The function of the cable drum used for measuring the length by the crane
The function of the cable drum used for measuring the length by the crane
The length-measuring cable reel on the crane is a very important component. Its function is far beyond simply winding and unwinding the cable. The core function is to achieve the automatic, synchronous and safe winding and unwinding of the cable, thereby providing continuous and reliable power or signal transmission for the moving crane.
Now let’s break down its specific functions and working principles in detail:
- Core Function: Synchronization and Automatic Control
This is the most fundamental and important function of the length-measuring cable drum. When the crane moves back and forth on the track, the cable needs to be retracted and extended accordingly. The core function of the length-measuring drum is to ensure:
The length of the cable released ≈ The moving distance of the crane
The length of the cable retracted ≈ The return distance of the crane
It uses the built-in measurement mechanism (i.e., the “length measurement” section) to continuously monitor the displacement of the crane and converts this displacement signal into instructions to control the motor (or hydraulic pump), driving the drum to synchronously wind and unwind the cable, thereby always keeping the cable in an ideal state of being “tightly stretched but not overly tight, relaxed but never dragging on the ground”.
II. Specific Functions and Benefits - Protect the cables and extend their lifespan
Avoid floor abrasion: The automatic retraction function prevents the cables from being rubbed and crushed on the ground for a long time, thus avoiding damage to the insulation layer.
Prevent excessive stretching: Synchronous control can prevent the cables from being forcibly pulled when the crane leaves or when the cables are piled up excessively during the crane’s return, thus avoiding damage caused by compression.
Orderly arrangement: Many drums are equipped with cable arrangement devices to ensure that the cables are neatly wound layer by layer on the drum, preventing tangled or overlapping cables that may cause deformation and damage to the cables. - Ensure Work Safety
Prevent tripping and crushing risks: The randomly laid cables pose a significant safety hazard to the on-site personnel, as they can easily cause tripping and also be crushed by other vehicles.
Avoid electrical accidents: Worn-out and broken cables may lead to leakage, short circuits, and even fires. The length-measuring drum indirectly ensures electrical safety by protecting the cables.
Prevent breakage accidents: If the cables are pulled apart by the crane, it will not only cause equipment to stop but also the broken cable ends may carry electricity, which is extremely dangerous. - Achieve automation and enhance efficiency
There is no need for manual intervention in the process of laying and retracting cables. The crane operator can focus on the lifting operation, thereby improving work efficiency and operational convenience. - Provide reliable energy transmission
Provide continuous power supply for all electrical equipment of the crane, including the motor, control system, lighting, air conditioning, etc. For cranes that require transmission of control signals, it also ensures the stable connection of the signal lines.
III. Length Measurement Principle (How does it “measure length”? )
“Length measurement” is the key to achieving synchronous control. The common technical solutions include the following:
Absolute encoder (most commonly used and precise)
Installation location: Usually installed on the main traveling wheel axle or driven wheel of the crane.
Working principle: The encoder rotates along with the wheels, accurately measuring the number of rotations and angles of the wheels, thereby directly calculating the actual traveling distance of the crane.
Advantages: High precision, unaffected by slippage (because it measures the wheel shaft), even after power loss and re-powering, the current position can be known, and no reset is required. - Torque Motor/Magnetic Hysteresis Coupler (Passive Synchronization)
This method does not directly “measure” the length, but achieves synchronization through mechanical characteristics.
Working principle: The driving part of the drum (such as the torque motor) is set to a constant output torque. When the crane moves to pull the cable, the tension on the cable increases, overcoming this constant torque, forcing the drum to release the cable. When the crane stops or moves in the opposite direction, the cable tension decreases, and the drum starts to retract the cable under the action of the constant torque.
- Advantages: The structure is relatively simple and the cost is lower.
- Disadvantages: The synchronization accuracy is not as good as that of encoder control, and the cable tension may fluctuate.
- Frequency Measurement
Working Principle: The speed of the crane’s traveling motor is measured to estimate its speed, and then the approximate distance is calculated through integration. This method has relatively low accuracy and is typically used in situations where high precision is not required.
In summary, the length-measuring cable drum on the crane is an intelligent device that integrates mechanical, electrical and control technologies. Its main functions are:
- Core: Through length measurement and feedback control, achieve precise synchronization of cable retraction and crane movement.
- Function: Protect the cable, ensure safety, and enhance automation level.
- Value: Ensure the continuous and reliable operation of the crane, reduce maintenance costs, and improve overall operational efficiency and safety factor.
It is an indispensable key component for modern medium-sized and large-scale track-type cranes (such as gantry cranes, bridge cranes, port quay cranes, etc.).
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