JPH09131690A - 6-shaft load detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect 6-shaft load accurately in a wide scope. SOLUTION: It is a 6-shaft load detector which controls the position and attitude of a specified movable plate 2 owing to the cooperation of a plurality of actuators (31 to 36). It is provided with a fixing plate 1 connected to one end of each actuator (31 to 36), the movable plate 2 which is connected to the other end of each actuator (31 to 36) and is mounted on the fixing plate 1 in such a manner that the change of a position and attitude of 6 degrees of freedom is possible, a plurality of displacement detection means which detect a stroke of each actuator (31 to 36), and a control means 5 which controls a stroke of each actuator (31 to 36) based on the stroke detected by each displacement detection means so that the position and attitude of the movable plate 2 relative to the fixing plate 1 are kept in a specified condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is typified by a load detector of a robot arm, and is also applicable to detection of a cutting load of a machine tool, indexing of the position of the center of gravity of a heavy object, display of the position of the center of gravity in slinging work, and the like. The present invention relates to an applied 6-axis load detection device.

[0002]

2. Description of the Related Art FIG. 5 is a diagram showing an example of a conventional 6-axis load detecting device of this type. The load detection device has a built-in load detection unit, and its shape and rigidity are designed such that a predetermined elastic deformation occurs when a 6-axis load is applied. A strain gauge is attached to the elastic deformation occurrence portion of the load detection unit so that the elastic deformation when a six-axis load is applied can be detected.

The load detector shown in FIG. 5 is a combination of three sets of parallel plate type load detectors.
Using the deformation of x 501, the translational load Fx and the moment load Mz are translated by the parallel plate PFy 502.
The parallel load PFz 503 detects the translational load Fz and the moment loads Mx and My. That is, 6-axis load F
= {Fx, Fy, Fz, Mx, My, Mz} ^T and the strain ε = {ε1, ε2, ε3, ε4, ε5, which occurs in the load detector,
The relationship with ε 6} ^T is expressed by the following equation (1). Note that x,
y and z are coordinate axes of the Cartesian coordinate system, F is a translational load along the coordinate axis indicated by the subscript, and M is a moment load about the coordinate axis indicated by the subscript.

Ε = K · F (1) In the equation (1), K is a 6 × 6 matrix that describes the relationship between the translational load F and the strain ε. Therefore, the following expression (2) is obtained by multiplying both sides of the above expression (1) by the inverse matrix K ⁻¹ of K.

F = K ⁻¹ · ε (2) That is, if K ⁻¹ is known, the strain generated in the elastic deformation generation portion of the load detection unit is detected to detect the 6-axis load detection device. The 6-axis load acting on can be detected.

[0006]

However, according to the conventional 6-axis load detection method as described above, in order to suppress the detection error and improve the detection accuracy, it is necessary to suppress the mutual interference between the respective axial forces. (For example, when a translational load is applied to any one axis, distortion is not generated in the detection section of the remaining load axis). That is, it is necessary to design the rigidity of the load detection unit so that the matrix K ⁻¹ becomes a diagonal matrix.

However, in practice, it is difficult to design the matrix K ^-1 so as to be a diagonal matrix because the distortions generated in the distortion detection units interfere with each other, and there is a limit in improving the detection accuracy. was there. Further, even if the matrix K ⁻¹ is obtained, the relationship of the above equation (2) is established only in the range where the linearity holds between the applied load and the generated strain. There was a technical problem of getting bigger. An object of the present invention is to provide a 6-axis load detection device capable of accurately detecting a 6-axis load over a wide range.

[0008]

In order to solve the above problems and achieve the object, the 6-axis load detecting device of the present invention is configured as follows. (1) The 6-axis load detection device of the present invention is a 6-axis load detection device that controls the position and orientation of a predetermined movable plate by the cooperation of a plurality of actuators, and is a fixed plate coupled to one end of each actuator. A movable plate coupled to the other end of each actuator so that the position and orientation of the fixed plate can be changed in six degrees of freedom, and a plurality of displacements for detecting strokes of each actuator. And a control means for controlling the stroke of each actuator based on the stroke detected by each displacement detection means in order to maintain the position / posture of the movable plate with respect to the fixed plate in a predetermined state. ing. (2) The 6-axis load detecting device of the present invention is the device according to (1) above, and further comprises a plurality of load detecting means for detecting a compressive load or a tensile load generated in each of the actuators.

