A device and method for measuring the rotation angle of a ball joint with a football-like structure

Abstract

The present invention discloses a device and method for measuring the rotation angle of a ball joint with a football-like structure; the measuring device includes a driving electrode and a sensing electrode system. During the measurement process, the driving electrode and the sensing electrode system are both installed in the ball joint to be measured; the ball joint includes a ball socket base and a ball head installed in the ball socket base. The driving electrode is fixed on the ball head; the sensing electrode system is fixed in the ball socket base. The sensing electrode system includes a plurality of regular hexagonal spherical electrode plates, and one or more regular pentagonal spherical electrode plates. Any regular pentagonal spherical electrode plate is surrounded by five regular hexagonal spherical electrode plates, so that each regular hexagonal spherical electrode plate and each regular pentagonal spherical electrode plate together form a spherical shell structure. The sensing electrode system in the present invention adopts a football-like layout, which can obtain a wide range of rotation angle measurements of the ball joint space and effectively avoid cumulative errors.

Description

Technical Field

[0001] The present invention belongs to the field of precision measurement technology, relates to a two-dimensional angular motion signal detection technology for a spherical motion pair, and specifically relates to a rotation angle measurement device and method for a ball joint with a football-like structure. Background Art

[0002] The ball joint is a commonly used three-degree-of-freedom mechanical joint. Its compact structure, flexible motion, and strong load-bearing capacity make it a key component in mechanical equipment such as parallel mechanisms, industrial robots (robotic arms), and automotive parts. Because the movement of a ball joint is constrained by the joint clearance and structural rigidity of the hinge, kinematic errors caused by these factors affect the system's transmission accuracy. Therefore, measuring the spatial rotation angle of the ball joint is essential for system error prediction, analysis, feedback, and compensation, facilitating the optimization of motion mechanism control.

[0003] The spatial rotation angle of a ball joint is measured by a spherical rotor rotating in three degrees of freedom about its center within a constrained socket. Traditional single-degree-of-freedom angular displacement measurement methods are difficult to directly apply. Currently, spherical rotor motion posture measurement can be categorized into contact and non-contact methods based on the measurement method. Contact measurement solutions primarily employ a slide-rail support mechanism and three rotary encoders to decouple the measurement structure, transforming it into a single-degree-of-freedom measurement problem. Non-contact measurement structures are primarily designed based on principles such as optical sensors, vision sensors, and Hall sensors, achieving decoupled measurement of multiple degrees of freedom angular displacement through data processing. However, these detection methods require complex system construction, are challenging to process measurement data, and are limited to measuring rotations within a narrow range of angles. Furthermore, practical applications impose strict requirements on installation space and working environment, resulting in significant costs and significant research limitations. Summary of the Invention

[0004] The purpose of the present invention is to address the deficiencies of the existing technology and propose a ball joint that can measure two-dimensional spatial angles. It is based on the principle that changes in the output capacitance result from changes in the facing area between the spherical capacitor plates, and aims to achieve large-scale spatial angle detection of the ball joint. On the basis of an ordinary ball joint, the spherical capacitor plates are arranged in a football-like distribution, so as to structurally realize the measurement of the two-dimensional spatial angles of the ball joint.

[0005] A device for measuring the rotation angle of a soccer-style ball-joint joint includes a drive electrode and a sensing electrode system. During measurement, both the drive electrode and the sensing electrode system are installed in the ball-joint being measured. The ball-joint comprises a ball socket base and a ball head mounted within the socket base. The drive electrode is fixed to the ball head, while the sensing electrode system is fixed within the socket base.

[0006] The sensing electrode system includes multiple regular hexagonal spherical electrode plates and one or more regular pentagonal spherical electrode plates. Each regular pentagonal spherical electrode plate is surrounded by five regular hexagonal spherical electrode plates, forming a spherical shell structure. Each regular hexagonal spherical electrode plate is not electrically connected to its adjacent regular pentagonal or hexagonal spherical electrode plates. There is no electrical continuity between the drive electrodes and the sensing electrode system.

[0007] During operation, a capacitive structure is formed between the drive electrode and the regular pentagonal and / or hexagonal spherical electrode plates it faces. As the drive electrode rotates with the ball head, the capacitance between the drive electrode and the regular pentagonal and / or hexagonal spherical electrode plates facing it changes. This allows the position of the drive electrode within the ball socket to be measured based on the capacitance values ​​of the different electrode plates in the sensing electrode system, thereby enabling the ball head's rotation angle to be measured.

