A three-dimensional measuring device for the centroid position of an object

Abstract

The present invention discloses a three-dimensional measurement device and method for the centroid position of an object, which relates to the field of high-precision mass metrology technology. It includes a triangular weighing bridge mechanism, a cushion block, two weighing pans, and two load cells. The triangular weighing bridge mechanism is formed by positioning and mating a T-shaped pillar with a quadrangular pyramid bottom with a trapezoidal platform through a pin shaft, and a right-opening pillar with a quadrangular pyramid bottom and a left-opening pillar with a quadrangular pyramid bottom are respectively positioned and mated with an isosceles V-groove trapezoidal platform through two pin shafts; the object to be measured is placed on the upper surface of the trapezoidal platform near the center position of the T-shaped pillar with a quadrangular pyramid bottom, and the T-shaped pillar with a quadrangular pyramid bottom of the triangular weighing bridge mechanism is placed on the cushion block. By measuring the difference in the load cells when the triangular weighing bridge mechanism is horizontal on the cushion block and the values of the load cells when the triangular weighing bridge mechanism is tilted, the three-dimensional centroid position coordinates of the object to be measured are calculated. The present invention solves the problems of low measurement accuracy and measurement position error in the traditional multi-point weighing centroid measurement method.

Description

Technical Field

[0001] The present invention can be applied in the technical field of high-precision mass metrology. Specifically, it is a three-dimensional measurement device for the centroid position of an object. Background Art

[0002] In the field of mass metrology, the mass characteristic parameters of an object, including mass, centroid, moment of inertia, etc., are all physical parameters describing its dynamic performance. Among them, centroid measurement is a method for calculating the position of the center of mass distribution of an object or a system. It is extremely widely used in fields such as aerospace, military industry, transportation, and precision instruments. However, it is difficult to quickly and accurately measure the centroid position of an object. Therefore, it is necessary to establish a centroid standard metrology device and method for value traceability.

[0003] Currently, centroid measurement mainly adopts the multi-point support weighing method. Among them, although the bilateral centroid measurement method based on a weighing bridge only requires one sensor, there is a gap between the object to be measured and the weighing bridge and only the centroid height in one direction can be obtained. While the three-point support centroid measurement method can obtain the three-dimensional centroid position of the object, it requires at least three weighing sensors.

[0004] The multi-point support weighing method mainly calculates the centroid position of the object by establishing a static moment balance equation. Its measurement accuracy is mainly determined by the coordinate position accuracy and the weighing sensor accuracy. For large-mass heterogeneous objects, large-range weighing sensors will be selected to meet the measurement requirements. However, the accuracy of large-range weighing sensors is generally not high and there are also measurement errors in the positions of the object and each support point. Therefore, the overall centroid measurement accuracy of the object is low and cannot meet the measurement accuracy requirements of the high-precision mass metrology technology field. To solve the above problems of measurement accuracy and measurement position error, the present invention provides a three-dimensional measurement device and method for the centroid position of an object based on the multi-point support weighing method. Summary of the Invention

[0005] To solve the above problems of measurement accuracy and measurement position error, the present invention provides a three-dimensional measurement device and method for the centroid position of an object based on the multi-point support weighing method.

[0006] The present invention includes a triangular weighing bridge mechanism, a cushion block, and two load cells. The cushion block and the two load cells are located on the same horizontal plane. The triangular weighing bridge mechanism includes a quadrangular pyramid bottom T-shaped pillar, a quadrangular pyramid bottom right-opening pillar, a quadrangular pyramid bottom left-opening pillar, and a trapezoidal platform. The quadrangular pyramid bottom T-shaped pillar of the triangular weighing bridge mechanism is arranged on the cushion block. The quadrangular pyramid bottom right-opening pillar and the quadrangular pyramid bottom left-opening pillar are respectively placed on the two load cells. The trapezoidal platform is positioned on the same vertical line as the tip cone of the quadrangular pyramid bottom T-shaped pillar. The bottom edge of the trapezoidal platform is parallel to and in the same plane as the connecting line of the tip cones of the quadrangular pyramid bottom right-opening pillar and the quadrangular pyramid bottom left-opening pillar. The object to be measured is placed on the upper surface of the isosceles V-shaped groove trapezoidal platform near the center position of the quadrangular pyramid bottom T-shaped pillar and closely attached to the main pillar, so as to measure the weighing difference of the cushion block through the triangular weighing bridge mechanism and the values of the load cells when the triangular weighing bridge mechanism is tilted, and calculate the three-dimensional centroid position coordinates of the object to be measured.

