JP4305340B2 - Calculation method of load mass and center of gravity position attached to robot - Google Patents

Description

  The present invention relates to a control method for calculating the weight of a load of a robot driven by a motor and the position of the center of gravity of the load.

The present invention relates to a control method for calculating the weight of a load of a robot driven by a motor and the position of the center of gravity of the load.

  In recent years, in a robot having a multi-axis arm driven by a motor, high accuracy of collision detection has been demanded in order to improve safety at the time of collision and to prevent loss due to destruction.

  In addition, the acceleration / deceleration motion performance and vibration suppression control performance for the purpose of further improving the actual tact performance of the robot, the expansion of the robot application field and deburring work, and the fitting work of complex shaped parts Realization of flexible control for the purpose of satisfying the demands of various uses is required.

  In order to realize such an application, the control method in each application requires the arm of the robot, the mass of the load attached to the tip of the arm, and the position of the center of gravity. Among these, the mass and the position of the center of gravity of the arm provided in the robot can be identified in advance by a design tool such as CAD used at the time of design. However, when an arbitrary load is attached to the end of the robot arm, it is necessary to know the load mass and the value of the center of gravity separately.

  Conventionally, as a method of knowing the mass of the load on the control method and the position of the center of gravity, there is a method in which the robot operator manually inputs these values from the robot controller.

  Further, as a method of not manually inputting, there is a method of measuring the current, torque, and angle of each axis of the motor provided in the robot and calculating the load mass and the center of gravity position. In this method, there are two methods: a method in which the robot is stationary, and a method in which each axis of the motor of the robot is driven.

  Of these, in the method of making the robot stand still, the torque calculated from the current value of each axis of the motor in the stationary state of the robot is used to subtract the torque component caused by the gravity of the robot alone and the friction torque at the stationary time. There is a method of extracting only the torque resulting from the gravity of the load and calculating the mass and the center of gravity of the load (see, for example, Patent Document 1).

In the method of driving each axis of the robot motor, the motor torque and arm angle for each axis when driving each axis of the robot are expressed by the number of the mass of the load to be calculated and the position of the center of gravity. There is a method of calculating the mass of the load and the position of the center of gravity by substituting into the relational expression caused by gravity (see, for example, Patent Document 2).
JP-A-9-91004 (FIG. 1) Japanese Patent Laid-Open No. 11-48181 (FIG. 1)

However, in the conventional method of knowing the load mass and the position of the center of gravity for the control method described above, the operator of the robot needs to obtain the load mass and the position of the center of gravity in advance by calculation or measurement. There was an adverse effect caused by forgetting to input.

  In addition, as a method that does not require manual input, the above-described method in which the robot is stationary causes the frictional torque at rest to fluctuate greatly depending on the mass of the load and the posture of the robot. The load mass and the accuracy of the center of gravity may be greatly affected.

  In the method of driving each axis of the motor of the robot, four motor torques including the main driving axis are provided because four independent calculation formulas are provided to calculate the load mass and the gravity center position. It was necessary to measure the value and arm angle. For this reason, when the movement range of the robot is restricted or when the movement itself is restricted, there is a possibility that the load mass and the gravity center position cannot be calculated.

  As described above, the conventional load mass and center-of-gravity position estimation method has a problem in that the load mass and the center-of-gravity position are estimated with high accuracy in a small number of operations.

  Therefore, in the present invention, it is possible to perform control based on the mass of the load and the position of the center of gravity even in a situation where only a small amount of operation is possible by accurately estimating the mass and the position of the center of gravity of the load attached to the robot with a small amount of operation. An object of the present invention is to provide a control method.