[0008] Preferably, the driving electrode, all regular hexagonal spherical electrode plates, and regular pentagonal spherical electrode plates are respectively led to a capacitance detection device through wires; the capacitance detection device can detect the capacitance value between any regular hexagonal spherical electrode plate or regular pentagonal spherical electrode plate and the driving electrode.

[0009] Preferably, each regular hexagonal spherical electrode plate is spaced apart from its adjacent regular pentagonal spherical electrode plate or regular hexagonal spherical electrode plate.

[0010] Preferably, the driving electrode is in the shape of a spherical crown.

[0011] Preferably, a gap d is provided between the driving electrode and the sensing electrode system; d≤200 μm.

[0012] Preferably, a connecting rod extending beyond the ball socket base is fixed to the ball head, and the driving electrode is located at a position of the ball head that is farthest from the connecting rod.

[0013] Preferably, the edge diameter of the driving electrode is equal to the inscribed circle diameter of the regular hexagonal spherical electrode plate.

[0014] Preferably, each regular hexagonal spherical electrode plate is separated from its adjacent regular pentagonal spherical electrode plate or regular hexagonal spherical electrode plate by an equipotential ring.

[0015] Preferably, the side lengths of the regular pentagonal spherical electrode plate and the regular hexagonal spherical electrode plate are equal.

[0016] In a second aspect, the present invention provides a method for measuring the rotation angle of a ball-joint joint with a soccer-style structure, employing the aforementioned ball-joint rotation angle measurement device. Each regular pentagonal spherical electrode plate and its five surrounding regular hexagonal spherical electrode plates constitute a detection unit. Two adjacent detection units share two regular hexagonal spherical electrode plates.

[0017] The method for measuring the rotation angle of a ball joint comprises the following steps:

[0018] Step 1: Establish an absolute coordinate system with the center of the sensing electrode system as the origin. For each detection unit, establish a sub-coordinate system. The origin of the sub-coordinate system coincides with the origin of the absolute coordinate system. The z-axis of the sub-coordinate system is the direction from the center of the sensing electrode system to the center of the corresponding regular pentagonal spherical electrode plate.

[0019] Step 2: Determine the target detection unit for measurement.

[0020] Calculate the output capacitance of all detection units. The output capacitance of a detection unit is the sum of the capacitances between the corresponding regular pentagonal spherical electrode plate and each regular hexagonal spherical electrode plate and the drive electrode. Select the detection unit with the largest output capacitance as the target detection unit.

[0021] Step 3: Obtain the deflection angle (γ, β) of the driving electrode relative to the sub-coordinate system corresponding to the target detection unit.

[0022] 3-1. Based on the capacitance values ​​between the regular pentagonal spherical electrode plate and each regular hexagonal spherical electrode plate and the driving electrode in the target detection unit, calculate the overlapping areas S0 to S5 between the driving electrode and one regular pentagonal spherical electrode plate and five regular hexagonal spherical electrode plates.

[0023] 3-2. Determine the coordinates of the center position of the driving electrode in the sub-coordinate system corresponding to the target detection unit based on the overlapping areas S0 to S5.

[0024] 3-3. Based on the coordinates of the driving electrode center position in the sub-coordinate system corresponding to the target detection unit, calculate the deflection angle (γ, β) between the driving electrode center position and the sub-coordinate system's z-axis. γ is the deflection angle of the driving electrode center position around the sub-coordinate system's x-axis; β is the deflection angle of the driving electrode around the sub-coordinate system's y-axis.

[0025] Step 4: Get the measured value of the ball joint rotation angle (γ sum ,β sum );γ sum =γ+γ0,β sum=β+β0; where γ0 is the deflection angle of the sub-coordinate system corresponding to the target detection unit relative to the absolute coordinate system, around the x-axis of the absolute coordinate system; β0 is the deflection angle of the sub-coordinate system corresponding to the target detection unit relative to the absolute coordinate system, around the y-axis of the absolute coordinate system.

