JPH0651268B2 - Pressing force control grinding machine - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pressing force control type grinding device, and more particularly to a grinding device in which position and force are controlled, and the pressing force of a grinding tool is always set. The present invention relates to a pressing force control type grinding device which is controlled to a desired value.

[Conventional technology]

Conventionally, in an industrial robot, a virtual compliance control method has been proposed in which a work machine having multiple degrees of freedom performs predetermined work by controlling position and force (Japanese Patent Laid-Open No. 62-62-62).
35915, etc.). Generally, in a work machine equipped with this control method, a force sensor is arranged on the wrist portion of the arm, and a work tool is attached via the force sensor. Then, the control device sets control parameters such as a virtual mass, a spring constant, a viscous damping coefficient, etc. that determine the motion characteristics of the tool, the set value, a reference position / posture command supplied from the outside, and force information applied to the tool. A speed command value for the tool is calculated based on information on the actual position and orientation of the tool, and this command value is supplied from the control device to the drive device for the tool via the drive circuit. As a result, the tool moves according to the shape of the work and performs the grinding work. In the virtual compliance control, the spring force according to the deviation is calculated by the deviation between the position where the tool specified by the control device should move and the actual position of the tool, and the virtual spring constant set as a control parameter. Then, this spring force is used as the pressing force of the tool against the work, and a force target command value is given to the tool.
By the above control method realized by software, it is possible to give a tool for performing a grinding operation a motion characteristic as if a true mechanical spring mechanism is attached.

[Problems to be Solved by the Invention]

In a conventional grinding device that operates according to virtual compliance control, by controlling the position and force, it is possible to perform grinding while pressing a tool against a workpiece to some extent. However, according to the control method of the conventional device, a problem such as an uncut portion is generated at the finishing position of the work, and sufficient consideration is given to adjusting the pressing force of the tool according to the scraped amount. Didn't. More specifically, for example, when the spring constant in the direction in which the pressing force is applied to the tool is a fixed value, it is virtually set as the grinding work progresses and the uncut amount decreases. Since the spring element is in a substantially stretched state, the pressing force of the tool is reduced, so that sufficient grinding cannot be performed on the work surface, and uncut residue occurs. In addition, in a grinding machine equipped with a control method that can change the spring constant in the pressing force direction, if the spring constant in the pressing force direction is set to a large value and the amount of scraping on the work surface is large, If an overload condition occurs and the spring constant in the pressing force direction is set to a small value and the amount of scraping on the work surface is small, the load will be insufficient.

An object of the present invention is to provide a position and force feedback loop, and in a grinding device in which a grinding operation is performed under the control of the position and force, the grinding end position is maintained while the pressing force of the grinding tool is maintained at a desired value. It is an object of the present invention to provide a pressing pressure control type grinding device which can be accurately controlled and can grind a ground portion with good accuracy to form an accurate finished surface.

The position and force control method employed in the pressing force control type grinding apparatus according to the present invention can be applied to other multi-degree-of-freedom working machines having similar functions.

[Means for Solving the Problems]

A pressing force control type grinding apparatus according to the present invention includes a force detection unit that detects a force of at least one axis applied to a grinding tool, a position detection unit that detects a position of the grinding tool, a force detection unit and a position detection unit. And a control means for controlling the position and force of the grinding tool using the data of the force and position detected in
In a grinding device that determines a pressing force of a grinding tool on a work by a virtual spring constant set by a control means, a pressing force setting means for setting a pressing force required for grinding work, a finishing position and a position of the work. A grinding deviation calculating means for calculating a grinding deviation at every interval in the moving direction of the grinding tool based on the position data of the grinding tool output by the detecting means,
Based on the output value of the pressing force setting means and the output value of the grinding deviation calculating means, a virtual spring constant is calculated so that the pressing pressure becomes the set value set in the pressing pressure setting means, and this virtual spring constant is used in the control means. And a spring constant calculation setting means for setting.

Whether the pressing pressure control type grinding apparatus according to the present invention takes in the grinding deviation calculated by the grinding deviation calculating means and compares the calculated grinding deviation with a preset deviation reference value to continue the grinding operation. Alternatively, it is characterized by having a determination means for determining whether or not to end.

