JP3871293B2 - Object gripping control method by hand or manipulator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gripping control method for an object using a robot hand or manipulator, and more particularly to a gripping control method for gripping and lifting an object whose weight and friction coefficient are unknown by a robot hand or manipulator.
[0002]
[Prior art]
In order to grip an object with unknown weight and friction coefficient and lift it with a robot hand or manipulator, it is necessary to use the minimum necessary force so that the object is not crushed by the gripping force and does not slide off the gripping part. Need to grip. Therefore, it detects the object's sliding displacement and sliding speed when it is gripped and lifted by a robot hand, etc., and detects the object's friction coefficient by feeding back this detection information and controlling the gripping force. The proposal of the method etc. is described in "Journal of the Robotics Society of Japan Vol.11 N0.7 959-965 pages 1993".
[0003]
However, the method of detecting slipping when an object starts to slide is not suitable for work such as positioning the object with high accuracy because the relative position between the robot hand and the object changes slightly. Further, if a method for detecting the friction coefficient is used, an appropriate gripping force within a range where the object does not start to slide can be obtained. However, there is a drawback that the apparatus becomes complicated.
[0004]
In view of this, the inventors of the present invention hold an object of unknown weight and friction coefficient with a curved elastic body and receive a load of the object on the contact surface between the object and the curved elastic body to generate a tangential force in the tangential direction. When the shear strain distribution inside the curved elastic body is observed and the tangential force is increased, the region of initial local slip grows from the end of the contact region, and the strain distribution finally becomes the whole This is a unique distribution when sliding. However, if the tangential force and the normal force for gripping an object are increased so that the overall slip distribution does not occur, an object whose weight and friction coefficient are unknown can be gripped and lifted by a robot hand or manipulator. This is published in “Mechanical Society of Japan (C), Vol. 64, No. 620, April 1998, pages 1258 to 1265”.
[0005]
In addition, the inventors of the present invention arrange a plurality of thin plates with strain gauges attached to the inside of the curved silicone rubber as a sensor capable of detecting the shear strain distribution inside the curved elastic body described above. In addition, the fact that the strain distribution described above can be measured by these strain gauges is disclosed in “The Japan Society of Mechanical Engineers, Vol. 64, No. 627, Volume C, November 1998, pages 4264 to 4270”.
[0006]
[Problems to be solved by the invention]
As described above, an object whose weight and friction coefficient are unknown is gripped by a curved elastic body, a strain distribution is detected by a strain gauge arranged inside the curved elastic body, and the object is not crushed from this strain distribution. It is disclosed that an object can be grasped and lifted by a robot hand or the like without sliding down, but any strain distribution pattern can be used to lift an object without squeezing and sliding down. Also, the gripping force control method was unknown.
[0007]
SUMMARY OF THE INVENTION An object of the present invention is to provide a grip control method capable of gripping and lifting an object whose weight and friction coefficient are unknown by a robot hand or a manipulator without causing a shift in grip position.
[0008]
[Means for Solving the Problems]
The present invention relates to a robot hand or manipulator provided with a finger having a curved elastic body on the object gripping surface in which a plurality of sensors are dispersed and arranged. An object gripping control method according to When gripping and lifting an object with a finger, Every predetermined period The size of the fixed region between the curved elastic body and the object due to the shear strain or shear stress of the curved elastic body obtained from each sensor. The Seeking Size of the fixed area By controlling the gripping force and lifting force by the fingers, the object can be lifted without being crushed and slipped off.
[0009]
Further, since the object is gripped via the curved elastic body, the gripping force and the lifting force are proportional to the movement amount of the finger in the object gripping direction and the movement amount in the lifting direction. Therefore, the gripping force and the lifting force are controlled by controlling the movement amount of the finger in the object gripping direction and the movement amount in the direction of lifting the object.
