CN1162679C - A three-degree-of-freedom space motion mechanism - Google Patents

Abstract

The invention provides a three-degree-of-freedom space motion mechanism, which belongs to the field of geometric measurement. The mechanism includes a frame and three telescopic connecting rod branches provided with hinges. It is characterized in that: the mechanism is connected with the frame through three branches, The three hinge points on the frame should form a plane, and each of the three branches contains a single-degree-of-freedom moving pair, in which the first and second branches each contain two spherical joints, and the third branch contains a Hooke hinge; 1. The second branch has a ball joint fixed to the frame, and the other ball joint is connected with the telescopic rod core of the third branch. One end of the telescopic connecting rod shell of the third branch is connected to the frame with a Hooke hinge. The Hooke hinge on the branch connecting rod and the two spherical hinges on the core are in a straight line. The above-mentioned mechanism has good rigidity and high precision, and its position forward and reverse solutions have explicit single solutions, which can be used in three-coordinate measuring machines and assembly robots.

Description

A three-degree-of-freedom space motion mechanism

technical field

The invention relates to the technical field of connecting rod space motion mechanism and geometric measurement, and also relates to the technical field of industrial robot.

Background technique

So far, the Cartesian coordinate system is still the most widely used coordinate system, so the spatial mechanism characterized by three mutually orthogonal linear moving guide rails constituting the X, Y, and Z space coordinates is the most widely used. The forward solution and inverse solution of the position of this space mechanism are the simplest, and it is still the mainstream form of the motion mechanism of the three-dimensional coordinate measuring machine, printer, and engraving machine. The three-coordinate measuring machine has a history of more than 40 years using the orthogonal space mechanism, and has reached a very high level in design, manufacture, calibration, inspection, and error compensation. However, the orthogonal mechanism has the following disadvantages: ①The beam is easily tilted due to the bending force, resulting in errors; ②The system error is the accumulation and amplification of the error of each coordinate axis; ③The structural components are heavy and the measurement speed is limited; ④The cost is high, And these shortcomings are difficult to overcome. With the development of computer technology and the theory of space mechanisms driven by robots, some non-orthogonal space mechanisms can overcome the mathematical problems involved in online analysis and control of their motion positions, so they have been gradually applied. Non-orthogonal mechanisms have open chain and There are two main forms of closed chain, and the open chain linkage mechanism has a large measurement space and flexible movement, so it is used more in modern robots. Portable 6-DOF joint coordinate measuring machines that have appeared in recent years, such as the series products of FARO in the United States and ROMER in France, use an open-chain series mechanism, which has a large measurement space and is easy to operate and carry. It is widely used in automobile manufacturing. It has been widely used in the industry. Its measuring mechanism has 2 arm rods and 6 single-degree-of-freedom rotary joints, and an angle encoder is set in each movable joint. Due to the error of the sensor itself and after assembly, as well as the amplification effect of the rod length , these deviations are accumulated and magnified at the measuring head. Although effective measures are taken, its accuracy is still relatively low, the system rigidity is poor, and it is easy to be damaged. At present, the parallel mechanism in the closed-chain mechanism has been used in robots and machine tools. Its characteristics are: the movable platform is supported by 3 to 6 connecting rods that expand and contract along their respective axes at the same time. The advantages are: ① High rigidity of the system; ② The motion error is small; ③The error of each rod is not accumulated and enlarged, and the measurement accuracy is high; ④The mass of the moving parts is small. However, it is undeniable that the positive solution of most parallel mechanisms is relatively difficult, and the online calculation is too difficult, and its use is limited due to the complex coupling relationship and difficult control.

Contents of the invention

The purpose of the present invention is to provide a three-degree-of-freedom space motion mechanism, which has a simple structure and good rigidity; the forward and reverse solutions of the motion position have simple explicit single solutions: the error of the motion position is not accumulated and magnified, and the precision is high, so it is convenient The precise calculation and closed-loop control of its spatial position can be implemented, and a new type of three-coordinate measuring machine and assembly robot can be formed by using this mechanism. In order to achieve the purpose of the present invention, it can be achieved through the following technical solutions: the kinematic mechanism includes a frame and three telescopic connecting rod branches provided with hinges, and the hinges and the machine are connected by three fixed telescopic connecting rod shell ends. The frame is connected to form a closed-loop structure, in which the first and second branches each contain a single-degree-of-freedom moving pair and two spherical joints, and the third branch contains a single-degree-of-freedom moving pair and a Hooke hinge. The end is connected with the Hooke hinge, and the other end is the free end of the telescopic link; the first and second branches each have a ball joint fixed on the frame, and the other ball joint is connected to the rod of the telescopic link of the third branch. Core connection, the Hooke hinge on the third branch and the two spherical hinges on the rod core of the first and second branch telescopic connecting rods are in a straight line, but the three hinge points of the frame should form a plane. One end of the telescopic connecting rod rod core of the first and second branches can also be connected with the third branch by a common compound ball joint.

