Rotary Impact Tool Speed Detection for Screw Protection
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Solution Overview
Problem
Existing rotary impact tools face challenges in accurately and rapidly detecting impacts during screw tightening, particularly in light-loaded conditions, leading to potential screw stripping or damage due to excessive torque from high-speed rotation.
Innovation Solution
A rotary impact tool configuration that includes a motor, hammer, anvil, rotation speed detection device, extreme value pair detection device, and impact detection device, utilizing the periodic changes in motor rotation speed to accurately detect impacts by setting threshold values for the difference between maximum and minimum rotation speeds, and considering the time interval and rotation number range for precise detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-speed rotation is used to tighten screws quickly, then productivity is improved, but the risk of screw head stripping or damage increases due to excessive torque from impact
Solution Approach 1:
The patent implements feedback control by detecting impact forces during screw tightening and automatically adjusting motor rotation speed in response. When an impact is detected (indicating the screw has been seated), the system reduces rotation speed from high-speed to low-speed mode, preventing excessive torque that would cause screw head damage while maintaining high productivity during the non-impact phase
2Difficulty of detecting and measuring
If impact detection is performed using vibration or impact sound sensors, then impact detection capability is improved, but detection accuracy deteriorates in light-loaded conditions or when object material causes unstable load
Solution Approach 1:
The patent changes the detection parameter from vibration/impact sound to motor rotation speed. By monitoring changes in rotation speed that occur when impact forces are applied to the motor, the system achieves reliable impact detection across varying load conditions and material types, eliminating the misdetection issues associated with vibration and acoustic sensors
3Object-affected harmful factors
If rotation speed is reduced immediately after screw seating to prevent damage, then screw head protection is improved, but response time increases making it difficult to stop the motor in time
Solution Approach 1:
The patent applies preliminary action by detecting impacts continuously during the screw tightening process rather than waiting for post-seating confirmation. The system proactively reduces rotation speed immediately when an impact is detected, eliminating the time delay associated with operator confirmation and enabling timely prevention of screw head damage
Data Source
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AI summary
There is provided a rotary impact tool (1) that includes: a motor (4); a hammer (14) configured to be rotated by the motor; an anvil (15) configured to be intermittently applied with an impact force in a rotation direction by a rotational force of the hammer; a rotation speed detection device (31, 40) configured to detect a rotation speed of the motor; an extreme value pair detection device (31) configured to detect an extreme value pair, which is a pair of a maximum value and a minimum value of the rotation speed, based on the rotation speed detected by the rotation speed detection device; and an impact detection device (31) configured to detect that the impact force is being applied when an extreme value difference, which is a difference between the maximum value and the minimum value, is equal to or more than a first threshold value.