[0010]
As an example of obtaining the size of the fixed region, the strain change rate obtained by dividing the amount of change in each shear strain in the predetermined period by the predetermined period. set, A value obtained by dividing the amount of change in each shear strain in the predetermined cycle by the increase in the object lifting force in the predetermined cycle. set, A value obtained by dividing the amount of change in each shear strain in the predetermined cycle by the amount of increase in the object gripping force in the predetermined cycle. set, A value obtained by dividing the amount of change in each shear strain in the predetermined period by the amount of increase in displacement in the object lifting direction in the predetermined period. set, A value obtained by dividing the amount of change in each shear strain in the predetermined cycle by the amount of increase in displacement in the object gripping direction in the predetermined cycle. set, The time derivative of the shear stress obtained by dividing the amount of change of each shear stress in the predetermined cycle by the predetermined cycle. set, A value obtained by dividing the amount of change in each shear stress in the predetermined cycle by the increase in the object lifting force in the predetermined cycle. set, A value obtained by dividing the amount of change in each shear stress in the predetermined period by the amount of increase in the object gripping force in the predetermined period. set, A value obtained by dividing the amount of change in each shear stress in the predetermined period by the increase in displacement in the object lifting direction in the predetermined period. set, A value obtained by dividing the amount of change in shear stress in the predetermined cycle by the amount of increase in displacement in the object gripping direction in the predetermined cycle. Pair of Any one Pair Sought and this set of sought of The size of the fixing region is determined based on whether or not the number of values exceeding a predetermined value exceeds a reference value, and the gripping force and lifting force by the finger are controlled based on the determination result.
[0011]
And one set of controls for gripping force and lifting force of When the number of values exceeding the predetermined value is smaller than the reference value, the increment of the force vector applied to the object by the finger is increased for each predetermined period, and conversely, it is larger than the reference value. Sometimes, the force applied to the finger is controlled so as to decrease the increment of the force vector for each predetermined period.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows that when an object having an unknown weight and friction coefficient is gripped and lifted, the force applied between the finger that grips the object and the object is normal force (grip force) Fn perpendicular to the contact surface and parallel to the contact surface. It is explanatory drawing of the force relationship analyzed by dividing into tangential force (friction force) Ft. The frictional force is assumed to follow Coulomb's law, and for the sake of simplicity, the dynamic friction coefficient and the static friction coefficient are assumed to be the same value μ.
[0013]
With this gripping force (normal force) Fn by gripping an object with a finger and a tangential force Ft that is a force to lift vertically upward, the condition for the object to slide is
Ft = μ · Fn (1)
It is. In addition, the condition for lifting an object of its own weight mg is
Ft = mg / 2 (2)
It is. In order to lift an object, first, a normal force Fn is applied, and then a tangential force (lifting force) Ft below a frictional force generated by the applied normal force Fn is gradually increased so that the tangential force Ft becomes the gravity of the object. When it is above mg, the object will lift. That is, in FIG. 1, if a force increase curve passing through the region below the straight line of the above formula 1 is obtained, the object can be lifted without sliding down.
[0014]
If the normal force Fn is too large, the object may be crushed or damaged. Therefore, the normal force of the force reaching point A when the tangential force Ft reaches the object gravity mg and lifts the object.
Fn = FL (3)
Is the intersection of 1 and 2 above
Fn = mg / 2μ (4)
It is better to be close enough.
[0015]
Therefore, according to the present invention, the normal force (gripping force) Fn = FL of the force reaching point A for lifting the object is close to the intersection Fn = mg / 2μ between the above formulas 1 and 2, and the straight line of the formula 1 in FIG. Controlling the normal force Fn and tangential force Ft so as to pass below the object, an object whose weight and coefficient of friction are unknown can be gripped and lifted with a robot hand or manipulator, and an object gripping control method using a hand or manipulator There is in getting.
[0016]
The present invention obtains the object gripping control method using a sensor that can detect the shear strain or shear stress with a curved elastic body, and FIG. The robot hand 10 is attached to the wrist 22, and the tips of the fingers 11a and 11b of the robot hand 10 are curved elastic bodies in which a plurality of sensors are embedded in the above-described manner facing the surface that grips the object W. The configured sensor units 12 and 12 are attached.
[0017]
In addition, the internal structure of the curved elastic body of the sensor units 12 and 12 is arbitrary, and the number of fingers is two in FIG. 2, but the number of fingers may be an arbitrary number of 2 or more. There may be five. Moreover, the sensor part should just be arrange | positioned at one or more of the fingers, and as shown in FIG. 2, you may provide the sensor parts 12 and 12 in the fingers 11a and 11b which oppose, respectively, or one finger | toe. A curved elastic body that does not constitute the sensor unit may be provided on the other side.
[0018]
The fingers 11a and 11b of the robot hand 10 can be opened and closed by a servo motor, and the finger portion 11 can be moved by the servo motor in a direction perpendicular to the opening and closing direction.
