Selection and Considerations for Tethered Sensors in Material Handling Robots

The draw-wire sensor consists of a draw-wire housing and an encoder. It is a compact sensor with small installation dimensions, a large measuring range, and high precision, with travel ranging from 100 millimeters to tens of meters.

The function of a draw-wire displacement sensor is to convert mechanical motion into an electrical signal that can be measured, recorded, or transmitted. The displacement sensor consists of a stretchable stainless steel cable wound around a threaded hub. This hub is connected to a precision rotary encoder, which may be an incremental encoder, absolute encoder, hybrid or conductive plastic rotary potentiometer, synchronizer, or resolver.

Operationally, the draw-wire displacement sensor is mounted at a fixed position, with the draw-wire attached to a moving object. The draw-wire's linear motion aligns with the axis of the moving object. During motion, the draw-wire extends and retracts. An internal spring maintains constant tension on the draw-wire. A threaded hub drives a precision rotary encoder, outputting an electrical signal proportional to the draw-wire's displacement. The measured output signal provides the displacement, direction, or velocity of the moving object.

Common parameters include measurement range, output signal mode, linearity, repeatability, resolution, cable diameter specifications, pull force at the cable exit, maximum reciprocating speed, weight, input resistance value, power, operating voltage, operating temperature, vibration resistance, and protection rating.

Cable displacement sensors offer digital or analog signal outputs. Digital models include options like incremental rotary encoders or absolute encoders, providing square wave ABZ signals, free RS485 signals, or MODBUS signals. They feature extended measurement ranges (100–35000mm), high accuracy (~%FS), and IP65 protection. Both the housing and cable reel undergo anti-corrosion treatment, while the pull cable is stainless steel, enabling operation in harsh environments (including seawater). Optional output types include: resistive, voltage, current, incremental pulse, and absolute pulse.

Analog output types include precision potentiometers, Hall effect encoders, and absolute encoders. Output signals can be 4–20 mA, 0–5 V, 0–10 V, or resistive signals. Maximum travel reaches 35,000 mm. Operating environment supports up to IP65 protection rating and a wide temperature range of -35°C to +85°C.

Cable Encoder Installation Notes:

1. Mount using the bottom rail bracket. Install directly or add protective covers/mechanical fixtures based on site and machine space requirements.

2. When installing stainless steel cables, ensure proper horizontal alignment. Maintain minimal angle deviation (+/-3°) between the cable exit port and moving mechanism during operation to preserve measurement accuracy and cable lifespan.

3. The cable body is stainless steel with a fluorinated coating. Avoid cuts, burns, impacts, or other damage from external forces. Excessive dust, accumulated debris, or objects capable of damaging the cable trapped inside pulleys or the cable exit port will cause cable damage, leading to operational failures.

4. Before installation on a workbench or fixed mount, do not manually pull the cable out and allow it to snap back suddenly. This action may cause cable breakage, damaging the main structure and posing a personal safety hazard.