The pressing force control type grinding apparatus according to the present invention is characterized by having a judging means for judging whether to continue or finish the grinding operation based on the force information output from the force detecting means.

Further, in the pressing force control type grinding apparatus according to the present invention, in each of the above-mentioned constitutions, the grinding deviation calculating means includes an averaging processing means, and the averaging processing means obtains a specific grinding work section at every arbitrary interval. An average value of the plurality of the obtained grinding deviations is obtained, and the grinding deviation of the mean value is used as an output value of the grinding deviation calculating means.

[Action]

In the pressing force control type grinding apparatus according to the present invention, the amount of uncut portion of the portion to be ground is obtained by the grinding deviation calculation means, the virtual spring constant is obtained according to the amount, and the obtained new virtual spring constant value is set in the control means. By doing so, the pressing force of the grinding tool against the work is adjusted to a desired constant pressing force even if the amount of uncut portion of the ground portion changes.

Further, in the pressing force control type grinding apparatus according to the present invention, the judgment means for judging whether or not to continue the grinding work is provided by comparing the grinding deviation with the deviation reference value or by the force information output from the force detecting means. The grinding work can be automated, and the efficiency and finishing accuracy of the grinding work can be improved.

In the pressing force control type grinding apparatus according to the present invention, the virtual spring constant is obtained by using the average value of the grinding deviations obtained by the averaging processing means, and the stable value of the stable value for generating the desired pressing pressure is obtained for the specific grinding work section. A virtual spring constant can be obtained.

〔Example〕

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows the overall configuration of a pressing force control type grinding apparatus according to the present invention. In FIG. 1, reference numeral 1 is a main body of a grinding machine, an arm 2 having a plurality of joints is attached to a support base 3,
Due to the movable action of each joint of the arm 2, the arm tip moves to a position required for work, and the posture of the entire arm changes to a posture required for work. A 6-axis force sensor 5 is attached to a wrist portion 4 located at the tip of the arm 2, and a grinding tool 7 as a hand effector for performing a grinding operation on a work 6 is attached to the tip of the force sensor 5. Has been. Reference numeral 8 denotes a controller. The controller 8 has a built-in control means such as a computer, and uses a predetermined arithmetic expression for position and force control and in a predetermined procedure in accordance with a predetermined procedure. It has a function to execute position / force control for. The controller 8 gives a command signal for instructing the operation of the grinding operation to the grinding apparatus main body 1 through the signal line 9 and obtains operation information of the motor or the like from the grinding apparatus main body 1, and also from the force sensor 5 to the grinding tool 7. They are electrically connected to each other so as to capture a detection signal regarding the applied force and moment, that is, the force signal 10. An operator 11 is carried by an operator and is operated at a proper time as necessary, and is provided with a ten key and a plurality of operation switches capable of giving various commands to the controller 8. When the operator operates various operation switches of the operation unit 11, for example, teaching of work operation, setting of work conditions, setting of pressing force of the grinding tool 7 as described later, reference value of grinding deviation with respect to finishing position Can be set.

Next, a specific configuration of the control mechanism according to the present invention realized by the controller 8 will be described based on the block diagram of FIG. The control method of the present invention applied to the grinding apparatus main body 1 is realized by software or by another hardware circuit using a computer or the like included in the controller 8, and FIG. 2 shows control elements. The block diagram is shown to clarify the structure.

In FIG. 2, a plurality of drive motors (not shown) for moving the joints and the like of the arm 2 are built in the grinding apparatus main body 1. An angle meter 21 for measuring the amount of driving is attached to each of these drive motors, and the axis angle data of each joint can be obtained by this angle meter 21.

First, the configuration of the position / force control calculation system will be described. The force and moment signals output from the force sensor 5 disposed at the tip of the arm are sent to the force calculator 22.
In step 2, the sensor coordinate system is converted to the reference coordinate system (absolute coordinate system), and the force at the contact point between the work and the grinding tool 7 is reduced by performing gravity compensation by subtracting the gravity of the grinding tool 7. To calculate. Further, the angle data of each axis detected by the above-described angle meter 21 is sent to the position calculation unit 23, and the position calculation unit 23 uses the angle data to determine the position and orientation of the grinding tool 7 in the absolute coordinate system. Is calculated. And this position and posture Is the target value of the position set by the position target value setting unit 24. Is compared with the position deviation calculator 25, and the position deviation Δ Is required. The method of setting the position target value in the position target value setting unit 24 will be described later in detail.
As described above, the force obtained by the force calculator 22 And position deviation relating to the position and orientation obtained by the position deviation calculator 25 Are input to the position / force control calculation unit 26, respectively.

