
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