Compared with the orthogonal kinematic mechanism, the above-mentioned mechanism has no high-precision linear guide rail, nor a typical parallel mechanism motion platform, so the structure is simple. Compared with the orthogonal mechanism or the series mechanism, since the three motion branches of the mechanism of the present invention are closed at the ends, the system rigidity is good.

The positive solution and inverse solution of the position of the third branch rod core spherical hinge are briefly described as follows: According to the position coordinates of the hinge center of the frame and the length of the telescopic rod, it is possible to list the Three spherical equations, and according to the characteristics of the three hinge centers on a straight line on the third branch of the telescopic connecting rod and the distance between the centers of the two spherical hinges, the equations of the three coordinates of the two spherical hinge centers can be listed. The one-dimensional quadratic equation is obtained by entering and eliminating elements, and finally two explicit solutions for the position of the spherical hinge of the third branch rod core can be obtained. In the structural design, simple limit measures can be used to ensure that the three determined rod lengths of the mechanism corresponds to a certain location. The inverse problem of finding the length of the rod according to the spatial position is actually to find the distance between two points in space, which is simpler. Therefore, the positive solution and reverse solution of the position of this space mechanism are quite easy.

Since the gap between the spherical hinge and the Hooke hinge is easier to eliminate than the gap between the linear guide rail, the straightness of the telescopic link has little influence on the length of the telescopic link. Using the grating ruler attached to the telescopic link, it can accurately measure and calculate the three telescopic links online. The distance between the centers of the hinges at both ends of the rod is the length of the telescopic rod, so a high repeatability of the measurement position can be achieved at a low cost. In addition, the center points of the three rack hinges pass through this point and the position error of the vertical plane with the corresponding rod There is also minimal impact on the position of the third branch core ball joint. It can be seen that the shape and position errors of the parts of the mechanism are not accumulated and enlarged, so the movement accuracy is high.

In addition, the telescopic link can also be designed as an active telescopic rod with power to realize online precise measurement and closed-loop control of the three-degree-of-freedom space position, which can be used in occasions where the space position is precisely measured and controlled, such as three-coordinate measuring machines and assembly robots. The simplest case where the spatial motion mechanism is used for coordinate measurement is: fix the contact probe at the free end of the third branch telescopic link, and the link passively expands and contracts. According to the relative position between the center of the probe and the third branch telescopic link, The spatial coordinates of the measuring points can be determined and made into a manual coordinate measuring machine. Since the telescopic rod of the third branch is connected with the frame by a Hooke hinge, it cannot rotate around the axis of the rod, and it can fix the measuring head with 2 graduations, which improves the flexibility of coordinate measurement and improves the measurement efficiency. Of course, if the telescopic link is equipped with a power device, automatic measurement can be realized. Compared with the conventional three-coordinate measuring mechanism, its structure is simple, light and handy, low in cost, good in rigidity and high in precision, and it is easy to be popularized and used in the production site of the manufacturing industry.

The kinematic mechanism can also be used for assembling robots. At this time, the telescopic link is designed as a powered active telescopic link, and a jointed manipulator or other executive components such as suction cups are installed on the free end of the third branch telescopic link. Its advantages are simple structure, light weight, low cost, good rigidity, and high precision. In particular, the forward and inverse solutions of the motion position have unique analytical solutions, which are convenient for real-time position measurement and position closed-loop control.

If the telescopic rod of the third branch is arranged vertically, the connection point between the first and second branches and the third branch can also be on the telescopic rod shell, so that the core of the third branch does not bear the weight of the first and second branches. It is more convenient to move when measuring manually.

Description of drawings

Fig. 1 is the overall structure schematic diagram that the present invention is used for three-coordinate measurement;

Fig. 2 is the overall structure schematic diagram that the present invention is used for assembly robot;

Detailed ways

Embodiment 1: The three-degree-of-freedom space motion mechanism is used for three-coordinate measurement. As shown in Figure 1, the structure of the three-coordinate measuring machine consists of a frame 1, a ball joint 2, a ball joint 7, a ball joint 8 and a ball joint 9, Hooke ( Cross) hinge 4, telescopic connecting rod 5 of the first branch telescopic connecting rod 3, the telescopic connecting rod 6 of the second branch, the 3rd branch and measuring head 10 are formed. The telescopic connecting rod 3 is horizontal, the telescopic connecting rod 6 is vertical, and the telescopic connecting rod 5 is arranged vertically. The upper end of the telescopic connecting rod 5 is hinged on the frame 1 with a cross hinge 4. One end is fixed on the frame 1 through the ball joint 2 and the ball joint 7, and the other end is also connected with the rod core of the telescopic link 5 through the ball joint 8 and the ball joint 9 to form a closed structure, and the lower end of the telescopic link 5 is fixed in contact Probe, the center of the probe is on a straight line with the centers of the Hooke hinge 4, the spherical hinge 8 and the spherical hinge 9. But the ball hinge 2, ball hinge 7 and Hooke hinge 4 fixed on the frame 1 should form a plane, and the lengths of the telescopic link 3, the telescopic link 5 and the telescopic link 6 are measured by displacement sensors such as a grating ruler.