[0019]
The sensor unit 12 constituted by the curved elastic body 13 described above may be formed in a cylindrical shape as shown in FIG. 3A, or may be formed in a spherical shape as shown in FIG. Good. In addition, although it may be formed in a surface shape with any other curvature, in any case, the magnitude of the vertical reaction force (normal force) varies depending on the location due to the curved surface shape, which will be described later. Any shape that causes local slipping may be used.
[0020]
FIG. 4 is an explanatory diagram of the internal structure of the sensor unit 12 composed of the curved elastic body 13. The example shown in FIG. 4A is an example in which several sensors 14 such as strain gauges and PVDF (polyvinylidene fluoride) are embedded in the elastic body 13. In the example shown in FIG. 4 (a), leaf springs 14 'such as phosphor bronze plates with strain gauges 14 attached as sensors are parallel to each other at an equal interval of about 45 degrees (not necessarily 45 degrees) with respect to the contact surface. A plurality of other angles may be embedded in the curved elastic body 13 at an angle. Note that a method of directly embedding the strain gauge 14 or a method of attaching the strain gauge 14 to a cantilevered position may be used.
[0021]
In the case of this sensor, when the object W is gripped by the curved elastic body 13 of the sensor parts 12 and 12, the curved elastic body 13 is bent and distorted, so this strain is detected by each strain gauge 14 and output. Is.
[0022]
In the example of the sensor unit 12 shown in FIG. 4B, a curved elastic body 15 having a protrusion on the surface opposite to the object gripping unit, a transparent optical waveguide 16, and a photodetection unit 17 such as a CCD are sandwiched. It is the sensor part 12 comprised by arranging and arranging. When the curved elastic body 15 undergoes shear deformation, the protrusion undergoes some deformation, so that the shape of the contact portion between the protrusion and the optical waveguide 16 changes. When light is passed through the optical waveguide 16 and viewed from the detection unit 17, the portion where the optical waveguide 16 and the projection are in contact appears diffusely reflected and appears bright, so that the shape of the projection contact portion can be grasped by image processing. . From this image information, the distribution of the shear strain rate of the curved elastic body 15 or the time differential distribution of the shear stress is detected.
[0023]
FIG. 5 is an explanatory diagram of a strain state when the curved elastic body 13 (15) of the sensor unit 12 described above is pressed against the object W and only the normal force Fn is applied, and when the tangential force Ft is also applied. .
[0024]
The left side of FIG. 5 is a diagram when only normal force Fn is applied, and the right side is a diagram when normal force Fn and tangential force Ft are applied. The vicinity of the contact surface of the curved elastic body 13 (15) with the object W is considered to be divided into 10 squares when only the normal force Fn is applied and deformed. In the figure on the left side where only the normal force Fn is applied, the contact points 1 to 11 of the curved elastic body 13 (15) with the square object W are fixed (fixed) to the object W. Therefore, when the tangential force Ft is also added upward as shown in the right figure, the curved elastic body 13 (15) is subjected to shear strain, so that the square is shear-deformed into a rhombus.
[0025]
If this point is examined in detail, the shearing force applied to the end portions (points 1 to 3 and points 9 to 11 in FIG. 5) of the curved elastic body 13 (15) to the object W is maximum static. Since the frictional force is exceeded, the contact point with the object W is slipping. However, the central portion (points 4 to 8 in the example of FIG. 5) remains fixed because the applied shear force does not exceed the maximum static friction force. As a result, the square of the fixed part becomes a rhombus and has a similar shape. The sliding part has a shape close to a square as much as it slides from the rhombus of the fixed part.
[0026]
As can be seen by comparing the left side and the right side in FIG. 5, in the contact region between the curved elastic body 13 (15) and the object W, the portion where the end portion slips (the points 1 to 1 in FIG. 5). 3 and points 9 to 11) indicate that the shear strain is small and the portion where the contact surface is fixed to the object without slipping in the center (points 4 to 8 in the example of FIG. 5) has a large amount of shear strain. ing. That is, the change rate of the shear strain is small at the end and large at the center. This means that the tangential force (lifting force) Ft is gradually increased and the shear strain change rate is detected. When this value is equal to or greater than the reference value, the curved elastic body 12 (15) and the object W are in contact with each other. It can be assumed that there is no slippage on the surface and is fixed, and if it is below the reference value, it can be assumed that slipping has occurred.