[0026] The present invention has the beneficial effects:

[0027] 1. The present invention adopts the principle of capacitance sensor, which has simple structure, high detection accuracy, fast dynamic response, simple operation, effectively improves measurement efficiency, convenient measurement operation, and reduces measurement cost while ensuring measurement accuracy.

[0028] 2. The sensing electrode system of the present invention adopts a football-like layout, which can obtain a wide range of rotation angle measurements in the ball joint space and effectively avoid cumulative errors.

[0029] 3. When analyzing rotation angles, the present invention can utilize spatial division to convert between the sub-coordinate system and the absolute coordinate system, effectively simplifying the analysis. Furthermore, the present invention has a compact structure and requires little installation space for the measurement device. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of a ball joint of the present invention.

[0031] Figure 2 It is a schematic diagram of the interaction between the driving electrode and the sensing electrode system of the present invention.

[0032] Figure 3 It is a schematic diagram of the combination of the sensing electrode system of the present invention.

[0033] Figure 4 Schematic diagram of the spatial rotation angle of the driving electrode of the present invention.

[0034] Figure 5 It is a schematic diagram of the coordinate system conversion for solving the angle in the present invention.

[0035] Figure 6 It is a schematic diagram of the sub-coordinate system corresponding to two adjacent detection units in the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described below with reference to the accompanying drawings.

[0037] like Figure 1 As shown, a ball joint rotation angle measuring device with a football-like structure is installed in the ball joint and is used to measure the rotation angular displacement of the two degrees of freedom of the ball joint; the ball joint includes a ball socket base 2 and a ball head 1 installed in the ball socket base 2 to form a spherical pair.

[0038] like Figure 2As shown, the ball-joint rotation angle measuring device of the football-like structure includes a driving electrode 3 fixed on the ball head 1, and a sensing electrode system 4 fixed in the ball socket base 2. The driving electrode 3 is located at the position of the ball head 1 farthest from the connecting rod. The driving electrode 3 is in the shape of a partial spherical crown and is installed concentrically, and there is a gap d, that is, it is necessary to ensure that the curvature radius of the outer surface of the driving electrode 3 is smaller than the curvature radius of the inner surface of the sensing electrode system 4; d≤200μm. The gap d between the driving electrode 3 and the sensing electrode system 4 is used to ensure that there is no conduction between the driving electrode 3 and the sensing electrode system 4. It is maintained by flotation, filling with insulating lubricating fluid, and arranging a solid dielectric layer on the adjacent sides of the driving electrode 3 and the sensing electrode system 4 (the solid dielectric layer can be fixed on either the driving electrode 3 or the sensing electrode system 4), or other methods in the prior art.

[0039] The sensing electrode system 4 includes a plurality of regular hexagonal spherical electrode plates 5 and a plurality of regular pentagonal spherical electrode plates 6. The regular hexagonal spherical electrode plates 5 and the regular pentagonal spherical electrode plates 6 are arranged in a soccer ball-like structure, forming a partial spherical shell with a gap that fits the inner surface of the socket base 2. The side lengths of the regular pentagonal spherical electrode plates 6 and the regular hexagonal spherical electrode plates 5 are equal. Any regular pentagonal spherical electrode plate 6 is surrounded by five regular hexagonal spherical electrode plates 5. The sides of the pentagonal spherical electrode plates and the hexagonal spherical electrode plates facing the center of the socket base 2 are all on the same spherical surface.

[0040] Each regular hexagonal spherical electrode plate 5 is spaced apart from its adjacent regular pentagonal spherical electrode plate 6 or regular hexagonal spherical electrode plate 5 to ensure that all regular hexagonal spherical electrode plates 5 and regular pentagonal spherical electrode plates 6 are not conductive to each other.

[0041] like Figure 3 As shown, the edge diameter of the driving electrode 3 is equal to the inscribed circle diameter of the regular hexagonal spherical electrode plate 5 .

[0042] This embodiment provides a preferred non-essential technical solution, in which all edges of the regular hexagonal spherical electrode plates 5 and the regular pentagonal spherical electrode plates 6 are sleeved with equipotential rings to reduce the influence of edge effects on the detection results.

[0043] This embodiment provides a preferred non-essential technical solution, wherein the electrode plates are made of a material with good conductivity, such as copper or silver. The housing is made of a material that is easy to process and not very conductive, such as PVC plastic or structural steel coated with insulating paint.

