Drive Unit PWM Control for Mobile Entity Torque Management
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Solution Overview
Problem
Existing drive units for mobile entities like hand pallet jacks and wheelchairs face issues with abrupt acceleration and slippage due to high torque output at low rotational speeds, which is mitigated by limiting motor voltage or current, resulting in reduced maximum rotational speed.
Innovation Solution
A drive unit with a motor, a first detector for vehicle speed, and a controller that performs PWM control by adjusting the duty cycle of the PWM signal based on vehicle speed information, increasing the duty cycle with increasing rotational speed to manage torque output effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the motor is driven with maximum performance to output high torque in starting, then the starting torque is improved, but abrupt acceleration or slippage of drive wheel undesirably occurs
Solution Approach 1:
The duty cycle is dynamically adjusted based on rotational speed feedback. At low speeds (starting condition), the duty cycle is automatically reduced to limit torque output and prevent slippage, while at higher speeds the duty cycle increases to maintain maximum rotational speed capability. This dynamic control resolves the contradiction between needing high starting torque and preventing abrupt acceleration.
Solution Approach 2:
The system uses rotational speed detection feedback to continuously adjust the duty cycle. The detector monitors rotational speed and feeds this information to the controller, which then adjusts the PWM duty cycle accordingly. This closed-loop feedback mechanism enables the system to automatically prevent slippage during starting while maintaining performance at higher speeds.
2Object-affected harmful factors
If the drive voltage value is uniformly limited to prevent abrupt acceleration, then the harmful factors are reduced, but the maximum rotational speed of the motor is undesirably reduced
Solution Approach 1:
Rather than uniform voltage limitation, the system dynamically adjusts the duty cycle based on rotational speed. At low speeds where slippage occurs, the duty cycle is reduced to limit torque. At higher speeds where maximum rotational speed is needed, the duty cycle is increased to allow full power delivery. This dynamic approach resolves the contradiction between preventing abrupt acceleration and maintaining maximum speed.
Solution Approach 2:
The control approach applies different duty cycle values to different operational conditions (low speed vs. high speed). Instead of a uniform limitation across all operating conditions, the system tailors the duty cycle to the specific rotational speed range, allowing optimal performance in each regime while preventing harmful effects only where necessary.
3Object-affected harmful factors
If the duty cycle is reduced to prevent slippage at low speeds, then the harmful factors are inhibited, but the maximum rotational speed capability is reduced
Solution Approach 1:
The duty cycle is made dynamic rather than static. The controller automatically increases the duty cycle as rotational speed increases, compensating for the reduced duty cycle at low speeds. This ensures that while slippage is prevented during starting (low speed), the motor can still achieve maximum rotational speed at higher operating speeds where the duty cycle has been increased back to appropriate levels.
Data Source
AI summary
A drive unit attached to a mobile entity is disclosed. The drive unit includes a motor, a first detector, and a controller. The first detector detects vehicle speed information regarding a vehicle speed of the mobile entity. The controller performs PWM control for the motor. The controller controls a duty cycle of a PWM signal in accordance with the vehicle speed information detected by the first detector.