JPH0211395B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a control method for a cylindrical component gripping device, and particularly to a control method for a cylindrical component gripping device, particularly for controlling the position and position of cylindrical components stacked in bulk in a box.
The present invention relates to a method of controlling a cylindrical component gripping device that grips a cylindrical component placed in an undetermined posture.

[Prior Art] Conventionally, a cylindrical part gripping device that grips cylindrical parts whose position and orientation are not fixed, such as cylindrical parts stacked in bulk in a box, has been used to grasp cylindrical parts using a television camera and an image processing device. There was a part that recognized the position and orientation of the part and was grasped by an industrial robot.

[Problem that the invention seeks to solve]

Conventional cylindrical component gripping devices such as those described above are expensive, and the reflectance varies depending on the surface condition of the cylindrical component, resulting in poor detection accuracy of the position and orientation of the cylindrical component, resulting in failure to detect the component. There was a problem.

The present invention was made to solve this problem, and an object of the present invention is to provide a method for controlling a cylindrical component gripping device that can reliably grip a cylindrical component.

[Means for solving problems]

A method for controlling a cylindrical component gripping device according to the present invention includes a hand having a pair of fingers each having a three-component force detector and a drive unit that moves the fingers in opposition, and a positioning device that changes the position and posture of the hand. and a control device that processes the output from the three-component force detector to control the hand and the positioning device. A first step of bringing one of the fingers into contact with the cylindrical part with a finger interval narrower than the diameter of the part, and the finger comes into contact with a line extending from the axis of the cylindrical part in the direction in which the hand approaches. The angle θ1 formed between the point where the cylindrical part and the axis of the cylindrical part are drawn is determined by the direction of the contact reaction force vector output from the three-component force detector, and the angle θ1 is determined by the angle θ1, which is larger than the friction angle between the finger and the cylindrical part. The magnitude is compared with the reference angle θc to determine whether the angle θ1 of the contact portion of the finger is less than or equal to the angle θc, and the position and posture of the hand are determined based on the contact reaction force vector output from the three-component force detector. Based on the two-way components,
a second step of determining whether the outer side of the finger is in contact with a portion where the angle θ1 is larger than the angle θc, and the case where the inner side of the finger is in contact with a portion where the angle θ1 is larger than the angle θc; Based on the second stage judgment,
If the finger is in contact with a portion where the angle θ1 is less than or equal to the angle θc, and if the outside of the finger is in contact with a portion where the angle θ1 is greater than the angle θc, the finger is in contact with a portion where the angle θ1 is greater than the angle θc. a third step in which the hand is moved by the positioning device so that the inside of the fingers are in contact with each other; and the first to third steps result in the positioning of the inside of the finger in a portion where the angle θ1 is larger than the angle θc. a fourth step of determining the relative posture of the hand to the axial direction of the cylindrical component and the outer periphery position of the cylindrical component in contact with the finger from the direction of the contact reaction force vector obtained when the finger is in contact with the cylindrical component; It is characterized in that the operation of the fifth step of correcting the position and posture of the hand and grasping the hand is performed sequentially.

[Effect]

In this invention, in the first step, one of the fingers of a pair is brought into contact with the cylindrical component from a direction substantially perpendicular to the axis of the cylindrical component at an interval narrower than the diameter of the cylindrical component, and then in the second step Then, the angle θ1 between the line extended from the axis of the cylindrical part in the direction in which the hand approaches and the line drawn from the point where the finger is in contact with the axis of the cylindrical part is determined by the three-component force detector. Determined from the direction of the contact reaction force vector to be output, and compared with a predetermined reference angle θc, which is slightly larger due to the friction angle between the finger and the cylindrical part, it is determined whether the angle θ1 is in contact with a portion less than the angle _θc . _{The position and posture state of the hand, such as whether the outside of the finger is in contact with a portion where angle θ 1 is} larger than angle _{θ c or} the inside of the finger is in contact with a portion where angle θ 1 is larger than angle θ c. Judgment is made based on the two-directional components of the contact reaction force vector output from the three-component force detector, and then in the third step, if the finger is in contact with a portion where the angle θ ₁ is less than or equal to the angle θ _c and the angle When the outside of the finger is in contact with a portion where θ ₁ is larger than the angle θ _c , the hand is positioned so that the inside of the finger is in contact with a portion where the angle θ ₁ is larger than the angle θ c. Then, in the fourth step, the direction of the contact reaction force vector obtained when the inside of the finger is in contact with the part where the angle θ ₁ is larger than the angle θ _c in the first to third steps. The position of the cylindrical part that the fingers are in contact with and the relative posture of the hand are determined from the cylindrical part, and in the fifth step, the position and posture of the hand are corrected according to the cylindrical part, and gripping operations are sequentially performed. With this, the cylindrical part can be reliably gripped with the pair of fingers.