[0027]
As described above, the strain of the curved elastic body 13 (15) is detected by the above-described sensor 14 such as a strain gauge, and the distribution of the change in shear strain of the curved elastic body 13 (15) and the shear strain rate are measured. Based on the distribution or the distribution of time differential of shear stress, etc., an amount related to the size of the fixed region between the curved elastic body 13 (15) and the object W is detected, and the hand or It is possible to obtain an object gripping control method in which the force applied to the manipulator or the amount of movement thereof is controlled to squeeze the object or the object can be gripped and lifted with an optimal gripping force without slipping down.
[0028]
That is, since the object W is about to slip down if the fixing region is reduced, the slope of the force increase curve shown in FIG. 1 is set so that the direction of the force vector approaches the normal direction of the contact surface. Decrease (increase normal force Fn increment or decrease tangential force Ft increment). On the contrary, if the sticking area becomes large, the normal force may be too large and the object W may be crushed. Therefore, the inclination of the force increase curve so that the direction of the force vector is far from the normal direction of the contact surface. May be increased (decrease the increment of the normal force Fn or increase the increment of the tangential force Ft). By performing such force control, an object whose weight and friction coefficient are unknown can be easily grasped and lifted without being crushed and slipped.
[0029]
Since the object W is gripped by the curved elastic body 13 (15), and the object W is gripped and lifted by the elastic force, the force and reaction force applied to the object W and the curved elastic body 13 (15) are reduced. The normal force Fn and the tangential force (friction force) Ft correspond to the amount of movement of the curved elastic body 13 (15) in the normal direction and the amount of movement in the tangential direction. Therefore, the control of the force increase curve according to the size of the above-described fixing region is performed by the amount of movement of the curved elastic body 13 (15), that is, the amount of movement in the normal direction of the fingers 11a and 11b of the hand 10 Amount), and the amount of movement in the tangential direction (the amount of movement of the finger portion 11 in the vertical direction) can be achieved.
[0030]
FIG. 6 is a principal block diagram of a robot system according to an embodiment to which the object gripping control method described above is applied.
Reference numeral 30 denotes a robot control device. The control device 30 includes a processor 31 for controlling the entire robot system, a memory 32 composed of ROM, RAM, nonvolatile RAM, etc. connected to the processor 31 and a bus 36, various commands and teaching operation programs for the robot. The teaching operation panel 33 with a display device used when teaching, the input / output circuit 34 connected to the sensor provided in the robot, the sensor and actuator of the peripheral device, the servo motor of each axis of the robot, A servo control circuit 35 for controlling the position, speed and force is provided.
[0031]
In the illustrated example, the robot body 20 includes a vertical movement shaft 24 that moves up and down in the vertical direction, a first arm 23 that is provided at the distal end of the vertical movement shaft and pivots about the vertical axis, and a distal end of the first arm 23. 2, a second arm 21 that pivots around a vertical axis, a wrist 22 provided at the tip of the second arm, and a hand 10 is attached to the wrist 22 as shown in FIG. 10 can open and close the fingers 11a and 11b by a servo motor, and can move the finger portion 11 vertically by the servo motor in the vertical direction (gravity direction) perpendicular to the opening and closing direction of the fingers 11a and 11b. .
[0032]
The above-described robot system is almost the same as the conventional robot system, but is different from the conventional robot system in that the hand 10 has a curved elastic body 13 (on the object gripping surfaces of the fingers 11a and 11b as described above. 15) The sensor unit 12 to which the sensor unit 12 is attached is used, a servo motor for opening and closing the fingers 11a and 11b of the hand 10 (hereinafter referred to as a gripping servo motor), and a finger unit 11 for lifting an object. Is controlled by a servo control circuit 35 for an additional axis provided in the robot controller 30, and each strain of the sensor unit 12 provided in the hand 10. A sensor 14 such as a gauge (in this embodiment, a plurality of (in the curved elastic body 13 shown in FIG. Output signal indicating the amount of strain from the sensor using the sensor with embedded (2) strain gauges 14) is detected by the processor 31 of the robot controller via the input / output circuit 34. It is a point. The output signal from the strain gauge 14 is converted into a digital signal by an A / D converter in the input / output circuit 34.
[0033]
FIG. 7 is a flowchart of processing executed by the processor 31 of the robot control device 30 in order to grip and lift the object W.
The robot control device 30 drives and positions each axis of the robot main body to a position where the object W can be gripped by the fingers 11a and 11b of the hand 10, and then starts the processing shown in FIG.
