CN1095417C - Six-freedom parallel mechanism with triaxial nearly orthogonal - Google Patents

Abstract

A three-axis approximately orthogonal six-degree-of-freedom parallel mechanism, including: a static table body, a moving table body and six driving rods, the length of the six driving rods is variable, and each of the driving rods passes through its two ends The respective spherical joints or universal joints are respectively hinged with the static table body and the dynamic table body; the directions of the six driving rods are respectively located in three orthogonal or approximately orthogonal directions of x, y, and z, and each direction has its own There are two driving rods; the characteristic is that the six spherical joints that are hinged between the six driving rods and the moving table body can be respectively located at the centers of the six faces of the hexahedron. At this time, its x, y, and z axes are decoupled, so the adjustment is simple, the control is easy, and the application is extensive.

Description

Three-axis near-orthogonal six-degree-of-freedom parallel mechanism

The invention relates to a mechanical structure for adjusting the spatial position with a novel structure, more precisely, it relates to a three-axis approximately orthogonal six-degree-of-freedom parallel mechanism. The mechanism can be applied to fields such as metal processing machine tools, sensors of force and torque, and the like.

Parallel mechanism can be applied to adjust the relative position of two rigid objects. In general, the relative position of two rigid bodies can be represented by three movements along the x, y, and z axes and three rotations around the x, y, and z axes, with a total of six degrees of freedom. The parallel mechanism originated from the Stewart Platform mechanism (Stewart Platform), see Fig. 1, Fig. 2, the mechanism is usually composed of 3-6 telescopically adjustable rods 1', and ball hinges ( That is: the spherical surface) 2' or the universal joint (that is: each hinge or the ball pin or the rotating hinge) connects two rigid bodies 3', 4' to form. Usually, one of the two rigid bodies is stationary and is called a static platform or a static platform. Moving table body 4'. In the original Stewart platform mechanism, the dynamic and static rigid bodies are both planar, or all the hinges 2' connecting the rod 1' and the rigid body 3' or the rod 1' and the rigid body 4' are on the same plane . Later on, a space-using platform-type mechanism began to appear, that is, the hinges 2' are not all on the same plane, which is a general parallel mechanism. Parallel mechanisms have many applications in industry, such as manipulators, position adjustment mechanisms, force and moment sensors, dynamic platforms for playgrounds, etc. Recently people use it as a virtual axis machine tool or virtual axis machine tool for short. This kind of machine tool has many special advantages, such as simple structure, high rigidity, high control precision, fast transmission speed, etc., and has a high performance-price ratio, and is called the machine tool of the 21st century.

For applications such as virtual axis machine tools, force and torque sensors, and position adjustment mechanisms, it is a very important issue to use what kind of position adjustment mechanical structure to obtain a mechanism with the best overall performance. Now, it is generally believed that the smaller the condition number of the Jacobian determinant for the transformation from the independent variable of 6 driving variables to the function of the six variables of the position and attitude of the moving platform, the better, and the theoretical minimum condition number is 1. However, people are not clear about what kind of mechanism can satisfy its condition number to be 1, that is to say, how the hinges on the rigid body in the parallel mechanism should be distributed in space is the most reasonable. Even so far, no definite conclusions have been drawn.

The main purpose of the present invention is to provide a three-axis approximately orthogonal six-degree-of-freedom parallel mechanism; that is, to provide a table-type mechanism that satisfies the Jacobian determinant with the minimum condition number.

The main purpose of the present invention is achieved like this: a kind of three-axis approximately orthogonal parallel mechanism with six degrees of freedom includes: a static platform body, a dynamic platform body and six driving rods, the length of the six driving rods is variable, and Each of the driving rods is respectively hinged with the static table body and the dynamic table body through the respective spherical joints or universal joints at both ends; the directions of the six driving rods are respectively located in the three orthogonal directions of x, y, z or approximately Orthogonal directions, and each direction has two drive rods; it is characterized in that: the six ball joints that are hinged between the six drive rods and the moving table body can be respectively located at the centers of the six faces of the hexahedron.

