JP2003094266A - Parallel robot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress vibrations of a traveling plate, in a parallel link robot having a parallel link mechanism. SOLUTION: While a braking surface 51 is provided to either sliding member 14 of a couple of sliding members, a braking means 52 is provided to the other sliding member 13. The braking means 52 is activated by a signal detected by a vibration detection means, whereby a pad 55 of the braking means 52 is thrust onto the breaking surface 51 to suppress vibrations of the sliding members 14 and 15, which leads to suppression of vibrations of the connected traveling plates.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a parallel robot using a parallel link mechanism.

[0002]

2. Description of the Related Art As a conventional parallel robot, for example, the one described in the first embodiment of Japanese Patent Laid-Open No. 8-150526 is known. The parallel robot is hung from a ceiling of a gate-shaped frame installed on a bed via a support column. A tool such as an end mill or a drill is attached to the traveling plate of the parallel robot, and by driving the parallel robot, the tool approaches the workpiece placed on the bed to perform processing.

The parallel robot has a base, three pairs of guides, three pairs of slide members, a drive unit, three pairs of rods, a traveling plate, and a control unit. On the base, three pairs of guides are fixed at three equal positions in the circumferential direction with a predetermined angle of inclination. Each of the three pairs of guides is provided with three pairs of slide members so as to be movable in the longitudinal direction of the guides. Further, each of the three pairs of guides is provided with a drive device that independently and independently moves the six slide members forming the three pairs.

One end of a rod is connected to each of the six slide members via a joint. The other end of the rod is coplanarly attached to the traveling plate via a joint. Below the traveling plate, there is a rotating spindle for mounting tools such as end mills and drills.

With the above structure, the control device drives the drive device by giving an operation command to move the slide members separately. The six rods are independently oscillated, and the traveling plate is controlled in six degrees of freedom, that is, position control and attitude control, by a combination of the oscillations of the six rods. Then, the control device directs the rotation axis of the rotation spindle provided on the traveling plate in a desired direction, moves the rotation spindle from one desired position to another position along a desired path, and attaches the tool to the rotation spindle. To process the work piece.

[0006]

As described above, in the parallel link robot of the prior art, the traveling plate can be controlled with 6 degrees of freedom (that is, position and attitude), so that a tool mounted on the rotary spindle, for example, an end mill, can be used for cutting. There is an advantage that it can be brought into contact with a work piece at an optimum angle for machining. Further, since all the driving devices are arranged on the fixed side, the mass of the moving assembly (the traveling plate, the assembly of the moving member mainly including the rotary spindle and the tool) can be reduced. , High acceleration can be set, which leads to improvement in productivity.

However, when the traveling plate is moved at high acceleration, the traveling plate (including the rotary spindle and the tool) may vibrate. The mode of vibration (movement direction, magnitude, etc.) depends on the current position of the traveling plate,
It changes depending on the moving direction, the current posture and the changing posture.

If machining is performed in a state where the vibration generated during the rapid-feed positioning continues, or if vibration occurs during the machining, for example, in the case of end mill machining, waviness occurs on the machined surface and normal machining surface is generated. Can't get
Especially, when the movement direction of the vibration of the traveling plate is not a straight line but a rotation (hereinafter referred to as “rotational vibration”), the displacement of the end mill tip located apart from the rotation axis is enlarged. Rotational vibration is considered to occur when a vector of a force acting on the traveling plate from the slide member via the rod acts on the traveling plate as a rotational moment.

As a result of researches aimed at solving such a problem, the present inventor has determined that the rotational vibration generated in the traveling plate is transmitted to the slide member via the joint and the rod and vibrates the slide member in the moving direction of the slide member. I paid attention. Then, they have found that the rotational vibration of the traveling plate increases when the phases of the vibrations of one slide member and the other slide member of the pair of slide members are opposite to each other.

The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to suppress the rotational vibration of the traveling plate.

[0011]

In order to solve the above-mentioned problems, a parallel robot according to a first aspect of the present invention has three pairs of guides fixed at three equal positions in the circumferential direction of a base.
Each pair of guides is provided with three pairs of slide members so as to be movable in the longitudinal direction of the guides, and each pair of guides is provided with a drive device for independently moving six slide members constituting three pairs. , One end of the rod is connected to each of the six slide members via a joint, and the other end of the rod is mounted on the traveling plate on the same plane via the joint. Further, there is provided a braking means for selectively permitting or restraining relative movement between both slide members of at least one pair of slide members of the three pairs of slide members.

A parallel robot according to a second aspect of the present invention further comprises detection means for detecting the vibration of the slide member, and when the vibration is detected by the detection means, the braking means is detected when the vibration is detected by the detection means. To restrain the relative movement between both slide members.