As a result of taking the above-mentioned means, the following actions will occur. (1) According to the 6-axis load detection device of the present invention, in order to maintain the position / posture of the movable plate with respect to the fixed plate in a predetermined state, each of the above-mentioned each is based on the strokes of the plurality of actuators detected by the plurality of displacement detection means. Since the stroke of the actuator is controlled, the 6-axis load, which cannot be accurately detected by the conventional detection method utilizing the elastic deformation of the detection member due to mutual interference between the axes, is used to control the position / posture of the movable plate. By suppressing the influence of mutual interference between the axial forces, it is possible to detect more accurately and in a wider range. Therefore, it greatly contributes to the industry. (2) According to the 6-axis load detection device of the present invention, since the compression load or the tensile load generated in each actuator is detected, the thrust force in each actuator can be detected,
The 6-axis load can be detected at the load detection point.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 is a diagram showing a configuration of a 6-axis load detecting device according to a first embodiment of the present invention. This 6-axis load detecting device is applied to a load detector of a robot. Has been done.

In FIG. 1, reference numeral 100 denotes a tip portion of an arm of the robot, and the fixing plate 1 of the 6-axis load detecting device is installed at the tip portion 100. Further, the gripper 101 of the robot is installed at a known position on the side of the movable plate (end effector) 2 facing the fixed plate 1. Then, the six-axis load acting on the gripper 101 is detected by the load detector.

Reference numerals 31 to 36 are linear actuators, and pneumatic cylinders are used for these linear actuators 31 to 36. It should be noted that each of the linear motion actuators 31 to 36 has a built-in displacement gauge (not shown) that detects a stroke. Magnetostrictive stroke sensors are used for these displacement gauges. Then, the strokes of the linear motion actuators 31 to 36 are detected by the displacement meters.

The output from the displacement meter is the servo amplifier 4
Is fed back as a feedback signal S1. On the other hand, the stroke command value from the controller 5 is input to the servo amplifier 4 as a command value S2. By controlling the spool opening of the servo valve 6 based on the deviation between the command value S2 and the feedback signal S1, the stroke of the pneumatic cylinder is controlled to a required value.

Further, in the controller 5, the pressure gauges 71, 72 provided on the pushing side and the pulling side of the pneumatic cylinders, respectively.
The load is obtained from the product of the indicated value from and the pressure receiving area of the linear motion actuators 31 to 36. And the controller 5
The compression or tension load generated in each of the linear motion actuators 31 to 36 is detected from the obtained difference between the push-side load and the pull-side load. In addition, each linear motion actuator 31-36
The movable plate 2 and the fixed plate 1 are connected to each other via a spherical bearing 8. As a result, the linear motion actuators 31 to 36 are designed so that a bending load is not applied, and only a tensile load and a compression load are applied.

In FIG. 1, for convenience, the servo amplifiers 4,
Only the connection state relating to the servo valve 6 and the pressure gauges 71, 72 and the linear motion actuator 31 is shown, but the other linear motion actuators 32 to 36 also relate to the linear motion actuator 31 shown in FIG. Similar to the connected state, a dedicated servo amplifier, a servo valve, and a pressure gauge, which are not shown, are connected to each other. Then, the plurality of servo amplifiers and the pressure gauge are each connected to the controller 5.

In the load detector having the above-described structure in the first embodiment, the movable plate 2 is moved to a predetermined position by the cooperative operation of the plurality of linear motion actuators 31 to 36.
Hold the posture. As a result, the 6-axis load acting on a predetermined point on the movable plate 2 determined in advance, that is, the 3 translational 3 axes along the coordinate axes of the orthogonal coordinate system and the 3 rotations around these coordinate axes, will be described below. Detect by the method shown.

A load (translational load and moment load) acting on a predetermined point (load detection point) on the movable plate 2
Fout is defined by the following equation (3). Fout = {Fx, Fy, Fz, Mx, My, Mz} ^T (3) where Fx, Fy, and Fz are the x-axis, the y-axis, and the z, respectively.
Axial translational loads are indicated, and Mx, My, and Mz are moment loads about the x-axis, y-axis, and z-axis, respectively. The subscript T represents transposition.

