KR101691941B1 - Robot joint driving apparatus and joint torque measuring method of the same - Google Patents

Abstract

A joint drive system for a robot including a joint encoder and a method for measuring a torque acting on the joint using the joint drive device are presented. To this end, a joint drive apparatus for a robot includes a drive motor, a drive motor encoder for measuring a rotation angle of the drive motor, a moving member for linear motion receiving the drive force of the drive motor, a cable connected in both directions of the movable member, An idler pulley rotating in contact with one side of the cable, a joint portion formed of an output pulley rotating in contact with the other side portion of the cable, and a joint encoder measuring a rotation angle of the joint portion. The torque of the joint is calculated by using the rotation angle error which is the difference between the rotation angle of the drive motor multiplied by the gear ratio and the rotation angle of the joint portion and the torsional stiffness coefficient of the cable.

Description

TECHNICAL FIELD [0001] The present invention relates to a joint driving apparatus for a robot and a method for measuring a joint torque of a joint driving apparatus for a robot,

The present invention relates to a humanoid driving apparatus for a robot and a method for measuring a joint torque of a humanoid driving apparatus for a robot applied to a humanoid robot,

Various types of robots capable of bipedal walking and quadruped walking are being developed for the purposes of household, military, and industrial use. Particularly, a humanoid robot is a robot made similar to a human body structure, and its purpose is to perform an operation similar to a human motion. These robots implement not only gait movements such as running and walking but also various movements through movement of joints similar to human joints.

At this time, in order to control the operation of the robot, it is necessary to measure the torque acting on the joint of the robot in real time. A torque sensor is used to measure the torque acting on the joint of the robot. However, the torque sensor is expensive and the structure becomes very complicated to mount the torque sensor.

A joint drive system for a robot including a joint encoder and a method for measuring a torque acting on the joint using the joint drive device are presented.

To this end, a joint drive device for a robot according to an aspect of the present invention includes: a drive motor rotatable in a forward direction and a reverse direction; A moving member that receives a driving force of the driving motor and linearly moves; A cable connected in both directions of the movable member; An idle pulley rotating in contact with one side of the cable; A joint formed by an output pulley rotating in contact with the other side of the cable; And a joint encoder for measuring a rotation angle of the joint part.

In addition, the joint drive device for a robot according to an aspect of the present invention may further include a drive motor encoder for measuring a rotation angle of the drive motor.

According to an aspect of the present invention, there is provided a joint drive apparatus for a robot, the joint drive apparatus including a body frame for supporting an idle pulley and a joint part, and a joint frame rotatably connected to the joint part, wherein the joint joint encoder includes a joint joint encoder body and a joint joint encoder shaft The joint encoder body portion may be coupled to the body frame, and the joint encoder shaft may be coupled to the joint frame.

The apparatus may further include a first bracket positioned between the joint encoder body and the body frame, and a second bracket positioned between the joint shaft encoder and the joint frame.

The joint encoder shaft may be formed with a tap for fastening members for coupling the joint encoder shaft and the second bracket. The fastening member tab may be located at a distance from the center of the end of the joint encoder shaft.

According to another aspect of the present invention, there is provided a joint torque measuring method for a joint driving device for a robot, comprising: a driving motor rotatable in a forward direction and a reverse direction; a driving motor encoder for measuring a rotation angle of the driving motor; An idle pulley that rotates in contact with one side of the cable; and an output pulley that rotates in contact with the other side of the cable, and an articulation encoder for measuring an angle of rotation of the articulation part, the method comprising the steps of: measuring a rotation angle of a drive motor measured by a drive motor encoder, A first rotation angle defined by a gear ratio multiplied by a rotation ratio of the joint portion is obtained, and a rotation angle of the joint portion measured by the joint encoder A second rotation angle is obtained, a rotation angle error of the first rotation angle and a second rotation angle are calculated, and a torque of the joint part is calculated by multiplying the rotation angle error by a torsion stiffness coefficient of the cable.

In this case, the torsional stiffness coefficient is determined by a function value having the torque of the joint part and the second rotation angle as the rotation angle of the joint part as variables, the torque of the joint part is calculated by multiplying the rotational angle error by the torsional stiffness coefficient, The torque of the joint part can be calculated by repeating the iteration by substituting the set value into the joint torque until convergence is made within the setting error range.

Further, the torque of the joint part can be calculated by multiplying the rotational angle error by the torsional stiffness coefficient, and by substituting the second rotational angle by the second rotational angle obtained by filtering so as to be proportional to the amount of change of the first rotational angle, have.

At this time, the second rotation angle is obtained by filtering the second rotation angle to be proportional to the change amount of the first rotation angle, and this can be performed by any one of the following two methods.

or

Thus, the torque acting on the joint of the robot can be easily measured without using the torque sensor by using the joint drive device for a robot including the joint encoder.

1 is a front view showing an appearance of a humanoid robot including a joint drive device for a robot according to an embodiment of the present invention.
Fig. 2 is a schematic perspective view schematically showing the configuration of the humanoid robot of Fig. 1. Fig.
3 is an external perspective view of a joint drive device for a robot according to an embodiment of the present invention.
4 is a view showing a structure in which a joint encoder is mounted on a joint of a joint driving device for a robot according to an embodiment of the present invention.
5 is a view showing a position of a tap for a fastening member formed on a joint encoder shaft of a joint driving device for a robot according to an embodiment of the present invention.
6 is an exploded perspective view of a joint drive device for a robot according to an embodiment of the present invention.
7A and 7B are diagrams showing the connection state of cables in different directions.
8 is an enlarged perspective view showing an enlarged joint formed by an output pulley.
Fig. 9 is a side view of Fig. 8. Fig.
10 is a view schematically showing a joint torque measurement method of a joint driving device for a robot according to an embodiment of the present invention.
FIG. 11 is a graph showing a torque value according to time measured using a torque sensor and an encoder. FIG.
12 is a diagram showing the linearity between the torque values measured using the torque sensor and the encoder.
13 is a diagram showing an improvement in resolution when a second rotation angle, which is a rotation angle of a joint, is filtered.
14 is a flowchart schematically showing a joint torque measurement method of a joint drive device for a robot according to an embodiment of the present invention.
15 is a view schematically showing a joint torque measurement method of a joint driving device for a robot according to another embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a front view showing the appearance of a humanoid robot according to an embodiment of the present invention, and FIG. 2 is a schematic perspective view schematically showing a configuration of the humanoid robot of FIG.

1 and 2, a humanoid robot 1 (hereinafter simply referred to as a robot) includes a body 10, arms 20R and 20L connected to both sides of the body 10, A head 30 connected to the upper end of the moving body 10 and legs 40R and 40L connected to both sides of the lower side of the moving body 10. [ The arms 20R and 20L are connected to the body 10 through the shoulder joint assemblies 210R and 210L and the head 30 is connected to the body 10 through the neck 50. [ In the reference numerals, "R" and "L" indicate the right side and the left side, respectively.

The inside of the body 10 is protected by a cover 11. A control unit 12, a battery 13, and a tilt sensor 14 may be installed in the body 10. The inclination sensor 14 detects the inclination angle of the moving body 10 with respect to the vertical axis and the angular velocity thereof.

The body 10 can be divided into a chest portion 10a and a waist portion 10b and a chest portion 10a is provided between the chest portion 10a and the waist portion 10b and is rotatable relative to the waist portion 10b The joint 15 can be installed. In Fig. 2, the body 10 is briefly shown as a body link.

Both arms 20R and 20L have an upper link 21, a lower link 22 and a hand 23. The upper limb link 21 is connected to the body 10 through the shoulder joint assembly 210. The upper link 21 and the lower link 22 are connected to each other through the elbow joint 220 and the lower link 22 and the hands 23 are connected to each other through the wrist joint 230.

The elbow joint part 220 has two degrees of freedom including a rotation joint 221 in the pitch direction and a rotation joint 222 in the yaw direction and the wrist joint part 230 has the rotation joints in the pitch direction 231 and a rolling joint 232 in the roll direction.

The hand 23 is provided with five fingers 23a. A plurality of joints (not shown) driven by a motor can be installed on each finger 23a. The finger 23a performs various operations such as grasping an object in conjunction with movement of the arm 20 or pointing to a specific direction.

The shoulder joint assemblies 210R and 210L are mounted on both sides of the moving body 10 and connect both arms 20R and 20L to the moving body 10. [ The two shoulder joint assemblies 210R and 210L are disposed between the moving body 10 of the robot 1 and the arms 20R and 20L to move the arms 20R and 20L.

The head 30 may be provided with a camera 31 functioning as the time of the robot 1 and a microphone 32 functioning as a hearing.

The head 30 is connected to the body 10 through the neck joint 310. The neck joint part 310 may have three degrees of freedom including a rotation joint 311 in the yaw direction, a rotation joint 312 in the pitch direction, and a rotation joint 313 in the roll direction.

Head rotation motors (not shown) are connected to the respective rotation joints 311, 312, and 313 of the neck joint 310. The control unit 12 can move the head 30 in a desired direction by controlling the respective motors to drive the revolute joints 311, 312 and 313 at an appropriate angle.

Both legs 40R and 40L include a femoral link 41, a lower link 42 and a foot 43, respectively. The femoral link 41 is connected to the body 10 through the femoral joint 410. The lower link 42 and the foot 43 are connected to each other through an ankle joint part 430. The lower link 42 and the lower link 43 are connected to each other via an ankle joint part 430. [

The femoral joint 410 has three degrees of freedom. Specifically, the femoral joint 410 includes a rotary joint 411 in the yaw direction (rotation around the Z axis), a rotary joint 413 in the pitch direction (rotation about the Y axis) roll direction (rotation around the X axis). The pitch joint 413 and the roll joint 414 of the femoral joint 410 constitute the hip joint 412.

The knee joint part 420 has a degree of freedom including a rotation joint 421 in the pitch direction. The ankle joint part 430 has two degrees of freedom including rotation joints 431 and 432 in the pitch direction and the roll direction.

The knee joint part 420 includes a rotation joint 421 in the pitch direction and has a single degree of freedom. The ankle joint part 430 has two degrees of freedom including rotation joints 431 and 432 in the pitch direction and the roll direction.

As described above, since each of the legs 40R and 40L is provided with six revolving joints with respect to the three joints, twelve revolving joints are provided with respect to the entire legs. Although not shown in the drawings, the motors for driving the rotating joints are provided on the respective legs 40R and 40L. The control unit 12 can implement various operations of the legs 40R and 40L including the walking of the robot 1 by appropriately controlling the motors provided on the legs 40R and 40L.

On the other hand, a multi-axial force and torque sensor 44 is installed between the foot 43 and the ankle joint part 430 on both legs 40R, 40L. The multiaxial F / T sensor 44 measures the three-directional components Fx, Fy and Fz of the force transmitted from the foot 43 and the three-directional components Mx, My and Mz of the moment, And the load applied to the foot 43 are detected.

Hereinafter, a robot joint driving apparatus 500 used in at least one of various joints of the robot will be described.

FIG. 3 is an external perspective view of a joint driving device for a robot according to an embodiment of the present invention, FIG. 4 is a view illustrating a structure in which a joint encoder is mounted on a joint of a joint driving device for a robot according to an embodiment of the present invention FIG. 5 is a view showing a position of a tap for a fastening member formed on a joint shaft encoder shaft of a joint driving device for a robot according to an embodiment of the present invention. FIG. FIG. 8 is an enlarged perspective view showing an enlarged joint part formed by an output pulley, FIG. 9 is an enlarged perspective view of the joint drive device of FIG. 8, and FIG. Side view.

3 to 6, the joint drive device 500 for a robot includes a drive motor 510 provided to be rotatable in forward and reverse directions, a drive motor 510 that receives a drive force of the drive motor 510, A cable 540 connected in both directions of the moving member 520 and a cable 540 connected to one side of the cable 540 A joint part 560 formed of an output pulley that rotates in contact with the other side of the cable 540 and a body frame 560 supporting the idle pulley 550 and the joint part 560. [ 503b and 503c which are rotatably coupled to the joint parts 560 and 503a and 503b and a joint encoder 501 which is coupled to the body frames 503a and 503b and the joint frame 505a, ).

The driving motor 510 provides a driving force for driving the joint driving device 500 for a robot. One end of the drive motor 510 is connected to the ball screw portion 535 by a drive belt 515 and the rotational force of the drive motor 510 is transmitted to the ball screw portion 535 through the drive belt 515, The screw portion 535 is rotated. The drive motor 510 is provided with a drive motor encoder 513 capable of measuring the rotation angle of a drive motor shaft (not shown).

The ball screw portion 535 is rotated by the driving motor 510 and includes a threaded portion 537 which is screwed to engage with the moving member 520.

When the ball screw portion 535 rotates, the moving member 520 linearly moves up and down along the screw portion 537. That is, the forward and reverse rotational movements of the driving motor 510 are transmitted to the moving member 520 and are changed into up and down linear motion.

The ball screw portion 535 to which the moving member 520 is coupled is coupled to the ball screw sub frame 590. In the ball screw sub frame 590, the ball screw portion 535 rotates in the forward and reverse directions, and the moving member 520 linearly moves in the vertical direction.

The ball screw sub frame 590 includes a guide slot 592 for guiding the rotation of the movable member 520 to be prevented. The guide slot 592 is formed in the vertical direction so that the moving member 520 moves only in the vertical direction and does not rotate by the rotational motion of the ball screw portion 535.

A cable 540 is connected to both sides of the movable member 520 in the vertical direction. The cable 540 is connected to the joint part 560 while maintaining a predetermined tension so as to rotate the joint part 560 by the driving force of the driving motor 510. The cable 540 is preferably made of steel and is arranged to enclose the idler pulley 550 and the joint portion 560 formed of a disc-shaped output pulley.

As described above, the overall operation of the joint drive device for a robot 500 is such that when the drive motor 510 rotates in the forward and reverse directions, the ball screw portion 535 also rotates together with the moveable member 520, And moves the cable 540 in the vertical direction. The vertical movement of the cable 540 causes the idle pulley 550 and the joint portion 560 formed of the output pulley to rotate in the forward and reverse directions.

3, when the joint part 560 is rotated by the tension caused by the rotation of the cable 540, the joint frames 505a, 505b, and 505c connected to the joint part 560 are simultaneously rotated, ) Are moved. At this time, a joint encoder 560 of the joint drive device 500 for a robot is provided with a joint encoder 501 capable of measuring a rotation angle of the joint shaft 560. The installation structure of the joint encoder 501 is shown in Fig.

4, the joint encoder 501 includes a joint encoder body 501a and a joint encoder shaft 501b. A first bracket 507 is provided between the joint encoder 501 and the body frame 503a to couple the first bracket 507 and the first bracket 507. A second bracket 509 is provided between the joint encoder 501 and the joint frame 505a, Respectively. As shown in FIGS. 4 and 5, the joint encoder shaft 501b is formed with a tap 501c for fastening member for coupling the joint encoder shaft 501b and the second bracket 509 to each other. The second bracket 509 also has a hole for engaging the fastening member on the fastening member tab. At this time, the fastening member tab 501c is formed to be deflected toward one side about the axis of the joint encoder shaft 501b. This is to facilitate assembly and prevent slippage of the articulation encoder shaft 501b upon rotation.

7A and 7B, the cable 540 forms a closed loop with one line of cables 540 and a one-line cable 540 to form a closed loop. The ends 540a and 540b of the cable 540 are connected by a connection loop sleeve 546 formed to compress the cable 540. That is, both ends 540a and 540b of cable 540 are connected and fixed by connecting loop sleeves 546.

The cable 540 is connected at least once in parallel between the idler pulley 550, the shifting member 520 and the joint 560. The cable 540 of the embodiment of the present invention includes a first line 541 formed between a joint part 560 formed at one side of the output pulley and the idle pulley 550 and a second line 541 formed between the first line 541 A third line 543 provided in parallel on the side of the second line 542 and a third line 543 provided in parallel on the side of the third line 543, Line 544.

The reason for connecting the cables 540 in parallel is to increase the torsional stiffness of the joint driving device 500 for the robot. The torsional stiffness can be expressed by the degree to which the joint part 560 moves with respect to an external force when an external force is applied to the joint part 560 in a stationary state from the outside. The greater the torsional stiffness, the less the joint 560 moves about the external force.

A method of increasing the torsional stiffness of the joint driving device 500 for the robot and a method of increasing the diameter of the joint portion 560 and the idle pulley 550 formed by the output pulley, However, if the diameters of the joint portion 560 and the idle pulley 550 formed by the output pulley are increased, there is a problem that the overall size of the joint driving device 500 for a robot is increased. If the free length of the cable 540 is shortened, the length of the ball screw portion 535 is also shortened, and the movable angle of the joint portion 560 is reduced. In an embodiment of the present invention, this problem is solved by connecting the cable 540 in parallel a plurality of times. The method of increasing the torsional stiffness by connecting the cable 540 in parallel a plurality of times is a principle in which a plurality of springs are connected in parallel to increase the spring constant.

8 and 9, the joint portion 560 formed of the output pulley includes a cable fixing portion 562 so as to prevent the slip phenomenon with the cable 540.

The cable fixing portion 562 includes cable guide brackets 563a and 563b for guiding the cable 540 to be disposed parallel to the axial direction of the joint portion 560 formed by the output pulley. That is, the cable 540 in contact with the joint part 560 and connecting the second line 542 and the third line 543 is arranged along the groove formed in the cable guide brackets 563a and 563b, The frictional force between the joint portion 560 formed by the pulley and the cable 540 is increased.

The cable fixing portion 562 also includes spacers 565a and 565b for fixing the cable 540 to the joint portion 560 formed by the output pulley. Loop sleeves 547a and 547b formed to press the cable 540 are inserted into the portions of the cables 540 of the first line 541 and the fourth line 544 which are in contact with the joint portion 560 And the spacers 565a and 565b are formed to fix the fixed loop sleeves 547a and 547b to the joint portion 560. [ That is, the spacers 565a and 565b formed with the inclined surfaces 566a and 566b are adhered to one side of the loop sleeve grooves 567a and 567b of the joint portion 560 with an adhesive, and the fixed loop sleeves (565a and 565b) 547a, and 547b are inserted. At this time, due to the pretension of the cable 540, the fixed lube sleeves 547a and 547b are fixed to the loop sleeve grooves 567a and 567b.

Hereinafter, a joint torque measurement method of the joint drive device 500 for a robot including such an apparatus will be described in detail. 10 is a view schematically showing a joint torque measurement method of a joint driving device for a robot according to an embodiment of the present invention.

The joint driving apparatus 500 for a robot according to an embodiment of the present invention is characterized by measuring the torque of the joint portion 560 by using the torsional rigidity of the cable without using a torque sensor. That is, in the case of the joint driving device 500 for transmitting a driving force by the cable 540, the force transmitted from the driving motor 510 to the joint part 560 formed by the output pulley and the change of the length of the cable 540 There is a certain correlation. More specifically, it is as follows.

That is, when the driving motor 510 in the body frame 503 (503a, 503b) is driven, the driving motor shaft is rotated. By this rotation, the gear train 512, the ball screw portion 535, The joint portion 560 rotates through the joints 520 and 520. However, the number of revolutions of the drive motor shaft and the number of revolutions of the joint portion 560 are different by a gear ratio. In an ideal case, multiplying the number of revolutions of the drive motor shaft by the gear ratio will match the number of revolutions of the joint. In terms of the rotation angle, the following will be described.

The measured value of the drive motor encoder 513 representing the rotation angle of the drive motor shaft (not shown) is denoted by N, the constant denoting the gear ratio is denoted by G, and the value obtained by multiplying N by G is referred to as a 'first rotation angle' define. That is, when the first rotation angle is? _M , it is expressed as follows.

& amp _; thetas; _M = G x N - (1)

(G: gear ratio constant, N: rotation angle of drive motor shaft)

At this time, θ _M is the rotation angle of the joint 560 estimated from the rotation angle of the drive motor shaft (not shown) assuming that the torsional stiffness coefficient of the cable 540 is infinite. However, since the cable 540 is deformed by the torque applied to the cable 540, there is a slight difference from the rotation angle of the actual joint portion 560.

Further, the rotation angle of the joint part 560 is measured from the joint encoder 501, and this is defined as a "second rotation angle". The second rotation angle is expressed by? _J. From this value, a rotation angle error (?? =? _M -? _J ) which is a difference between the first rotation angle and the second rotation angle is calculated.

This angular error is proportional to the torque acting on the cable, which is known through studies of capstan drive stiffness. That is, as the torque acting on the cable 540 has a large value, deformation such as elongation and twisting of the cable is made, and the rotational angle error becomes larger. When the torsional stiffness coefficient of the cable 540 is K _torsion , the torque τ acting on the joint part 560 is defined as follows.

τ = K _torsion × Δθ - (2)

(K _torsion : torsional stiffness coefficient, ??: rotational angle error)

In this case, in the case of a robot which permits a relatively large error, the torsional stiffness coefficient K _torsion of the cable 540 may be treated as a constant, and the torque tau may be calculated using the K _torsion . However, since the torsional stiffness coefficient K _torsion is determined as a function value that is a function of the torque of the joint part 560 of the robot driving device and the second rotation angle which is the rotation angle of the joint part 560 (K _torsion (τ, θ _J )), If small errors are not allowed, both of these variables should be considered. Hereinafter, a method of measuring the torque of the joint portion 560 more accurately by taking these two variables into account will be described.

As described above, the torsional stiffness coefficient K _torsion is a variable of the torque of the joint part 560 and the second rotation angle, which is the rotation angle of the joint part 560. The joint angle encoder 501 measures the rotation angle of the joint part 560 at predetermined sampling periods. The rotation angle? _J of the joint part 560 at the sampling time to be measured can be obtained as a constant value. However, the torque τ and the torsional stiffness coefficient K _torsion of the joint part 560 to be measured can not immediately know the correct value. This is because the torsional stiffness coefficient K _torsion is determined by the torque of the joint part 560 and the rotation angle of the joint part 560. The rotation angle of the joint part 560 can be obtained as a constant value at the sampling time to be measured, Since the torque? Is an unknown value.

At this time, an iteration method is used to accurately measure the torque? Of the joint part 560. If there is a result value determined by a function expression containing a variable and there is an unknown variable in the result value and the function expression, the iteration method is repeatedly performed after a predetermined value is substituted, And the output value is calculated by a method performed until convergence to the convergence. The reason why the torque τ of the joint part 560 is obtained by the iteration method is that when the absolute value of the torque τ becomes large, the torsional stiffness coefficient K _torsion becomes small. Thus, if the iteration is repeated, the value of the torque τ converges to a constant value . Considering the torsional stiffness factor considering the above two variables, equation (2) is expressed as equation (3) as follows, and equation considering repeated iteration number i is expressed as equation (4).

τ = K torsion (τ, θ _J ) × Δθ - (3)

τ _{i + 1} = K torsion (τ _i , θ _J ) × Δθ - (4)

That is, the torque τ of the joint part 560, which is an unknown value at the sampling time to be measured, is substituted into the equation (4) for calculating the torque of the joint part after substituting a set value such as 0, Get the value. When the torque of the joint part 560 is obtained, the torque of the new joint part 560 is calculated by substituting this into the equation (4) based on this value. If this process is repeated continuously, the torque value? Of the joint part 560 converges to a constant value. At this time, if | τ _{i + 1} - τ _i |, which is an error of the measured value of the torque of the joint part 560, converges within a predetermined error range, the calculated value of the torque of the joint part 560 is converted into the torque value . In this way, the value of the torque of the joint part 560 can be measured more accurately.

However, even in this case, the calculated torque value of the joint part 560 has a different value from the actual value because there is an error according to the resolution of the joint encoder 501. Here, 'resolution' represents the smallest angle unit that the joint encoder 501 can measure. That is, the higher the resolution, the smaller the unit measurement angle, the more accurately the angle can be measured. When the resolutions of the drive motor encoder 513 and the joint encoder 501 are compared, the resolution of the joint encoder 501 is not so bad. However, considering the gear ratio, the resolution of the joint encoder 501 is much lower than that of the drive motor encoder 513. When the resolution of the joint encoder 501 becomes lower than the resolution of the drive motor encoder 513, an error occurs in calculating the torque of the joint part 560 according to the above equations (1) to (4).

By passing the measured value of the joint encoder 501, which is calculated in order to minimize the error, to a low pass filter (LPF), it is possible to obtain a more accurate value than the resolution of the joint encoder 501. However, when the low-pass filter is used, the value of the rotation angle of the joint part 560, which is measured, is delayed in time, resulting in an error. In the present invention, a method of filtering the second rotation angle measured by the articulation encoder 501 so that the amount of change of the first rotation angle is proportional is used in order to eliminate the time delay and minimize the error caused by the resolution of the joint encoder 501 do. Thus, the second rotation angle is filtered to obtain the second rotation angle, and the torque of the joint part 560 is calculated using this value. The specific calculation method is performed by the following equation.

에 제1회전각의 변화량 θ_M[k]-θ_M[k-1]를 반영하여 샘플링 시간 k에서의 제2'회전각

를 획득한다. 이때, 제1회전각의 변화량 θ_M[k]-θ_M[k-1]를 반영하는 것은 제1회전각의 변화량에 θ_J[k]/θ_M[k]를 곱하여 더하는 방식을 사용할 수 있다. 이는, 제1회전각과 제2회전각이 정확하게 일치하지 않기 때문에 이 비율을 나타내는 상수를 곱해줌으로써 정확도를 향상시키기 위함이다. 위 식은 제1회전각의 변화량과 제2회전각의 변화량이 비례하다는 사실을 이용한 것으로, 이 식을 이용하여 필터링하여 관절부 인코더(501)의 해상도에 의하여 정확도가 떨어지는 것을 보상한 비교적 정확한 제2'회전각을 구할 수 있게 된다.As mentioned above, the first rotation angle is represented by? _M , and the second rotation angle is represented by? _{J. In} this equation, a variable k representing the measurement sampling time is further displayed. That is, the first rotation angle [theta] _M [k] and the second rotation angle [theta] _J [k] are acquired at a specific sampling time k. At the next previous sampling time k-1, the second rotation angle

The first rotating second "rotation at each amount of change θ _M [k] -θ _M to reflect the [k-1] for each sampling time k

. In this case, the first rotation angle is to reflect the change in _{θ M [k] -θ M [} k-1] of the available methods of adding the multiplied first rotating each amount of change _{θ J [k] / θ M} [k] have. This is to improve the accuracy by multiplying the first rotation angle and the second rotation angle by a constant representing the ratio because the first rotation angle and the second rotation angle do not exactly coincide with each other. The above equation is based on the fact that the amount of change in the first rotation angle is proportional to the amount of change in the second rotation angle. By filtering using this equation, a relatively accurate second ' The rotation angle can be obtained.

But. In the case of using the above method, the accuracy of the second 'joint angle may be lowered due to the maximum resolution of the joint encoder 501, that is, the minimum angle unit?. That is, if the value of the second articulation angle is larger or smaller in the range of Δ / 2 which is half of the maximum resolution based on the second articulation angle θ _J [k] at k, which is the previous sampling time, There is no problem even if it is set to a value by Δ / 2. However, when the value is larger or smaller than the range of Δ / 2, a large error occurs. In this case, in order to reduce the error range to within the maximum resolution range of the joint encoder 501, the second 'joint angle can be determined using the method shown in the following equation.

That is, as shown in the above equation, if the value of the second 'joint angle is larger than the range of Δ / 2 which is half of the maximum resolution based on the second joint angle θ _J [k] at k, which is the previous sampling time The error is minimized by adopting the second joint angle with a value of the maximum error range that the maximum resolution of the joint encoder 501 can have. In this way, it is possible to more accurately measure the joint 560 torque by acquiring the second 'joint angle more accurately and calculating the torque of the joint 560 using this second joint angle.

 Hereinafter, the effect of measuring the torque of the joint portion 560 in this manner will be described with reference to Figs. 11 to 13. Fig. Fig. 11 is a diagram showing a torque value according to a time measured using a torque sensor and an encoder, Fig. 12 is a diagram showing a linearity between torque values measured using a torque sensor and an encoder, And the second rotation angle, which is an angle, is filtered.

When a certain load torque is applied to the joint drive device for a robot 500 according to the embodiment of the present invention, the value of the torque measured using the torque sensor is compared with the value of the torque measured by the drive motor encoder 513 and the encoder 501 of the joint part, The value of the torque measured on the basis of the value of the torque is shown in FIG. It can be seen that these two values are generally consistent.

Referring to the graph of FIG. 12, it can be seen that the slope of the value of the torque measured by the two methods is close to 1. It is also confirmed that the measured values of the two methods agree with each other.

FIG. 13 shows a result of performing filtering in order to minimize the error due to the relatively low resolution of the second joint angle described above. 13, it can be seen that there is no time delay error unlike the case of using the low-pass filter. In this respect, a filter using this filtering method will be referred to as a "delay-less filter". That is, while the rotation angle of the joint part 560 is measured in a step shape by the low resolution of the joint encoder 501, when performing the delay-less filtering, smooth curve is obtained as in the case of using the low- At the same time, it can be seen that there is no time delay. When the torque of the joint part is measured using the filtered second rotation angle, the accuracy is improved.

Hereinafter, a method of measuring the torque of the joint part using the joint driving device 500 for a robot according to an embodiment of the present invention will be described in detail with reference to FIGS. 14 and 15. FIG. FIG. 14 is a flowchart schematically illustrating a joint torque measurement method of a joint drive device for a robot according to an embodiment of the present invention, FIG. 15 is a flowchart illustrating a method of measuring joint torque of a joint drive device for a robot according to another embodiment of the present invention Fig.

14, the rotation angle of the drive motor 510 is measured using the drive motor encoder 513. (600) When the rotation angle of the drive motor 510 is measured, this value is multiplied by the gear ratio, (620) Next, a second rotation angle, which is the rotation angle of the joint portion 560, is acquired using the joint encoder 501. (640) The error between the first rotation angle and the second rotation angle is calculated (660a) to complete the torque measurement of the joint (560) (700) by multiplying the rotational angular error by the torsional stiffness coefficient of the cable (680a) The coefficient is not considered to be a constant, and accuracy is somewhat deteriorated because the error due to the low resolution of the joint encoder 501 is not considered. A method of measuring the torque of the joint part 560 for compensating for both errors due to these two factors will be described with reference to the flowchart of FIG.