The position / force control calculation unit 26 includes a subtractor 27, a spring constant calculation unit 28, and a characteristic compensation calculation unit 29. Output of the force calculation unit 22 Is given to the subtractor 27, and the position deviation obtained by the position deviation calculator 25 Is input to the spring constant calculator 28. Spring constant calculator 2
In 8, the virtual spring constant matrix K is set. The spring constant calculation unit 28 uses the input position deviation By multiplying the virtual spring constant matrix K set to To calculate. In this embodiment, the value of each axis of the spring constant matrix K is not a fixed value, but can be changed to an appropriate value if necessary. The virtual spring constant in the direction in which the grinding tool 7 is pressed against the work 6 is calculated by the spring constant calculation setting unit 30 as described later. Output of spring constant calculator 28 Is given to the subtractor 27. In the subtractor 27, Is calculated, and the calculation result of the subtracter 27 is given to the characteristic compensation calculation unit 29. The controller gain Kc is set in the characteristic compensation calculation unit 29, and is input by this Kc. Receives the characteristic compensation in the control, and the characteristic compensation calculation unit 29 makes the speed command value. Is calculated. In this way, the position / force control calculation unit 26
Speed command value obtained by Is supplied to the drive command unit 31, and the drive command unit 31 outputs the speed command value. Is the drive command value for each drive motor of the grinding machine body 1. Is converted to. Converted drive command value Is supplied to each drive motor of the grinding apparatus main body 1, and the motor operates according to the command value.

Next, the spring constant calculation setting unit 30 having a function of changing the spring constant value of the spring constant matrix K of the spring constant calculation unit 28 in the pressing force direction will be described. Spring constant calculation setting unit 30
Is a control system circuit part for sequentially calculating, changing and setting the virtual spring constant in the pressing force direction by the grinding tool set by the spring constant calculating part 28. The configuration of the spring constant calculation setting unit 30 and the method of calculating the virtual spring constant by the configuration will be described below.

In the spring constant calculation setting unit 30, when the grinding apparatus main body 1 applies a pressing force to the work 6 with the grinding tool 7, the virtual spring constant in the direction of the pressing force is set to the grinding finishing position of the work 6 and the currently processed work. The feature (6) is that the difference (distance) with respect to the grinding position 6, that is, the difference (6), is changed according to the uncut amount with respect to the finishing position.

Reference numeral 32 is a pushing pressure setting unit, and a desired pushing pressure Fgr is set in the pushing pressure setting unit 32 by the operator operating the operating device 11. The desired pressing force Fgr refers to the pressing force with which the grinding tool 7 can exert its maximum capacity in the grinding operation by the grinding apparatus body 1, or the optimum pressing force determined based on the material of the workpiece 6 and the like. means. This pressing force Fgr is maintained at a constant value during the grinding operation. The pressing force Fgr set in the pressing force setting unit 32 is given to the spring constant calculating unit 33.

On the other hand, during the grinding work, the data regarding the position of the grinding tool 7 obtained by the position calculation unit 23 is obtained by the position extraction unit 3
In 4, the data is extracted at an arbitrary interval, for example, a predetermined distance interval. The position data of the grinding tool 7 extracted by the position extraction unit 34 is supplied to the finishing position calculation unit 35 and the grinding deviation calculation unit 36. The finishing position calculator 35 calculates the finishing position of the work 6 based on the position data of the grinding tool extracted by the position extractor 34. As this finishing position, the finishing position set at the start of the work may be used. Further, it is also possible to use the already set finishing position and then apply interpolation calculation to newly calculate the finishing position. Then, the grinding deviation calculation unit 36 performs grinding in the direction in which the pressing pressure is applied, based on the current grinding position of the grinding tool 7 extracted by the position extraction unit 34 and the finishing position obtained by the finishing position calculation unit 35. The deviation is calculated and sent to the storage unit 37 in the next stage and stored therein. The above grinding deviation is represented as Δhi (i = 1, 2, 3, ...). This grinding deviation is obtained for each of the above-mentioned arbitrary distance intervals.

