Inertial Drive Actuator Position Detection via Electrostatic Capacitance
Solution Overview
Problem
Conventional inertial drive actuators face challenges in accurately detecting the position of a mobile object over its entire range of movement due to misalignment of mobile and detection shafts, leading to inaccuracies in electrostatic capacitance measurements.
Innovation Solution
The inertial drive actuator employs a design with multiple coils to independently control magnetic adsorption forces and uses divided detecting electrodes to maintain a consistent gap between the mobile object and electrodes, enabling precise position detection by varying electrostatic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If separate actuator section and position sensor section are installed, then each section can function independently, but misalignment of mobile shaft and detection shaft occurs causing inaccurate position detection
Solution Approach 1:
The patent combines the actuator section and position sensor section into a single integrated unit, eliminating the separate installation of two independent sections. The mobile object serves dual purposes: it is both the actuator component and the detection target, ensuring that the mobile shaft and detection shaft are inherently aligned rather than requiring separate alignment procedures.
2Ease of manufacture
If mobile shaft and detection shaft are misaligned in gap direction, then assembly is simpler, but electrostatic capacitance changes according to position causing detection inaccuracy
Solution Approach 1:
By integrating the sensor function into the mobile object itself, the patent eliminates the need for separate detection shaft alignment. The mobile object's position directly modulates the electrostatic capacitance between its electrode and the stationary electrode, ensuring that capacitance changes reflect only positional information without gap misalignment errors.
3Reliability
If pinching member is fitted tightly to mobile object, then frictional force is acquired for stable driving, but complexity of structure increases
Solution Approach 1:
The patent extracts the friction acquisition function from a separate mechanical pinching mechanism and integrates it into the magnetic adsorption system. The magnetic adsorption force between the mobile object and stationary object provides the necessary frictional force for stable driving, eliminating the need for additional pinching members and their associated complexity.
4Measurement precision
If magnetic adsorption force is controlled independently for multiple mobile objects, then position control precision is improved, but device complexity increases
Solution Approach 1:
The patent employs a single coil that generates a magnetic field affecting multiple mobile objects simultaneously. By controlling the current in this universal coil, the magnetic adsorption force is regulated for all mobile objects, enabling independent position control of each object through their respective positions in the magnetic field without requiring separate control systems for each.
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 design allows for accurate position detection across the entire range of movement by synchronizing magnetic adsorption forces with piezoelectric vibrations, improving detection accuracy and reducing the complexity of assembling the actuator.
Implementation Method 1
one end of a piezoelectric element is fixed to one end in the longitudinal direction of the vibration substrate, and the other end of the piezoelectric element is fixed to the fixed member. The piezoelectric element, by applying or releasing a voltage, generates a minute displacement in a direction of elongation (a first direction) and in a direction of contraction (a second direction).
Implementation Method 2
A coil is disposed around an outer peripheral surface of the protrusion. The fixed member and / or the vibration substrate are made of a magnetic body, and an adsorption section is formed on a lower surface of the mobile object. A magnetic field is generated when an electric current is applied to (is passed through) the coil 25.
Implementation Method 3
a detecting electrode 26 for detecting a position of the mobile object 24 is disposed on the vibration substrate 33. The detecting electrode 26 and the mobile object 24 form a condenser of electrostatic capacitance. By moving of the mobile object 24, an electrostatic capacitance between the mobile object 24 and the detecting electrode 26 changes periodically.
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
An inertial drive actuator includes a fixed member (11), a displacement generating mechanism (12) which is connected to the fixed member, and which generates a minute displacement in a first direction and a second direction, a vibration substrate (13) which reciprocates by the minute displacement generated by the displacement generating mechanism, a mobile object (24) which is disposed on the vibration substrate, and which is movable by inertia, a driving mechanism which is connected to the mobile object, and which controls a frictional force between the mobile object and the vibration substrate by making an electromagnetic force to act in the mobile object by applying a current, a detecting electrode (35,36) having a position detection function, which is disposed on a flat surface of the vibration substrate, to be facing the mobile object via an insulating body layer, and which is formed such that, an area face-to-face thereof with the mobile object either increases continuously or decreases continuously with the movement of the mobile object, and a position detecting mechanism which detects a position of the mobile object by detecting an electrostatic capacitance generated between the mobile object and the detecting electrode.