〔Example〕

FIG. 1 is a schematic diagram of a cylindrical component gripping device to which the control method of the present invention is applied, in which 1 is a cylindrical component to be gripped, 2a and 2b are claw portions that grip the cylindrical component 1, and 3a and 3b are claw portions, respectively. This is a three-component force detector that detects forces in three directions acting on 2a and 2b, and generally, for example, a weight sensor or a load sensor is provided in the X, Y, and Z component directions, and Thus, the force of each component is detected. 4
a, 4b are a pair of fingers composed of the claw portions 2a, 2b and three-component force detectors 3a, 3b; 5 is a finger drive unit that drives the pair of fingers 4a, 4b in opposition; 6;
Reference numeral 8 indicates a hand consisting of a pair of fingers 4a and 4b and a finger drive unit 5, 7 a robot arm positioning device for changing the position and attitude of the hand 6, and 8 a control device.

This control device 8 includes the three component force detectors 3a and 3b.
An analog multiplexer 10 that sequentially selects analog outputs from the amplifiers _{9 1} to 9n, and an A/D converter 11 that converts the output selected by the analog multiplexer 10 into a digital quantity. , this A/D converter 11
an input circuit 12 that inputs digital quantities from the input circuit 12; a CPU that inputs the output of this input circuit 12 and the output of an auxiliary storage device 13 that stores a program for a control method described later or data from the three component force detectors 3a and 3b; (Central processing unit) 14, this CPU14
A positioning device control circuit 16 that receives commands from the CPU 14 via an output circuit 15 and drives the actuators of each axis of the positioning device 7 according to the commands, and a positioning device control circuit 16 that receives commands from the CPU 14 via an output circuit 15 and drives the actuators of each axis of the positioning device 7 according to the commands. It is composed of a driving hand control circuit 17.

Hereinafter, a control method of the present invention based on the cylindrical component gripping device configured as described above will be explained with reference to FIGS. 2 to 5. For convenience of explanation, the direction in which the hand approaches the cylindrical component 1 with respect to the hand 6 is defined as the z direction, the direction in which the fingers 4a and 4b open and close is defined as the x direction, and the direction perpendicular to the x and z directions is defined as the y direction. do.

First, a first-stage contact operation consisting of steps (22) to (25) in the flowchart shown in FIG. 2 is performed. At step (22), fingers 4a, 4
The interval between the fingers is made narrower than the diameter of the cylindrical part so that the cylindrical part 1 does not pass between the spaces b. In step (23), the hand 6 is moved in the z direction by the minimum movement distance of the positioning device 7, and one of the fingers is brought into contact with the cylindrical part. Next, in step (24), the outputs of the three component force detectors 3a and 3b are read. In step (25), any of the forces in the x, y, and z directions of the fingers 4a and 4b are stored in advance in the auxiliary storage device 1.
If the value is smaller than the value stored in step 3, return to step (23) and repeat steps (23) to (25); if larger, proceed to the next second step.

The second stage is an operation for determining the positional relationship between the fingers 4a and 4b that are in contact with the cylindrical part 1, and consists of steps (26) and (27). As shown in FIG. 3, the step (26) is based on the axis of the cylindrical part 1 and the perpendicular line from the z-direction axis in the approach direction of the hand 6 and the contact position P of the fingers 4a, 4b to the axis of the cylindrical part 1. A comparison is made between the angle θ ₁ and a predetermined angle θ _c stored in the auxiliary storage device 13.

That is, in step (26), the angle θ1
is determined by the direction of the contact reaction force vector output from the three-component force detector, and compared with the predetermined reference angle θc, which is larger than the friction angle between the finger and the cylindrical part, to determine the angle θ1 of the contact portion of the finger. Determine whether or not is less than or equal to the angle θc.

In FIG. 3, when the angle θ ₁ is larger than the friction angle θ _f (≦θ _c ), the resultant force F of the reaction force N in the normal direction and the frictional force μ |N | acts, and the three-component force detector 3 detects forces in the three directions of x, y, and z given by the following equations.

