Electrostatic Encoder Electrode Arrangement for Parasitic Capacitance Reduction
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Solution Overview
Problem
Conventional electrostatic encoders face issues with parasitic capacitance variations due to differing shapes of transmission and reception elements, leading to voltage deviations in amplitude modulation signals and structural challenges in downsizing, particularly with increased spacing between disks.
Innovation Solution
The electrostatic encoder employs an alternate arrangement of transmission and detection electrodes on the stator and rotor, with two or more relay electrodes on one insulation member and transmission and detection electrodes on the other, allowing for uniform electrode shapes and reduced parasitic capacitance, enabling downsizing by minimizing the number of radially arranged electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transmission elements and reception elements have different shapes, then the encoder can function with basic position detection capability, but parasitic capacitance varies causing voltage deviation in amplitude modulation signals
Solution Approach 1:
The patent applies homogeneity by making all transmission elements and reception elements have identical shapes and dimensions. This uniformity ensures that parasitic capacitance values remain consistent across all electrode pairs, eliminating the voltage deviation problem that occurs when elements have different shapes. The homogeneous design allows the encoder to maintain accurate position detection without signal distortion.
2Reliability
If the number of reception elements is increased, then detection coverage is improved, but the fixed disk becomes larger and harder to downsize
Solution Approach 1:
The patent merges the functions of transmission and reception elements by using the same electrode structure for both purposes. Each element can serve as either a transmission element or a reception element depending on its operational state, eliminating the need for separate dedicated reception elements. This combination reduces the total number of elements required and enables downsizing of the fixed disk while maintaining full detection coverage.
Solution Approach 2:
The patent implements multi-functionality by designing electrodes that can perform both transmission and reception functions. The same electrode structure is used for signal transmission during one phase and for signal reception during another phase. This universal design reduces the number of components needed and allows the encoder to achieve comprehensive detection coverage with a compact fixed disk structure.
3Length of moving object
If spacing between movable disk and fixed disk is increased, then mechanical clearance is improved, but voltage deviation in amplitude modulation signals increases
Solution Approach 1:
The patent applies parameter changes by optimizing the electrode dimensions, spacing patterns, and arrangement configurations to compensate for increased disk spacing. By adjusting these parameters, the system maintains consistent capacitance coupling between transmission and reception elements even when the overall disk spacing is larger, thereby preventing voltage deviation in the amplitude modulation signals while providing necessary mechanical clearance.
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 arrangement reduces voltage deviations in amplitude modulation signals and allows for a more compact design by minimizing the number of detection electrodes, effectively addressing the parasitic capacitance issues and enabling downsizing of the encoder.
Implementation Method 1
a high-frequency signal 16, when being applied to the transmission electrode 12, is transmitted to the detection electrode 13 via a capacitance Ctc defined between the transmission electrode 12 and the relay electrode 15 and a capacitance Ccs defined between the relay electrode 15 and the detection electrode 13
Implementation Method 2
The high-frequency signal 16 causes the capacitance Ctc defined between the transmission electrode 12 and the relay electrode 15 to generate an electrostatically induced potential at the relay electrode 15, and the induced potential in turn causes the capacitance Ccs defined between the relay electrode 15 and the detection electrode 13 to generate a detection signal 18 at the detection electrode 13
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
An electrostatic encoder (40) detects the rotation angle of a rotor (42) with great accuracy based on the change in the capacitance between electrodes arranged on a stator (41) and the rotor (42). Detection electrodes (44a to 44d) and transmission electrodes (45a to 45d) are arranged circumferentially and alternately on the stator (41). Detection signals (phase A, phase B) amplitude-modulated based on the rotation of the rotor (42) and having a mutual phase difference of 90 degrees are output from adjacent ones of the detection electrodes. Modulated signals (V1, V2) are generated by demodulating the detection signals having a mutual phase difference of 90 degrees. Applying resolver-digital (RD) conversion processing to the modulated signals allows obtaining the rotation angle of the rotor.