Screwdriver Motor Control via Cutoff Speed
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Solution Overview
Problem
Existing screwdriver control methods using current as a control variable face inaccuracies due to interferences with torque control, require complex sensors to account for motor characteristic deviations, and can result in uncontrolled torque increases and motor damage from short circuit currents.
Innovation Solution
The method involves predefining an effective voltage and cutoff rotational speed to control the screwdriver, switching off the motor when the cutoff rotational speed is reached, allowing flexible torque adjustment without operating the motor until standstill, and using pulse width modulation or phase angle control to maintain voltage accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current is used as the control variable for torque control, then torque control can be implemented, but current fluctuations from the commutator cause measurement inaccuracies and delays
Solution Approach 1:
The patent replaces the electrical measurement method (current measurement) with a mechanical measurement method (torque sensor). This substitution eliminates the interference from commutator current fluctuations, providing accurate torque measurement without the delays and inaccuracies caused by electrical noise and smoothing requirements.
2Manufacturing precision
If the motor is operated until standstill to reach cutoff torque, then the desired torque can be achieved, but short circuit currents occur causing motor damage
Solution Approach 1:
The patent replaces the electrical control method (current-based torque control requiring motor to stall) with a mechanical control method (torque sensor-based control). This allows the motor to be switched off precisely when the cutoff torque is reached during rotation, avoiding the short circuit currents that occur when the motor is operated to standstill.
Solution Approach 2:
The patent implements a feedback control system using a torque sensor that continuously monitors the actual torque and provides feedback to the control unit. This feedback enables precise detection of when the cutoff torque is reached, allowing the motor to be switched off at the exact moment the desired torque is achieved, rather than operating until standstill.
3Measurement precision
If additional sensors are added to account for motor characteristic deviations, then measurement accuracy can be improved, but device complexity increases
Solution Approach 1:
The patent replaces complex electrical measurement and compensation systems with a direct mechanical torque sensor. This single sensor directly measures the actual torque without requiring complex calculations, motor characteristic data, or additional sensors to compensate for deviations, thereby reducing overall system complexity while improving measurement accuracy.
4Productivity
If high rotational speed is maintained during operation, then productivity is improved, but uncontrolled torque increase occurs after switch-off due to kinetic energy
Solution Approach 1:
The patent uses real-time torque feedback from the torque sensor to detect when the cutoff torque is reached during high-speed operation. This enables the control system to switch off the motor precisely at the desired torque point, preventing uncontrolled torque increases after switch-off that would occur with kinetic energy from high rotational speeds.
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
This approach enables precise and flexible cutoff torque control, preventing short circuit currents and motor damage, while allowing the use of standard motors, with high reliability and accuracy in switching off the screwdriver at the desired torque.
Implementation Method 1
an electric motor (7), wherein at a given effective voltage the electric motor (7) has a distinct ratio of rotational speed to torque
Implementation Method 2
switching off the electric motor (7) when reaching the cutoff rotational speed
Data Source
AI summary
A method for controlling a screwdriver that has an electromotor, the electromotor having a clear ratio of rotational speed (n) to torque (M) at a defined effective voltage (Ueff soll), involving the following method step: —defining an effective voltage (Ueff soll) for operating the electromotor, —defining a cut-off rotational speed (nab) that corresponds to a pre-defined cut-off torque (Msoll) at the pre-defined effective voltage (Ueff soll), —operating the screwdriver under load with the pre-defined effective voltage (Ueff soll), —during operation of the screwdriver: —determining the rotational speed (n), —shutting down the electromotor when the cut-off rotational speed (nab) is attained.