Power Screwdriver Voltage Limiter Circuit
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Solution Overview
Problem
High-torque power wrenches face challenges in safely dissipating stored energy in the support arm after switching off, leading to potential counter-torques and component damage due to high motor voltages during generator operation.
Innovation Solution
A voltage limiter circuit that limits the motor voltage to a predetermined limiting voltage when the electric motor operates as a generator, preventing counter-torques and protecting the control circuit from high voltages, combined with a battery voltage drop compensation circuit to maintain torque setpoints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the electric motor is switched off abruptly when torque setpoint is reached, then the tightening torque precision is improved, but the stored energy in the support arm causes the electric motor to rotate counter to drive direction generating high voltages that can damage control circuit components
Solution Approach 1:
A voltage limiter circuit is introduced as an intermediary component between the electric motor and the control circuit. This circuit limits the motor voltage to a predetermined limiting voltage when the electric motor operates as a generator during support arm energy dissipation, preventing high voltages from reaching and damaging control circuit components while allowing the support arm to safely dissipate its stored energy.
2Strength
If the electric motor is allowed to coast to stop naturally, then the mechanical stress on components is reduced, but the kinetic energy of rotating masses causes overrun and the screw connection is tightened with higher torque than the specified setpoint
Solution Approach 1:
The patent replaces the purely mechanical coasting method with an electronic control system that monitors motor current as a measure of torque. The control circuit detects when the torque setpoint is reached and switches off the electric motor at the precise moment, eliminating the overrun problem while using electronic rather than mechanical means to achieve the switch-off.
3Loss of time
If the electric motor is switched off at high speed, then the response time is reduced, but the kinetic energy of rotating masses causes significant overrun and torque peaks
Solution Approach 1:
The control circuit uses feedback from motor current measurement to determine the actual torque being applied. This feedback mechanism allows the system to switch off the electric motor at the precise moment the torque setpoint is reached, regardless of the motor's rotational speed, thereby eliminating overrun while maintaining fast response time.
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
Ensures safe dissipation of stored energy without counter-torques and protects the control circuit from high voltages, allowing for efficient operation and component safety.
Implementation Method 1
the electric motor, which operates as a generator when the energy stored in the support arm is reduced and rotates counter to the drive direction
Implementation Method 2
a voltage limiter circuit which limits the motor voltage occurring at the electric motor to a predetermined limiting voltage
Implementation Method 3
a battery voltage drop compensation circuit to compensate for voltage drops in the battery and maintain the torque setpoint
Data Source
Figure 1
Figure 2
Figure 3a~3d
AI summary
The invention relates to a power screwdriver (10) comprising a motor (12) and a control circuit (22) which switches the motor (12) off by means of a switch-off signal (s_Stop) when it reaches a preset desired torque value (Md_Soll), and a supporting arm (18) which absorbs energy during screwing. The invention is characterized by a voltage limiting circuit (46) that limits the motor voltage (u_Mot) occurring on the motor (12) when the energy stored in the supporting arm (18) of the motor (12), which is driven as the generator and rotates counter to the direction of drive, is dissipated, to a predetermined limiting voltage (u_Lim). Said limiting voltage (u_Lim) is fixed in such a manner that the motor (12) is capable of rotating without counter-torque counter to the direction of drive when operated in the generator mode and that yet no inadmissible overvoltages occur.