The load mass attached to the robot of the present invention and the method of calculating the position of the center of gravity are driven by a motor and the plane formed by the straight line connecting the two rotation center axes and one rotation center axis is the other rotation. In the robot having a plurality of arms having at least one set of two rotational axes that are in a torsional relationship substantially orthogonal to the central axis, one of the two rotational axes is the most advanced rotational axis of the robot, and the other Is the rotation axis on the most advanced side next to the most advanced rotation axis, and it rotates around the most advanced rotation axis and calculates the mass and center of gravity of the load mounted on the most advanced arm. A method for calculating the mass of the attached load and the position of the center of gravity , wherein the motor torque when the two rotating shafts are moved at a constant angular velocity for each axis is calculated, and the calculated motor torque is converted into the mass of the arm . Start Obtains a torque component caused by the mass of the load by subtracting the torque components for each rotation shaft, arm and maximum value of the torque component caused by the load demanded torque component caused by the load becomes 0 The joint angle is calculated for each rotation axis, and the load component is calculated from the maximum value of the torque component, the arm joint angle at which the torque component is zero, and the linear distance that connects the two rotation center axes at the shortest distance. The mass is calculated, and the center of gravity position is calculated using the calculated mass .

  In the robot control method of the present invention, when the arm is moved at an equal angular velocity for each axis, the motor is rotated in both directions, and the motor torque is calculated for each rotation direction.

  In the robot control method of the present invention, when the motor is rotated in both directions, the calculated motor torque is monitored, and the motor rotation direction is reversed after the motor torque reaches a maximum or zero. In the robot control method according to the present invention, when the motor rotation direction is reversed after the motor torque reaches the maximum, the rotation is stopped after the motor torque after the rotation becomes zero. Further, in the robot control method of the present invention, when the motor rotation direction is reversed after the motor torque becomes zero, the rotation is stopped after the motor torque after the reversal becomes maximum.

Furthermore, in the robot control method of the present invention, when the arm moves at an equal angular velocity for each axis, the motor torque is calculated by measuring the motor current value.

  The robot control method of the present invention makes it possible to know the numerical values of unknown loads for both mass and center of gravity very easily, and by using the obtained numerical values for the control method, realizing flexible control and improving the accuracy of collision detection, There is an effect that the actual tact performance can be further improved.

Hereinafter, a preferred embodiment showing a robot control method of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 is a block diagram for implementing the control method in the present embodiment. The entire robot has a block diagram similar to that in FIG. 1 for a plurality of axes. FIG. 1 is representative of control for one motor axis.

In FIG. 1, reference numeral 1 denotes a controller, and 2 denotes a motor + arm controlled by the controller 1. Then, the controller 1 can obtain the current value I _M and the motor rotation angle θ _M during driving of the motor that drives the arm from the motor + arm 2. Further, a memory 4 built in a controller (not shown) in the controller 1 stores a torque component Tgai caused only by the mass of the arm to be controlled without attaching a load.

  Here, the end i of the torque component Tgai indicates the number of axes, and in the present embodiment, an example of a 6-axis robot is shown, so i takes one of 1 to 6. The same applies to the following.

  This torque component Tgai is a known numerical value in advance because it is inherent to the axis, is caused only by the mass of the arm, and is inherent depending on the configuration of the robot arm. This numerical value is stored in the memory 4 in advance, and as will be described later, the mass of the load mounted on the most advanced shaft and the position of the center of gravity are calculated by calculating the torque component caused by the mass of the arm + load obtained by measurement. .

Reference numeral 13 denotes gravitational torque calculation means for obtaining a torque component Tgal caused by the mass of the arm and the load from the current value I _M obtained from the motor + arm 2 and the value of the motor rotation angle θ _M. Further, the torque component Tgai is subtracted from the obtained torque component Tgal to obtain the torque component Tgi caused only by the load. Further, the amplitude Ai and the phase difference φi of the torque component Tgi are obtained by the amplitude / phase difference calculating means 17, and finally the center of gravity position / mass calculating means 18 is used to determine the load mounted on the arm tip from the arm rotation center position of the sixth axis. The distances Xl, Yl, Zl and mass m in three directions to the center of gravity are obtained.

