Power Tool Adaptive Speed Control for Torque Accuracy
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Solution Overview
Problem
Power tools face challenges in achieving torque accuracy during tightening cycles due to increased motor load and dynamic effects at high speeds, which can lead to inaccuracies in torque application.
Innovation Solution
A power tool with a power control assembly that adaptively changes motor speed in response to measured torque, slowing down when a predefined torque value is reached to reduce dynamic drift and enhance accuracy, using a clutch to interrupt drive power at a target torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the power tool operates at high speeds to increase assembly efficiency, then productivity is improved, but torque accuracy deteriorates due to dynamic effects
Solution Approach 1:
The power tool employs variable speed control that dynamically adjusts motor speed during the tightening cycle. The system transitions from high speed during the initial phase to reduced speed during the final torque application phase, allowing the tool to maintain both high productivity and high torque accuracy by adapting speed to the specific phase of operation
Solution Approach 2:
The tightening cycle is divided into distinct phases with different speed characteristics. The system implements periodic action by operating at high speed during the run-out phase and transitioning to controlled low-speed operation during the critical torque application phase, optimizing both efficiency and precision across different operational periods
2Loss of time
If the motor runs at full speed to reduce cycle time, then loss of time is reduced, but measurement precision of torque deteriorates
Solution Approach 1:
The system performs preliminary high-speed operation to quickly bring the fastener up to speed and complete the initial portion of tightening. This preliminary action reduces the overall cycle time while setting up conditions for the subsequent precision phase, where speed is reduced to ensure accurate torque measurement and application
3Manufacturing precision
If the clutch interrupts drive power at target torque to achieve accurate shut-off, then manufacturing precision is improved, but the tool cannot adapt to varying torque requirements during the tightening cycle
Solution Approach 1:
The system incorporates feedback control by continuously monitoring motor current, which correlates with applied torque. This feedback enables the control system to detect when target torque is approached and trigger the clutch interruption, while also allowing for adaptive speed adjustment throughout the tightening cycle based on real-time torque conditions
Solution Approach 2:
The system replaces purely mechanical clutch-based shut-off with a hybrid electro-mechanical control system. The electronically controlled clutch provides both the mechanical interruption for accurate shut-off and the adaptability to adjust operating parameters throughout the tightening cycle, combining the precision of mechanical systems with the versatility of electronic control
Data Source
AI summary
A power tool may include an end effector configured to enable a fastener to be applied by the power tool via a fastening cycle, a power unit, a drive assembly configured to apply drive power to the end effector responsive to application of input power thereto, and a motor configured to supply the input power to the drive assembly selectively based on operation of a power control assembly that controls coupling of the motor to the power unit. The drive assembly includes a clutch configured to interrupt application of the drive power at a target torque. The power control assembly may be configured to adaptively change speed of the motor in response to the power tool reaching a predefined torque value that is less than the target torque during the fastening cycle.