Forklift Motor Control for Residual Torque Release at Stop
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Solution Overview
Problem
Forklift trucks experience maneuverability issues during inserting operations due to increased torque in the travelling motor when the error between the target and actual rotational speeds becomes zero, leading to unexpected movement upon completion of the operation.
Innovation Solution
A control method for forklift trucks that calculates a target rotational speed based on accelerator member operation, adjusts an output ratio using proportional and integral gains, and performs acceleration torque subtraction to maintain stable motor control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If feedback control is performed to make rotational speed follow target rotational speed, then rotational speed control precision is improved, but torque remains in the traveling motor after accelerator operation is released causing unintended movement
Solution Approach 1:
The controller detects when the forklift is in a stopped state with the accelerator member not operated, and proactively sets the torque command value to a predetermined value (zero or near-zero) before any unintended movement can occur. This preliminary action prevents the harmful effect of residual torque causing movement after load insertion operations.
Solution Approach 2:
The torque command value is made dynamic based on operational conditions. The controller adjusts the torque command value between different states: during normal operation it responds to accelerator input, but when stopped with accelerator released it transitions to a predetermined low-torque state. This dynamic adjustment resolves the contradiction by adapting torque control to prevent unintended movement while maintaining normal speed control functionality.
2Measurement precision
If torque is increased to reduce error between target and actual rotational speed during inserting operation, then rotational speed control is improved, but torque cannot be released after operation causing strange maneuverability
Solution Approach 1:
The controller proactively releases torque by setting the command value to a predetermined level when the accelerator member is not operated and the forklift is stopped. This preliminary torque release action ensures smooth maneuverability after load insertion operations, preventing the strange feeling caused by residual torque while maintaining precise speed control during actual operation.
Data Source
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AI summary
A forklift truck (10) includes an accelerator member (25), a traveling motor (24), an inverter (22), and a controller (30). The controller (30) obtains a rotational speed command. The controller (30) calculates a target rotational speed, an error between a rotational speed and the target rotational speed, an output ratio, and a toque current command value. The controller (30) performs a control of such that the rotational speed of the traveling motor (24) follows the target rotational speed. The component of the output ratio is defined as an acceleration component. The controller (30) sets the output ratio at a current control cycle to a value obtained by decreasing only the acceleration component of the output ratio at a previous control cycle by a predetermined value when the rotational speed command at the current control cycle is zero and an acceleration output ratio is a value excluding zero.