[0044] Each regular pentagonal spherical electrode plate 6 and its surrounding five regular hexagonal spherical electrode plates 5 constitute a detection unit. Two adjacent detection units share two regular hexagonal spherical electrode plates 5. In this structure, the drive electrode 3 must be within the range of one of the detection units.

[0045] When the sensing electrode system 4 and the driving electrode 3 rotate in space within the ball joint, the position of the driving electrode 3 in the sensing electrode system 4 will change, and the facing area of ​​the regular hexagonal spherical electrode plate 5 and the regular pentagonal spherical electrode plate 6 in the driving electrode 3 and the sensing electrode system 4 will change.

[0046] The capacitance C is calculated as follows:

[0047]

[0048] Among them, ε is the dielectric constant, which is only related to the properties of the material between the plates; S is the area between the plates, and d is the distance between the plates.

[0049] The principle of a capacitive sensor states that when the area between the plates changes, the output capacitance value also changes. Based on this principle, the spatial rotation angle of the ball joint can be calculated from the change in output capacitance. The solution process is described below.

[0050] A fixed spatial coordinate system OXYZ is established with the center of the socket as the coordinate origin and the direction of gravity as the Z axis. Each detection unit establishes a spatial rectangular coordinate system oxyz with the center of the socket as the coordinate origin. The direction from the coordinate origin to the center of the corresponding regular pentagonal spherical electrode plate 6 is the z axis of this spatial rectangular coordinate system. When the driving electrode 3 moves in space, it may contact the regular pentagonal spherical electrode plates 6 of both systems at the same time. At this time, the overlapping area between the driving electrode 3 and the regular pentagonal spherical electrode plates 6 of the two systems is used as the criterion for selecting the measurement system, that is, the measurement is performed with the measurement system centered on the pentagonal spherical electrode plate with the largest capacitance output value.

[0051] The overlapping areas of the driving electrode 3 and the regular pentagonal spherical electrode plate 6 and the five regular hexagonal spherical electrode plates 5 in the sensing electrode system 4 are S0, S1, S2, S3, S4, and S5, respectively. The six capacitance values ​​output by the regular pentagonal spherical electrode plate 6 and the five regular hexagonal spherical electrode plates 5 in the sensing electrode system 4 are C0, C1, C2, C3, C4, and C5, respectively. According to the capacitance calculation formula, the capacitance of each corresponding surface can be expressed as follows:

[0052]

[0053] So the overlapping area S can be obtained by the capacitance value. i for:

[0054]

[0055] like Figure 5As shown, a mathematical model for the overlapping area between the drive electrode 3 and the sensing electrode system 4 is established. The drive electrode 3 in the figure is the cap portion of a sphere intercepted by a plane. The regular pentagonal spherical electrode plate 6 in the sensing electrode system 4 is obtained by intercepting a regular pentagonal cylinder and a sphere, and the regular hexagonal spherical electrode plate 5 is obtained by intercepting a regular hexagonal cylinder and a sphere. Therefore, all three surfaces can be expressed using mathematical expressions, but due to the complexity of the formula, they are not shown here. Because the gap d between the drive electrode 3 and the sensing electrode system 4 is very small, the curvature radius of the outer surface of the drive electrode 3 and the curvature radius of the inner surface of the sensing electrode system 4 are assumed to be the same when calculating the area, and both are set to r.

[0056] Assume that each corner point of the regular pentagonal spherical electrode plate 6 is A, B, C, D, and E respectively; the intersection points of the edges of the regular pentagonal spherical electrode plate 6 and the regular hexagonal spherical electrode plate 5 in the driving electrode 3 and the sensing electrode system 4 are denoted as F, G, H, and I respectively; in this case, there is an overlapping area between the four pairs of electrodes, and the area size can be expressed as:

[0057]

[0058] The above equations are nonlinear and constitute a set of hyperstatic equations. In the Matlab software optimization toolbox, the fsolve function is based on the least squares method and can be used to solve nonlinear equations. After giving appropriate initial values, a good iteration effect can be obtained and the convergence condition can be met. Through the area expression, the coordinates of points F, G, H, and I are solved as F(x f ,y f ,z f )、G(x g ,y g ,z g )、H(x h ,y h ,z h )、I(x i ,y i ,z i ). After determining the coordinates of the four points, substitute them into the spherical circle equation:

