Handheld Power Tool Motor Control for Stalling Prevention
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Solution Overview
Problem
Hand-held power tools, particularly cutting devices like pruning shears, face issues with user safety and functionality due to the risk of motor stalling, clutch jamming, and inadequate feedback during charging, which can lead to operational inefficiencies and user hazards.
Innovation Solution
The integration of a DC motor with a control device that performs a functional test when connected or disconnected from a charging device, limits maximum current output based on battery voltage and temperature, and includes an automatic clutch unit for decoupling the drive unit in certain operating states, ensuring safe and efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If the motor is driven continuously during charging to provide feedback, then user feedback and functional testing are improved, but the risk of motor stalling and safety hazards increases
Solution Approach 1:
The motor is driven periodically for brief test durations (a few milliseconds) during charging to provide feedback and perform functional testing, rather than continuous operation. This periodic brief activation achieves the necessary feedback and testing while minimizing the risk of motor stalling and safety hazards.
Solution Approach 2:
The control device performs a functional test by briefly driving the motor before full operational use. This preliminary action verifies that the motor, battery, wiring, and control components are intact and functioning properly, preventing harmful situations from developing during actual use.
2Reliability
If the maximum current output is limited as a function of battery voltage, then motor stalling is prevented, but the power output and cutting capability are reduced
Solution Approach 1:
The maximum current limit is not fixed but dynamically adjusted as a function of the battery voltage. As the battery voltage decreases during discharge, the maximum current limit is reduced proportionally. This dynamic adjustment prevents motor stalling across the entire operating range while maximizing power output at each voltage level.
Solution Approach 2:
The control device changes the electrical parameters (maximum current output) based on the battery voltage state. By continuously monitoring battery voltage and adjusting the current limit accordingly, the system maintains reliable operation without unnecessary power restrictions.
3Power
If the clutch is designed to engage under high load, then cutting capability is improved, but the clutch may become jammed and prevent device opening
Solution Approach 1:
The control device detects clutch engagement status and preemptively applies a reverse torque signal to the motor to release the clutch before it becomes jammed. This preliminary anti-action prevents the harmful effect of clutch jamming by counteracting the engagement force when release is needed.
Solution Approach 2:
The mechanical clutch release mechanism is supplemented or replaced with an electrical control system. The control device uses electrical signals to the motor to generate reverse torque that releases the clutch, substituting purely mechanical release with electromechanical control.
4Object-affected harmful factors
If the functional test is performed with limited drive time, then safety is improved, but the completeness of functional testing may be reduced
Solution Approach 1:
The functional test uses periodic brief motor activations (a few milliseconds each) rather than continuous operation. Multiple brief test cycles can be performed sequentially, each testing different aspects of motor function while maintaining safety through limited exposure time.
Solution Approach 2:
The control device monitors the motor response during brief test activations to determine if the motor, battery, wiring, and control components are functioning properly. This feedback mechanism allows comprehensive functional assessment within safe time limits by analyzing electrical characteristics and motor performance during brief test periods.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enhances user safety by preventing motor stalling, resolving clutch jamming, and providing clear feedback during charging, while allowing for adjustable power modes to suit different cutting tasks, thereby improving the overall functionality and user-friendliness of hand-held power tools.
Implementation Method 1
The drive unit (20) is designed as an electric motor. The electric motor is intended to be supplied with a voltage of less than 110 V, in particular with a voltage of 1 V to 36 V, preferably 3.6 V.
Implementation Method 2
The cutting device (10) has a drive unit (20) to support a movement of the second cutting element (14) relative to the first cutting element (12). The drive unit (20) is designed as an electric motor. The electric motor is intended to be supplied with a voltage of less than 110 V
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to 1. a hand-held power tool, in particular a cutting device (10), comprising a motor (20), a battery (54, 58), in particular a rechargeable battery, which supplies the motor (20) with energy, a voltage monitoring device, which monitors the voltage of the battery (54, 58), and a control device (52), which monitors or regulates the current supply from the battery (54, 58) to the motor (20). It is proposed that the maximum current output of the battery (54, 58) to the motor (20) be limited as a function of a decreasing battery voltage (U) due to discharge, in particular to prevent the motor from stalling.