[0007] Further, the load cell mechanism includes a load cell and an embedded weighing pan.

[0008] Further, the trapezoidal platform is an isosceles V-shaped groove trapezoidal platform. The isosceles V-shaped groove trapezoidal platform is matched with the quadrangular pyramid bottom T-shaped pillar through a pin shaft. The quadrangular pyramid bottom right-opening pillar and the quadrangular pyramid bottom left-opening pillar are respectively positioned and matched with the long bottom edge of the isosceles V-shaped groove trapezoidal platform through pin shafts.

[0009] A method for three-dimensional measurement of the centroid of an object includes the following steps:

[0010] Step 1: Obtain the air buoyancy density ρ of the experimental environment, the mass m of the object to be measured a , and the volume V; c

[0011] Step 2: Calibrate the triangular weighing bridge mechanism. Taking the bottom cone of the quadrangular pyramid bottom T-shaped pillar as the origin, taking the vertical direction from the origin to the connecting line of the bottom tip cones of the quadrangular pyramid bottom right-opening pillar and the quadrangular pyramid bottom left-opening pillar as the X-axis, and taking the line segment direction of the connecting line of the bottom tip cones of the quadrangular pyramid bottom right-opening pillar and the quadrangular pyramid bottom left-opening pillar as the Y-axis, establish a three-coordinate measurement system;

[0012] Step 3: Place the triangular weighing bridge mechanism at the center positions of the cushion block and the weighing pans of the 2 load cell mechanisms, and adjust the positions of the load cell mechanisms to make them at the same height as the cushion block;

[0013] Step 4: Place the object on the triangular weighing bridge mechanism and close to the center position of the quadrangular pyramid bottom T-shaped pillar, and read the readings m 2 、m 3 of the two load cell mechanisms. According to the principle of static moment balance and combined with the measurement data, the centroid coordinates (xc , y c ) can be obtained by the following formula:

[0014]

[0015] In the formula, m c is the mass of the object to be measured, V is the volume of the object to be measured, m 2 , m 3 are the readings of the two load cell mechanisms respectively, l is the vertical distance from the coordinate origin to the load cell mechanism in the X direction, l 2 is the vertical distance from the coordinate origin to one of the load cell mechanisms in the Y direction, ρ a is the air buoyancy density;

[0016] Step Five: When calculating the centroid of the object in the Z direction, remove the cushion block to make the triangular weighing bridge mechanism tilt at an angle of θ. According to the static moment balance equation, the centroid coordinate z c of the object to be measured relative to the origin in the Z direction can be obtained by the following formula:

[0017]

[0018] In the formula, m' 2 , m' 3 are the readings of the two load cell mechanisms when the weighing bridge is tilted respectively;

[0019] Step Six: According to the measurement data and coordinate transformation, the three-dimensional centroid coordinates of the object to be measured relative to itself can be obtained by the following formula:

[0020]

[0021] In the formula, (x c , y c , z c ) is the three-dimensional centroid position of the object relative to the coordinate origin, a is the distance from the contact surface between the T-shaped support at the bottom of the quadrangular pyramid and the object to the origin in the X direction, r is the vertical distance from the origin to the bottom of the object to be measured in the Y direction, and c is the distance from the origin to the upper surface of the isosceles V-shaped groove trapezoidal platform (7) in the Z direction.