[0034]
First, a movement command in the direction of closing the fingers 11a and 11b at a low speed is output to the gripping servo motor (step S1). The servo control circuit of the gripping servo motor receives this movement command, and based on the feedback signal from the position / velocity detector such as a pulse coder attached to the servo motor, converts the position / velocity and current detector to the feedback signal. Torque (current) control is performed based on this, and drive control of the gripping servo motor is performed. The fingers 11a and 11b move, the fingers 11a and 11b grip the object W via the curved elastic body 12, the curved elastic body 13 of the sensor unit 12 is deformed, and the elastic force becomes a load, and the gripping servo motor. Drive current Ih increases.
[0035]
The processor 31 detects the drive current (feedback current) Ih of the gripping servomotor via the servo control circuit 35, and the current Ih has reached a current value I0 or more corresponding to a predetermined gripping force (normal force). (Step S2), when it reaches, the movement command is stopped (step S3), and the state in which the object W is held by the hand 10 is maintained. Then, the strain amount signal εi output from each strain gauge 14 of the sensor unit 12, 12 is read through the input / output circuit 34 and stored in each register Ri (ε) (step S4). In the present embodiment, each sensor unit 12 has (M / 2) strain gauges 14, and the register Ri (ε) for storing the strain amount εi of each gauge 14 has i = 1 to 1. It is assumed that M of M are provided.
[0036]
Next, “0” is stored in the register P that stores the movement command amount to the gripping servomotor, and the set amount “Δyb” is set to the register Q that stores the movement amount to the lift servomotor. Further, "0" is set in a register R (IL) that stores the drive current value IL of the lift servomotor (step S5). In order to simplify the description, the opening / closing direction of the fingers 11a and 11b of the hand 10 is defined as the X-axis direction, and the lift direction (gravity direction) is defined as the Y-axis direction. Further, as will be described later, the movement command amount in the closing direction of the fingers 11a and 11b is preset with a large amount Δxb and a small amount Δxs, and a large amount Δyb with respect to the lift amount (lifting amount). Each small amount Δys is preset.
[0037]
After performing the process of step S5, the processor 31 executes the processes of step S6 to step S22 every predetermined period Δt.
[0038]
First, the movement amount stored in the register P is output to the gripping servo motor ("0" set in step S5 is output first) (step S6), and then stored in the register Q to the lift servo motor. The amount of movement (initially Δyb set in step S5) is output (step S7), and the lift servomotor is driven. Since the object W is gripped with a predetermined gripping force (normal force) in the processing of steps S1 and S2, even if the lift servomotor is driven to raise the fingers 11a and 11b by a predetermined minute amount Δyb. Even if the slip at the contact surface between the curved elastic body 13 of the sensor and the object W occurs locally, the overall slip phenomenon does not occur.
[0039]
Next, the drive current IL of the lift servomotor is read through the servo control circuit 35 (step S8). After the process of step S7, the lift servomotor is delayed by a predetermined time until the drive current becomes stable. The drive current IL may be read. It is determined whether the value obtained by subtracting the value stored in the register R (IL) from the read drive current IL is equal to or less than the set value β (step S9). Until the object W is lifted, the tangential force (frictional force) Ft increases and the load applied to the lift servomotor also increases, so that the drive current also increases. However, when the object W is lifted, only the gravity mg of the object is applied as a load to the lift servomotor as a tangential force, so that the drive current of the lift servomotor does not change and the detection value of the previous cycle and the detection of the current cycle The difference between the values becomes very small, and is less than the set value β.
[0040]
At first, it exceeds the set value β Ru Then, the process proceeds from step S9 to step S10, and the drive current value IL of the lift servomotor of the current cycle read in step S8 is stored in the register R (IL).
[0041]
Next, the index i specifying the strain gauge 14 of the sensor unit 12 is set to “1” and the counter N is set to “0” (step S11), and the strain amount εi output from the strain gauge 14i is input / output. Reading is performed via the circuit 34 (step S12). Then, the value of the register Ri (ε) (initially stored in step S4) is subtracted from the read strain amount εi, and the value is divided by the period Δt to obtain the strain rate change rate (Δεi / Δt). (Step S13).
[0042]
Thereafter, the strain amount εi of the strain gauge 14i read in step S12 is stored in the register Ri (ε) (step S14), and the strain change rate (Δεi / Δt) obtained in step S13 exceeds the set value α. Counter N is incremented by "1" (step S16), and if not exceeded, no count up is performed. To Tep S1 Proceed to 7. In step S17, the index i is incremented by “1”, and it is determined whether the value of the index i exceeds the number M of the strain gauges 14 of the sensor units 12 and 12 (step S18). The process from step S12 to step S18 is repeatedly executed until the number M of 14 is exceeded, the change rate (Δεi / Δt) is obtained from the strain amount εi detected by each strain gauge 14i, and this change rate sets the set value α. Counter exceeding number N Count with.