The structure, features and effects of the present invention will be described in detail below in conjunction with the accompanying drawings.

Fig. 1 is a structural schematic diagram of a Stewart platform mechanism.

Fig. 2 is a structural schematic diagram of another Stewart platform mechanism.

Fig. 3 is a schematic diagram of an embodiment of the combination of the moving table body and the driving rod of the present invention.

FIG. 4 is a schematic diagram of adding a static platform in FIG. 3 .

Fig. 5 is a schematic diagram of another embodiment of the combination of the moving table body and the driving rod of the present invention.

FIG. 6 is a schematic diagram of adding a static platform in FIG. 5 .

Fig. 7 is a schematic diagram of another embodiment of the present invention. The mechanism is rotated through a certain angle so that its diagonal points to the vertical direction, and the drive rod is no longer parallel to the x, y, z axes.

Fig. 8 is a schematic diagram of another embodiment of the present invention.

Refer to the schematic diagrams of an embodiment of the present invention shown in FIG. 3 and FIG. 4 . The present invention is a three-axis approximately orthogonal six-degree-of-freedom parallel mechanism, which includes: a static table body 3, a moving table body 4 and six driving rods 1, the lengths of the six driving rods 1 are all telescopically variable, And wherein each driving rod 1 is respectively hinged with the static table body 3 and the moving table body 4 through the respective ball joints 2 at its two ends, and its characteristic is that the above-mentioned six driving rods 1 are respectively located at three positive positions of x, y, and z. There are two driving rods 1 in each direction.

As shown in FIG. 3 , the moving table body 4 located at the space center of the six driving rods 1 is a hexahedron, and each spherical joint 2 in the six driving rods 1 is respectively located on each surface of the moving table body 4 . The moving table body 4 is connected with six variable-length drive rods 1 through six ball joints 2, and the six drive rods 1 are connected with the static table body 3 through other six ball joints 2 at the other ends thereof. The elongated rigid body shown in FIG. 4 represents the static platform body 3 or the frame, and there are two driving rods in each of the three directions of x, y, and z. When the moving table body is at the center position as shown in Figure 3 or Figure 4, the driving rods in the above three directions of x, y, and z are orthogonal to each other, and the condition number is 1, that is, the minimum value of the Jacobian is reached . Near this minimum value, that is, when the driving rods in the three directions of x, y, and z are approximately orthogonal to each other, although the condition number is slightly greater than 1, its value is still small. Therefore, the use of this mechanism has some special advantages.

First, the mechanism of the present invention is decoupled from each other for the three movements in the directions of x, y, and z axes and the three rotations around the x, y, and z axes at its central position. As we all know, in general, the relative position of two rigid bodies can be represented by the movement along the three directions of x, y, and z and the rotation around the three axes of x, y, and z, with a total of six degrees of freedom. In a general parallel mechanism, when the drive in one direction changes, it will simultaneously cause the movement of the other two directions of the moving table body and the rotation of the moving table body. This phenomenon is called the coupling between motions. For example, when It is hoped that when the moving table body moves purely along the x direction, not only the driver along the x-axis direction is required, but also the drivers in the y and z directions are required to coordinate and cooperate at the same time; or only one or two drivers can not be purely along the x axis direction movement. In the central position of the platform-type mechanism of the present invention, since the three axes x, y, and z are perpendicular to each other, the three axes x, y, and z are decoupled. That is to say, when the moving table body moves along the x-axis, the four drivers in the other two directions y and z can be left unadjusted or seldom adjusted.

