Rotary Impact Tool Voltage Control for Motor Temperature Management
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Solution Overview
Problem
Conventional rotary impact tools experience significant temperature rises in motors and switching elements due to high currents, leading to potential degradation and reduced fastening performance, as existing control methods either maintain constant high currents or abruptly reduce voltage, causing inefficiencies in torque application and temperature management.
Innovation Solution
The rotary impact tool employs a control unit that gradually increases and decreases the voltage supplied to the motor between rotary impacts, alternating between increasing and decreasing periods to manage motor current, thereby maintaining sufficient torque while minimizing temperature increases and maintaining performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the duty ratio for PWM control is maintained at 100% to ensure sufficient torque for fastening operations, then fastening performance is improved, but the electric current flowing in the motor increases significantly causing temperature rise and potential degradation of motor and switching elements
Solution Approach 1:
The patent applies dynamic control by making the duty ratio variable rather than constant. The control unit dynamically adjusts the duty ratio based on the operational phase: maintaining 100% during impacts for maximum torque, reducing to 70% just prior to impact to limit current, and increasing to 100% immediately after impact to ensure readiness for the next operation. This dynamic adjustment resolves the contradiction between maintaining high performance and controlling temperature.
Solution Approach 2:
The patent implements periodic control by applying different duty ratios at different periodic stages of the impact cycle. The control pattern repeats with each impact cycle: high duty ratio (100%) during impact, medium duty ratio (70%) during the interval before impact, and high duty ratio (100%) after impact. This periodic variation in control parameters allows the system to achieve both high fastening performance and temperature management.
2Temperature
If the duty ratio is reduced to suppress excessive retraction of the hammer and control current, then temperature rise is suppressed, but the fastening performance may be degraded due to insufficient torque
Solution Approach 1:
The patent applies preliminary action by reducing the duty ratio to 70% just prior to the impact moment. This preemptive reduction in duty ratio limits the current and prevents excessive hammer retraction before the impact occurs, thereby suppressing temperature rise in switching elements. The control unit anticipates the impact event and adjusts the duty ratio in advance to optimize both temperature control and subsequent fastening performance.
3Productivity
If the duty ratio is increased immediately after impact to ensure readiness for the next impact, then fastening performance is maintained, but a large current flows causing heat generation in the motor and switching elements
Solution Approach 1:
The patent maintains continuity of useful action by keeping the duty ratio at 100% immediately after impact. This ensures the motor and impact mechanism remain at full readiness for the next impact event without interruption. The continuous high-duty-ratio operation after impact guarantees that the system is prepared for the next fastening operation, maintaining productivity while the periodic reduction to 70% during intervals manages heat generation.
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 effectively suppresses temperature rises in motors and switching elements while maintaining or improving fastening performance by optimizing current flow and torque application, reducing vibrations, and enhancing tool operability.
Implementation Method 1
the temperatures of the motor and the switching elements used to control the motor rises due to the large current that flows to the motor during each rotary impact and the current that flows in the interval between one rotary impact and a successive rotary impact
Data Source
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Figure 3(a)~3(b)
AI summary
To provide a rotary impact tool capable of: suppressing a rise in temperature in a motor or switching elements and a current flowing in the motor or switching elements while suppressing a degradation in tightening performance; and improving operability. The rotary impact tool includes: a motor; an end-bit holding part driven by the motor; an impact mechanism provided on a drive transmission path from the motor to the end-bit holding part and configured to intermittently produce rotary impacts, the rotary impacts transmitting a drive force of the motor to the end-bit holding part; a switching element configured to change a voltage supplied to the motor; and a control unit controlling the switching element. The control unit is configured such that the voltage supplied to the motor begins to gradually rise within a period of time from a timing when a first rotary impact ends to a timing when a second rotary impact subsequent to the first rotary impact starts.