15, the rotation angle of the drive motor 513 is measured using the drive motor encoder 501 as shown in Figure 14. The reference numeral 600 denotes a rotation angle of the drive motor 510 multiplied by a gear ratio, (620) Next, a second rotation angle, which is the rotation angle of the joint part 560, is acquired using the joint encoder 501. (640) At this time, the second rotation angle is delay- (650) The error of the second rotation angle and the first rotation angle obtained after the non-delay filtering is calculated to obtain the rotation angle error (660b). The rotation angle error of the cable (540) And the torque of the joint part 560 is calculated by multiplying the stiffness coefficient (680b)

In this case, when calculating the torque of the joint part 560, a predetermined value such as 0 is assumed as a torque, and the torque is substituted into the above-mentioned equation (4). When the torque of the joint part 560 is calculated as described above, iteration is repeatedly performed to calculate the torque of the joint part 560 (685). It is judged whether or not the torque of the joint part 560 converges within the set error range while performing iteration (690) At this time, if the torque of the joint part 560 converges within the set error range, the iteration continues. If the torque of the joint part 560 has converged within the set error range, this value is adopted as the value of the joint part 560 torque and the torque measurement of the joint part 560 is completed. (700)

As described above, the joint encoder 501 is installed in the joint part 560 of the joint driving device 500 of the robot, and the torque sensor is mounted by using the measured rotation angle of the joint part 506 and the torsional stiffness coefficient of the cable 540 The torque acting on the joint part 560 can be easily measured.

1: Humanoid robot 500: Joint drive device for robot
501: joint encoder 510: drive motor
513: Driving motor encoder 520: Moving member
540: Cable 550: idler pulley
560: joints

Claims (11)

A drive motor rotatable in a forward direction and a reverse direction;
A moving member that receives a driving force of the driving motor and linearly moves;
A cable connected in both directions of the moving member;
An idle pulley rotating in contact with one side of the cable;
A joint formed by an output pulley rotating in contact with the other side of the cable; And
And a joint encoder for measuring a rotation angle of the joint,
Wherein the joint encoder includes a joint joint encoder body and a joint joint encoder shaft. The method according to claim 1,
And a drive motor encoder for measuring a rotation angle of the drive motor. The method according to claim 1,
A body frame supporting the idler pulley, the joint part, and an articulation frame connected to the joint part and rotating,
Wherein the joint encoder body is coupled to the body frame and the joint encoder shaft is coupled to the joint frame. The method of claim 3,
A first bracket positioned between the joint encoder body and the body frame, and a second bracket positioned between the joint encoder shaft and the joint frame. 5. The method of claim 4,
And a joint tap for coupling the joint shaft encoder and the second bracket is formed on the joint shaft encoder shaft. 6. The method of claim 5,
Wherein the fastening member tab is located at a position which is a predetermined distance away from a center position of an end of the joint shaft encoder shaft. A drive motor rotatable in forward and reverse directions,
A drive motor encoder for measuring a rotation angle of the drive motor,
A moving member which is linearly moved to receive the driving force of the driving motor,
A cable connected in both directions of the moving member,
An idle pulley rotating in contact with one side of the cable,
A joint formed by an output pulley rotating in contact with the other side of the cable,
And a joint encoder for measuring a rotation angle of the joint part, the joint torque measuring method comprising:
A rotation angle of the drive motor measured by the drive motor encoder is multiplied by a gear ratio, which is a rotation ratio between the drive motor and the joint portion, to obtain a first rotation angle,
Obtaining a second rotation angle, which is a rotation angle of the joint part measured by the joint encoder,
Calculating a rotation angle error which is a difference between the first rotation angle and the second rotation angle,
Wherein the torque of the joint part is calculated by multiplying the rotation angle error by a torsional stiffness coefficient of the cable. 8. The method of claim 7,
Wherein the torsional stiffness coefficient is determined as a function value having the torque of the joint part and the second rotation angle which is the rotation angle of the joint part as a variable,
Wherein the torque of the joint part is calculated by multiplying the rotational angle error by the torsional stiffness coefficient,
Wherein the controller calculates the torque of the joint by repeatedly performing iteration by substituting a set value into the joint torque until the torque of the joint is converged to a set error range. Joint torque measurement method. 8. The method of claim 7,
Wherein the torque of the joint part is calculated by multiplying the rotational angle error by the torsional stiffness coefficient,
Wherein the torque of the joint part is calculated by replacing the second rotation angle by a second rotation angle acquired by filtering the second rotation angle so as to be proportional to the change amount of the first rotation angle. 10. The method of claim 9,
Wherein the second rotation angle is obtained by filtering the second rotation angle to be proportional to the change amount of the first rotation angle by the following equation.

10. The method of claim 9,
Wherein the second rotation angle is obtained by filtering the second rotation angle to be proportional to the change amount of the first rotation angle by the following equation.

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