Articulated arm robot, control method and control program

An articulated arm robot includes a support part capable of extending and contracting upward and downward, a first arm part with one end joined to the support part through a first joint to be rotatable about a yaw axis and having a second joint rotatable about a roll axis between both ends, a second arm part with one end joined to the other end of the first arm part through a third joint to be rotatable about the yaw axis or a pitch axis, an end effector part joined to the other end of the second arm part through a fourth joint to be rotatable about the yaw axis or the pitch axis, and drivers that respectively cause the first to fourth joints to rotate and the support part to extend and contract, and a controller that performs drive control of the drivers of the first to fourth joints by switching the arm between a SCARA mode where the first, second and third arm parts rotate only in a horizontal plane and a perpendicular mode where the second and third arm parts rotate only in a vertical plane.

This is a 371 national phase application of PCT/JP2011/000523 filed 31 Jan. 2011, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an articulated arm robot having a plurality of joints, a control method, and a control program.

BACKGROUND ART

In general, an arm robot that works together with human is required to have high safety, and, in order to safely operate the arm robot, it is desirable to sufficiently reduce its driving force and assure the safety. However, to achieve both a wider range of motion and a heavier work weight capacity using a typical vertical articulated arm with an arm axis structure similar to a human arm, a large driving force is required especially at a joint of the arm base where a moment length is long. This results in the arm structure which is not very safe and not low power consumption.

On the other hand, assembly work or the like is performed using an industrial robot such as a SCARA (Selective Compliance Assembly Robot Arm) robot combining a horizontal articulated axis and a vertical axis. Further, an articulated robot in which a plurality of stages of offset rotational joints are mounted between a robot main body and an end effector, each offset rotational joint including a rotation control structure mounted on the plane tilted with respect to a link axis line between a driving link and a driven link, the driven link having an offset rotational axis line tilted with respect to the link axis line, is known (see Patent Literature 1, for example).

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, although the above mentioned SCARA robot has an advantage that the weight of the work or arm itself does not act on a pivot axis and therefore its driving force can be suppressed to be low, it has a disadvantage that the upper and lower range of motion of the arm is limited and narrowed.

Further, although the articulated robot disclosed in Patent Literature 1 has a wider range of motion, there is a concern that the structure is complicated.

The present invention has been accomplished to solve the above problems and a primary object of the present invention is thus to provide an articulated arm robot capable of driving an arm with a small driving force and movable over a wide range in a simple structure, a control method, and a control program.

Solution to Problem

One aspect of the present invention to attain the above object is an articulated arm robot including a support part capable of extending and contracting upward and downward, a first arm part with one end joined to the support part through a first joint to be rotatable about a yaw axis and having a second joint rotatable about a roll axis between both ends, a second arm part with one end joined to the other end of the first arm part through a third joint to be rotatable about the yaw axis or a pitch axis, an end effector part joined to the other end of the second arm part through a fourth joint to be rotatable about the yaw axis or the pitch axis, and drivers that respectively cause the first to fourth joints to rotate and the support part to extend and contract, the articulated arm robot including a controller that performs drive control of the drivers of the first to fourth joints by switching the arm between a SCARA mode where the first, second and third arm parts rotate only in a horizontal plane and a perpendicular mode where the second and third arm parts rotate only in a vertical plane.

In this aspect, the controller may control the arm to switch between the SCARA mode where rotation axes of the first, third and fourth joints are in a vertical direction and the perpendicular mode where rotation axes of the third and fourth joints are in a horizontal direction by controlling the drivers to rotate the second joint about the roll axis. It is thus possible to drive the arm with a small driving force in the SCARA mode and move the arm over a wide range in the perpendicular mode.

In this aspect, the controller may control rotation of the first, third and fourth joints by controlling the drivers to minimize a torque imposed on the roll axis of the second joint in the SCARA mode. It is thus possible to employ the second driver with a small driving force and achieve the improved safety and lower power consumption of the arm.

In this aspect, the controller may control rotation of the first, third and fourth joints by controlling the drivers to minimize a moment force acting on the second joint by a center of gravity position from the second joint to the end effector part.

In this aspect, the center of gravity position may include a work weight.

In this aspect, the controller may control rotation of the third and fourth joints by controlling the drivers to minimize a torque imposed on the pitch axis of the third joint in the perpendicular mode. It is thus possible to employ the third driver with a small driving force and achieve the improved safety and lower power consumption of the arm.