Through the lengths of the three rods and the center positions of the three frame hinge points, the spatial coordinates of the center point of the spherical joint 9 can be determined, further determined according to the proportional relationship, and the spatial position of the probe center is realized to realize three-coordinate measurement. The measuring mechanism can be used to make a simple manual coordinate measuring machine, and of course, if the telescopic rod can be actively retracted, the motorized and automatic measurement can be realized.

The advantages of this mechanism are: the gap of the hinge joint is easy to eliminate, the precise measurement of the rod length is relatively easy, and the straightness of the telescopic link 3 and the telescopic link 6 has little influence on the final measurement result, so it can achieve a high measurement position repeatability Accuracy, which is beneficial to the error calibration of the space coordinates of the hinge point and the length of the rod. It can be seen that the mechanism does not require too high machining accuracy, it only needs to eliminate the gap of the hinge, and achieve higher measurement accuracy through careful calibration. Compared with the three-coordinate measuring machine of the orthogonal mechanism, it is simple, light and easy to produce. Promoted on site.

Embodiment 2: Three-degree-of-freedom space motion mechanism is used for assembly robot

As shown in Figure 2, the robot structure consists of a frame 1, a ball joint 2, a ball joint 7, a ball joint 8 and a ball joint 9, a Hooke joint 4, a telescopic link 3, a telescopic link 5 and a telescopic link 6. The degree of freedom rotary joint 11, the rotary rod 12, the single degree of freedom rotary joint 13, the swing rod 14 and the claw 15 are composed. The frame 1 can be a stable structure on the production site, or other structures. Its structural features are: the telescopic link 3 is horizontal, the telescopic link 5 is vertical, and the telescopic link 6 is arranged longitudinally. The upper end of the telescopic link 5 is hinged on the frame with a Hooke hinge 4. The telescopic link 3, One end of the telescopic link 6 is fixed on the frame 1 through the ball joint 2 and the ball joint 9, and the other end is also connected with the rod core of the telescopic link 5 through the ball joint 8 and the ball joint 9 to form a closed structure, and the telescopic link 5 The free end of the free end is connected with the rotating rod 12 of telescoping connecting rod 5 coaxials by single-degree-of-freedom rotating joint 11, and the lower end of rotating rod 12 is connected swinging rod 14 by rotating joint 13, and the other end of swinging rod 14 fixes pawl 15. The axis of swing is vertically intersected with the axis of the rotating rod 12, the length of the telescopic rod 3, the telescopic rod 5 and the telescopic rod 6, the rotation angle of the rotating rod 12 relative to the telescopic rod 5 and the swing angle of the telescopic connecting rod 3 relative to the rotating rod 12 can be controlled and measure.

By measuring the length of the three rods as the accurate position feedback in three-dimensional space, the center point of the ball joint 9 can be located at the specified spatial position, and the large-scale precise positioning of the manipulator can be completed. The influence of the straightness error of rod 3 and rod 6 on the positioning accuracy Small, so the mechanism has most of the advantages of the parallel mechanism, but the position online calculation is very simple. The rotation angles of the joints 11 and 13 are further controlled to realize the posture control of the paw. Since the rotating rod 12 and the swinging rod 14 only need a small length, the error of the position and attitude control of the claw 15 is also small.

Claims (4)

1. spatial motion mechanism of three freedoms, comprise frame (1) and three extensible link that are provided with hinge, first branch's shrinking connecting-rod (3) is horizontal, second branch's shrinking connecting-rod (6) is vertical, the 3rd branch's shrinking connecting-rod (5) is vertical layout, the upper end of the 3rd branch's shrinking connecting-rod (5) is hinged on the frame (1) with Hooke's hinge (4), first, respectively there is a ball pivot (2 in two branches, 7) be fixed on the frame (1), another ball pivot is connected with the bar core of the shrinking connecting-rod of the 3rd branch, it is characterized in that: fixedly the hinge and the frame (1) of shrinking connecting-rod bar shell end are connected to form closed loop configuration to this motion by three, wherein first, a single-degree-of-freedom moving sets is respectively contained in second branch, two ball pivots, a single-degree-of-freedom moving sets is contained in the 3rd branch, a Hooke's hinge (4), pole core end was the free end of shrinking connecting-rod in the 3rd minute; The ball pivot (2), ball pivot (7) and the Hooke's hinge (4) that are fixed on the frame (1) should constitute a plane, and the ball pivot (8) on the bar core of the Hooke's hinge in the 3rd branch (4), first and second branch's shrinking connecting-rod and the center of ball pivot (9) are point-blank.

2. spatial motion mechanism of three freedoms according to claim 1 is characterized in that an end of the shrinking connecting-rod bar core of first and second branch also can be connected with the 3rd branch by a public compound spherical hinge.

3. spatial motion mechanism of three freedoms according to claim 1 is characterized in that the free end of the 3rd branch's shrinking connecting-rod can installation manipulator.

4. spatial motion mechanism of three freedoms according to claim 1 is characterized in that the free end of the 3rd branch's shrinking connecting-rod can install and measure head.

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