[0059] (xa) 2 +(yb) 2 +(zc) 2 =r 2

[0060] Where r is the radius of the sphere. After determining the edge analytical expression of the driving electrode 3, the center position of the driving electrode 3 can be determined as N'(a, b, c). The normal vector of the plane where the circular trajectory after rotation is located is The vector of the initial plane is The process of driving the electrode 3 from the initial position to the final position through spatial rotation can be expressed by the rotation matrix as follows:

[0061]

[0062] In the above formula, γ is the rotation angle of the ball joint around the x-axis, and β is the rotation angle of the ball joint around the y-axis.

[0063] Simplify the above formula to:

[0064]

[0065] The above formula can be used to solve the values ​​of γ and β.

[0066]

[0067] like Figure 6 As shown, the soccer-shaped layout of the sensing electrode system 4 can be divided into a plurality of repeated detection units (the regular pentagonal spherical electrode plate and the five regular hexagonal spherical electrode plates surrounding it are regarded as one detection unit).

[0068] The structures of the different detection units are exactly the same, differing only in the presence of a certain angle in their spatial positions. Therefore, when the driving electrode rotates with the ball joint space, the driving electrode 3 moves from the sub-coordinate system oxyz corresponding to the first detection unit a to the sub-coordinate system o'x'y'z' of the second detection unit b. The angles of rotation in the different sub-coordinate systems can be calculated according to the above-mentioned solution process. Adding the fixed spatial angle between the two coordinate systems, the actual spatial angle of the ball joint based on the fixed spatial coordinate system OXYZ can be obtained.

[0069] When the driving electrode intersects with multiple detection units at the same time, each detection unit will output a capacitance value at the same time. At this time, the capacitance value output by each detection unit (the sum of the output capacitance of each electrode plate in the detection unit) is used to determine which detection unit is used to determine the position of the driving electrode, and the detection unit with the largest output capacitance value is used as the reference for measurement.

[0070] This football-like layout method can wrap the entire sphere with a system of five regular hexagonal spherical electrode plates around a regular pentagonal spherical electrode plate as the center. Therefore, in theory, it can realize the measurement of 360° spatial rotation angle of the ball joint and effectively avoid cumulative errors.

[0071] Based on the above description, the rotation angle (γ) of the driving electrode relative to the x-axis and y-axis of the fixed spatial coordinate system OXYZ can be obtained. sum ,β sum );γ sum =γ+γ0,β sum=β+β0; where γ0 is the deflection angle of the sub-coordinate system corresponding to the target detection unit relative to the absolute coordinate system, around the x-axis of the absolute coordinate system; β0 is the deflection angle of the sub-coordinate system corresponding to the target detection unit relative to the absolute coordinate system, around the y-axis of the absolute coordinate system.