[0043]
When the value of the index i exceeds the number M of the strain gauges 14, the process proceeds to step S 19, where it is determined whether the value of the counter N exceeds the set reference value Nα, and if it exceeds, the fingers 11 a and 11 b are driven. The smaller set value Δxs is stored in the register P that stores the movement amount to the gripping servomotor, and the larger set value Δyb is stored in the register Q that stores the movement amount to the lift servomotor ( Step S20).
[0044]
When the value of the counter N does not exceed the set reference value Nα, it is determined whether the value of the counter N is smaller than the set reference value Nα (step S21). The value of Q is not changed, and when it is small, the larger setting value Δxb is stored in the register P, and the smaller setting value Δys is stored in the register Q (step S22), and the processing of the processing cycle is finished. . Thereafter, the processes in and after step S6 are repeatedly executed for each cycle. In the process of FIG. 7, the process after step S6 is a process for every predetermined period Δt, but for the sake of simplicity, the process returns from step S22 to step S6.
[0045]
As described above, the minute movement amount commands stored in the registers P and Q are output to the gripping servo motor and the lift servo motor every predetermined period Δt (steps S6 and S7), and the gripping force (method) on the object W is calculated. The linear force Fn) increases and the tangential force (lifting force and corresponding to frictional force) also increases. Then, the strain rate (Δεi / Δt) at the position where each strain gauge 14 is arranged is obtained from the output of each strain gauge 14 detected in the previous period and the present period. The counter N counts the number at which the strain rate exceeds a predetermined reference value α (steps S12 to S18).
[0046]
That is, as described above, the portion where the slip occurs on the contact surface between the object W and the curved elastic body 13 of the sensor 12 has little change in the strain amount in the previous cycle and the current cycle, so the change rate of the strain amount (Δεi / Δt) is small and does not exceed the set reference value α. However, since the portion where the contact surface between the object W and the curved elastic body of the sensor is fixed does not slip, the lift servomotor increases the strain corresponding to the movement of the fingers 11a and 11b. . For this reason, the strain rate change rate (Δεi / Δt) exceeds the set reference value α. This is counted by the counter N. As a result, the value of the counter N indicates the size of the area where the contact surface between the object W and the curved elastic body of the sensor is fixed.
[0047]
When the value of the counter N exceeds the set reference value Nα, the size of the fixing region is larger than the size corresponding to the set reference value Nα, and the normal force Fn is larger than the tangential force Ft. Show. Furthermore, if the normal force Fn and the tangential force Ft are increased at an increasing rate, an excessive normal force Fn may be applied to the object, and the object may be crushed. Therefore, in this case, the movement command amount to the gripping servomotor is set to the smaller amount Δxs, and the movement command amount to the lift servomotor is set to the larger amount Δyb, The inclination of the force increase curve shown in FIG. 1 is increased (step S20).
[0048]
On the other hand, when the value of the counter N does not exceed the set reference value Nα, it indicates that the size of the fixing region is smaller than the size corresponding to the set reference value Nα, and the normal force Fn is smaller than the tangential force Ft. ing. When the normal force Fn and the tangential force Ft are increased at an increasing rate, the normal force Fn Is Since it is relatively small with respect to the tangential force Ft, there is a possibility that the entire surface slips on the contact surface between the object W and the curved elastic body 13 of the sensor, and the object W slips. Therefore, in this case, the movement command amount to the gripping servo motor is set as the larger amount Δxb, and the movement command amount to the lift servo motor is set as the larger amount Δys. The inclination of the force increase curve shown in FIG. 1 is reduced (step S22).
[0049]
In addition, when the value of the counter N is equal to the set reference value Nα, the increasing ratio of the normal force Fn and the tangential force Ft is the optimum state in the current state, so that the values of the registers P and Q are not changed. Using the values used in the previous cycle, the gripping servo motor and the lift servo motor are driven without changing the inclination of the force increase curve.
[0050]
The above-described reference values α and Nα are obtained by setting optimum values through experiments or simulations.