  In this embodiment, a robot provided with an arm having a rotation center axis as shown in FIG. 2 expressed in a vertical coordinate system and in FIG. 3 expressed in a horizontal coordinate expression will be described. Further, in the present embodiment, as shown in FIGS. 2 and 3, the rotation center axes of the two rotation shafts 5 and 6 on the arm tip side are in a twisted position, and are straight lines connecting between the shortest axes. An example of a robot is shown in which a plane formed by one rotation center axis is arranged substantially perpendicular to the other rotation center axis. In addition, although the example in which the rotation center axis in this embodiment is in the position of twist is shown, the following explanation is valid even in the case of being orthogonal to other than this, and in this embodiment, the explanation is simplified. For the sake of simplicity, the description will be made assuming that the rotation axis is orthogonal even when the rotation axis is in the twisted position.

2 and 3, Xl, Zl, and Yl indicate distances in three directions from the arm rotation center position of the sixth axis to the gravity center position of the load attached to the tip of the arm. In FIG. 2, Lii and Lj indicate arm lengths in two directions from the rotation center of the fifth shaft 24 to the rotation center of the sixth shaft 25. The arm length in the other direction is the fifth axis 24 and the sixth axis 2 in FIG.
Since 5 is an example having the rotation center on the same line, it is set to 0.

  Of these dimensions, the center of gravity positions Xl, Zl, Yl of the load are unknown numerical values, and the arm lengths Lii and Lj of the fifth shaft 24 and the sixth shaft 25 are known numerical values in advance.

  4 is a diagram corresponding to the vertical coordinate system of FIG. 2, and is a diagram showing a state in which the arm 124 rotating about the fifth axis rotation center is rotated, and FIG. 6 is a diagram corresponding to the horizontal coordinate system of FIG. FIG. 6 is a diagram illustrating a state in which the load 28 attached to the sixth shaft is rotated, and (a), (b), and (c) in each figure indicate the respective rotational position states. Reference numeral 123 denotes a part of the arm of the fourth shaft 23 shown in FIG.

  Further, in FIGS. 4 and 6, L5 and L6 indicate the lengths in three directions to the load center of gravity when the rotation center of the fifth shaft 24 is the origin, and as shown in the figure, the arm lengths Lii and Lj , And the combined length of the center of gravity positions Xl, Zl, Yl of the load.

  Next, a method for calculating the mass and the position of the center of gravity of the load provided at the arm tip as described above will be described.

In this calculation, first, the motor torque required for the motor to drive the arm is calculated. Here, the motor torque to be calculated corresponds to the torque T _M of the motor + arm 2 in Figure 1, to measure the motor current value I _M is in order to calculate the torque T _M, the measurement of gravity The torque calculation means 13 performs conversion using the torque conversion value Kt stored in advance.

Note in Figure 1, in a block diagram in the motor + arm 2, describes a transfer of control amount around the torque amount, in this figure, the reciprocal of the torque corresponding value from the detected motor torque T _M 1 / It has become a diagram for obtaining the motor current value I _M by calculating the Kt8. However, in the actual configuration, the motor current is first measured, the current value is obtained on the controller 1 side, and the motor torque is calculated based on the current value.

Thus it was able to measure the motor torque T _M and. Incidentally, the motor torque T _M obtained, a torque component due to the mass of the arm and a load including a friction torque Tfrci in motor + arm 2 shown in FIG. Therefore, the obtaining only the torque component caused by both the mass of the load arm and mounted from the motor torque T _M, it is necessary to subtract this frictional torque Tfrci. The method will be described.

When obtains the torque T _M, is equal angular velocity reciprocate in the positive and negative directions fifth shaft 24, the sixth shaft 25 respectively each shaft as shown, respectively in FIGS. 4 and 6 (a) ~ (c) Then, the motor current value I _M and the motor rotation angle θ _M in each direction are measured. The motor current value I _M measured at this time is used for calculating the torque T _M , and the motor rotation angle θ _M is used for calculating the mass and the center of gravity position of the load 28 described later.