[0022] Furthermore, use a coordinate measuring machine to obtain the distance a from the contact surface between the T-shaped support at the bottom of the quadrangular pyramid and the object to the origin in the X direction, the vertical distance l from the origin to the X direction on the connecting line of the bottom tips of the right-opening support and the left-opening support at the bottom of the quadrangular pyramid, and the vertical distance l 2 from the origin to the bottom tip of the left-opening support at the bottom of the quadrangular pyramid in the Y direction, and the vertical distance c from the origin to the upper surface of the isosceles V-shaped groove trapezoidal platform in the Z direction; the vertical distance r from the origin to the bottom of the object to be measured in the Y direction.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) By transforming a general weighing bridge and based on the principle of three-point support inclination measurement, during measurement, the object only needs to be fixed at one position, and the three-dimensional coordinates of the centroid of the object can be obtained by reading the readings of the load cell mechanism when the weighing bridge is horizontal and inclined; compared with the traditional bilateral measurement method of the weighing bridge, the measurement error caused by moving the object is eliminated, the measurement steps are simplified, and the measurement efficiency is improved.

[0025] (2) By introducing 2 load cells, the three-dimensional coordinates of the centroid position of the object can be obtained, which reduces the accuracy error caused by introducing a large-range load cell compared with the traditional multi-point support weighing method, and saves the tooling cost.

[0026] (3) The present invention takes into account the measurement error caused by air buoyancy during the measurement process, further improves the measurement accuracy of the centroid of the object, has a low cost, is safe and convenient to use, can not only measure objects with regular shapes, but also measure the three-dimensional centroid position of large-mass heterogeneous objects. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of the overall structure of the present invention;

[0028] Figure 2 is a front view of the present invention and a schematic diagram for measuring the centroid coordinates in the Y direction and Z direction in the horizontal plane of the measuring device;

[0029] Figure 3 is a top view of the present invention;

[0030] Figure 4 is a side view of the present invention and a schematic diagram for measuring the centroid coordinates in the X direction and Z direction in the horizontal plane of the measuring device;

[0031] Figure 5 is a side view of the present invention in an inclined state and a schematic diagram for measuring the centroid coordinates in the X direction and Z direction of the measuring device. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] In order to more clearly express the technical solution of the present invention, the present invention will be further described below with reference to the accompanying drawings.

[0033] The three-dimensional centroid measurement device for an object in this embodiment is composed of a cushion block, 2 load cell mechanisms, and a triangular weighing bridge mechanism; the load cell mechanism is composed of a weighing pan and a load cell; the triangular weighing bridge mechanism is composed of a quadrangular pyramid bottom T-shaped support column, an isosceles V-shaped groove trapezoidal platform, a quadrangular pyramid bottom right-opening support column, and a quadrangular pyramid bottom left-opening support column.

[0034] The quadrangular pyramid bottom T-shaped support of the triangular weighing bridge mechanism is placed on the cushion block, and the right-opening support with a quadrangular pyramid bottom and the left-opening support with a quadrangular pyramid bottom are respectively placed at the center of the weighing pans of the two load cell mechanisms.

[0035] Specifically, as Figure 2 , Figure 3 , Figure 4 shown, the cushion block and the load cell mechanism are at the same horizontal height. The triangular weighing bridge mechanism is placed on it, with a total length of 220 mm, a total length of the upper base of 60 mm, and a total length of the lower base of 320 mm. It is made of 304 stainless steel material; the load-bearing platform is an isosceles V-shaped groove trapezoidal platform, which can be used to place heterogeneous objects such as spheres to prevent the measured object from falling.

[0036] Specifically, as Figure 2 , Figure 3 , Figure 4 , Figure 5 shown, the isosceles V-shaped groove trapezoidal platform in the triangular weighing bridge mechanism is matched with the quadrangular pyramid bottom T-shaped support through 3 pin shafts, and the isosceles V-shaped groove trapezoidal platform and the pointed cone of the quadrangular pyramid bottom T-shaped support are positioned on the same vertical line; the right-opening support with a quadrangular pyramid bottom and the left-opening support with a quadrangular pyramid bottom are respectively matched with the two corners of the bottom edge of the isosceles V-shaped groove trapezoidal platform through 2 pin shafts, and the bottom edge of the isosceles V-shaped groove trapezoidal platform is parallel and in the same plane as the connecting line of the pointed cones of the right-opening support with a quadrangular pyramid bottom and the left-opening support with a quadrangular pyramid bottom.