The thrust vector Finp generated in each of the linear motion actuators 31 to 36 is defined by the following equation (4). Finp = {F1, F2, F3, F4, F5, F6} ^T (4) where Fi (i = 1, 2, 3, 4, 5, 6) is the i-th linear motion of the six It represents the thrust generated by the actuator. For example, the x, y, and z coordinate axis components of Fi are Fxi, Fyi, and Fzi, respectively, and similarly, the x, y, and z of Mi are the same.
If the respective coordinate axis components are Mxi, Myi, and Mzi, the following relationships will be obtained.

[0019]

(Equation 1)

[0020]

(Equation 2)

[0021]

(Equation 3)

[0022]

(Equation 4)

[0023]

(Equation 5)

[0024]

(Equation 6) Here, Fxi, Fyi, and Fzi are each linear motion actuator 3
1 to 36 mounting pitch circle on the movable plate 2 side, mounting pitch circle on the fixed plate 1 side of each linear motion actuator 31 to 36, geometrical shape of the parallel mechanism obtained from the distance between the movable plate 2 and the fixed plate 1, etc. Determined by

Considering the above points, the above equation (5)
Rewriting ~ (10) and expressing the relationship between Fout and Finp,
It becomes like the following formula (11). Fout = JF × Finp (11) In the above equation (11), JF is a 6 × 6 matrix that describes the relationship between Fout and Finp, and is the load detection point for the reference coordinate system installed on the fixed plate 1. It is expressed as a function of relative position and orientation. Here, the relative position / posture of the load detection point with respect to the reference coordinate system installed on the fixed plate 1 is determined by the strokes of the linear motion actuators 31 to 36 under a fixed constraint condition. Therefore, the change matrix JF in the above equation (11) is a function of the stroke of the linear motion actuators 31 to 36.

Therefore, if the change matrix JF and the thrust vector Finp generated in each of the linear motion actuators 31 to 36 are known in the above equation (11), the 6-axis load at the load detection point can be known. For this purpose, the strokes of the linear motion actuators 31 to 36 can be controlled so that the conversion matrix JF has a known value, and the linear motion actuators 31 to 36 can be controlled.
It is necessary to be able to detect the thrust vector Finp generated at 36. These problems can be solved by the 6-axis load detection device having the above-mentioned configuration.

During measurement in the above-mentioned 6-axis load detection device, the stroke of each pneumatic cylinder is feedback-controlled so that the movable plate 2 maintains a fixed position / posture with respect to the fixed plate 1, and each linear motion actuator 31. The controller 5 obtains the loads acting on .about.36 from the indicated values of the pressure gauges 71 and 72 described above. And from the above formula (11), the gripper 1
The six-axis load acting on 01 will be detected.

(Second Embodiment) FIG. 2 is a diagram showing a configuration of a 6-axis load detecting device according to a second embodiment of the present invention. This 6-axis load detecting device is a load of a machine tool. It is applied to detectors. In FIG. 2, the same parts as those in FIG. 1 are denoted by the same reference numerals.

In FIG. 2, reference numeral 200 denotes a bite stand of the machine tool, and the fixing plate 1 of the 6-axis load detecting device is installed on the bite stand 200. Further, a cutting tool 202 is installed at a known position on the movable plate 2 side facing the fixed plate 1 via a chuck 201 of the machine tool. Then, the six-axis load received by the cutting tool 202 from the work (workpiece) 203 is detected by the load detector.

Further, 31 to 36 are linear actuators, and pneumatic cylinders are used for these linear actuators 31 to 36. Each linear actuator 31-36 has a built-in displacement gauge that detects a stroke. Magnetostrictive stroke sensors are used for these displacement gauges. Then, the strokes of the linear motion actuators 31 to 36 are detected by the displacement meters.

The output from the displacement meter is the servo amplifier 4
Is fed back as a feedback signal S1. On the other hand, the stroke command value from the controller 5 is input to the servo amplifier 4 as a command value S2. By controlling the spool opening of the servo valve 6 based on the deviation between the command value S2 and the feedback signal S1, the stroke of the pneumatic cylinder is controlled to a required value.

In the second embodiment, a load meter 9 is installed at the tip of the piston rod of each of the pneumatic cylinders, and the load meter 9 acts on each of the linear actuators 31 to 36. Detects compressive or tensile load.