Here, FIG. 4 is a view showing only a part of the fourth axis arm of the robot in the vertical coordinate system of FIG. 2 with a load attached to the tip, (a) is a basic position, (b) shows the position rotated in the negative direction, and (c) shows the figure at the position rotated in the positive direction. And when the determined torque T _M, as shown in Figure 4, the fifth shaft 24 is constant angular velocity reciprocate to each positive and negative directions for each axis, measuring the respective motor current value I _M and the motor rotation angle theta _M To do.

Similarly, FIG. 6 is a diagram showing a state where only the sixth axis 25 portion of the robot in the horizontal coordinate system of FIG. 3 is loaded at the tip, where (a) is the basic position, and (b) is rotated in the forward direction. (C) shows a view at a position rotated in the negative direction. The sixth shaft 25 is reciprocated at a constant angular velocity in each of the positive and negative directions for each axis, and each motor current value I _M and motor rotation angle θ are moved. Measure _M.

Note fifth axis 24 and the sixth shaft 25 used for measuring the torque T _M, as shown in FIGS. 2 and 3 is a rotating shaft for rotating the arm being attached to the load, the axis of rotation perpendicular Yes.

Further, the motor rotation angle theta _M seeking simultaneously converted into arm angle theta _L using the reciprocal 1 / Rg11 arm angle conversion value Rg. The arm angle conversion value Rg is 1 if the device is connected between the motor and the arm and the arm is directly connected to the motor.

Then, from the calculated motor torque _{T M,} and cancel the frictional torque component Tfrci contained in the motor torque _{T M,} obtaining the only torque component Tgali due to the mass of the arm and the load. This friction torque component Tfrci has a characteristic that depends on the rotation direction of the motor. Therefore, the frictional torque component Tfrci the motor angle initially performed forward rotation to become operational and negative rotation to become operational measures the motor torque T _M in each case, by calculating from both values included in the motor torque T _M cancel.

In the case where the operating range of the motor at the time of measurement of torque T _M is limited, constantly monitors the value of the torque T _M, is first rotated in one direction, the shaft after the value of the torque T _M reaches the maximum or 0 Reverse the direction of rotation. When the torque T _M is maximized and then reversed, the rotation is stopped after the reversed torque T _M becomes zero. In the case where the inverted after the value of the torque T _M becomes 0, to stop the rotation after the torque T _M after inversion becomes maximum.

This will be described in more detail with reference to FIGS. 5 and 7 are views showing an example of the data measured on the rotation angle of the arm motor current value I _M obtained by the controller 1, it is shown for both during forward rotation and negative rotation. As described above, since the torque T _M is obtained by multiplying the constant (torque corresponding value Kt) to the motor current value I, a similar view and the motor current in the torque T _M FIG.

  First, starting from the arm angle position at point a in FIG. 5, the fifth axis is rotated forward to measure the motor current. And it reverses at the point b immediately after the measured motor current becomes maximum, and makes it rotate negatively. Next, the operation is stopped at the arm angle position near the point c that has passed the point where the motor current becomes zero.

  In contrast to the above-described method, a method may be used in which the arm is reversely rotated immediately after the motor is positively rotated after the arm is positively rotated and stopped immediately after the motor is negatively rotated and then maximized. The order of positive rotation and negative rotation may be switched.

  In this way, motor current data of ¼ period for one rotation of the arm is obtained. Note that the motor current data for one rotation of the arm is not measured, and the rotation is stopped by about a quarter cycle, as will be described later, in this embodiment, the torque applied to the shaft during arm rotation is a sine wave, This is because at least about ¼ period is required to obtain the amplitude and phase difference. Thereby, since it is not necessary to rotate the arm 360 degrees, it is possible to measure sufficiently even when the operation range is limited.

