Power-Assist Wheelchair Turning Torque Control at Low Speeds
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Solution Overview
Problem
Existing power assist wheelchairs exhibit excessive turning performance in low speed regions due to single flow prevention control, which emphasizes turning and deviates from intended direction, especially at the start of movement.
Innovation Solution
A control device and method that calculates predicted and actual turning torques, adjusts compensation torques based on vehicle speed and inclination, and determines target currents for electric motors to suppress turning performance while maintaining single flow prevention, using sensors and encoders to detect manual and motor torques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If single flow prevention control is executed in low speed region, then turning performance is emphasized, but vehicle direction deviates from intended direction
Solution Approach 1:
The control system dynamically adjusts the compensation turning torque based on vehicle speed. At low speeds, the compensation torque is reduced or set to zero to prevent excessive turning performance that causes direction deviation. At higher speeds, the compensation torque is increased to effectively prevent single flow. This dynamic adjustment resolves the contradiction by adapting the control strength to the operating conditions.
Solution Approach 2:
The patent changes the parameter of compensation turning torque based on vehicle speed threshold. When vehicle speed is below the threshold, the compensation turning torque is set to a first value (zero or reduced), and when above the threshold, it is set to a second value (increased). This parameter change strategy allows the system to optimize turning performance at low speeds while maintaining direction accuracy, and effectively prevent single flow at higher speeds.
2Reliability
If compensation turning torque is increased to prevent single flow, then direction stability improves, but turning performance becomes excessive in low speed region
Solution Approach 1:
The system employs dynamic control where the compensation turning torque varies with vehicle speed. At low speeds, the torque is reduced to prevent excessive turning that compromises operational control. At higher speeds, the torque is increased to ensure direction stability and prevent single flow. This dynamic approach balances reliability and ease of operation across different operating conditions.
Solution Approach 2:
The compensation turning torque parameter is changed based on vehicle speed threshold. Below the threshold, the torque is set to a lower value to maintain appropriate turning performance. Above the threshold, the torque is increased to ensure direction stability. This parameter adaptation resolves the contradiction between reliability and ease of operation.
3Ease of operation
If single flow prevention control is disabled in low speed region, then turning performance is suppressed, but direction control becomes less stable
Solution Approach 1:
Instead of completely disabling single flow prevention control, the system adjusts the compensation turning torque parameter to a reduced value (first value) at low speeds. This partial activation maintains some level of direction control stability while suppressing excessive turning performance. The parameter is then increased to a higher value (second value) at higher speeds for full single flow prevention effectiveness.
Data Source
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AI summary
A control device for a power assist wheelchair includes: a vehicle speed calculation unit that calculates a vehicle speed; a predicted turning torque calculation unit that calculates a predicted turning torque value based upon a first manual torque value acting on the first wheel, a first motor torque value outputted by the first electric motor, a second manual torque value acting on the second wheel, and a second motor torque value outputted by the second electric motor; an actual turning torque calculation unit that calculates an actual turning torque value based upon a detection signal of the first encoder and a detection signal of the second encoder; a compensation turning torque calculation unit that calculates a compensation turning torque value for compensating for at least a part of the shortage or excess of the actual turning torque value with respect to the predicted turning torque value, in which the compensation turning torque value is smaller when the vehicle speed is a first speed than when the vehicle speed is a second speed faster than the first speed; a first target current determination unit that determines a target current of the first electric motor based upon the first manual torque value and the compensation turning torque value; and a second target current determination unit that determines a target current of the second electric motor based upon the second manual torque value and the compensation turning torque value.