As in the first embodiment, the linear motion actuators 31 to 36 are connected to the movable plate 2 and the fixed plate 1 via spherical bearings 8, and the linear motion actuators 31 to 36 are connected to the linear motion actuators 31 to 36, respectively. Is designed to have no bending load and only tensile and compression loads.

Note that, in FIG. 2, for convenience, only the connection state relating to the servo amplifier 4 and the servo valve 6 and the linear actuator 31 is shown, but the other linear actuators 32 to 36 are also shown in FIG. Similarly to the connected state related to the linear motion actuator 31, a dedicated servo amplifier and servo valve (not shown) are connected. The plurality of servo amplifiers are connected to the controller 5, respectively.

During measurement in the 6-axis load detector, the stroke of each cylinder is feedback-controlled so that the movable plate 2 maintains a fixed position and posture with respect to the fixed plate 1, and each linear motion actuator 31-36. Find the load acting on. Then, the 6-axis load received by the cutting tool 202 from the work 203 is detected from the load and the above equation (11).

(Third Embodiment) FIG. 3 is a diagram showing the structure of a 6-axis load detecting device according to a third embodiment of the present invention. It is applied to measuring instruments. In FIG. 3, the same parts as those in FIGS. 1 and 2 are designated by the same reference numerals.

In the third embodiment, the basic construction and the principle of detecting a 6-axis load are the same as those described above except that hydraulic cylinders having a large generated force are used for the linear motion actuators 31 to 36. This is similar to the first embodiment.

That is, each of the linear motion actuators 31 to 3
The stroke of 6 is detected by the magnetostrictive stroke sensor, and this is fed back to the servo amplifier 4, and the servo valve 6
To control the spool opening. As a result, the strokes of the linear motion actuators 31 to 36 are controlled so that the movable plate 2 is always parallel to the fixed plate 1. At this time, the controller 5 causes each of the linear actuators 31 to 3 to move.
The tensile and compressive loads acting on 6 are indicated by the pressure gauges 71 and 72 and the linear actuators (hydraulic cylinders) 31 to 3
It is detected from the product of the pressure receiving area of 6 and the 6-axis load is obtained from the equation (11).

Of the 6-axis loads obtained from the equation (11), focusing on the load of the non-measuring object 300 placed on the movable plate 2 in the direction of gravity (z axis), the xy plane, that is, The coordinates {xG, yG} of the center of gravity G on the horizontal plane are obtained by the following equations (12) and (13).

[0040]

(Equation 7)

[0041]

(Equation 8)

Here, {xi, yi} (i = 1, 2,
3, 4, 5, 6) are linear motion actuators 31 to 36.
Coordinates of the geometrical contact point between the and movable plate 2 (reference coordinate notation)
Represents In the above description, in order to simplify the explanation, it is assumed that the movable plate 2 is kept horizontal with respect to the fixed plate 1. As described above, in the third embodiment, not only the 6-axis load acting on the heavy object but also the coordinates of the center of gravity thereof can be determined.

(Fourth Embodiment) FIG. 4 is a diagram showing the configuration of a 6-axis load detecting device according to a fourth embodiment of the present invention. This 6-axis load detecting device is for supporting slinging work. Is applied to the center of gravity position indicator of. In FIG. 4, the same parts as those in FIGS. 1 to 3 are designated by the same reference numerals.

In the fourth embodiment, the fixed plate 1 is firmly connected to a hoisting machine (not shown) via a wire 401 and a wire connecting portion 402 suspended from the hoisting machine. It should be noted that the movable plate 2 is provided with a circular hole, and the wire connecting portion 402 penetrates the hole without contacting the movable plate 2. In addition, the movable plate 2 is a pillar 40.
The lower indicator plate 403 is firmly coupled via 5, 406, and the lower indicator plate 403 is further firmly coupled to a hook 404 for suspending a suspended load (not shown). The arrow A indicates the direction of gravity.

Here, the fixed plate 1 is attached so that its surface 11 is perpendicular to the center line of the wire 401. Then, the strokes of the linear motion actuators 31 to 36 are controlled in the same manner as in the case of the third embodiment so that the movable plate 2 is always parallel to the fixed plate 1. At this time, the tensile and compressive loads generated in the linear motion actuators 31 to 36 are detected by the load meter 9 installed at the tips of the linear motion actuators 31 to 36.