[0037] Specifically, a measurement method using the above three-dimensional measurement device for the centroid position of an object includes the following steps:

[0038] Step 1: Calibrate the load cell; use a standard weight to calibrate the load cell;

[0039] Step 2: Obtain the air buoyancy density ρa of the experimental environment through the air buoyancy density measurement device;

[0040] Step 3: Calibrate the triangular weighing bridge mechanism;

[0041] Specifically, as Figure 2 , Figure 4As shown in the figure, taking the tip of the bottom knife of the quadrangular pyramid bottom T-shaped support as the origin, taking the vertical direction from the origin to the connection line of the bottom sharp cones of the right-opening support of the quadrangular pyramid bottom and the left-opening support of the quadrangular pyramid bottom as the X-axis, and taking the line segment direction of the connection line of the bottom sharp cones of the right-opening support of the quadrangular pyramid bottom and the left-opening support of the quadrangular pyramid bottom as the Y-axis to establish a three-coordinate measurement system. Use a three-coordinate measuring machine to obtain the distance a in the X direction from the contact surface between the quadrangular pyramid bottom T-shaped support and the object to the origin, the vertical distance l in the X direction from the origin to the connection line of the bottom sharp cones of the right-opening support of the quadrangular pyramid bottom and the left-opening support of the quadrangular pyramid bottom, the vertical distance l2 in the Y direction from the origin to the bottom sharp cone of the left-opening support of the quadrangular pyramid bottom, and the vertical distance c in the Z direction from the origin to the upper surface of the isosceles V-shaped groove trapezoidal platform;

[0042] Step 4: Obtain the mass mc, volume V of the object to be measured, and the vertical distance r from the origin to the bottom of the object to be measured in the Y direction;

[0043] Step 5: Place the triangular weighing bridge mechanism at the center positions of the cushion block and the weighing pans of the two load cell mechanisms. Adjust the positions of the load cell mechanisms to make them at the same height as the cushion block, and zero the instrument;

[0044] Step 6: Place the object on the triangular weighing bridge mechanism, close to the center position of the quadrangular pyramid bottom T-shaped support, read the readings m2 and m3 of the two load cell mechanisms. According to the principle of static moment balance and combined with the measurement data, the centroid coordinates (xc, yc) of the object on the OXY plane relative to the origin can be obtained by the following formula:

[0045]

[0046] In the formula, mc is the mass of the object to be measured, V is the volume of the object to be measured, m2 and m3 are the readings of the two load cell mechanisms respectively, l is the vertical distance from the coordinate origin to the load cell mechanism in the X direction, l2 is the vertical distance from the coordinate origin to one of the load cell mechanisms in the Y direction, and ρa is the air buoyancy density;

[0047] When calculating the centroid of the object in the Z direction, remove the cushion block to make the weighing bridge tilt at an angle θ. According to the static moment balance equation and based on the measurement data output by the two load cell mechanisms at this time, the centroid coordinate zc of the object to be measured in the Z direction relative to the origin can be obtained by the following formula:

[0048]

[0049] In the formula, m’2 and m’3 are the readings of the two load cell mechanisms when the weighing bridge is tilted;

[0050] Furthermore, based on the measurement data and coordinate transformation, the three-dimensional centroid coordinates of the object to be measured relative to itself can be obtained by the following formula:

[0051]

[0052] In the formula, (xc, yc, zc) is the three-dimensional centroid position of the object relative to the coordinate origin, a is the distance in the X direction from the contact surface between the bottom T-shaped support of the quadrangular pyramid and the object to the origin, r is the vertical distance in the Y direction from the origin to the bottom of the object to be measured, and c is the distance in the Z direction from the origin to the upper surface of the isosceles V-shaped groove trapezoidal platform.