Claims

1. A method for measuring the rotation angle of a ball joint of a football-shaped structure; characterized by: The ball joint rotation angle measuring device used comprises a driving electrode (3) and a sensing electrode system (4); during the measurement process, the driving electrode (3) and the sensing electrode system (4) are both installed in the ball joint to be measured; the ball joint comprises a ball socket base (2) and a ball head (1) installed in the ball socket base (2); the driving electrode (3) is fixed on the ball head (1); and the sensing electrode system (4) is fixed in the ball socket base (2); The sensing electrode system (4) includes a plurality of regular hexagonal spherical electrode plates (5) and one or more regular pentagonal spherical electrode plates (6); any regular pentagonal spherical electrode plate (6) is surrounded by five regular hexagonal spherical electrode plates (5), so that each regular hexagonal spherical electrode plate (5) and each regular pentagonal spherical electrode plate (6) together form a spherical shell structure; each regular hexagonal spherical electrode plate (5) is not conductive with its adjacent regular pentagonal spherical electrode plate (6) or regular hexagonal spherical electrode plate (5); the driving electrode (3) and the sensing electrode system (4) are not conductive; each regular pentagonal spherical electrode plate and the five regular hexagonal spherical electrode plates surrounding it constitute a detection unit; The ball joint rotation angle measurement method comprises the following steps: Step 1: Establish an absolute coordinate system with the center position of the sensing electrode system (4) as the coordinate origin; establish a sub-coordinate system for each detection unit; the coordinate origin of the sub-coordinate system coincides with the coordinate origin of the absolute coordinate system; the z-axis direction of the sub-coordinate system is the direction from the center position of the sensing electrode system (4) to the center position of the corresponding regular pentagonal spherical electrode plate (6); Step 2: Determine the target detection unit for measurement; Calculate the output capacitance values ​​of all detection units respectively; the output capacitance value of a detection unit is the sum of the capacitance values ​​between the regular pentagonal spherical electrode plate (6) corresponding to the detection unit and each regular hexagonal spherical electrode plate (5) and the driving electrode (3); take the detection unit with the largest output capacitance value as the target detection unit; Step 3: Obtain the deflection angle (γ, β) of the driving electrode (3) relative to the sub-coordinate system corresponding to the target detection unit; 3-1. Based on the capacitance values ​​between the regular pentagonal spherical electrode plate (6) and each regular hexagonal spherical electrode plate (5) and the driving electrode (3) in the target detection unit, the overlapping areas S0 to S5 of the driving electrode (3) and one regular pentagonal spherical electrode plate (6) and five regular hexagonal spherical electrode plates (5) are calculated; 3-2. Determine the coordinates of the center position of the driving electrode (3) in the sub-coordinate system corresponding to the target detection unit based on the overlapping areas S0 to S5; 3-3. Based on the coordinates of the center position of the driving electrode (3) in the sub-coordinate system corresponding to the target detection unit, calculate the deflection angle (γ, β) between the center position of the driving electrode (3) and the z-axis of the sub-coordinate system; γ is the deflection angle of the center position of the driving electrode (3) around the x-axis of the sub-coordinate system; β is the deflection angle of the driving electrode (3) around the y-axis of the sub-coordinate system; Step 4: Get the measured value of the ball joint rotation angle ( , ); , ;in, is the deflection angle of the sub-coordinate system corresponding to the target detection unit relative to the absolute coordinate system around the x-axis of the absolute coordinate system; It is the deflection angle of the sub-coordinate system corresponding to the target detection unit relative to the absolute coordinate system around the y-axis of the absolute coordinate system.

2. The method for measuring the rotation angle of a ball joint of a football-shaped structure according to claim 1, characterized in that: The driving electrode, all regular hexagonal spherical electrode plates (5), and the regular pentagonal spherical electrode plates (6) are respectively led to a capacitance detection device through wires; the capacitance detection device can detect the capacitance value between any regular hexagonal spherical electrode plate (5) or regular pentagonal spherical electrode plate (6) and the driving electrode (3).

3. The method for measuring the rotation angle of a ball joint of a football-shaped structure according to claim 1, characterized in that: Each regular hexagonal spherical electrode plate (5) is spaced apart from its adjacent regular pentagonal spherical electrode plate (6) or regular hexagonal spherical electrode plate (5).

4. The method for measuring the rotation angle of a ball joint of a football-shaped structure according to claim 1, characterized in that: The driving electrode (3) is in the shape of a spherical crown.

5. The method for measuring the rotation angle of a ball joint of a football-shaped structure according to claim 1, characterized in that: A gap d is provided between the driving electrode (3) and the sensing electrode system (4); d≤200 μm.

6. The method for measuring the rotation angle of a ball joint of a soccer-type structure according to claim 1, characterized in that: A connecting rod extending beyond the ball socket base is fixed to the ball head (1); the driving electrode (3) is located at a position of the ball head (1) farthest from the connecting rod.

7. The method for measuring the rotation angle of a ball joint of a soccer-type structure according to claim 1, characterized in that: The edge diameter of the driving electrode (3) is equal to the inscribed circle diameter of the regular hexagonal spherical electrode plate (5).

8. The method for measuring the rotation angle of a ball joint of a soccer-type structure according to claim 1, characterized in that: Each regular hexagonal spherical electrode plate (5) is separated from its adjacent regular pentagonal spherical electrode plate (6) or regular hexagonal spherical electrode plate (5) by an equipotential ring.

9. The method for measuring the rotation angle of a ball joint of a soccer-type structure according to claim 1, characterized in that: The side lengths of the regular pentagonal spherical electrode plate (6) and the regular hexagonal spherical electrode plate (5) are equal.

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