38 is an averaging processing unit, and this averaging processing unit 38
After completion of a series of grinding operations, for example, after one grinding operation is completed for a designated grinding section, all grinding deviations in the section calculated at every arbitrary distance interval and stored in the storage unit 37. The average value Δh of them is calculated based on the value of Δhi. As a method of obtaining the average value in this case, for example, a well-known arithmetic average is used. In this way, the average value Δh of the grinding deviation in the specific grinding section calculated by the averaging processing unit 38 is the spring constant calculating unit 33.
Is given to the end determination unit 39 described later.

The spring constant calculation unit 33 uses the desired pressing force Fgr and the average value Δh to use the spring constant Kn for applying the desired pressing force Fgr from the grinding tool 7 to the work 6.
To calculate. This calculation formula is as follows.

Kn = Fgr / Δh The spring constant Kn thus obtained is set in the virtual spring constant setting unit 40, and the set value is given to the spring constant calculating unit 28 of the position / force control calculating unit 26. Thus, the spring constant value in the pressing force direction of the virtual spring constant matrix K of the spring constant calculator 28 is changed. In this way, every time the grinding operation is completed for the predetermined grinding section, the spring constant in the pressing force direction is set for the grinding operation for the new predetermined section.

Next, the end determination unit 39 will be described. End determination unit 39
Has a function of determining whether the grinding operation should be continued or ended, and includes a comparison determination unit 41 and a deviation reference value setting unit 42 that gives a deviation reference value H to the comparison determination unit 41. In the comparison / determination unit 41, the average value Δh of the grinding deviation from the averaging processing unit 38 and the deviation reference value H from the deviation reference value setting unit 42.
And are input and the two values are compared. Then, the comparison / determination unit 41 outputs a command to end the grinding work when Δh ≦ H, and outputs a command to continue the grinding work when Δh> H. The command for finishing the grinding and the command for continuing the grinding work are sent to the grinding processing operation unit 43 at the next stage. The deviation reference value H set by the deviation reference value setting unit 42 is a value such as a finishing tolerance.

Next, when the grinding process calculation unit 43 receives a command to finish the grinding work from the comparison determination unit 41, the grinding process calculation unit 43 executes a control procedure for ending the grinding work, and when receiving a command to continue the grinding work, the next series of grinding operations is performed. The position target value of the work route for is calculated, and this position target value is given to the position target value setting unit 24 and set here.

FIG. 3 shows an example of a grinding work operation of the grinding apparatus main body 1 based on the pressing pressure control system having the above-mentioned configuration and operation. In FIG. 3, 2 is an arm, 5 is a force sensor, 7 is a grinding tool,
6 is a work. Reference numeral 50 denotes a portion to be ground left uncut on the surface of the work 6, and the grinding tool 7 grinds the portion to be ground 50 to the finishing position C. The grinding section by the grinding tool 7 is a linear section between the taught points A and B, and the z-axis direction (vertical direction in the figure) in FIG. Is the moving direction.
Further, the surface C of the work 6 is a finishing position, and a deviation reference value H for ending the grinding work is set above the finishing position. This deviation reference value H is the deviation reference value setting unit 4
It is set to 2. In such a state, the grinding tool 7
Grinds the portion to be ground 50 from point A to point B, and when the grinding is completed, returns to point A and repeats the same grinding operation. In one grinding operation of moving from point A to point B, the distance between AB is finely divided by Δl. This distance Δl is the above-described arbitrary interval for the position extracting unit 34 to extract the position of the grinding tool 7 at an appropriate interval.

