Screw Tightening Torque Control via Dynamic Speed Segmentation
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Solution Overview
Problem
Existing methods for achieving a predetermined tightening torque in screw connections require low screwing-in speeds to prevent dynamic effects from mass inertia, limiting process speed and accuracy.
Innovation Solution
A method involving a controlled electric motor with varying speeds, including maximum speed for initial screw insertion, reduced speed for torque detection, and minimum speed for precise tightening, with torque control and model calculations to compensate for inertia and vibrations, ensuring accurate torque application without overtightening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If low screwing-in speed is used to prevent dynamic effects, then tightening torque precision is improved, but process speed deteriorates
Solution Approach 1:
The screwing process is divided into multiple phases with different speed characteristics: a first phase with increasing speed to a maximum value, and a second phase with reduced speed for precise torque control. This segmentation allows each phase to optimize for its specific function, resolving the contradiction between speed and precision.
Solution Approach 2:
The patent implements dynamic speed adjustment during the screwing process, transitioning from a first speed profile (increasing to maximum) to a second speed profile (reduced for precision). This dynamic adaptation allows the system to achieve both high process speed and precise torque control at different stages.
2Productivity
If high screwing-in speed is used to increase process speed, then productivity is improved, but tightening torque precision deteriorates due to dynamic effects
Solution Approach 1:
The process is segmented into phases where high speed is used only in the first phase for rapid advancement, while the second phase uses reduced speed for precision torque application. This temporal segmentation resolves the contradiction by applying speed appropriately to each process stage.
Solution Approach 2:
The first phase performs preliminary action by rapidly advancing the screw to near-final position using high speed, preparing for the precision torque application in the second phase. This preliminary high-speed action increases productivity without compromising final torque precision.
3Loss of time
If abrupt braking is applied to stop the electric motor, then process time is reduced, but vibrations and measurement accuracy deteriorate
Solution Approach 1:
The patent applies cushioning by gradually reducing speed in the second phase and allowing vibrations to subside before torque measurement and evaluation. This beforehand cushioning prevents abrupt braking, reducing vibrations and maintaining measurement accuracy while still optimizing process time.
Solution Approach 2:
The system skips the intermediate waiting period by continuously reducing speed through the second phase and only pausing briefly after vibrations subside. This approach minimizes process time while ensuring measurement accuracy, avoiding both abrupt braking and excessive waiting.
4Manufacturing precision
If the electric motor is braked to minimum speed immediately after torque increase detection, then overtightening is prevented, but vibrations from braking affect torque measurement
Solution Approach 1:
The system cushions the braking effect by gradually reducing speed in the second phase and allowing vibrations to subside before torque evaluation. This beforehand cushioning prevents measurement errors while still preventing overtightening through controlled speed reduction.
Solution Approach 2:
The patent uses feedback by continuously monitoring torque during the second phase and evaluating it after vibrations subside. This feedback mechanism ensures precise torque control and prevents overtightening while maintaining measurement accuracy through timing the evaluation after vibration subsidence.
Data Source
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AI summary
The invention relates to a method for screwing in a screw (4) to a predetermined breakaway torque by means of a screwing-in tool (3) connected to an electric motor (2) controlled by a control system (8). The method comprises the following method steps: - accelerating the electric motor (2) in the screwing direction (15) to a predetermined maximum rotational speed; - operating the electric motor (2) at maximum rotational speed until a drive shaft (11) of the electric motor (2) has completed a predetermined number of spindle rotations; - reducing the rotational speed of the electric motor (2) to a predetermined reduced rotational speed; - operating the electric motor (2) at a reduced rotational speed until a torque increase exceeding a predetermined threshold value is detected by a measuring unit (14) downstream of the electric motor (2); - tightening the screw (4) or nut again until the predetermined tightening torque is reached.