In this aspect, the controller may control rotation of the third and fourth joints by controlling the drivers to minimize a moment force around the pitch axis of the third joint by a center of gravity position from the third joint to the end effector part.

In this aspect, the center of gravity position may include a work weight.

In this aspect, in a low posture where the third joint is higher than the fifth joint, the controller may control rotation of the third and fourth joints so that the fourth joint is placed lower than a line connecting the third joint and the fifth joint, and in a high posture where the third joint is lower than the fifth joint, the controller may control rotation of the third and fourth joints so that the fourth joint is placed higher than the line connecting the third joint and the fifth joint.

In this aspect, the articulated arm robot may further include a third arm part with one end joined to said the other end of the second arm part through a fourth joint to be rotatable about the yaw axis or the pitch axis, and the end effector part may be joined to the other end of the third arm part through a fifth joint to be rotatable about the roll axis, the pitch axis and the yaw axis.

In this aspect, the controller may switch the arm to the perpendicular mode and control rotation of the third and fourth joints so that the second arm part, the third atm part and the end effector part are housed. It is thus possible to compactly house the arm.

In this aspect, an irreversible transmission mechanism that transmits an output torque from the driver side to the roll axis side of the second joint and does not transmit a torque from the roll axis side of the second joint to the driver side may be mounted on the second joint. It is thus possible to employ the second driver with a small driving force and achieve the safe and low power consumption arm structure.

In this aspect, a weight compensation mechanism that supports gravity of the first joint to the end effector part may be mounted on the support part. It is thus possible to employ the sixth driver with a small driving force and achieve the improved safety and lower power consumption of the arm.

In this aspect, the articulated arm robot may further include a movable body joined to the support part and being movable. It is thus possible to move the arm over a wider range.

On the other hand, one aspect of the present invention to attain the above object may be a control method of an articulated arm robot including a support part capable of extending and contracting upward and downward, a first arm part with one end joined to the support part through a first joint to be rotatable about a yaw axis and having a second joint rotatable about a roll axis between both ends, a second arm part with one end joined to the other end of the first arm part through a third joint to be rotatable about the yaw axis or a pitch axis, an end effector part joined to the other end of the second arm part through a fourth joint to be rotatable about the yaw axis or the pitch axis, and drivers that respectively cause the first to fourth joints to rotate and the support part to extend and contract, the method performing drive control of the drivers of the first to fourth joints by switching the arm between a SCARA mode where the first, second and third arm parts rotate only in a horizontal plane and a perpendicular mode where the second and third arm parts rotate only in a vertical plane.

Further, one aspect of the present invention to attain the above object may be a control program of an articulated arm robot including a support part capable of extending and contracting upward and downward, a first arm part with one end joined to the support part through a first joint to be rotatable about a yaw axis and having a second joint rotatable about a roll axis between both ends, a second arm part with one end joined to the other end of the first arm part through a third joint to be rotatable about the yaw axis or a pitch axis, an end effector part joined to the other end of the second arm part through a fourth joint to be rotatable about the yaw axis or the pitch axis, and drivers that respectively cause the first to fourth joints to rotate and the support part to extend and contract, the program causing a computer to execute processing of performing drive control of the drivers of the first to fourth joints by switching the arm between a SCARA mode where the first, second and third arm parts rotate only in a horizontal plane and a perpendicular mode where the second and third arm parts rotate only in a vertical plane.

Advantageous Effects of Invention

According to the present invention, it is possible to provide an articulated arm robot capable of driving an arm with a small driving force and movable over a wide range in a simple structure, a control method, and a control program.

DESCRIPTION OF EMBODIMENTS

First Embodiment

Embodiments of the present invention are described hereinafter with reference to the drawings.FIG. 1is a perspective view showing a schematic structure of an articulated arm robot according to a first embodiment of the present invention.FIG. 2is a block diagram showing a schematic arm structure of the articulated arm robot according to the first embodiment.FIG. 3is a block diagram showing a schematic system configuration of the articulated arm robot according to the first embodiment.