Next, the friction torque component Tfrci is removed from the measured motor current at the time of positive rotation and negative rotation. In this method, the positive rotation torque Ti + is obtained at a position where the arm angles in the positive rotation operation and the negative rotation operation are the same (the forward rotation torque about the fifth axis is T5 because FIG. 5 is a graph for the fifth axis). And the negative rotation torque Ti- (T5-) is divided by 2 to remove the friction torque component Tfrci. When the friction torque component Tfrci is removed, the torque component Tgal (Tgal5 in the case of the fifth shaft) due to the mass of the arm and the load can be extracted as shown in the figure. This torque component Tgal is a torque component caused by the mass of both the arm and the load.

Further, when the range of the equiangular velocity motion cannot be widened, the number of data of the torque component Tgal that can be extracted decreases, and there is a possibility that an error may be included when extracting the torque component Tgi caused only by the load described later. Therefore, as already described, in the case where the range is narrowed, the motor torque T _M in the constant angular velocity motion with limited 1/4 period, cancel the frictional torque component Tfrci, using a least squares estimation method, torque Extraction of the torque component Tgal can be realized by calculating the amplitude and phase of the component Tgal and using the calculated value by the approximate expression.

  Next, the torque component Tgai caused only by the arm is removed from the extracted torque component Tgali. As already described, the torque component Tgai caused only by this arm is unique to the robot and is known in advance, and is stored in the memory 4 built in the controller.

  Here, a method for storing the torque component Tgai in the memory 4 will be described. This torque component Tgai differs depending on the angular position of the arm, and data for each angular position is stored. In addition to this, a method may be used in which only the coefficients used for the calculation are stored in the memory 4 and the torque component Tgai is obtained according to a predetermined calculation formula.

Then, the torque component Tgali, arm angle theta _L is removed torque component Tgai at the same angular position, to calculate the torque component Tgi load only caused.

In this calculation, to perform the calculations in the absolute value of two different points of at least the arm angle theta _L, in the two points, it calculates a torque component Tgi only the mass of the load is caused.

Furthermore, the amplitude value Ai and the phase difference φi of the torque component Tgi are calculated from the torque Tgi calculated at the two points and the arm angle θ _{L at} that time using the least square estimation method.

  In the approximate function used in the least square estimation method, the mathematical formula used differs depending on the relationship of the arm posture with respect to the arm angle. That is, when the arm angle θL = 0 ° and the arm to be driven is held in a posture close to the horizontal direction, the torque component Tgi is expressed as (Equation 1).

Further, when the arm angle θL = 0 ° and the arm to be driven is held in a posture close to the vertical direction, the torque component Tgi is expressed as (Equation 2).

The formula is properly used according to each condition.

  Incidentally, the function of the fifth axis 24 in FIG. 2 uses (Equation 1), and the function of the sixth axis 25 in FIG. 3 uses (Equation 2).

8 and 9 show the torque component Tgi caused only by the loads of the sixth shaft 25 and the fifth shaft 24.
Is a graph in which is plotted. In each figure, A6 and A5 indicate the amplitude values of the torque component Tgi on the sixth axis and the fifth axis, respectively, and φ5 and φ6 indicate the phase difference between the torque components Tgi on the sixth axis and the fifth axis, respectively.

Here, the phase difference φi is the arm angle θ when the torque component Tgi calculated by the above equation (Equation 1) or (Equation 2) is 0 or the maximum when the center of gravity of the load is not all zero. _L has a value other than zero. That is, the phase difference φi has a value other than zero.