[0013]

In the invention according to claim 1 configured as described above, the rotary vibration generated in the traveling plate is transmitted to the rod through the joint and further transmitted to the slide member through the joint. . Since the slide member is guided so as to be movable in the longitudinal direction of the guide, it is vibrated in the longitudinal direction by the transmitted vibration.

The control means actuates the braking means when the phases of the vibration in the longitudinal direction are opposite to each other between the one slide member and the other slide member of the pair of slide members. The sliding contact surface of the braking means is pressed or sucked by the braking surface with an appropriate load to generate a frictional force between the surfaces. This frictional force acts in a direction to cancel each other's longitudinal vibrations. As a result, the vibration of the slide member is suppressed, and the vibration of the traveling plate connected via the rod is also suppressed.

In the invention according to claim 2 configured as described above, it further has a detection means for detecting the vibration of the slide member, and when the vibration is detected by the detection means, the braking means is actuated. This makes it possible to automatically suppress the vibration when the vibration occurs.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An example of a first embodiment of the present invention will be described with reference to FIGS. Hereinafter, the case where the parallel robot is used as a machine tool will be described, but the field of use of the parallel robot is not limited to the machine tool. As shown in FIG. 1, a parallel robot PR is suspended via a support pillar P fixed to the outside. A tool T such as an end mill or a drill is attached to the traveling plate 2 of the parallel robot PR.

The parallel robot PR includes a base 1, three pairs of guides 6, 7 and three pairs of slide members 13, 14, drive devices (six in the figure) 15, 16 and six rods 4, 5 and a braking surface. 51 (three in the figure) and braking means 52 (three in the figure)
Two) and a control means 61.

The pair of guides 6 and 7 are provided on every other side of the base 1 which is a hexagonal member, and are constructed as follows. Evenly distributed around the circumference of the base 1 by 120 degrees,
The guide frames 8 and 9 are provided in parallel as a pair, with guide grooves 8 radially formed in the longitudinal direction with a predetermined inclination angle of outward opening.

As shown in FIG. 2, in the guide grooves of the guide frames 8 and 9, respective slide members 13 and 1 slidable along the grooves.
4 is attached. The guide frames 8 and 9 are rotatably provided with feed screws 11 and 12 extending over the base end portions and the tip end portions of the guide frames 8 and 9. Also, the slide members 13, 1
4 is screwed into each feed screw 11, 12,
Reference numeral 12 is coupled to the output shafts of servomotors 15 and 16 provided at the tip ends of the guide frames 8 and 9. Servo motor 1
Encoders 1 and 5 for detecting the respective rotations
5a and 16a are provided.

As shown in FIG. 3, a pair of two rods 4,
5 includes a first rod portion 21, a second rod portion 22, a third rod portion 23, and a flange joint 24 and a second flange portion 24 that fixedly connect the first rod portion 21 and the second rod portion 22, respectively.
The rod portion 22 and the third rod portion 23 are composed of a rotary shaft joint 25 that rotatably connects the rod portion 22 and the third rod portion 23 around the L1 axis.

The upper ends of the rods 4, 5 respectively, that is, the upper ends of the first rod portions 21, are firstly attached to the slide members 13, 14.
It is rotatably connected about two orthogonal axes via a connecting portion 26. The lower end of each of the rods 4 and 5, that is, the lower end of the third rod portion 23 is a second connecting portion 27 at two connecting points at appropriate intervals on the sides of the traveling plate 2 which is a triangular plate member. Is rotatably connected around two orthogonal axes. Therefore, the rods 4 and 5 are connected to the first connecting portion 26.
With respect to the fulcrum, the slide members 13 and 14 can be swung in three-dimensional directions with respect to the traveling plate 2 with the second connecting portion 27 as a fulcrum.

As shown in FIG. 1, the controller 61 is a programmable numerical controller having a central processing unit (CPU) 62 as a core and a memory 63. The CPU 62 drives the drive unit (DU) 165 via the interface 64.
The target value of the amount of rotation of the servomotors 15 and 16 is output to 166, and based on this, each drive unit (DU) 165 and
166 is adapted to drive the servomotors 15 and 16 to rotate. The rotations of the servomotors 15 and 16 are detected by the encoders 15a and 16a and fed back to the drive units (DU) 165 and 166. An input / output device 67 is connected to the CPU 62 via an interface 66, and a sequencer 69 is connected via an interface 64.

The memory 63 stores a vibration detecting program 70 as a vibration detecting means. The vibration detection program 70 uses the rotation amount target value and the encoders 15a and 16
This is a known method for measuring the frequency from the difference (positional deviation) from the current value of the rotation amount detected in a, and the description is omitted.