An articulated arm robot10according to the first embodiment includes a support part6fixed to a given position, a first arm part11with one end joined to the top end of the support part6through a first joint1, a second arm part12with one end joined to the other end of the first arm part11through a third joint3, a third arm part13with one end joined to the other end of the second arm part12through a fourth joint4, an end effector part7joined to the other end of the third arm part13through a fifth joint5, first to sixth drivers21,22,23,24,25and26that respectively cause the first to fifth joints1,2,3,4and5to rotate and the support part6to extend and contract, and a controller8that controls driving of the first to sixth drivers21,22,23,24,25and26.

The support part6(vertical elevation axis)6has an extensible mechanism capable of upward and downward extension and contraction, which allows the first joint1joined to its top to move upward and downward and thereby allows the entire arm to move upward and downward. One end of the first arm part11is joined to the support part6through the first joint1so that it is rotatable about the yaw axis (shoulder axis1, horizontal pivot axis) L1. Further, the second joint2which is rotatable about the roll axis (shoulder axis2) L2is mounted between the both ends of the first arm part11.

One end of the second arm part12is joined to the other end of the first arm part11through the third joint3so that it is rotatable about the yaw axis or the pitch axis (shoulder axis3) L3. One end of the third arm part13is joined to the other end of the second arm part12through the fourth joint4so that it is rotatable about the yaw axis or the pitch axis (elbow axis) L4. The end effector part7is joined to the other end of the third arm part13through the fifth joint5so that it is rotatable about the roll axis (wrist axis1) L5, the pitch axis (wrist axis2) L6, and the yaw axis (wrist axis3) L7.

Note that the roll axis L5, the pitch axis L6and the yaw axis L7at the fifth joint5are arranged to form three orthogonal axes. An analytic solution of the inverse kinematics of the arm can be thereby obtained, which makes control easy. The end effector part7is configured as a gripper having a plurality of fingers and capable of gripping an object, for example; however, it is not limited thereto, and any structure is applicable.

The first to fifth drivers21,22,23,24and25are actuators such as servomotors incorporated into the first to the fifth joints1,2,3,4and5, for example, and rotationally drive the first to fifth joints1,2,3,4and5, respectively, through a speed reduction mechanism or the like. The sixth driver26is a hydraulic or electric actuator incorporated into the support part6, for example, and causes the support part6to extend and contract upward and downward using the extensible mechanism. The first to sixth drivers21,22,23,24,25and26are connected to the controller8through a drive circuit or the like, and rotationally drive the first to fifth joints1,2,3,4and5or cause the support part6to extend and contract according to a control signal transmitted from the controller8.

First to fifth rotation angle sensors31,32,33,34and35capable of measuring the rotation angles of the first to the fifth joints1,2,3,4and5are respectively mounted on the first to fifth joints1,2,3,4and5. The first to fifth rotation angle sensors31,32,33,34and35are potentiometers, for example, and respectively connected to the controller8and output the measured rotation angles of the first to the fifth joints1,2,3,4and5to the controller8.

Note that the first rotation angle sensor31can measure the rotation angle about the yaw axis L1(#1) of the first joint1, the second rotation angle sensor32can measure the rotation angle about the roll axis L2(#2) of the second joint2, the third rotation angle sensor33can measure the rotation angle about the yaw axis or the pitch axis L3(#3) of the third joint3, the fourth rotation angle sensor34can measure the rotation angle about the yaw axis or the pitch axis L4(#4) of the fourth joint4, and the fifth rotation angle sensor35can measure the rotation angle about the roll axis L5(#5), the pitch axis L6(#6) and the yaw axis L7(#7) of the fifth joint5, respectively.

Further, a position sensor36that measures the height position (#0) of the support part6is mounted on the support part6. The position sensor36is connected to the controller8and outputs the measured height position of the support part6to the controller8.

The controller8performs feedback control or the like so that the first to fifth joints1,2,3,4and5have target rotation angles based on the rotation angles from the first to fifth rotation angle sensors31,32,33,34and35and so that the support part6is at a target height position based on the height position from the position sensor36.

Note that the controller8is configured as hardware including a microcomputer composed of a CPU (Central Processing Unit)8athat performs control, operation and the like, a control program that is executed by the CPU8a, a ROM (Read Only Memory)8bthat stores an operation program and the like, a RAM (Random Access Memory)8cthat stores processing data and the like.

The controller8performs drive control of the first to fifth drivers21,22,23,24and25of the first to fifth joints1,2,3,4and5by switching the arm between the SCARA mode (FIGS. 4 and 5) in which the first, third and fourth joints1,3and4rotate only in the horizontal direction and the perpendicular mode (FIGS. 6 and 7) in which the third and fourth joints3and4rotate only in the perpendicular direction.