  In the case of the sixth axis 25 of the robot shown in FIGS. 2 and 3, when the amplitude is A6 and the phase difference is φ6 as shown in FIG. 8, these values are substituted into the equation (Equation 2). Thus, the torque component Tg6 caused only by the load attached to the arm is

It becomes. (However, θ6 is a variable indicating the rotation angle of the sixth axis arm.)
Similarly, in the case of the fifth axis 24, the torque component Tg5 caused only by the load is measured to have an amplitude of A5 and a phase difference of φ5 as shown in FIG. Substituting into Equation 1)

It becomes. (However, θ5 is a variable indicating the rotation angle of the fifth axis arm.)
In the above equations (Equation 3) and (Equation 4), A5 and A6 are the maximum values of the torque component Tg. Therefore, as shown in FIG. 2, FIG. 3, FIG. 4, and FIG. When m and the gravitational acceleration are g, the torque component Tg takes the maximum value when the center of gravity of the load is in the horizontal direction of the center of rotation. Therefore, the combined length L5 from each rotation center to the position of the center of gravity of the load, L6 and force by load

It is represented by
As described above, the combined length L5 is obtained by combining the load center-of-gravity positions Xl, Zl, Yl and the arm lengths Lii and Lj of the fifth shaft 24 and the sixth shaft 25 as shown in the following equation (Equation 7). expressed.

In the equation (Equation 6), L6 is a combined length of the vertical component Zl of the load centroid position and the horizontal component Yl of the load centroid position,

It is represented by

  Further, for the phase differences φ5 and φ6, from the arm angle of the fifth shaft 24 and the sixth shaft 25 and the condition of arm arrangement,

It becomes. Equation (Equation 9) is when the load position shown in FIG. 4A is the arm angle θ5 = 0 in Equation (Equation 3), and the rotation center of the fifth axis and the load gravity center position at this time are expressed as follows. This is derived from the fact that the angle between the connecting line and the horizontal axis is φ5. Further, Expression (10) is when the load position shown in FIG. 6A is the arm angle θ6 = 0 in Expression (Expression 4), and the rotation center of the sixth axis and the load gravity center position at this time are connected. This is derived from the fact that the angle between the line and the vertical axis is φ6.
Further, by substituting the equations (Equation 5) and (Equation 6) into the equations (Equation 9) and (Equation 10), the following equations (Equation 11) and (Equation 12) are derived.

By the way, since the equations (Equation 11) and (Equation 12) are calculated with respect to the center of gravity position of the same load, Zl in the equations (Equation 11) and (Equation 12) is naturally equal. Therefore,

It becomes.

  Furthermore, it can be derived from the equation (Equation 13) into a relational expression for calculating the mass m of the load,

The formula is obtained.

  Furthermore, Zl can be calculated by substituting the mass m calculated by the equation (Equation 14) into the equation (Equation 11) or the equation (Equation 12).

  Further, by substituting the calculated Zl and the robot arm lengths Lii and Lj into the equations (Equation 7) and (Equation 8), Xl and Yl are obtained as in Equations (Equation 15) and Equations (Equation 16). .

Can be calculated.

As described above, by measuring the current value I _M and the motor rotation angle θM at the time of driving the motor for driving the arm of the two-axis rotation center axis is orthogonal, the torque component load only caused equation The mass and the center of gravity position can be obtained by using the equations (7), (8), (9), and (10) that can be obtained by the equations (3), (4), (5), and (6), and can be derived by the arrangement of the drive shaft of the robot. The mass m of the unknown load and the gravity center positions Xl, Zl, Yl could be calculated.

  In the present embodiment, as already described, the torque component due to the mass of the arm and load of the robot is monitored, and the axis rotation direction is reversed after the magnitude of the torque component reaches a maximum or zero. When the torque component is maximized and reversed, the rotation is stopped after the torque component becomes zero. When the torque component is reversed and reversed, the torque component is maximized. By stopping the rotation, the motor current when the constant angular velocity motion is minimized is measured. Then, simultaneous equations are derived using the characteristic that the rotation center axis of the robot has from the amplitude value and phase difference obtained from the motor torque of the two axes having different rotation center axes obtained by converting this. Furthermore, by calculating the mass and position of the center of gravity of the tip load from simultaneous equations and using them in the control method, it is possible to realize flexible control, improve the accuracy of collision detection, and further improve the actual tact performance. It is.

