Power Tool Vibration Control via Motor Speed Feedback
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Solution Overview
Problem
Power tools with reciprocating tool bits generate vibrations that are transferred to the user, causing discomfort and potential health issues, and existing vibration reduction methods, such as oscillating counter masses, can enhance vibrations if not properly tuned.
Innovation Solution
A method and power tool design that monitor and control the rotational speed of the electric motor to maintain the vibration frequency below the resonance frequency of the spring-mass system, using detection devices like induction coils or Hall sensors to adjust the motor speed and limit the oscillation amplitude, ensuring effective vibration dampening without relying on precise spring assembly tolerances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the vibration frequency exceeds the resonance frequency of the spring-mass-assembly, then the counter mass oscillates in parallel with the ram, but the vibrations of the entire tool are enhanced rather than reduced
Solution Approach 1:
The patent implements a control unit that receives signals from detection devices (induction coils or Hall sensors) monitoring the oscillation amplitude of the counter mass, and adjusts the motor rotational speed accordingly. This closed-loop feedback system ensures the vibration frequency remains below the resonance frequency of the spring-mass-assembly, preventing the counter mass from oscillating in parallel with the ram and avoiding enhancement of tool vibrations.
Solution Approach 2:
The control unit dynamically adjusts the rotational speed of the motor, thereby changing the vibration frequency parameter. By maintaining the vibration frequency below the resonance frequency of the spring-mass-assembly, the system ensures the counter mass oscillates in anti-phase with the ram, maximizing vibration dampening effectiveness.
2Object-affected harmful factors
If the resonance frequency of the spring-mass-assembly is set well above the vibration frequency to ensure dampening, then the vibration dampening effect is maximized, but the oscillation amplitude of the counter mass is reduced
Solution Approach 1:
The patent makes the system dynamically adjustable by allowing the control unit to modify the motor rotational speed based on real-time detection of counter mass oscillation amplitude. This enables the system to adapt to varying operating conditions and maintain optimal vibration dampening performance without requiring the resonance frequency to be fixed well above the vibration frequency.
Solution Approach 2:
The detection devices (induction coils or Hall sensors) provide real-time feedback on the oscillation amplitude of the counter mass to the control unit. This feedback mechanism allows the system to adjust the motor speed to maintain the vibration frequency below the resonance frequency, ensuring sufficient oscillation amplitude for effective dampening while avoiding excessive counter mass movement.
3Object-affected harmful factors
If the vibration frequency is kept close to but below the resonance frequency to maximize dampening, then the oscillation amplitude of the counter mass is maximized, but the system becomes sensitive to tolerance variations in spring assembly
Solution Approach 1:
The control unit uses detection devices to monitor the actual oscillation amplitude of the counter mass and adjusts the motor rotational speed accordingly. This feedback mechanism compensates for tolerance variations in the spring assembly by dynamically adapting the operating parameters, ensuring consistent vibration dampening performance without requiring extremely tight manufacturing tolerances.
Solution Approach 2:
The system transitions from a static design with fixed resonance frequency to a dynamic system where the control unit can adjust motor speed in real-time. This dynamic adjustment capability allows the system to maintain optimal dampening performance despite variations in spring assembly tolerances, as the control unit can compensate by modifying the vibration frequency within the acceptable range.
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 approach reduces user-experienced vibrations by optimizing the vibration dampening effect, ensuring the counter mass oscillates in anti-phase with the ram, thereby minimizing tool housing vibrations and adhering to health and safety standards.
Implementation Method 1
the spring-mass-assembly has a resonance frequency which is mainly determined by the spring stiffness, the weight of the counter mass and the dampening effect due to friction
Implementation Method 2
Due to the vibrations generated by the hammer mechanism, oscillations of the mass are induced wherein these vibrations have a frequency which is equal to the frequency with which the ram applies impacts on the beat piece and the tool bit, respectively
Implementation Method 3
the hammer (1) comprises a first induction coil (43) and a second induction coil (45) surrounding the path along which the counter mass (33) travels
Implementation Method 4
a plurality of Hall sensors (59) are mounted in the tool housing (1) wherein the distance the sensors (59) have to the neutral position of the counter mass (33), differs for each sensor (55)
Implementation Method 5
the oscillation amplitude with which the counter mass (33) oscillates, is determined via simultaneously monitoring the inductance of the first and second coils (43, 45)
Data Source
AI summary
The present invention relates to a method for controlling a power tool comprising a housing, an electric motor, a tool holder for supporting a tool bit and a conversion mechanism for converting the rotational movement of the output shaft of the motor into a reciprocating movement of the tool bit when being supporting in the tool holder, wherein oscillations of an element of the power tool are detected, wherein a quantity characterizing the oscillations is monitored and wherein the rotational speed of the electric motor is controlled such that the quantity does not exceed a preset value.