The state of FIG. 3 shows a state in which the grinding tool 7 is moving from point A to point B while performing a grinding operation.
The spring constant in the pressing force direction in this grinding work is set to the value obtained in the grinding work just before this. In this grinding operation, the grinding deviation Δhi is obtained from the teaching point A at every arbitrary distance interval Δl while performing the grinding operation. This Δhi is calculated by the position extraction unit 34 and the finish position calculation unit 3 described above.
5 and the grinding deviation calculation unit 36. The calculated grinding deviation Δhi is stored in the storage unit 37. The storage unit 37 stores all the grinding deviations Δhi calculated between the points A and B. When the grinding work from the teaching point A to the teaching point B is completed, a plurality of grinding deviations Δhi (i = 1, 2, 3 ...
.) By the averaging processing unit 38.
Find h. Using this average value Δh, the spring constant calculation unit 3
3 calculates the virtual spring constant Kn required when applying the pressing force Fgr in the pressing force direction (z-axis direction) in the next grinding work step. The calculated virtual spring constant Kn is given to the virtual spring constant setting unit 40, and the spring constant in the pressing force direction of the spring constant matrix K of the spring constant calculation unit 28 is changed according to the set value. On the other hand, the average value of the above-mentioned grinding deviation Δ
h is sent to the end determination unit 39 and compared with the deviation reference value H by the comparison determination unit 41, and as described above, it is determined whether or not to perform the next grinding operation. When the grinding operation is continued, a predetermined position target value is obtained by the grinding processing calculation unit 43, and this target value is set in the position target value setting unit 24. Based on this action, the normal function of the position / force control calculation unit 26 causes the grinding tool 7 to return to the position of the teaching point A again, and the teaching point B
The grinding operation is started while a desired pressing force Fgr is applied to the work 6 by the newly set spring constant Kn. Also in this grinding operation, similarly to the above, in the spring constant setting unit 30 and the end determination unit 39, the average value of the grinding deviation is calculated, a new virtual spring constant in the pressing direction based on this average value, and the grinding operation. It is determined whether or not to end. In this way, the part to be ground 50 is repeatedly ground until it is determined that the grinding operation is completed. The grinding tool 7 may be moved back and forth between the teaching points A and B for the grinding work.

Next, a second embodiment of the present invention will be described with reference to FIG.
FIG. 4 shows the main structure of the second embodiment. In this embodiment, the average value Δh of the grinding deviations is not calculated, but the virtual spring constants are calculated by the spring constant calculation unit 33 based on the grinding deviations Δhi calculated by the grinding deviation calculation unit 36 at arbitrary intervals. Is configured to calculate. Therefore, in this embodiment, the averaging processing section 38 is omitted, and the value of the grinding deviation Δhi obtained by the grinding deviation calculating section 36 is directly given to the spring constant calculating section 33 and the storage section 37. The subsequent control processing subsequent to the spring constant calculation unit 33 is the same as in the case of the first embodiment. Each grinding deviation Δhi stored in the storage unit 37 is compared with all the Δhi (i = 1, 2, 3 ...) After the series of grinding operations is completed, the comparison determination unit 4
The end judgment is made at 1. At that time, if at least one of the conditions in the grinding path satisfies H <Δhi, it is determined that the grinding operation should be continued. The control process thereafter is the same as that of the first embodiment.

According to the configuration of the present embodiment, the grinding deviation is measured for each arbitrary distance interval Δl, whereby the virtual spring constant in the pressing force direction can be changed and set finely at short distance intervals. Therefore, in this embodiment, the finished surface of the work 6 is an irregular surface, and the desired pressing pressure set in the pressing force setting unit 32 is made uniform with respect to the work in which the grinding deviation changes irregularly. It has the advantage that it can be added.

Next, a third embodiment of the present invention will be described with reference to FIG.
FIG. 5 shows the essential structure of the third embodiment. In this embodiment, it is configured to determine whether the grinding operation is completed or continued based on the force information obtained by the force calculation unit 22 without using the grinding deviation as a value. In the grinding operation, the reaction force obtained from the work 6 that opposes the pressing force applied from the grinding tool 7 to the work 6 is detected by the force sensor 5 and converted into an absolute coordinate system by the force calculator 22. In this case, the grinding tool 7
When reaches the finishing position, the amount to be ground becomes 0,
The reaction force applied from the work 6 to the grinding tool 7 does not occur. Therefore, if the force detected by the force sensor 5 is monitored, it can be determined whether or not the grinding tool 7 has reached the finishing position. Therefore, the force output by the force calculator 22 Is provided with a force extraction unit 60 for inputting a force in the pressing force direction detected by the force sensor 5 at arbitrary intervals in the force extraction unit 60. Extract this power Is supplied to the force determination unit 61. In the force determination unit 61, the reaction force value 0 when the grinding amount given from the force reference value setting unit 62 is 0.
When Compare If the value is greater than 0, it is determined that there is uncut material, and the grinding operation is repeated and the continuation signal is sent to the grinding processing calculation unit 43.

