Analysis & Solutions for Asynchronous Operation of Crane Trolley & Bridge Travel Mechanisms
For long-span overhead and gantry cranes, the bridge travel mechanism and wide-gauge trolley frequently suffer from asynchronous operation between both sides during installation, commissioning and service. If left unresolved, this fault will lead to frame twisting, rail gnawing and wheel climbing, resulting in severe flange wear, rail damage and overload of transmission components. In extreme cases, derailment hazards may occur. This article systematically introduces fault identification, classified troubleshooting, countermeasures and optimization suggestions for reference. ………..
1. Identification of Asynchronous Travel Faults
Typical symptoms: The crane body twists and swings laterally during start-up or continuous travel; wheel flanges continuously squeeze the rails, showing signs of rail gnawing or wheel climbing.
Once the above phenomena appear, the asynchronous driving issue is confirmed. Stop operation for troubleshooting immediately. Continuous operation under faulty conditions is prohibited. ………..
2. Asynchronous Only at Start-up, Synchronous During Stable Travel
2.1 Root Causes
This issue is mainly triggered by electrical failures, commonly seen on traditional wound rotor resistance-regulated cranes: broken resistance wires inside resistors, loose resistor wiring terminals, burned-out contacts of cam controllers.
Mechanism: Graded resistors limit starting current and balance starting torque during acceleration. Abnormality on one starting circuit creates unequal starting torque on two sides, causing lateral deviation and twisting at start. After reaching steady speed, starting resistors are fully short-circuited, torque becomes balanced and operation returns synchronous.
2.2 On-site Solutions
(1) Resistor maintenance: Slightly broken resistance wires can be welded reliably. Severely or multiply damaged resistors shall be replaced with identical models.
After repair, conduct root-cause inspection: verify resistor model matching; check if operators frequently use reverse braking which causes overheating; confirm whether actual working conditions exceed the crane’s designed duty cycle.
(2) Loose wiring: Tighten all resistor circuit terminals. Complete comprehensive inspection and fastening of all power and control cables to avoid poor contact and overheating.
(3) Controller defects: Repair or directly replace controllers with burned and poorly contacted contacts. ………..
3. Continuous Asynchronous Operation from Start to Running
3.1 Fault Triggers
Faults originate from either electrical or mechanical systems, which require differentiated verification.
Electrical failures: Broken cores inside stator / rotor cables, phase loss, loose bolt connections; damaged motor windings leading to unbalanced output torque between two motors.
Mechanical failures: Damaged bearings on one driving side increasing travel resistance; insufficient lubrication and heavy wear of internal & external gear teeth of couplings resulting in inefficient power transmission; inconsistent reduction ratios of two gearboxes; mismatched motors with incorrect nameplates after component replacement; for integrated three-in-one reducers, mismatched tooth counts of connecting gears between motor and reducer.
3.2 Step-by-step Troubleshooting Procedures
(1) Clarify service background: Confirm whether the crane is newly installed or the fault occurs after a period of normal operation.
(2) Troubleshooting for newly installed cranes
Prioritize electrical wiring inspection, focus on wrong connections within resistance circuits.
Measure stator and rotor current of both motors under no-load operation. Obvious current deviation indicates defective motors or mismatched models.
If motors are normal, check consistency of reduction ratios.
For three-in-one drive units, verify identical tooth counts of connecting gears between motors and reducers.
(3) Troubleshooting for in-service cranes with sudden faults
Listen for abnormal noise from driving units, inspect overheating or jamming bearings, check coupling lubrication and wear status.
Electrically inspect cables for broken cores, loose terminals and phase loss and perform corresponding rectification.
After eliminating electrical faults, disassemble and inspect wear conditions of all transmission parts.
Manufacturers shall strengthen factory inspection. Ensure unified models and technical parameters for supporting motors and reducers. Prevent mixed use of mismatched transmission components and wrong nameplate labeling to eliminate asynchronous risks at source.
4.2 Installation Management
Entrust qualified certified crane installation teams. Strictly calibrate rail gauge, straightness and elevation difference according to standards and standardize wiring to reduce extra resistance caused by installation deviations.
4.3 Daily Operation & Maintenance
Equipment users shall establish regular maintenance schedules: replenish lubricant for bearings and couplings periodically; fasten all electrical terminals routinely; standardize operation behaviours to avoid frequent reverse braking and overloading, lowering wear on transmission and electrical components.
4.4 Synchronization Optimization for VFD-controlled Cranes
Variable frequency drive has become mainstream for modern cranes. Two solutions are recommended for long-span bridges and wide-gauge trolleys to prevent asynchronous travel and rail gnawing:
Option 1: Mechanical guiding improvement. Install two sets of horizontal guide wheels on one rail to restrict lateral frame offset and mitigate rail gnawing caused by asynchronous movement.
Option 2: Closed-loop electrical synchronization. Fit encoders on both drive motors. Activate master-slave synchronous control on inverters to compare and adjust motor speeds in real time, eliminating speed difference fundamentally and avoiding rail gnawing.
Conclusion
Asynchronous travel of crane running mechanisms is a frequent typical fault. Follow the troubleshooting principle: check electrical systems first, then mechanical systems; conduct static inspection first, then no-load trial run. Pinpoint faults according to occurrence timing and implement timely repairs. Combined with structural modification, control system upgrade and standardized maintenance, the crane running stability can be continuously improved to guarantee long-term safe operation.