[0051]
After the processes from step S6 to step S22 are repeatedly executed every predetermined period Δt and the object W is lifted, the load applied to the lift servomotor is the weight W of the object W and does not change. The torque for the motor to lift the object W and hold the position, that is, the drive current value IL is not changed. Therefore, in step S9, the difference between the drive current value IL of the lift servomotor detected in the current cycle and the drive current value (value stored in the register R (IL)) of the lift servomotor detected in the previous cycle is calculated. If it is less than or equal to the set value β, it is determined that the object W has been lifted, and this process ends.
[0052]
In the above embodiment, the strain change rate (Δεi / Δt) is obtained in step S13. However, since the predetermined period Δt is constant, the strain change amount Δεi may be obtained. In this case, the determination in step S15 is Δεi> α · Δt = set value.
[0053]
Instead of the strain change rate, the strain change Δεi is divided by the lift amount Δyb or Δys in the cycle to obtain the ratio of the strain change amount to the increase in the tangential force Ft, or the strain change amount Δεi is calculated. Dividing by the movement amount Δxb or Δxs of the fingers 11a and 11b in the period, the ratio of the strain change amount to the increase amount of the normal force tangential force Fn is obtained, and the size of the fixing region is determined by the magnitude of these ratios. You may make it do.
[0054]
In the above embodiment, in order to change the inclination of the force increase curve, the movement amount and lift amount of the fingers 11a and 11b are set to Δxb, Δxa, Δyb, Δys and large and small amounts to increase the force. The slope of the curve is controlled, but one of the values may be fixed, and the other may be set to two values, large and small, to control the slope of the force increase curve. For example, the lift amount is fixed to Δy, the movement amount in the gripping direction of the fingers 11a and 11b is set to a small movement amount Δxs in step S20, and the large movement amount Δxb is set in step S22. Thereby, the inclination of the force increase curve is increased by the setting in step S20, and the inclination is decreased by the setting in step S22. Similarly, the movement amount Δx of the fingers 11a and 11b may be fixed, the lift amount may be changed to Δyb and Δys, and the slope of the force increase curve may be adjusted.
[0055]
Moreover, although the sensor which measures the amount of distortion was used as a sensor, even if it uses the sensor which measures a shearing strain, this invention is applicable.
[0056]
Further, in the above embodiment, the normal force Fn and the tangential force (friction force) Ft of the force and reaction force applied to the object W and the curved elastic body 13 are the amount of movement of the curved elastic body 13 in the normal direction, the tangent In order to correspond to the amount of movement in the direction, the control of the force increase curve according to the size of the fixing region is performed by the amount of movement of the curved elastic body 13, that is, the amount of movement in the normal direction of the fingers 11a and 11b of the hand 10 The amount of movement in the direction), and the amount of movement in the tangential direction (the amount of movement of the finger portion 11 in the vertical direction) were controlled. Naturally, the normal force Fn and the tangential force Ft may be directly controlled instead of controlling the movement amount.
[0057]
In this case, the parameter for determining the size of the fixed region may be the strain change rate (Δεi / Δt) obtained by dividing the strain change Δεi by the time Δt as described above. Is obtained by dividing the change amount Δεi by the normal force increase amount ΔFn or the tangential force increase amount ΔFt in the period, step S1 3 In place of the strain change rate (Δεi / Δt), the ratio of the strain change to the normal force increase (Δεi / ΔFn), or the ratio of the strain change to the tangential force increase (Δεi / ΔFt) is obtained, and the same process as in step S14 and subsequent steps is performed to determine the size of the fixed region.
[0058]
Further, in this case, when gripping an object to the gripping servo motor and the lift servo motor, a force command of normal force Fn and tangential force Ft is given, and the drive current of each servo motor is detected. Based on the feedback signal from the current detector, switching to force feedback control is performed, and the normal force Fn and tangential force Ft are adjusted in the same manner as the algorithm shown in FIG. It is controlled so that the object can be lifted without being crushed and without sliding down.
[0059]
Further, one of the gripping servo motor and the lift servo motor may be a position control and the other may be a force control. For example, the lift servomotor is moved by a predetermined amount every predetermined cycle as the position control, and the gripping servomotor is controlled by force, and the normal force is increased while adjusting the magnitude every predetermined cycle. do it.
[0060]
Further, in the above embodiment, the gripping servo motor and the lift servo motor are used as the fingers 11a and 11b and the actuator for driving the finger portion 11, but other fluid cylinders such as a hydraulic cylinder and a pneumatic cylinder are used. An actuator may be used. When using a fluid cylinder, it is better to control the inclination of the force increase curve by force control. Furthermore, other actuators such as an ultrasonic motor and a polymer gel actuator may be used.