When is smaller than 0, a signal for ending the grinding work is sent to the grinding processing operation unit 43. Other configurations and operations are the same as those of the embodiment shown in FIG. 2 except for the position-based end determination unit 39. Note that the reaction force value set by the force reference value setting unit 62 may be, for example, the value of the reaction force generated in the finish intersection of the work.

In the above embodiment, an example in which the pressing force control method according to the present invention is applied to the grinding device is set, but even if the remaining amount of the processed part changes, the virtual spring constant is changed to make the pressing force a desired constant value. It goes without saying that the control method can be applied to other multi-degree-of-freedom work machines similar to the grinding device.

〔The invention's effect〕

As is apparent from the above description, the present invention has the following effects.

A grinding machine having a position / force control unit is provided with a pressing force setting unit and a spring constant calculation setting unit, and a virtual spring constant is obtained from a grinding deviation so that a desired pressing force can be obtained even when the remaining amount of grinding decreases. With this configuration, it is possible to perform the grinding work with a constant pressing force regardless of the remaining amount of grinding.

Further, since the virtual spring constant increases as the grinding work progresses and the remaining grinding amount decreases, the rigidity equivalent to that of the position control can be finally obtained, and the efficiency of the grinding work and the finishing accuracy can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram of a grinding device to which the present invention is applied, FIG. 2 is a block diagram showing a concrete structure of a pressing force control device, and FIG. 3 is a work explanatory diagram showing a state of grinding work. FIG. 4 is a block diagram of the essential parts showing another modified embodiment of the pressing force control device, and FIG. 5 is a block diagram of the essential parts showing another modified embodiment of the pressing force control device. [Explanation of symbols] 1 ... Grinding machine main body 2 ... Arm 5 ... Force sensor 6 ... Workpiece 7 ... Grinding tool 8 ... Controller 11 ... Manipulator 22 ... Force calculation unit 23 ... Position calculation unit 24: Position target value setting unit 26: Position / force control calculation unit 28: Spring constant calculation unit 30: Spring constant calculation setting unit 32: Push pressure setting unit 33: Spring constant calculation unit 36: Grinding Deviation calculation unit 38 ... Averaging processing unit 39 ... End determination unit 60 ... Force extraction unit

Claims (4)

[Claims] 1. A force detecting means for detecting a force of at least one axis applied to a grinding tool, a position detecting means for detecting a position of the grinding tool, and the force detecting means and the position detecting means respectively. In a grinding device, which comprises a control means for controlling the position and force of the grinding tool using force and position data, and which determines the pressing force of the grinding tool on the workpiece by a virtual spring constant set by the control means, A pressing force setting means for setting a pressing force required for work, an arbitrary moving direction of the grinding tool based on the finish position of the work and the position data of the grinding tool output by the position detecting means. Based on the output value of the pressing pressure setting means and the output value of the grinding deviation calculating means, the pressing pressure is set in the pressing pressure setting means. And a spring constant calculation setting means for calculating the virtual spring constant so as to obtain the set value and setting the virtual spring constant in the control means. 2. The pressing pressure control type grinding apparatus according to claim 1, wherein the grinding deviation calculated by said grinding deviation calculating means is taken in and the calculated grinding deviation is compared with a preset deviation reference value. And a grinding means for judging whether to continue or finish the grinding operation. 3. The pressing force control type grinding apparatus according to claim 1, further comprising a judging means for judging whether to continue or finish the grinding operation based on the force information output from the force detecting means. Characteristic pressing pressure control type grinding machine. 4. The pressing pressure control type grinding apparatus according to any one of claims 1 to 3, wherein the grinding deviation calculating means includes an averaging processing means, and the averaging processing means is used for a specific grinding work section. A pressing force control type grinding apparatus characterized in that an average value of a plurality of grinding deviations obtained at arbitrary intervals is obtained, and the grinding deviation of the average value is used as an output value of the grinding deviation calculating means.