Electric Tool Automatic Gear Shift Control Circuit
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Solution Overview
Problem
Existing electric tools face challenges in efficiently and cost-effectively switching reduction ratios in response to load variations, often leading to inappropriate or undesired automatic gear shifts due to reliance on single conditions like motor current, which can result in malfunctions and reduced working speed.
Innovation Solution
An electric tool that employs multiple conditions, including motor driving current, rotation rate, and temperature, to control automatic gear shifts, using a control circuit to switch reduction ratios only when specific conditions are met, thereby reducing the likelihood of inappropriate shifts and ensuring stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If automatic gear shift is performed based on motor current monitoring, then cost increase is suppressed, but malfunction occurs due to rush motor current at start or rapid trigger switch operation
Solution Approach 1:
The patent applies dynamics by making the gear shift determination conditions variable rather than fixed. The control circuit dynamically adjusts the current threshold and time window based on motor operating state (idle, acceleration, constant speed, deceleration), allowing the system to adapt to changing conditions and distinguish between normal rush current and abnormal overload conditions.
Solution Approach 2:
The patent changes multiple parameters simultaneously: the current threshold value, the time window for current monitoring, and the determination conditions are all adjusted based on the motor's operating phase. This multi-parameter adjustment enables reliable distinction between startup rush current and actual overload conditions requiring gear shift.
2Device complexity
If gear shift is performed manually, then structure remains simple, but worker burden increases due to required switching operations
Solution Approach 1:
The patent implements self-service by enabling the system to automatically monitor its own operating conditions and autonomously determine when gear shift is necessary. The control circuit continuously monitors motor current and operating state, automatically making the decision to shift gears without requiring worker intervention, thus reducing operational burden while maintaining relatively simple structure.
3Device complexity
If gear shift is determined based on only motor current, then device complexity is reduced, but inappropriate gear shift occurs during rapid motor acceleration
Solution Approach 1:
The patent transitions from one-dimensional current monitoring to multi-dimensional assessment by incorporating both temporal dimension (time window for current integration) and operational dimension (motor operating state classification). This allows the system to evaluate current in context of the motor's acceleration phase, distinguishing between normal acceleration current and abnormal overload conditions.
4Device complexity
If reduction ratio is switched at fixed current threshold, then control is simplified, but working speed decreases due to temperature-induced N-T characteristic variation
Solution Approach 1:
The patent makes the gear shift determination dynamic by continuously monitoring motor operating state and adjusting the current threshold and time window accordingly. As temperature increases and N-T characteristics deteriorate, the system adapts its determination criteria to account for the changed motor performance, preventing premature gear shift that would reduce working speed.
Data Source
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AI summary
An electric tool of the present invention includes a transmission for switching a reduction ratio between a motor as a rotational power source and an output unit rotatably driven by the motor. The electric tool further includes a driving state detecting means detecting at least two driving states, of driving states that vary in response to a magnitude of a load when the output unit is driven, and a controlling means making the transmission switch the reduction ratio when the at least two driving states detected by the driving state detecting means satisfy predetermined conditions preset for the respective driving states.