On the other hand, the coordinates of the center of gravity of the suspended load are
The controller 5 calculates based on the above equations (11) to (13). The calculation result, that is, the coordinates of the center of gravity of the suspended load is displayed on the center-of-gravity position indicator 10 and transmitted to the operator. Thereby, the operator can perform the slinging work while referring to the instruction displayed on the indicator 10 so that the center of the sling is located right above the center of gravity of the suspended load.

The present invention is not limited to the above-mentioned embodiments, and can be carried out by appropriately modifying it without departing from the scope of the invention. (Modifications) (1) In the linear actuators used in the actuator units in the above-described embodiments, hydraulic cylinders, pneumatic cylinders, hydraulic cylinders, electric motors, etc. can be freely selected according to the size of the load and the operating environment. Can be selected and applied. Further, the direct-acting actuator can appropriately select a configuration such as direct connection between the electric motor and the ball screw or connection between the electric motor and the ball screw via a speed reducer. (2) Not only a load meter but also a strain gauge can be applied to the means for detecting the compressive or tensile load generated by the actuator.

(Summary of Embodiments) In each of the above-described embodiments, since the controller 5 maintains the position / posture of the movable plate 2 with respect to the fixed plate 1 at a predetermined value, each linear actuator 3
Calculate the required stroke of 1 to 36,
Is output to. On the other hand, each actuator unit is equipped with a displacement gauge for detecting the stroke of the linear motion actuators 31 to 36, and the stroke command signal S2 from the controller 5 is used as a command value to the servo amplifier 4 and the displacement is performed. By configuring a feedback loop in which the displacement signal from the meter is used as the feedback signal S1 to the servo amplifier 4, it is possible to control the strokes of the six linear motion actuators 31 to 36 to a predetermined value.

Further, in order to detect the compressive and tensile loads generated in the linear motion actuators 31 to 36, each actuator unit is equipped with a load meter 9, which detects the thrust in each linear motion actuator 31 to 36. It will be possible. Due to the operation of the constituent elements of the present invention as described above, it is possible to detect a 6-axis load at a load detection point.

The position of the movable plate 2 with respect to the fixed plate 1
Since the posture is always kept constant, the relation of the above formula (11) is always established as long as the applied load has a value equal to or less than the thrust of the linear motion actuators 31 to 36. Therefore, the detection error does not increase even if the applied load increases.

[0051]

According to the present invention, it is possible to provide a 6-axis load detecting device capable of accurately detecting a 6-axis load over a wide range.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a 6-axis load detection device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a 6-axis load detection device according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a 6-axis load detection device according to a third embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a 6-axis load detection device according to a fourth embodiment of the present invention.

FIG. 5 is a diagram showing an example of a conventional 6-axis load detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Fixed plate 2 ... Movable plate 31-36 ... Linear actuator 4 ... Servo amplifier 5 ... Controller 6 ... Servo valve 71 ... Pressure gauge 72 ... Pressure gauge 8 ... Spherical bearing 9 ... Load gauge 10 ... Center of gravity position indicator 100 ... Tip of arm 101 ... Gripper 200 ... Tool holder 201 ... Chuck 202 ... Tool 203 ... Workpiece 300 ... Non-measuring object 401 ... Wire 402 ... Wire connecting part 403 ... Lower indicator plate 404 ... Hook 405 ... Pillar 406 ... Pillar S1 ... Return Signal S2 ... Command value 501 ... Parallel plate PFx 502 ... Parallel plate PFy 503 ... Parallel plate PFz

Claims (2)

[Claims] 1. A six-axis load detection device for controlling the position and orientation of a predetermined movable plate by cooperation of a plurality of actuators, wherein a fixed plate coupled to one end of each actuator and the other end of each actuator. A movable plate attached to the fixed plate so that the position / posture can be changed in 6 degrees of freedom with respect to the fixed plate; a plurality of displacement detection means for detecting strokes of the actuators; In order to maintain the position / orientation of the movable plate in a predetermined state, control means for controlling the stroke of each actuator based on the stroke detected by each displacement detection means, and a six-axis load. Detection device. 2. The six-axis load detecting device according to claim 1, further comprising a plurality of load detecting means for detecting a compressive load or a tensile load generated in each actuator.