The roll axis L2of the second joint2has a function as a mode switch axis for switching between the SCARA mode and the perpendicular mode. The controller8controls the second driver22to rotate the second joint2about the roll axis L2to thereby switch between the SCARA mode in which the first, third and fourth rotation axes L1, L3and L4of the first, third and fourth joints1,3and4are in the vertical direction and the perpendicular mode in which the third and fourth rotation axes L3and L4of the third and fourth joints3and4are in the horizontal direction. The SCARA mode and the perpendicular mode are described hereinafter in detail.

The controller8rotates the second joint2about the roll axis L2and switches the arm to the SCARA mode (FIGS. 4 and 5), and then controls the horizontal rotation of the first, third and fourth joints1,3and4through the first, third and fourth drivers21,23and24to thereby control the arm posture. This effectively reduces the load imposed on the joint axis at the base (especially, the roll axis L2of the second joint2) during grasping and handling of a heavy load, for example.

In the SCARA mode, the load caused by the gravity of the arm or work acts on the support part6, the second joint2and the fifth joint5. On the other hand, the moment length of the fifth joint5is short, and the moment force is small, thereby the driving force of the fifth driver25that drives the fifth joint5can be suppressed to be low. Further, the driving force of the second joint2can be suppressed to be low as described later, and, on the other hand, a large driving force is required for the extension and contraction of the support part6; however, as for the driving force of the support part6, a large extension and contraction force can be generated with a small driving force by use of a weight compensation mechanism41as described later. In this manner, the controller8can drive the arm with a small driving force and low power consumption by switching the arm to the SCARA mode.

Note that, in the SCARA mode, the position in the vertical direction of the fifth joint5is determined only by the height position of the support part6, and therefore the upper and lower range of motion of the fifth joint5is determined by the upper and lower extensible range of the support part6(FIG. 8). It is therefore desirable to perform work at an intermediate height such as desk work, for example.

The controller8rotates the second joint2about the roll axis L2and switches the arm to the perpendicular mode (FIGS. 6 and 7). Then, the controller8controls the perpendicular rotation of the third and fourth joints3and4through the third and fourth drivers23and24to thereby control the arm posture. This enables the arm operation over a wide range of motion such as grasping and handling an object at a low or high position, for example.

For example, at a low position such as on a floor, the controller8switches the arm to the perpendicular mode in the state where the first joint1is lowered by the contraction of the support part6through the sixth driver26, and performs work with the end effector part7moving lower than the first to third joints (shoulder axes1to3)1,2and3(FIG. 9).

On the other hand, at a high position such as on a shelf, the controller8switches the arm to the perpendicular mode in the state where the first joint1is raised by the extension of the support part6through the sixth driver26, and performs work with the end effector part7moving higher than the first to third joints (shoulder axes1to3)1,2and3(FIG. 10). In this manner, the controller8can expand the range of motion of the end effector part7to a wide range from a low position to a high position by switching the arm from the SCARA mode to the perpendicular mode (FIG. 11).

Note that, in the perpendicular mode, because the third and fourth joints3and4rotate about the pitch axes L3and L4, the load caused by the gravity is likely to act thereon, and the movable weight capacity is lower than that in the SCARA mode. Therefore, work at a low or high position (region X inFIG. 11) is based on the premise that it does not grasp a heavy load exceeding the maximum driving torque. In this manner, the controller8can move the arm over a wide range from a low position to a high position to perform work by switching the arm to the perpendicular mode.

Further, the controller8switches the arm to the perpendicular mode, and controls the rotation of the third and fourth joints3and4so that the second arm part12, the third arm part13and the end effector part7are housed (FIGS. 12A and 12B). For example, the controller8switches the arm to the perpendicular mode, rotates the third joint3so that the second arm part12is in the vertically downward orientation, and rotates the fourth joint4so that the third arm part13in the vertically upward orientation.

The arm can be housed more compactly by the structure in which the second arm part12and the third arm part13do not interfere with each other when the fourth joint4rotates to house the arm as shown inFIGS. 12A and 12B.