Next, the means for suppressing the rotational vibration generated in the traveling plate 2 will be described with reference to FIG. The braking means is mainly composed of a cylinder 52 and a braking surface 51.

A cylinder 52 is fixed to a side surface of one of the slide members 13 and 14 arranged in parallel on the side of the other slide member 14 by a bolt (not shown). The cylinder 52 has a piston rod 53 that can move forward and backward toward the other slide member 14.
A disc-shaped brake pad 55 is fixed to the forward end face of the piston rod 53.

On the opposite side of the fixed surface of the brake pad 55,
It is a sliding contact surface that comes into sliding contact with a braking surface (described later), and a material that prevents galling during sliding contact and generates an appropriate frictional force, such as bakelite resin containing reinforcing fibers, is used.
A braking surface 51 is formed on a side surface of the other slide member 14 on the side of the one slide member 13 so that the slide contact surface of the brake pad 55 can slide. Cast iron is used as the material of the braking surface 51, but any other metal may be used as long as it produces an appropriate frictional force when it comes into contact with the sliding contact surface of the brake pad 55.

The parallel link robot PR of the present embodiment configured as described above operates as follows. In the original position, all the slide members 13 and 14 are located in the original slide position, and the position of the traveling plate 2 connected to the joints 26 and 27 by the rods 4 and 5 is the uppermost part of the moving range. Piston rod 5 of cylinder 52
3 is retracted, and a gap is formed between the sliding contact surface of the brake pad 55 and the braking surface 51 (hereinafter, referred to as a brake OFF state).

The workpiece is mounted on a bed (not shown),
A tool T required for processing, for example, an end mill 90 is attached to a rotary spindle 91 of the traveling plate 2. The control device 61 drives the respective servo motors 15 and 16,
The slide members 13 and 14 are respectively advanced by a required stroke. As the slide members 13 and 14 move forward, the traveling plate connected by the rod is changed in inclination, and the rotation axis of the end mill 90 is oriented in a desired direction. At the same time, the end mill 90 is rapidly positioned at the machining start position, the rotating spindle 91 on which the end mill is mounted is rotated by an electric motor (not shown), and the end mill 90 is moved in a desired path to perform machining of a workpiece (not shown).

When the machining is completed, the controller 61 stops the rotation of the rotary spindle 91 on which the end mill 90 is mounted and drives the servomotors 15 and 16 to move the traveling plate 2.
To the original position. The processed workpiece is removed from the bed.

Next, the vibration suppressing function of the parallel link robot PR of the present embodiment will be described with reference to FIGS. When the operation of the machine is started and a cycle start signal is given, for example, the routine of FIG. 4 is executed at predetermined intervals. In step S101, the vibration detection program 70 is executed to cause the slide members 13, 1
Measure the amplitude and phase of 4 vibration. Slide member 13,
The amplitude and phase of the vibration of 14 are measured by measuring the position deviation of the encoders 15a and 15b. As an example of the measurement result, FIG. 5 shows a state where no vibration is generated, and FIG. 6 shows a state where vibration is generated. FIG. 5A shows an encoder 15
5B shows the position deviation of the encoder 16a, and FIG. 5B shows the position deviation of the encoder 16a. The protruding position deviations A and C in FIGS. 5A and 5B are caused at the time of start-up, and the position deviations B and D are caused at the time of stop, due to the follow-up delay of the servo system caused by the slide members 13, 14 and the like. Is. After that, the positional deviation becomes almost zero, and the state of zero positional deviation continues. As a result, it is determined that the slide members 13 and 14 are not vibrating.

FIG. 6A shows the positional deviation of the encoder 15a, and FIG. 6B shows the positional deviation of the encoder 16a. A1 in FIG. 5A shows the position deviation in the negative direction because the follow-up of the slide member is delayed with respect to the command value. After that, the position deviation returns to zero and this time overshoots in the positive direction (A2). Then, the positional deviation returns to zero and overshoots again in the negative direction (A3), and this is repeated periodically.

By detecting the frequency of periodic fluctuation of this position deviation, it is judged that vibration is occurring. B
1, B2 ... Indicate the stop time. Also in this case, the position deviation periodically fluctuates in the plus direction and the minus direction, as in acceleration. 6 (b) has the same frequency as FIG. 6 (a),
The vibration phase is shifted by π radians. That is, the phases of vibration are opposite to each other.

In step S102, the measured amplitude is compared with a preset amplitude threshold value, and if it is less than the amplitude threshold value, the process proceeds to step S105 and the brake is maintained in the OFF state. If it is equal to or larger than the amplitude threshold, the process proceeds to step S103. In step S103, it is determined whether the measured phase difference is π radians. If NO, step S1
Move to 05 and maintain the brake in the OFF state.