[0053] In this embodiment, the object to be measured is set as a sphere, where the radius r = 35 mm, the mass mc = 1479.0879 g, the volume V = 187.03 cm3, the air buoyancy density ρa = 1.2173 kg / m3, and the weighing bridge dimensions are l = 200.031 mm; l2 = 149.967 mm; a = 9.998 mm; θ = 14.48°; c = 114.805 mm. The measured values are m2 = 164.78 g; m3 = 167.19 g.

[0054]

[0055] After tilting the weighing bridge, the measured values are m'2 = 15.65 g; m'3 = 29.94 g.

[0056]

[0057] Finally, the centroid coordinates of the sphere are obtained as:

[0058]

[0059] The above only elaborates in detail on the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention, and all such changes should be included within the protection scope of the present invention.

Claims

1. A method for three-dimensional measurement of the centroid of an object, characterized in that: The following steps are involved: Step 1: Obtain the air buoyancy density ρ of the experimental environment a , the mass of the object being measured is m c and volume V; Step 2: calibrate the triangular weighing bridge mechanism, take the bottom vertebra of the four-sided pyramid T-shaped support as the origin, take the vertical direction from the origin to the line connecting the right open support and the bottom sharp cone of the left open support of the four-sided pyramid as the X-axis, and take the line segment direction of the line connecting the right open support and the bottom sharp cone of the left open support of the four-sided pyramid as the Y-axis to establish a three-coordinate measurement system; Step 3: Place the triangular weighing bridge mechanism at the center of the pad and the two weighing sensor mechanism scales, the tetrahedral pyramid bottom T-shaped support of the triangular weighing bridge mechanism is set on the pad, the tetrahedral pyramid bottom right open support and the tetrahedral pyramid bottom left open support are respectively placed on the two weighing sensors, and adjust the position of the weighing sensor mechanism to be at the same height as the pad; Step 4: Place the object on the triangular weighing bridge mechanism and close to the center of the T-shaped support at the bottom of the quadrangular pyramid. Read the readings m2 and m3 of the two weighing sensor mechanisms. Based on the principle of static moment balance and the measured data, the centroid coordinates (x c ,y c ) can be obtained by the following formula: In the formula, m c is the mass of the object being measured, V is the volume of the object being measured, m2 and m3 are the readings of the two weighing sensor mechanisms, l is the vertical distance from the origin of the coordinate system to the weighing sensor mechanism in the X direction, l2 is the vertical distance from the origin of the coordinate system to one of the weighing sensor mechanisms in the Y direction, ρ a is the buoyancy density of air; Step 5: When calculating the center of mass of the object in the Z direction, take out the pad to tilt the triangular weighing bridge mechanism by an angle of θ. According to the static moment equilibrium equation, the center of mass coordinates z of the object in the Z direction relative to the origin are c It can be obtained by the following formula: In the formula, m'2 and m'3 are the readings of the two weighing sensor mechanisms when the weighing bridge is tilted; Step 6: Based on the measurement data and coordinate conversion, the three-dimensional coordinates of the center of mass of the object being measured relative to itself can be calculated by the following formula: In the formula, (x c ,y c , z c ) is the three-dimensional centroid position of the object relative to the coordinate origin, a is the distance from the contact surface of the tetrahedral T-shaped support (4) and the object to the origin in the X direction, r is the vertical distance from the origin to the bottom of the object in the Y direction, and c is the distance from the origin to the upper surface of the isosceles V-groove trapezoidal platform (7) in the Z direction.

2. The method for three-dimensional measurement of the centroid of an object according to claim 1, characterized in that: Use a three-dimensional coordinate measuring machine to obtain the distance a in the X direction from the contact surface between the T-shaped support at the bottom of the quadrangular pyramid and the object, the vertical distance l in the X direction from the origin to the connecting line of the right open support at the bottom of the quadrangular pyramid and the left open support at the bottom of the quadrangular pyramid, the vertical distance l2 in the Y direction from the origin to the tip of the bottom of the left open support at the bottom of the quadrangular pyramid, the vertical distance c from the origin to the upper surface of the isosceles V-groove trapezoidal platform in the Z direction, and the vertical distance r from the origin to the bottom of the object to be measured in the Y direction.

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