In a typical SCARA arm, the second arm part sticks out horizontally from the third joint position by the length of the second arm part or more when the arm is housed, and the footprint (floor projected area) of the entire arm robot is large. On the other hand, in the articulated arm robot10according to the first embodiment, the arm is switched to the perpendicular mode and then folded, which makes the footprint in the state where the arm is housed small. In this manner, it is possible to improve the capability of being housed, which has been the disadvantage of the SCARA arm, as well as keeping the advantage of the SCARA arm.

As described above, in the articulated arm robot10according to the first embodiment, the controller8performs drive control of the first to fourth drivers21,22,23and24of the first to fourth joints1,2,3and4by switching the arm between the SCARA mode in which the first, third and fourth joints1,3and4rotate only in the horizontal direction and the perpendicular mode in which the third and fourth joints3and4rotate only in the perpendicular direction. It is thus possible to drive the arm with a small driving force in the SCARA mode and move the arm over a wide range in the perpendicular mode.

Note that the switching between the SCARA mode and the perpendicular mode can be easily implemented by placing the second joint2between the both ends of the first arm part11and rotating the second joint2about the roll axis L2. It is thus possible to provide the articulated arm robot10capable of driving the arm with a small driving force and moving the arm over a wide range in a simple structure.

Second Embodiment

In the articulated arm robot10according to a second embodiment of the present invention, the controller8controls the rotation of the first, third and fourth joints1,3and4by controlling the first, third and fourth drivers21,23and24to minimize the torque imposed on the roll axis L2of the second joint2in the SCARA mode. In the SCARA mode, a large torque is likely to act on the roll axis L2of the second joint2; however, by minimizing the torque of the second joint2, the second driver22with a small driving force can be employed, which allows the improved safety and lower power consumption of the arm.

For example, the controller8controls the rotation of the first, third and fourth joints1,3and4by controlling the first, third and fourth drivers21,23and24so as to minimize a moment force (moment length X1) by the center of gravity position G of the second joint2to the end effector part7(FIG. 13).

Next, an example of a method of minimizing the torque imposed on the roll axis L2of the second joint2in the SCARA mode as mentioned above is described in detail.FIG. 14is a flowchart showing an example of a method of minimizing the torque imposed on the roll axis of the second joint in the SCARA mode according to the second embodiment.

First, the controller8sets a target position posture, which is a target hand position posture, of the end effector part7(Step S101). Next, the controller8performs a known inverse kinematics operation using a redundant degree-of-freedom parameter so that the arm is at the set target hand position posture (Step S102), and calculates target rotation angles of the first to fifth joints1,2,3,4and5(Step S103).

In the inverse kinematics operation, the rotation angle of the first joint1is treated as a constant indicating the redundant degree-of-freedom parameter, for example, and the second joint2is fixed in the state of the SCARA mode, and therefore the arm structure according to the second embodiment can be regarded as a six-axis arm, though it is actually an eight-axis arm including the elevation axis, and, assuming that the fifth joint5has three orthogonal axes, an analytic solution of the inverse kinematics can be obtained.

After that, the controller8performs a known forward kinematics operation based on the preset weight parameters of the first to third arm parts11,12and13and the end effector part7and the calculated target rotation angles of the first to fifth joints1,2,3,4and5(Step S104) and calculates the center of gravity position G from the second joint2to the end effector part7(Step S105).

Then, the controller8calculates a vertical plane S1including the roll axis L2of the second joint2(Step S106). Note that the weight parameters are preset to a ROM8bor a RAM8cof the controller8, for example.

Then, the controller8calculates a distance (moment length) X1between the calculated center of gravity position G from the second joint2to the end effector part7and the vertical plane51including the roll axis L2of the roll axis L2(FIG. 13) (Step S107).

The controller8changes the redundant degree-of-freedom parameter by a convergence operation such as Newton's method and sets the redundant degree-of-freedom parameter to minimize the distance X1between the center of gravity position G from the second joint2to the end effector part7and the vertical plane S1including the roll axis L2of the roll axis L2(Step S108), and then returns to the above (Step S102).

Note that the controller8can calculate the center of gravity position G with higher accuracy by modeling the work weight in advance or measuring the work weight after grasping of the work using a load sensor or the like and then modifying the weight parameter.

Further, the controller8may minimize the load torque imposed on the roll axis L2of the second joint2in the SCARA mode based on the torque of the roll axis L2of the second joint2measured by a torque sensor or the like. It is thus possible to easily reduce the load torque imposed on the roll axis L2of the second joint2even when it is difficult to directly measure an external force acting on the arm, such as a work weight or a contact force with the environment, using a force sensor or the like.