If YES, that is, if the phase difference is π radian (reverse phase), the process proceeds to step S104, the solenoid valve (not shown) is switched, and compressed air is supplied to the cylinder 52. The piston rod 53 is moved forward to press the sliding contact surface of the brake pad 55 against the braking surface 51 of the slide member 14 (brake ON state). Sliding surface is braking surface 5
When the slide members 13 and 14 are pressed against each other with a desired load, the vibrations of the slide members 13 and 14 cancel each other due to the frictional force generated between the surfaces. Encoder 15 when the braking means is operated
The positional deviations of a and 16a are as shown in FIG. 7, indicating that no periodic vibration occurs.

As described above, since the vibration of the slide members 13, 14 in the moving direction of the slide members 13, 14 is suppressed, the rotational vibration of the traveling plate 2 connected via the rods 4, 5 is also suppressed. The end mill 90 mounted on the rotary spindle 91 does not vibrate, and the processed surface does not have undulations, and a normal processed surface can be obtained.

An example of the second embodiment of the present invention will be described with reference to FIG. This is different from the first embodiment in the structure of the braking means, and only the difference will be described. The braking means is mainly composed of a cylinder 152 and an angle member 150.

A cylinder 152 is fixed to a side surface of one slide member 13 of the slide members 13 and 14 arranged in parallel by a bolt (not shown). Cylinder 15
2 includes a cylinder body 153 and two pistons 155.

The cylinder main body 153 has a U-shaped cross section, and pistons 155 are coaxially arranged at two facing portions so as to face each other. Piston 15
5 can be moved forward and backward by supplying pressure oil (not shown), and a tip end portion of the piston 155 is formed with a sliding contact surface that is in sliding contact with one plate-shaped portion of the angle member 150.

One plate portion of the angle member 150 is located at a position where a gap is provided between the two inner side surfaces of the opening portion of the cylinder body 153, and a braking surface on which the sliding contact surface of the piston 155 makes sliding contact is provided on both surfaces. Is forming. The other plate-shaped portion is fixed to the side surface of the slide member 14 so as to extend in the moving direction of the slide members 13 and 14.

When the braking means is turned on, the two pistons 155 move forward with each other to clamp one plate-shaped portion of the angle member 150 from both sides. Since the acting forces of the two pistons 155 face each other and are equal, the angle member 150
Does not work as an external force to displace. Therefore, even if the brake means is turned on, the slide members 13 and 14 are not relatively displaced, and the positioning accuracy of the slide members 13 and 14 is not reduced.

Although the cylinder is used as the braking means in the first and second embodiments, an electromagnet may be used instead of the cylinder so that the sliding surface is attracted to the braking surface.

[Brief description of drawings]

FIG. 1 is a perspective view of a machine using a parallel robot according to a first embodiment of the present invention.

FIG. 2 is a view from H of FIG.

FIG. 3 is a detailed view of the rod portion of FIG.

FIG. 4 is a flowchart illustrating a vibration suppressing function according to the first embodiment of the present invention.

FIG. 5 is a graph showing a positional deviation of the encoder in a state where the slide member does not vibrate according to the first embodiment of the present invention.

FIG. 6 is a graph showing a positional deviation of the encoder when the slide member vibrates in the first embodiment of the present invention.

FIG. 7 is a graph showing a position deviation of the encoder when the brake means according to the first embodiment of the present invention is operated.

FIG. 8 is a diagram showing a braking means according to a second embodiment of the present invention.

[Explanation of symbols]

1: base, 2: traveling plate, 4, 5: rod, 6, 7: guide, 13, 14: slide member, 1
5, 16: Drive device, 51: Braking surface, 52: Brake means (cylinder), 61: Control means, PR: Parallel robot, T: Tool

Claims (2)

[Claims] 1. A base and a pair of circumferential bases 3 each.
3 pairs of guides fixed to the base at equal positions, 3 pairs of slide members provided on each of the 3 pairs of guides and movable in the longitudinal direction of the guides, and constituting the 3 pairs 6 A driving device for independently moving the two slide members, six rods each having one end connected to each of the six slide members via a joint, and the other end of each of the six rods having a joint. A parallel robot equipped with a traveling plate mounted on the same plane via a braking means for selectively permitting or restraining relative movement between both slide members of at least one pair of slide members of the three pairs of slide members. A parallel robot characterized by having. 2. The parallel robot according to claim 1,
A detection unit that detects vibration of at least one slide member of the six slide members is further provided, and when the vibration is detected by the detection unit, the brake unit is operated to perform relative movement between the slide members. A parallel robot characterized by being restrained.