As a position adjustment mechanism, the parallel mechanism of the present invention is very convenient in actual use. When the two drives in the x-axis are adjusted at the same speed and in the same direction, the moving table body moves in translation along the x-axis. When the two drives move in opposite directions at the same speed, the moving table body rotates around the z-axis. Because of the movement of these two driving rods, the movement in other axes is very small or zero, so in order to obtain pure movement along the x-axis or rotation around the z-axis, the four driving rods or drive pairs in the other two directions The driving amount of can be very small or zero (that is, high-order infinitesimal). And, it's exactly the same when moving along the y-axis or z-axis, or turning around the x-axis or y-axis. Therefore, the moving table body of the present invention is approximately decoupled in three directions near the above-mentioned central position. Therefore, in some occasions where the requirements are not strict, the position and rotation angle of each direction can be adjusted separately, so the adjustment is very convenient. In addition, since the adjustments in the three directions are orthogonal or approximately orthogonal, the sensitivities to the adjustments in each direction are relatively balanced.

Secondly, change the six driving rods in the mechanism into length-fixed rods, and add a sensor on each driving rod, the present invention can be transformed into a sensor of force and torque. This sensor can naturally separate forces and moments in three directions. For example: when there is only force in the direction of the x-axis, only the two sensors along the x-axis have output, and the value is the sum of the two sensors. When there is only torque around the z-axis, only a pair of sensors along the x-axis has an output, which is the difference between the pair of sensors multiplied by the distance between the pair of driving rods. Because the displacement of the moving table body is very small, it has a very high precision.

The mechanism of the present invention also has some special advantages if it is used on a virtual axis numerical control machine tool. Because its condition number is approximately 1, it belongs to the most ideal state. Therefore, under the same circumstances, the machining accuracy is high, the machine tool has a large working space, and the attainable working speed is high, etc., which is a machine tool structure form with good application prospects.

Since the motion decoupling position of the mechanism of the present invention is at the center of the moving table body and surrounded by several spherical joints, it is not very convenient to use as a virtual axis machine tool or for other purposes. Therefore, some improvements can be made in the present invention, that is, the above-mentioned six driving rods are hinged in groups of two on the three surfaces of the above-mentioned movable table body that are perpendicular to x, y, and z, as shown in Fig. 5 and Fig. 6 . 5 is a schematic diagram of the structural layout of the moving table body 4 , the driving rod 1 and the ball joint 2 , and after adding the static table body 3 , it is shown in FIG. 6 . At this time, the moving table body 4 is located on one side of the six driving rods 1. With this structure, when the moving table body is at its center position, the condition number of the Jacobian is still 1. However, its adjustment law is different when doing pure rotation.

If the mechanism of the present invention is rotated at an angle, a diagonal line of the moving table body is turned into a vertical direction, and the static table body is slightly changed, as shown in Fig. 7 . It can be seen that it is very similar to the current virtual axis machine tool. It's just that the directions of the driving rods are mutually orthogonal or approximately orthogonal, and the distribution of the spherical joints is special. It is precisely because of these characteristics that the machine tool has the advantages of high machining accuracy, large working space and high working speed. If the z axis is selected as the vertical direction, then the three orthogonal directions are no longer x, y, and z axes, but only the directions of the three driving rods at the center position.

Other variants of the mechanism of the present invention are also possible. As shown in Figure 8, the lengths of the six legs 1 between each pair of ball joints 2 are fixed, and the six sliding pairs 5 and their driving rods for adjusting the length are installed on the frame 3, which can also achieve the adjustment The purpose of the platform body 4 position. At this time, there are still six degrees of freedom, and the advantage of the condition number being 1 at the center is still maintained. However, when calculating the positive and negative solutions, the calculation methods and calculation formulas are different.

Claims (1)

1. A three-axis approximately orthogonal six-degree-of-freedom parallel mechanism, including: a static table body, a moving table body and six driving rods, the length of the six driving rods is variable, and each of the driving rods passes through its The respective spherical joints or universal joints at both ends are respectively hinged with the static table body and the dynamic table body; the directions of the six driving rods are respectively located in the three orthogonal or approximately orthogonal directions of x, y, and z, and each There are two driving rods in each direction; the feature is that the six spherical joints that are hinged between the six driving rods and the moving table body can be respectively located at the centers of the six faces of the hexahedron.

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