  The present invention provides a control method for quickly and easily calculating the weight of a load of a robot driven by a motor and the position of the center of gravity of the load by a simple measurement method and calculation method. It can be used for various uses such as expanding the field of use of robots, deburring work, and fitting work of complex shaped parts.

Block diagram for carrying out the control method in Embodiment 1 of the present invention The figure which shows an example of arrangement | positioning in the vertical coordinate system of the drive axis which comprises a robot The figure which shows an example of arrangement | positioning in the horizontal coordinate system of the drive axis which comprises a robot The figure which shows an example in which one drive shaft carries out equal acceleration movement of the positive / negative direction The figure which shows an example of the motor current characteristic at the time of performing the equal acceleration motion of FIG. The figure which shows an example in which the other drive shaft performs equal acceleration motion in the positive and negative rotation directions The figure which shows an example of the motor current characteristic at the time of performing the equal acceleration motion of FIG. The figure which shows an example of the characteristic of the torque component resulting from the load at the time of performing the equal acceleration motion of FIG. The figure which shows an example of the characteristic of the torque component resulting from the load at the time of performing the equal acceleration motion of FIG.

Explanation of symbols

2 Motor + Arm 24 5th axis 25 6th axis 28 Load _TM Motor torque _IM Motor current

Claims (6)

At least one set of two rotating shafts that are driven by a motor and have a torsional relationship in which the plane formed by the straight line connecting the two rotation center axes and the one rotation center axis is substantially orthogonal to the other rotation center axis In the robot having a plurality of arms, one of the two rotation axes is the most advanced rotation axis of the robot, and the other is the rotation axis on the most advanced side next to the most advanced rotation axis, A method for calculating a mass and a gravity center position of a load attached to a robot that rotates about the most advanced rotation axis and calculates a mass and a gravity center position of a load attached to the most advanced arm. torque component of the rotation axis to calculate the motor torque when obtained by equiangular velocity movement for each axis, resulting from the calculated the motor torque to the mass of the load by subtracting the torque component caused by the mass of the arm Determined for each rotation shaft, the obtained local maximum value of the torque component caused by the load, and an arm joint angle torque component due to the load becomes 0 is calculated for each rotation axes obtained, the torque component The mass of the load is calculated from the local maximum value of the angle, the arm joint angle at which the torque component is 0, and the linear distance connecting the two rotation center axes in the shortest distance, and the center of gravity is calculated using the calculated mass. A method for calculating the mass and center of gravity of the load attached to the robot. When equiangular velocity motion arm for each axis, it rotates the motor in both directions, it calculates the motor torque for each direction of rotation, and calculates the motor torque by dividing the sum of the motor torque in 2 above for each direction of rotation The method for calculating the mass and the position of the center of gravity of the load attached to the robot according to claim 1 , wherein the friction torque component is canceled out . The robot according to claim 2, wherein when the motor is rotated in both directions, the calculated motor torque is monitored, and the operating range of the arm is limited by reversing the motor rotation direction after the motor torque reaches a maximum or zero. Of calculating the mass and center of gravity of the load attached to the load . When obtained by inverting the rotating direction of the motor after the motor torque becomes the maximum, attached to the robot of claim 3, wherein limiting the operation range of the arm by stopping the rotation after the post-inversion motor torque becomes 0 Of calculating the mass and the center of gravity of the loaded load . If the motor torque is obtained by reversing the rotating direction of the motor after a 0, attached to the robot of claim 3, wherein limiting the operation range of the arm by stopping the rotation after the post-inversion motor torque reaches the maximum Of calculating the mass and the center of gravity of the loaded load . 6. The method for calculating the mass and the position of the center of gravity of a load attached to a robot according to claim 1, wherein the motor torque is calculated by measuring a motor current value when the arm is moved at an equal angular velocity for each axis.