Screwdriver Control via Dynamic Voltage and Torque Monitoring
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Solution Overview
Problem
Existing screwdriver control methods are inadequate for checking and retightening screws that have already been tightened, as they are only suitable for tightening screws and do not effectively verify the torque applied to screws over time.
Innovation Solution
A method for controlling a screwdriver with an electric motor that regulates voltage to monitor speed and torque, involving multiple speed and torque limit values to determine if screws are tightened to the target torque, allowing for the identification of screw status and potential retightening needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage is limited to a predetermined value during control phase, then the electric motor cannot exceed a certain torque, but this prevents effective testing of screws already tightened to high torque
Solution Approach 1:
The patent implements dynamic voltage adjustment in three distinct phases: start-up phase with voltage ramp-up, control phase with limited voltage for safety, and test phase with increased voltage for retightening. This dynamic adaptation allows the same control system to handle both initial tightening and verification of already tightened screws, resolving the contradiction between reliability and versatility.
Solution Approach 2:
The system changes operational parameters (voltage limits, speed thresholds, torque limits) based on the detected state of the screw. By monitoring speed and comparing it against thresholds, the system determines whether a screw needs tightening or verification, then adjusts voltage and torque parameters accordingly. This enables the system to adapt to different screw states while maintaining control reliability.
2Measurement precision
If the electric motor is switched off when torque reaches a preselected value, then tightening control is reliable, but the system cannot distinguish between properly tightened and loose screws
Solution Approach 1:
The system continuously monitors motor current (proportional to torque) and rotational speed, providing real-time feedback about screw tightening status. By analyzing the relationship between torque and speed throughout the operation, the system can determine whether a screw was loose and required retightening or was already properly tightened, preserving screw status information while maintaining precise torque control.
Solution Approach 2:
The system performs preliminary monitoring during the start-up and control phases to assess screw status before final tightening. By observing speed and torque characteristics in these initial phases, the system gathers information about the screw's initial state, enabling differentiation between already-tightened and loose screws even after the motor switches off at the torque limit.
3Measurement precision
If multiple speed and torque thresholds are implemented, then screw status can be accurately determined, but control system complexity increases
Solution Approach 1:
The control process is segmented into three distinct phases (start-up, control, and test phases), each with specific voltage limits and monitoring parameters. This segmentation allows the system to use different threshold sets appropriately for each phase, managing complexity by organizing multiple thresholds into structured, phase-specific groups rather than requiring all thresholds to be active simultaneously.
Solution Approach 2:
The control system uses a universal monitoring framework that tracks the same parameters (speed, torque, current) across all phases, but applies different threshold criteria based on the phase and detected screw status. This multi-functional approach allows the same hardware and basic software structure to handle multiple screw states and control scenarios, reducing overall system complexity despite the presence of multiple thresholds.
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
Enables efficient checking and retightening of screws by distinguishing between screws tightened below, at, or above the target torque, ensuring screws are securely tightened by applying appropriate torque limits and monitoring speed and torque thresholds.
Implementation Method 1
a screwdriver having an electric motor (10)
Implementation Method 2
control is carried out via the voltage applied to the electric motor (10)
Implementation Method 3
A support arm (3) allows the screwdriver to support itself in the surrounding area during the screwdriving process
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Method for controlling a rotary screwdriver comprising an electric motor, mounted on a screw, wherein control is effected via the voltage applied to the electric motor, comprising the following steps: in a start-up phase: a) controlling the rotary screwdriver with respect to a target speed and monitoring the speed; after reaching a predetermined speed threshold, a control phase is carried out with the following steps: - b) controlling the rotary screwdriver with respect to a target speed, whereby the voltage applied to the electric motor is limited to a predetermined value and - monitoring the speed with respect to a predetermined first speed limit, which is lower than the speed threshold; c) upon reaching the first speed limit: increasing the voltage applied to the electric motor above the predetermined value, monitoring the speed with respect to a predetermined second speed limit.the speed is lower than the first speed limit and the torque applied to the screw is monitored with respect to a predetermined first torque limit, wherein in a standard case 1, where the speed does not reach the second speed limit, the electric motor is switched off directly or is switched off when the torque applied to the screw reaches the first torque limit, and wherein in a standard case 2, where the speed reaches or falls below the second speed limit, the first torque limit is increased to a second torque limit and the torque applied to the screw is monitored with respect to the second torque limit, the electric motor being switched off when the torque applied to the screw reaches the second torque limit.