F _x = (|N→|sinθ ₁ −μ|N→|cosθ ₁ ) cosθ ₂ F _y = (|N→|sinθ ₁ −μ|N→|cosθ ₁ ) cosθ ₂ F _z = (|N→| cosθ ₁ +μ|N→|sinθ ₁ (1) μ is the friction coefficient and θ _f = tan ^-1 μ, so x,
From the forces F _x , F _y , and F _z in the three directions of y and z, the attitude angle θ ₂ around the z-axis and θ 1 of the contact point in the x and z directions are given by the following equation.

On the other hand, if the angle θ ₁ is less than the friction angle θ _f , the finger 4a,
No forces in the x and y directions act on 4b, and forces in three directions
Since F _x , F _y , and F _z are given by the following equations, the position and orientation of the cylindrical part 1 cannot be obtained.

F _x =0 F _y =0 F _z = |N→|cosθ _1Also , even if the angle θ ₁ >friction angle θ _f , the θ ₁
If the value of is slightly larger than the θ _f , the position and orientation detection error is large. Therefore, the angle θ ₂ that does not impair the detection accuracy of position and orientation is set in advance, and the magnitudes of the angle θ ₁ and the angle θ _c are compared.
If the angle θ ₁ is larger than the angle θ _c , proceed to step (27).

In step (27), it is determined whether the inner or outer parts of the fingers 4a, 4b are in contact with the cylindrical part 1. That is, in the second step, further in step (27), the angle θ1 is changed to the angle θc based on the two-directional components of the contact reaction force vector output from the three-component force detector to determine the position and posture state of the hand.
It is determined whether the outside of the finger is in contact with a larger portion or the inside of the finger is in contact with a portion where the angle θ1 is larger than the angle θc.

Specifically, as shown in FIG. 6, the three-component force detector 3 is generally capable of detecting the xy2 direction of the contact reaction force vector and the magnitude of the force. When one finger 4a equipped with the force detector 3 contacts the cylindrical component 1 at the contact point P, it is possible to detect from which direction a force is applied to the finger.

For example, if the finger 4a in FIG. 6a receives a force in the closing direction, this means that the outside of the finger is in contact with the finger, and if the finger 4a in FIG. 6b receives a force in the opening direction, It can be understood that this is the case when the inside of the finger touches.

As shown in the figure, the directions of the xy components of the contact reaction force vector acting on fingers a and b are opposite, so the direction of the xy components of the three-component force detector (the contact reaction force vector shown in the figure) is By looking at the force vectors Fx, Fy), it is possible to determine the difference between a and b, that is, whether the inside of the finger 4a or the outside of the finger 4a has contacted the component.

Of course, here, when the pair of fingers 4a and 4b come into contact, the two fingers will have completely opposite different discrimination results, but the distinction between the pair of fingers 4a and 4b is determined by, for example, another control system (not shown). This is done by

As described above, the three-component force detector 3 can detect the contact point position of the finger and the state of the finger on the inside or outside. Note that if the outsides of the fingers 4a and 4b are in contact, the relative positions of the hand 6 and the cylindrical part 1 may differ even if the force is in the same state as shown in FIGS. 4a and 4b. .

Furthermore, if the cylindrical component 1 moves due to the force exerted upon contact, an accurate relative position between the hand 6 and the cylindrical component 1 cannot be obtained.

Therefore, in step (26) of the second stage, the contact state is such that angle θ ₁ is less than angle θ _c , and in step (27), finger 4 is
If it is determined that the outsides of a and 4b are in contact, the third step (28),
Proceed to (29), and move the hand 6 so that the inside of fingers 4a and 4b touch where the angle θ ₁ is larger than the angle θ _c .
Move the position/posture of.

In step (28), if the finger 4a is in contact with the cylindrical part 1 as shown in FIG. Predetermined amount Δx ₁ (＞
2r sinθ _c ).

In step (29), if the finger 4a is in contact with the cylindrical part 1 as shown in FIG. move by a predetermined amount Δx ₂ .

In the next fourth step, the finger makes contact from the direction of the contact reaction force vector obtained when the inside of the finger is in contact with a portion where the angle θ ₁ is larger than the angle θc in the first to third steps. The relative posture of the hand with respect to the outer peripheral position of the cylindrical part and the axial direction of the cylindrical part is determined.