In this case, as shown inFIG. 15, the controller8first sets a target position of the end effector part7and thereby sets a target hand position posture (Step S201). Next, the controller8performs a known inverse kinematics operation using a redundant degree-of-freedom parameter so that the arm posture becomes the set target hand position posture (Step S202) and calculates rotation angle reference input values of the first to fifth joints1,2,3,4and5(Step S203).

The controller8outputs the calculated rotation angle reference input values of the first to fifth joints1,2,3,4and5to the first to fifth drivers21,22,23,24and25, and the first to fifth drivers21,22,23,24and25rotate the first to fifth joints1,2,3,4and5, respectively, according to the rotation angle reference input values of the first to fifth joints1,2,3,4and5from the controller8(Step S204).

A torque sensor of the second joint2measures the torque imposed on the roll axis L2of the second joint2(Step S205) and outputs the measured torque to the controller8.

The controller8sets a redundant degree-of-freedom parameter so that the torque imposed on the roll axis L2of the second joint2is small (Step S206) and returns to the above (Step S202). Note that a method of minimizing the torque imposed on the roll axis L2of the second joint2in the SCARA mode is described above, the method is just an example, and any method may be used for calculation.

As described above, in the articulated arm robot10according to the second embodiment, although a large torque is likely to act on the second joint2at the arm base in the SCARA mode, the controller8controls the rotation of the first, third and fourth joints1,3and4to minimize the torque imposed on the roll axis L2of the second joint2in the above-described manner. This allows the second driver22with a small driving force to be employed, thus achieving the safe and low power consumption arm structure.

Third Embodiment

In the articulated arm robot10according to a third embodiment of the present invention, the controller8controls the rotation of the third and fourth joints3and4by controlling the third and fourth drivers23and24to minimize the torque imposed on the pitch axis L3of the third joint3in the perpendicular mode. In the perpendicular mode, a large torque is likely to act on the third joint3; however, by minimizing the torque of the third joint3, the third driver23with a small driving force can be employed, which achieves the improved safety and lower power consumption of the arm.

For example, the controller8controls the rotation of the third and fourth joints3and4by controlling the third and fourth drivers23and24by selecting a solution of the inverse kinematics with a smaller moment force (moment length X2) around the pitch axis L3of the third joint3by the center of gravity position G from the third joint3to the end effector part7.

To be more simple, in the case of a low posture where the third joint3is higher than the fourth and fifth joints4and5, the controller8controls the rotation of the third and fourth joints3and4so that the fourth joint4is placed lower than a line connecting the third joint3and the fifth joint5(FIG. 16).

On the other hand, in the case of a high posture where the third joint3is lower than the fourth and fifth joints4and5, the controller8controls the rotation of the third and fourth joints3and4so that the fourth joint4is placed higher than the line connecting the third joint3and the fifth joint5(FIG. 17).

As described above, in the articulated arm robot10according to the third embodiment, although a large torque is likely to act on the third joint3at the arm base in the perpendicular mode, the controller8controls the rotation of the third and fourth joints3and4to minimize the torque imposed on the pitch axis L3of the third joint3in the above-described manner. This allows the third driver23with a small driving force to be employed, thus achieving the safe and low power consumption arm structure.

Fourth Embodiment

In the articulated arm robot10according to a fourth embodiment of the present invention, the support part6may include a weight compensation mechanism41that supports the gravity of the first joint1to the end effector part7. Although a large driving force is required for the extension and contraction of the support part6at the arm base, by mounting the weight compensation mechanism41on the support part6, the gravity of the first joint1to the end effector part7is always supported by the weight compensation mechanism41, and the support part6can thereby extend and contract with the minimum necessary driving force corresponding to a substantial effective work force. This allows the sixth driver26with a small driving force to be employed for the extension and contraction of the support part6, which achieves the improved safety and lower power consumption of the arm.

For example, the support part6includes a base42fixed to a given position, a lower member43fixedly joined to the base42, and an upper member44engaged with the lower member43to be movable upward and downward (FIG. 18). In the lower and upper members43and44, a direct-acting actuator (sixth driver)26that displaces the upper member44up and down relatively to the lower member43is mounted along the longitudinal direction. Further, in the lower and upper members43and44, a gas spring (weight compensation mechanism)41that urges the upper member44upward all the time with the same force as the gravity from the first joint1to the end effector part7is mounted side by side with the direct-acting actuator26.

Note that, although a gas spring, for example, is used as the weight compensation mechanism41, it is not limited thereto, and a structure using a counter weight may be employed, and any mechanism may be used as long as it can support the gravity acting on the first joint1to the end effector part7.

Fifth Embodiment

In the articulated arm robot10according to a fifth embodiment of the present invention, an irreversible transmission mechanism51that transmits an output torque from the second driver22side to the roll axis L2side of the second joint2and does not transmit a torque from the roll axis L2side of the second joint2to the second driver22side may be mounted on the second joint2(FIG. 20). As the irreversible transmission mechanism51, a torque diode (registered trademark), a worm gear or the like is used, for example, to prevent reverse driving.

Especially in the SCARA mode, a large torque is likely to act on the second joint2at the arm base; however, the roll axis L2of the second joint2serving as the mode switch axis is driven only during the mode switching operation between the SCARA mode and the perpendicular mode. After the mode switching, an external force due to the arm gravity or work from the roll axis L2of the second joint2is held by the irreversible transmission mechanism51, so that the arm posture after the mode switching can be maintained even in the state without the driving force of the second driver22. The second driver22thus only needs to be able to output a driving force required for the mode switching operation. This allows the second driver22with a small driving force to be employed, thus achieving the safe and low power consumption arm structure.

For example, in the second joint2, an input axis of a speed reducer52is joined to an output axis of a servomotor, which is the second driver22, an input axis of the irreversible transmission mechanism51is joined to an output axis of the speed reducer52, and the roll axis L2of the second joint2is joined to an output axis of the irreversible transmission mechanism51.

In this structure, even when an external force due to the arm gravity or work from the roll axis L2of the second joint2is generated in the state where the output axis of the second driver22does not rotate, the roll axis L2of the second joint2is locked by the irreversible transmission mechanism51. Thus, the rotation angle of the roll axis L2of the second joint2is kept even when the driving force of the second joint2is zero. Note that, in the case where the allowable input number of revolutions of the irreversible transmission mechanism51is more than the maximum number of revolutions of the input axis of the speed reducer52, the sequence of assembly of the speed reducer52and the irreversible transmission mechanism51may be reversed. Further, although the irreversible transmission mechanism51is mounted on the roll axis L2of the second joint2in this example, it may be further mounted on the yaw axis or the pitch axis L3of the third joint3and/or the yaw axis or the pitch axis L4of the fourth joint4.

Sixth Embodiment

The articulated arm robot10according to a sixth embodiment of the present invention may further include a movable body61which is joined to the support part6and movable (FIG. 21). Although a bogie61with a plurality of wheels62is used as the movable body61, for example, it is not limited thereto, and any structure is applicable.

Thus, even when an object to be grasped and handled is not within the reachable range of the arm such as on a floor, desk or shelf, it is possible to move the movable body61to a place where work can be conducted and then handle the object by grasping or the like, thus enabling grasping and handling of an object in a wide range. It is thus possible to drive the arm with a small driving force and move it over a wide range in a simple structure.

Note that the present invention is not limited to the above-described embodiments, and various changes and modifications may be made without departing from the scope of the invention.

Although the present invention is described as being a hardware configuration in the above embodiments, the present invention is not limited thereto. The present invention may be implemented by causing a CPU8ato execute a computer program to perform the processing of the controller8.

A program can be stored and provided to a computer using any type of non-transitory computer readable medium. The non-transitory computer readable medium includes any type of tangible storage medium. Examples of the non-transitory computer readable medium include a magnetic storage medium (such as a floppy disk, magnetic tape, hard disk drive, etc.), an optical magnetic storage medium (e.g. a magneto-optical disk), CD-ROM (Read Only Memory), CD-R, CD-R/W, and semiconductor memory (such as mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, RAM (Random Access Memory), etc.).

Further, the program may be provided to a computer using any type of transitory computer readable medium. Examples of the transitory computer readable medium include electric signals, optical signals, and electromagnetic waves. The transitory computer readable medium can provide the program to a computer via a wired communication line such as an electric wire or an optical fiber or a wireless communication line.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a robot arm that works together with human and performs work to move a person, object and the like.

REFERENCE SIGNS LIST