[0061]
In the above-described embodiment, an example in which the gripping servo motor and the lift servo motor, which are actuators of the hand, are controlled by the robot control device 30 has been described. However, the hand itself includes a control device, and the robot control device 30 When a gripping / lifting command is issued to the hand control device, the processor of the hand control device may perform processing shown in FIG. 7 to perform gripping / lifting control of the object.
[0062]
【The invention's effect】
In the present invention, an object having an unknown weight and coefficient of friction can be gripped, and the object can be lifted without being crushed or slipped, and the gripping position does not change. It is possible to carry and position at a proper position.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a force increase curve when an object is gripped and lifted.
FIG. 2 is an explanatory diagram of a hand according to an embodiment of the present invention.
FIG. 3 is an explanatory view of a curved elastic body of a sensor attached to a finger tip of a hand.
FIG. 4 is an explanatory diagram of a sensor structure.
FIG. 5 is an explanatory diagram of a phenomenon of slipping and sticking on a contact surface between an object and a curved elastic body.
FIG. 6 is a schematic explanatory diagram of a robot system according to an embodiment of the present invention.
FIG. 7 is a flowchart of an object gripping and lifting operation process executed by the processor of the robot control apparatus according to the embodiment;
[Explanation of symbols]
10 hands
11 Finger part
11a, 11b Finger
12 Sensor part
W object
14 Strain gauge (sensor)

Claims (5)

  An object gripping control method by a robot hand or a manipulator having a finger having a curved elastic body arranged in a plurality of sensors in the object gripping surface, and gripping and lifting an object by the finger, The size of the fixed area between the curved elastic body and the object is obtained by the shear strain or shear stress of the curved elastic body obtained from each sensor at predetermined intervals, and the finger is determined by the size of the fixed area. An object gripping control method using a hand or a manipulator, characterized by controlling a gripping force and a lifting force caused by a hand.   2. The object gripping control method using a hand or a manipulator according to claim 1, wherein the gripping force and the lifting force are controlled by controlling a movement amount of the finger in the object gripping direction and a movement amount in the direction of lifting the object. The sensor is a sensor for detecting the shear strain of a curved elastic body, and the amount of change in each shear strain in the predetermined cycle is divided by the predetermined cycle from the shear strain of the curved elastic body obtained from each sensor. strain rate of change in the set, the value divided by the increment of the object lifting force of the variation of each shear strain in the predetermined period at a predetermined period set, the shear strain variation of the predetermined in the predetermined cycle A set of values divided by the amount of increase in the object gripping force in a cycle, a set of values obtained by dividing the amount of change in each shear strain in the predetermined cycle by the increase in displacement in the object lifting direction in the predetermined cycle , the predetermined cycle obtains one set of pairs divided by the increase in the object gripping direction displacement at the predetermined cycle variation of the shear strain at, although more than a predetermined value among the set of values the calculated Depending on whether the number exceeds the reference value Discriminated, object grasping control method according to claim 1 or hand or manipulator of claim 2, wherein controlling the gripping force and lifting force by the finger based on 該判 by results of. The sensor is a sensor for detecting the shear stress of the curved elastic body, and the amount of change in each shear stress in the predetermined period is divided by the predetermined period from the shear stress of the curved elastic body obtained from each sensor. the time derivative of the set of shear stress, the object lifting force divided by the amount of increase in the predetermined period the amount of change in the shear stress at a predetermined period set, the variation of the shear stress at the predetermined cycle said predetermined set of values divided by the increment of object grasping force at periodic set of objects lifted divided by the amount of increase in the direction displacement at the predetermined cycle an amount of change in the shear stress at the predetermined cycle, the the variation of the shear stress at a predetermined period determined either set of pairs divided by the increment of the object gripping direction displacement at the predetermined period exceeds a predetermined value among the set of values the calculated Determining the size of the fixed area based on whether the number of objects exceeds the reference value Claim 1 or claim 2 object grasping control method by the hand or manipulator according to control clamping force and the lifting force by the finger based on 該判 by results. The number of those exceeding the predetermined value among the set values, increases the increment of the predetermined period for each of the force vector exerted toward the object by the finger when it becomes smaller than the reference value, on the contrary, the reference value 5. The object gripping control method using a hand or a manipulator according to claim 3 or 4, wherein the force applied to the finger is controlled so as to decrease the increment of the force vector for each predetermined period when the force vector becomes larger.

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