That is, when the inside of the fingers 4a, 4b is in contact with the cylindrical part 1 at a point where the angle θ ₁ is larger than the angle θ _c , check whether the cylindrical part 1 is moving at the time of contact, and then remove the fingers 4a, 4b. This is an operation to calculate the position and orientation of the cylindrical part 1 using the above equation (2) from the state of the force acting on the cylindrical part 1, and steps (30) and (31)
It is made up of

At step (30), at step (27) finger 4a,
After it is determined that the inside of 4b has contacted the cylindrical part 1, the 3-component force detectors 3a, 3 are activated again after a while.
The output of b is taken in, and it is determined whether the cylindrical part 1 has moved due to contact with the hand 6, based on whether any one of the six outputs is greater than a predetermined value. Both outputs are less than the given value,
If it is determined that the cylindrical part 1 has moved due to contact with the hand 6, the process returns to step (23).

If the cylindrical part 1 is not moving, proceed to step (31) and change the cylindrical part 1 from the captured force information.
The position and orientation of are calculated by the CPU 14.

In the fifth step, based on the calculation results of the position and orientation of the cylindrical part 1 obtained in the fourth step,
The distance between a and 4b is made larger than the diameter of the cylindrical part 1, the position and posture of the hand 6 is moved by the positioning device 7 (step (32)), the fingers 4a and 4b are closed (step (33)), and the cylindrical part Complete the grip of 1.

〔Effect of the invention〕

As explained above, this invention detects the position and orientation of a cylindrical part by bringing a finger equipped with a three-component force detector into contact with a place where the position and orientation of the cylindrical part can be detected with high accuracy. This provides the effect that a cylindrical part whose posture is not fixed can be reliably gripped with a pair of fingers.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a cylindrical part gripping device to which this invention is applied, Fig. 2 is a flowchart, and Figs. 3 a, b, and c are states of the force that acts when the fingers of the hand contact the cylindrical part. FIGS. 4a and 4b are explanatory diagrams regarding the relative positions of the hand and the cylindrical part when the outsides of the fingers touch each other. FIGS. 5a and b are explanatory diagrams showing the operation of the hand, and FIGS. b is an explanatory diagram showing the operation of determining the contact state of a finger using a three-component force detector; In the figure, 1 is a cylindrical part, 3a and 3b are three-component force detectors, 4a and 4b are fingers, 6 is a hand, 7 is a positioning device, and 8 is a control device. In addition, in the figure,
The same reference numerals indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. A hand having a pair of fingers each having a 3-component force detector and a drive unit that moves the fingers in opposition, a positioning device that changes the position and posture of the hand, and the 3-component force. A control method for a cylindrical component gripping device comprising a control device that processes output from a detector to control the hand and a positioning device, wherein the cylindrical component is narrower than the diameter of the cylindrical component from a direction substantially perpendicular to the axis of the cylindrical component. a first step of bringing one of the fingers into contact with the cylindrical part at finger intervals; a line extending from the axis of the cylindrical part in the direction in which the hand approaches; and a line extending from the axis of the cylindrical part in the direction in which the hand approaches, The angle θ1 made with the line drawn to the axis of the part is
Obtained from the direction of the contact reaction force vector output by the component force detector, and compared with a predetermined reference angle θc that is larger than the friction angle between the finger and the cylindrical part, the angle θ1 of the contact part of the finger is less than or equal to the angle θc. In addition to determining whether the position and posture of the hand are
Based on the directional component, the outside of the finger is in contact with a portion where the angle θ1 is larger than the angle θc;
a second step of determining whether the inner side of the finger is in contact with a portion where the angle θ1 is greater than the angle θc; and as a result of the determination in the second step, whether the finger is in contact with a portion where the angle θ1 is less than or equal to the angle θc; If the outside of the finger is in contact with the part where the angle θ1 is larger than the angle θc, the hand should be adjusted so that the inside of the finger is in contact with the part where the angle θ1 is larger than the angle θc. a third unit in which the positioning device moves the
and a cylindrical part that the finger is in contact with from the direction of the contact reaction force vector obtained when the inner side of the finger is in contact with a portion where the angle θ1 is larger than the angle θc in the first to third steps. A fourth step in which the relative posture of the hand with respect to the outer circumferential position and the axial direction of the cylindrical part is determined, and a fifth step in which the position and posture of the hand are corrected and gripped according to the cylindrical part are sequentially performed. A method for controlling a cylindrical part gripping device, characterized in that: