JP7638098B2 - Polishing method, manufacturing method for metal die-cast product, polishing device, computer program and control device - Google Patents

Description

The present invention relates to a polishing method, a manufacturing method for metal die-cast products, a polishing device, a computer program, and a control device.

When forming metals by die casting, reaction inhibitors or fluxes containing calcium, sulfur, etc. are added to suppress oxidation reactions when the metal is melted. In particular, when die casting metals such as magnesium and aluminum, which have a high ionization tendency and are easily oxidized, such reaction inhibitors are added.

However, metal die-cast products formed using this method may have residual deposits or coatings (hereinafter, foreign matter such as deposits and coatings present on the surface of the product will be collectively referred to as "deposits") on the surface due to reactions during molding or added substances. If residual deposits remain, part of the surface of the die-cast product will be covered by the deposits, making it difficult to detect defects such as pinholes by visual inspection. Another problem is that the aesthetic appearance of the metal die-cast product will be impaired.

For this reason, it is preferable to remove the precipitates after die casting. Conventionally, this has been done by workers polishing the surface of metal die castings with polishing materials such as buffs and brushes.

Patent Document 1 describes a grinding device equipped with a robot arm equipped with a belt sander for grinding excess weld beads on welded structures. This grinding device makes it possible to adjust the grinding depth by adjusting the position of the guide plate.

Patent document 2 describes a polishing device for polishing press dies, in which a polishing tool for polishing workpieces is attached to the tip of a robot arm. This polishing device enables polishing with a constant force by feedback controlling the output of a force sensor.

Patent document 3 describes a polishing device for buffing the front grille of an automobile, which issues an offset signal to the robot hand to correct the position when the current value of the motor is below a certain value. This polishing device controls the position of the robot hand so that the current value to the motor is above a certain value, enabling polishing with a force above a certain level.

Japanese Patent Application Publication No. 10-202493 Japanese Patent Application Publication No. 3-149171 Japanese Patent Application Publication No. 6-8130

However, the devices described in each of the patent documents all have specialized configurations for polishing specific workpieces, and the surfaces of the workpieces to be polished are limited to flat surfaces. For this reason, it is difficult for any of the devices to effectively polish complex surfaces with irregularities. In particular, burrs often occur on the edges of molded products, and there is an issue that the shape and size of the burrs are uncertain, making it impossible to deal with cases where the shape of the object to be polished is not constant.

The present invention aims to provide a polishing method, a manufacturing method for metal die-cast products, a polishing device, a computer program, and a control device that can effectively polish even workpieces with complex surfaces.

The present disclosure provides a polishing method that includes a step of polishing the surface of a workpiece by rotating a polishing member held by a robot arm having a flexible drive mechanism.

The present invention also provides a polishing method that includes a step of polishing the surface of a workpiece held by a robot arm having a flexible drive mechanism by following the movement of a rotating polishing member.

Here, "flexible" refers to having elasticity, viscosity, or both elasticity and viscosity. Elasticity refers to the property of being deformed when stress is applied and returning to the original shape when the stress is removed, and is sometimes expressed as flexibility, which indicates the ease of elastic deformation. Viscosity refers to the property of generating stress that makes the flow speed of a fluid uniform. A flexible drive mechanism may be equipped with at least one of the following to impart flexibility: a magnetic fluid, a mechanical spring, an air spring, a magnetic spring, and a vane motor.

"The polishing member" "is made to conform to the surface of the workpiece being polished" and "the surface of the workpiece being polished" "is made to conform to the polishing member" refer to moving the polishing member relative to the surface of the workpiece being polished while keeping the polishing member in contact with the surface of the workpiece being polished. Moving relatively is not limited to translational movement, but also includes relative rotational movement.

The polishing may be performed while maintaining the force acting from the polishing member on the surface of the polished member within a substantially constant range.

Here, "approximately a constant range" includes, for example, a range in which the maximum and minimum values of force within a certain period of time are within ±50% of the average value.

In one aspect of the present disclosure, the polished member is made of a magnesium alloy. The polished member may be a metal die-cast product.

In one aspect of the present disclosure, the polishing member is made of brass.

In one aspect of the present disclosure, the robot arm may have multiple drive shafts, and each of the multiple drive shafts may be equipped with a series elastic actuator as the flexible drive mechanism.

The series elastic actuator includes, for example, a motor and an elastic body such as a spring. The torque output from the motor is transmitted to a rigid link via the elastic body. This makes it easy to bring the polishing member or polishing member held by the robot arm into contact with the polishing member or polished member to conform to the surface of the polishing member. It is preferable to make the polishing member conform to the surface of the polishing member so that the elastic body included in the series elastic actuator is elastically deformed.

In one aspect of the present disclosure, the polishing member is composed of a brush having a plurality of linear bodies. When such a polishing member is rotated, the centrifugal force causes the tips of the linear bristles to spread in a direction perpendicular to the axis of rotation. By making the tip of the polishing member rotate in this manner conform to the surface of the polished member held by the robot arm, it is possible to make the tip of the polishing member reach recesses on the surface. The robot arm may change the position of the polishing member or the polished member so that the extension direction of the polishing member when rotated roughly coincides with the normal line of the surface of the polished member it faces. Changing the position here includes changing the posture. In addition, "the extension direction of the polishing member roughly coincides with the normal line of the surface of the polished member it faces" means that the absolute value of the angle between a straight line approximating the extension direction of the polishing member and the normal line at the position on the surface of the polished member through which the straight line passes is 45 degrees or less.

In one aspect of the present disclosure, the method may further include, after the polishing step, applying a coating material to the surface of the polished member using the robot arm.

In one aspect of the present disclosure, the method may further include a step of setting a path along which the polishing member and the member to be polished interfere with each other, and in the polishing step, the robot arm may move the polishing member or the member to be polished based on the path.

An aspect of the present disclosure provides a method for manufacturing a metal die-cast product, comprising the steps of performing metal die-casting and performing the polishing method on the metal die-cast product formed by the step as the polished member.

In one aspect of the present disclosure, the robot arm may hold a runner portion of the workpiece to be polished and perform the polishing method.

The embodiment of the present disclosure may further include a step of removing flash and runner portions of the metal die-cast product formed by the metal die casting.

One aspect of the present disclosure provides a polishing device that has a flexible drive mechanism, includes a robot arm configured to hold a polishing member, and is configured to polish the surface of a workpiece by rotating the polishing member.

One aspect of the present disclosure provides a polishing device that has a flexible drive mechanism, includes a robot arm configured to hold a member to be polished, and is configured to polish the surface of the member to be polished by following the rotation of a polishing member.

One aspect of the present disclosure provides a control device that controls a robot arm that has a flexible drive mechanism and a holding mechanism capable of holding a polishing member, and is configured to execute a step of polishing the polishing member by rotating the polishing member using the robot arm so that the polishing member conforms to the surface of the member to be polished.

One aspect of the present disclosure provides a control device that controls a robot arm that has a flexible drive mechanism and a holding mechanism capable of holding a member to be polished, and is configured to be capable of executing a step of using the robot arm to polish the surface of the member to be polished by following the rotating polishing member.

One aspect of the present disclosure provides a computer program for generating control instructions for operating a robot arm to execute a step of polishing a workpiece by rotating the polishing member using a robot arm having a flexible drive mechanism and a holding mechanism capable of holding the polishing member, in accordance with the surface of the workpiece. The computer program may be non-temporarily stored in a recording medium such as a semiconductor memory.

One aspect of the present disclosure provides a computer program for generating control instructions for operating a robot arm to execute a step of polishing a surface of a polished member by following the rotating polishing member using a robot arm having a flexible driving mechanism and a holding mechanism capable of holding the polished member. The computer program may be non-temporarily stored in a recording medium such as a semiconductor memory.

FIG. 1 is a diagram showing a schematic diagram of a manufacturing process of a metal die-cast product. FIG. 2 is a schematic diagram showing an example of a robot arm of the polishing apparatus. FIG. 3 is an example of a functional block diagram of the polishing apparatus. FIG. 4 is an example of a flow chart of a manufacturing process for a metal die-cast product. FIG. 5 is a schematic diagram showing an example of a mold used in metal die casting. FIG. 6 is a schematic diagram showing how the tip of the brush polishes the recesses on the surface of the workpiece. FIG. 7 is a graph for explaining the deceleration operation when the allowable range is exceeded during the tracing operation. FIG. 8 is a schematic diagram showing a state in which a workpiece having a convex surface is being polished.

The following describes an embodiment of the present invention with reference to the drawings. The following embodiment is an example for explaining the present invention, and is not intended to limit the present invention to only that embodiment.

Figure 1 is a diagram showing a schematic diagram of a manufacturing process for metal die-cast products, including a polishing method according to this embodiment. Figure 2(A) is a schematic diagram showing an example of a robot arm 20 of a polishing apparatus 100 according to this embodiment. Figure 3 is an example of a functional block diagram of the polishing apparatus 100 according to this embodiment. Figure 4 is an example of a flowchart of a manufacturing process for metal die-cast products. Figure 5 is a schematic diagram showing an example of a mold used in metal die-casting.

Figure 1 shows a workpiece W (an example of a "part to be polished"; hereinafter, simply referred to as a "molded product"), which is a metal die-cast product formed by performing metal die casting, being transported on a conveyor C1. The workpiece W transported to the conveyor C1 is picked up by a robot arm 20, and polished by having the surface of the workpiece W imitate a rotating brush B (an example of a "polishing member"). The robot arm 20 then places the polished workpiece W on the downstream conveyor C2. Burrs and runners remaining on the workpiece W are then removed by a deburring die. Metal die-cast products are manufactured through this process. This is described in detail below.

[Configuration of the polishing apparatus]
The polishing apparatus 100 ( FIG. 3 ) according to this embodiment includes a robot arm 20, a control device 10 that controls the robot arm 20, an imaging device 30 that images a workpiece W, and a teaching device 40. The polishing apparatus 100 according to this embodiment is configured to be capable of polishing the surface of the workpiece W by causing the rotating brush B to follow the surface of the workpiece W held by the robot arm 20.

As shown in FIG. 2(A), the robot arm 20 is, for example, a vertical articulated robot, and includes a base (not shown) fixed to the floor or the like, a plurality of links 20L, joints 20J connecting the links 20L, and a plurality of serial elastic actuators 20D (FIG. 3) for rotationally driving the links 20L at the joints 20J. The robot arm 20 according to this embodiment is a seven-axis vertical articulated robot, and is configured to be able to move the workpiece W held by the tip link 20L by a large amount by extending the links 20L without moving the base. However, the robot arm is not limited to this embodiment, and may be, for example, a horizontal articulated robot device or a parallel link robot device.

The link 20L is made of a rigid member, and includes a plurality of links 20L, including, for example, a link 20L corresponding to a torso rotatably attached to the base, a link 20L corresponding to an upper arm rotatably attached to the torso, a link 20L corresponding to a forearm rotatably attached to the upper arm, and a link 20L corresponding to a hand rotatably attached to the forearm.

The link 20L at the tip of the robot arm 20 is provided with a holding mechanism for holding a workpiece. The holding mechanism can be composed of an end effector 20L1 equipped with a pair of movable plates (sometimes called grippers) that open and close by an actuator. Such an end effector 20L1 is attached to the tip link 20L, and the workpiece W can be held by clamping it with the movable plates or the like. Other holding mechanisms include a configuration equipped with multiple suction pads for holding the workpiece W and an actuator that generates negative pressure on the suction pads based on a control signal transmitted from the control device 10, or, in the case of a workpiece W made of a magnetic material, a configuration equipped with a coil for electromagnetically generating a magnetic field for magnetically holding the workpiece W.

The robot arm 20 according to this embodiment is equipped with multiple series elastic actuators 20D (an example of a "flexible drive mechanism") for rotationally driving each of the multiple links 20L.

The serial elastic actuator 20D is a known drive mechanism also known as an SEA (Serial Elastic Actuator), and an example of an SEA is described, for example, in European Patent No. 2,890,528. The serial elastic actuator 20D is composed of a drive unit 20DA and an elastic body 20DE connected to the drive unit 20DA. The drive unit 20DA is composed, for example, of a servo motor. The elastic body 20DE is composed, for example, of a mechanical spring. In the serial elastic actuator 20D, the power output from the drive unit 20DA is transmitted via the elastic body 20DE to the output side link 20L (however, in the case of the tip link 20L, this includes the workpiece), causing it to rotate.

Furthermore, the series elastic actuator 20D is equipped with multiple sensors, including a sensor for acquiring the magnitude of the load, a sensor for acquiring the amount of displacement of the elastic body 20DE, and a sensor for acquiring the amount of displacement of the servo motor.

The magnitude of the load can be obtained, for example, from a current sensor that acquires the amount of current flowing through the servo motor that constitutes the drive unit 20DA.

The amount of displacement of the elastic body 20DE can be obtained from optical sensors provided at both ends of the elastic body 20DE to obtain the amount of displacement (rotation angle) at both ends of the elastic body 20DE, a magnetic sensor that detects the magnetic field generated by a magnet or the like attached to the elastic body 20DE, or a strain sensor or the like provided on the elastic body 20DE. It is also possible to obtain the torque generated based on the amount of displacement of the elastic body 20DE and the elastic constant of the elastic body 20DE.

As above, the displacement of the servo motor can be obtained from an optical sensor such as an encoder, a magnetic sensor such as a Hall element, or a strain sensor.

With the above configuration, an equation of motion is established with parameters including the inertia, mass, and length of the part driven by the series elastic actuator 20D, which corresponds to a flexible driving mechanism, external force, and the elastic modulus of the mechanical spring, which is the elastic body 20DE. Therefore, the control device 10 is configured to perform mechanical compliance control that controls impedance based on the elastic modulus and displacement amount of the mechanical spring, etc.

The series elastic actuator 20D may be connected to the drive shaft of a servo motor, which is the drive unit 20DA, and may include a gear that transmits power to an elastic body 20DE, such as a mechanical spring. Furthermore, the series elastic actuator 20D may include a damper mechanism that absorbs impact based on viscosity, and a clutch mechanism for switching the transmission of power. When a viscous body, such as a viscous damper mechanism, is added, or when damping caused by friction between gear teeth is added, an equation of motion is established in which a viscosity constant is added as a parameter.

For example, in the case of a series elastic actuator 20D in which a gear is connected to the drive shaft of a servo motor and a load (such as a downstream link) is connected to the output shaft of the gear via an elastic body, the torque generated in the output shaft of the gear is proportional to the current flowing through the servo motor and the gear ratio, and an equation of motion is established in which this torque is equal to the sum of the angular acceleration of the output shaft of the gear multiplied by the inertia, the angular acceleration of the output shaft of the gear multiplied by the viscosity of the gear, and the displacement of the elastic body multiplied by the elastic modulus. By deriving the transfer function of the series elastic actuator 20D based on this equation of motion, mechanical compliance control that controls impedance becomes possible.

The above configuration makes it possible to rotate multiple links 20L of the robot arm 20, making it possible to freely change the position and posture of the workpiece W attached to the tip of the link 20L. Note that the information indicating the position in this disclosure may include information indicating the posture if it is considered reasonably necessary.

The robot arm 20 further includes an input/output unit 20C including a display for transmitting information to and from the user. An imaging device is mounted on the input/output unit 20C for image recognition of the brush B, which is the member to be polished. Image information of the brush B captured by this imaging device is sent to the control device 10. The polishing member information acquisition unit 10F of the control device 10 acquires information indicating the degree of wear and the degree of spread of the brush B by extracting the outline of the brush B based on the image information of the brush B. If the brush B is significantly worn and shortened, the surface of the member to be polished can easily be scratched. Also, if the brush B has spread too much, polishing cannot be performed properly. In such a case, the control device 10 causes the input/output unit 20C to issue a warning indicating that it is time to replace the brush B.

The robot arm 20 may also have a link in part that is driven by a non-elastic drive unit 20A.

The polishing apparatus 100 further includes an imaging device 30 for imaging the workpiece W transported on the conveyor C1 and acquiring information about the workpiece W. The image information of the workpiece W captured by the imaging device 30 is transmitted to the control device 10. The polished member information acquisition unit 10G of the control device 10 identifies the portion held by the robot arm 20 by extracting the contour of the workpiece W based on the image information of the workpiece W. The conveyor C1 may be configured to remain stationary until the workpiece W is imaged by the imaging device 30 and held by the robot arm 20. In addition, when multiple types of workpieces W are transported on the conveyor C1, the polished member information acquisition unit 10G is configured to be able to identify the type of workpiece W based on the image information of the workpiece W.

The control device 10 controls the robot arm 20. As described above, the control device 10 controls the robot arm 20 based on mechanical compliance control using the series elastic actuator 20D, rather than the conventional position control. Therefore, even if the relative positional relationship between the workpiece and the polishing member (brush) changes, it is possible to bring the polishing member into contact with the surface of the workpiece.

For example, in a brush made up of many elongated linear bodies, if the linear bodies become shorter due to wear, the relative positions of the tips of the linear bodies and the workpiece will change when the brush is rotated. In addition, there are individual differences in the shape of burrs and the positions of deposits formed in molded products formed by die casting, which also causes the relative positions of the two to change.

The robot arm of a conventional polishing device has the structural rigidity and servo rigidity as high as possible to improve the accuracy of position and posture control. For this reason, if the positional relationship between the two changes due to wear or burrs on the brush, it is difficult to polish the material appropriately. If the distance between the polished material and the polishing member is too close, the polished material will be damaged, while if the polished material and the polishing member are brought into contact with each other with as little force as possible to suppress damage, the polished material cannot be polished sufficiently, and it is particularly difficult to polish the material while avoiding burrs. The polishing device of this embodiment is capable of bringing the polishing member into contact with the surface of the polished material appropriately even if the relative positional relationship between the polished material and the polishing member changes. This will be described in detail below.

As shown in FIG. 3, the control device 10 includes a start position acquisition unit 10A that acquires the start position and posture at the reference position of the robot arm 20 (for example, the center point of the link 20L or the end effector 20L1 corresponding to the hand position, or the center point on the surface of the workpiece W, etc., hereinafter referred to as the "reference position"); a target position acquisition unit 10B that acquires the target position and the posture at that time; an allowable range acquisition unit 10C; a path acquisition unit 10D that acquires a path connecting the start position and the target position; a control command acquisition unit 10E that acquires control commands for controlling the servo motors corresponding to the drive units 20DA of each series elastic actuator 20D according to the path acquired by the path acquisition unit 10D; a polishing member information acquisition unit 10F that acquires information about the polishing member; a polished member information acquisition unit 10G that acquires information about the workpiece W; and a memory unit 10H that stores information necessary for each process described in this disclosure.

The start position acquisition unit 10A acquires the start position of a series of operations and the posture of the robot arm 20 at that time. For example, the start position acquisition unit 10A acquires the position (including posture) at which holding of the workpiece W starts as the start position. In this case, the start position acquisition unit 10A acquires information indicating the outline of the workpiece W on the conveyor C1 from the polished member information acquisition unit 10G, and based on this, acquires the position (including posture) of the robot arm 20 when holding of the workpiece W starts as the start position. Note that the start position input from a teaching device 40 connectable to the control device 10 and the posture of the robot arm 20 at that time may also be acquired as the start position.

Regarding the portion where the robot arm 20 holds the workpiece W, the manufacturing process for metal die-cast products in this embodiment is specified to execute a process of removing the portion of the workpiece W that includes the runner after executing a polishing process. This manufacturing process makes it possible for the robot arm 20 to hold the portion of the workpiece W that will ultimately be removed and execute the polishing process. Therefore, it becomes possible for the robot arm 20 to polish most of the surface of the product portion of the workpiece W without having to change the workpiece W over.

In particular, the robot arm 20 is configured to hold a portion of the workpiece W that includes a gate runner (hereinafter, may be simply referred to as the "runner portion"). The portion that includes the gate runner is located in a suitable position for spreading molten metal throughout the cavity, and is therefore also suitable as a portion to be held by the robot arm 20.

The target position acquisition unit 10B acquires, for example, the target position and the posture at that time input from the teaching device 40. The target position acquisition unit 10B is capable of acquiring multiple target positions and the postures at that time.

The target position is set to a position and posture that allows the polishing member to optimally polish the workpiece. Specifically, the target position is set so that the polishing member and the workpiece interfere with each other. In this embodiment, the target position is set so that the surface of the workpiece W, which is the workpiece to be polished, is within the area through which the polishing member, the brush B, rotates and passes.

By setting the target position in this manner, the series elastic actuator 20D of the robot arm 20 can demonstrate its flexibility, making it possible to polish the brush B by conforming it to the surface of the workpiece W.

Furthermore, it is preferable to set the target position so that the tip of the linear body of the rotating brush B can reach recesses, gaps, etc. on the surface of the workpiece to be polished even when the tip is worn. Therefore, it is preferable to set the target position so that the surface of the workpiece W, which is the workpiece to be polished, is within the area through which the brush B rotates and passes when it is replaced due to wear or immediately before replacement. By setting the target position in this manner, it is possible to make the tip of the brush B reach recesses, gaps, etc. on the surface of the workpiece to be polished even when the brush B is worn. The position of the tip of the linear body of the brush can be known in advance based on the rotation speed of the brush and the material, shape, mass, etc. of the linear body. Therefore, it is preferable to determine the target position based on the rotation speed, material, shape, mass, etc. of the workpiece to be polished.

In addition, if the extension direction of the linear body of brush B becomes parallel to the surface of the workpiece facing the linear body, it becomes difficult to polish the surface of the workpiece appropriately. For this reason, it is preferable to set the target position (including posture) so that the extension direction of the linear body, which is the polishing member, when brush B is rotated, roughly coincides with the normal to the surface of the workpiece W facing it. For example, when the tip of brush B faces vertically, it is preferable to set the target position so that the surface of the opposing workpiece W faces roughly upward. If the extension direction of the linear body is tilted due to rotation, the surface of the workpiece W may be tilted taking this into consideration.

As described later, even at positions on the path connecting adjacent target positions, the position and posture of the workpiece W can be set so that the extension direction of the linear body, which is the polishing member, roughly coincides with the normal line of the surface of the workpiece W facing it, making it possible to suitably polish the surface of the workpiece W while making the brush B conform to the surface of the workpiece W. In this way, by setting the position of the robot arm 20 on the path connecting the target positions, it becomes possible to suitably polish complex surfaces with unevenness.

By setting the target position in this manner and polishing a workpiece W having a complex surface, the position and posture of the workpiece W is frequently changed by the robot arm 20 while it is polished, demonstrating the unique operation of the polishing method according to this embodiment.

The allowable range acquisition unit 10C acquires information indicating the allowable range within which the actual reference position of the robot arm 20 can deviate from the path, based on the path of the reference position. For example, when the angle of the link 20L driven by the series elastic actuator 20D is α when the reference position of the robot arm 20 reaches a certain target position, information indicating the allowable range of the link 20L is acquired as angle information, for example, α±β. β is information in angle units that can be set in advance as the range of elastic deformation based on the elastic modulus of the elastic body 20DE of the series elastic actuator 20D. When the robot arm 20 is equipped with multiple series elastic actuators 20D to have flexibility in multiple directions, the allowable range acquisition unit 10C can acquire information indicating the allowable range for each of the multiple links 20L driven by the series elastic actuator 20D.

The information indicating the allowable range may be position information indicating a predetermined area that a reference position, which is another part of the robot arm 20, can take as a result of a change in the angle of the link 20L. That is, when the angle of a given link 20L is α+β, the tip of that link 20L is displaced by a distance obtained by multiplying β by the length of the link 20L, and accordingly, the downstream part of the robot arm 20 is also displaced. Therefore, the allowable range acquisition unit 10C may set another part of the robot arm 20 as the reference position and acquire position information indicating a predetermined area that this reference position can take. The following mainly describes the case where the position on the surface of the workpiece W held by the tip link 20L is set as the reference position of the robot arm 20.

The tolerance range is preferably set so as to compensate for any shortening of the linear body length due to wear. For example, if the linear body of brush B is set to be replaced when it becomes 5 mm shorter, the tolerance range is preferably set so as to allow the reference position to be at least 5 mm away from the path. With such a setting, it becomes possible to polish the workpiece W in a way that compensates for any shortening of the linear body length due to wear that does not exceed 5 mm.

The information indicating the tolerance range can be defined in advance in a computer program stored in the memory unit 10H as a constant based on the elasticity or viscosity of the drive mechanism. Therefore, the control device 10 may be configured so that the arithmetic element reads out the computer program to obtain the information indicating the tolerance range. Alternatively, the control device 10 may obtain the information indicating the tolerance range from the teaching device 40.

The path acquisition unit 10D acquires a path (planned trajectory) that connects the start position and multiple target positions by calculation processing or the like. Here, the path acquisition unit 10D sets the path so that the polishing member and the member to be polished interfere with each other. In this embodiment, the path is set so that the surface of the workpiece W, which is the member to be polished, passes through an area through which the polishing member, brush B, rotates and passes. By setting the path in this manner, the series elastic actuator 20D of the robot arm 20 can demonstrate its flexibility, making it possible to polish the brush B by conforming it to the surface of the workpiece W.

However, the path does not need to be set so that the polishing member and the member being polished always interfere with each other during polishing. For example, after polishing a curved surface on the surface of the member being polished, the polishing member and the member being polished may be temporarily separated from each other when polishing another curved surface.

The control command acquisition unit 10E acquires, by calculation or the like, control commands for controlling each motor to move the reference position along a path, and supplies them to the robot arm 20. For example, the control command acquisition unit 10E can calculate the rotation angle of each motor for positioning the reference position on a path by inverse kinematics calculation, generate control commands based on this, and store them in the memory unit 10H.

The polishing member information acquisition unit 10F extracts, for example, the outline of the brush B based on the image information of the brush B received from the imaging device of the robot arm 20, and acquires information indicating the degree of wear of the brush B (sometimes called the "amount of wear"). It also acquires information indicating the degree of spread of the linear body of the brush B. If the brush B is composed of many linear bodies, the outline of the brush B varies because the tips of the linear bodies are worn or the linear bodies spread with use. Therefore, the polishing member information acquisition unit 10F can acquire information indicating the degree of wear and spread of the brush B. In addition, in the case of a polishing member whose appearance changes depending on the amount of use, such as a plate-shaped pad, it is possible to similarly acquire information indicating the amount of wear of the polishing member using the imaging device. Furthermore, when polishing multiple types of workpieces W as described above, the polished member information acquisition unit 10G may be configured to identify the type of workpiece W. In that case, the path acquisition unit 10D and the like are configured to acquire a path or the like according to the type of workpiece W identified.

The polished member information acquisition unit 10G, for example, extracts the contour of the workpiece W based on the image information of the workpiece W received from the imaging device 30, and acquires information that identifies the portion held by the robot arm 20. In this embodiment, the runner portion, which is the portion of the workpiece W that will ultimately be removed, is held by the robot arm 20.

The memory unit 10H stores computer programs (including route generation algorithms) for executing the processes shown in each embodiment, as well as necessary data and other information.

Regarding the hardware configuration of the control device 10, the control device 10 can be configured from a computer equipped with, for example, a computing element, which is a processor such as a CPU (Central Processing Unit) or a GPU (Graphical Processing Unit), a volatile memory element such as an SRAM (Static Random Access Memory) or a DRAM (Dynamic Random Access Memory), a non-volatile memory element such as a NOR flash memory, a NAND flash memory, or a HDD (Hard Disc Drive), and a communication means such as a bus connecting these. The non-volatile memory element is a storage medium that stores information non-transitory. The volatile memory element temporarily stores at least a portion of these computer programs and the results of arithmetic processing, etc. The memory unit 10H is configured from these memory elements. Furthermore, by executing the computer program stored in the memory unit 10H, the calculation element functions as a start position acquisition unit 10A, a target position acquisition unit 10B, an allowable range acquisition unit 10C, a path acquisition unit 10D, a control command acquisition unit 10E, a polishing member information acquisition unit 10F, and a polished member information acquisition unit 10G. However, at least some of these calculation elements, non-volatile memory elements, etc. may be installed in a remote location connected to a communication network such as the Internet. For example, the calculation element may be configured to acquire the computer program or necessary data via the communication network.

The control device 10, the robot arm 20, and the imaging device 30 are configured to be able to transmit and receive information to each other via wireless or wired communication means.

The polishing apparatus 100 further includes a teaching device 40. The teaching device 40 may be provided on the robot arm 20, and for example, the input/output unit 20C including a display may be used as a part of the teaching device 40. The teaching device 40 may be configured as a portable teaching pendant for performing online teaching, for example, by actually moving the robot arm 20 on-site and teaching the position and posture at that time as a starting position or a target position. The teaching device 40 includes a calculation element, a volatile memory element, and a non-volatile memory element, similar to the control device 10, and further includes a display means having a display and an input means having a plurality of operation keys and a lever. The input means may be configured as a touch panel type input means for inputting by pressing the display. The teaching device 40 may be a teaching device that follows offline teaching, such as a text type, a simulator type, an emulator type, or an automatic teaching type, in which the position and posture of the reference position are taught as the starting position by a computer program.

[Metal Die Cast Product Manufacturing Method]
The method for producing a metal die-cast product according to this embodiment will be described below.
First, molding is performed by metal die casting to form a workpiece W (step S41). Metal die casting is a process in which a metal such as aluminum, zinc, magnesium, copper, etc. is pressed into a die. In this embodiment, metal die casting is performed using a magnesium alloy as the molten metal. Fig. 5(A) shows a schematic configuration of a die 50 exemplified in this embodiment, and Fig. 5(B) shows a cross-sectional view thereof.

As illustrated in these drawings, the mold 50 includes a movable main mold 50A1 and a movable insert 50A2 that is fitted into the movable main mold 50A1, which constitute the movable mold, and a fixed main mold 50B1 and a fixed insert 50B2 that is fitted into the fixed main mold 50B1, which constitute the fixed mold. The fixed main mold 50B1 is provided with a pouring port bush 50C for pouring molten metal into the mold cavity. The movable main mold 50A1 is provided with a diverter 50D for directing the molten metal poured from the pouring port bush 50C to the product part. In the gap between the fixed mold and the movable mold, a gate runner GR for guiding the molten metal into the mold cavity C that becomes the product part, the mold cavity C that becomes the product part, and a gate G that connects the gate runner GR to the mold cavity C are provided. In addition, a plurality of overflow gates, overflows OF, and air vents OB are provided to discharge the molten metal containing gas, oxides, etc., so that it does not remain in the product part when filled. The workpiece W, which is the molded product formed in this way, has a product portion that will be the final product and a runner portion that remains on the gate runner GR. Many burrs are also formed on the workpiece W.

Then, the conveyor C1 (FIG. 1) transports the workpiece W (step S42). The workpiece W is cooled while being transported. When the conveyor C1 stops transporting the workpiece W at a predetermined position, the imaging device 30 captures an image of the workpiece W and transmits image information of the workpiece W to the control device 10. The polished member information acquisition unit 10G of the control device 10 acquires information indicating the outline of the workpiece W on the conveyor C1 based on the received image information of the workpiece W (step S43).

The start position acquisition unit 10A of the control device 10 acquires information indicating the outline of the workpiece W on the conveyor C1 from the polished member information acquisition unit 10G, and based on this, acquires the position (including posture) of the robot arm 20 when it starts holding the workpiece W as the start position. Note that if the conveyor C1 transports multiple types of workpieces W, the start position acquisition unit 10A may be configured to acquire information identifying the type of workpiece W from the polished member information acquisition unit 10G and hold different parts of the workpiece W depending on the type of workpiece W.

The target position acquisition unit 10B and the tolerance acquisition unit 10C acquire information indicating one or more target positions and information indicating the tolerance range, respectively (step S44). However, the control device 10 may acquire this information by reading it from the memory unit 10H that stores this information in advance, or may acquire this information from the teaching device 40. Furthermore, when acquiring a path by calculation based on the information indicating the start position and the information indicating the target position, the control device 10 may acquire information indicating the tolerance range by reading a path generation algorithm that causes the distance between the object surface and the reference position to be within the tolerance range, and acquiring a path based on this.

Next, the control command acquisition unit 10E acquires a control command for the series elastic actuator 20D based on the path information (step S45). Note that if the control commands for realizing a series of operations are stored in advance in the storage unit 10H, the control device 10 may acquire this information by reading out the control commands from the storage unit 10H.

Next, the robot arm 20 drives each link 20L based on the control command received from the control device 10. First, the robot arm 20 moves to the starting position, holds the runner portion of the workpiece W on the conveyor C1, and starts the movement of the workpiece W (step S46).

Next, the imaging device mounted on the input/output unit 20C of the robot arm 20 captures an image of the brush B, which is the workpiece to be polished, and obtains image information of the brush B (step S47).

The polishing member information acquisition unit 10F of the control device 10 acquires information indicating the degree of wear and the degree of spread of brush B by extracting the outline of brush B based on the image information of brush B. If the amount of wear of brush B is large or brush B has spread too much to be suitable for polishing, the polishing member information acquisition unit 10F causes the input/output unit 20C to issue a warning indicating that it is time to replace brush B. Note that this step may be executed at different times. For example, this step may be executed after polishing is completed.

If it is determined that the brush B is suitable for polishing, the brush B starts to rotate (step S48). In this embodiment, the brush B is placed on a rotary drive device such as a drill press or machining center so that the tip faces vertically. However, the brush B may also be held by a separate robot arm and rotated. In this case, it is preferable to use a normal, highly rigid robot arm that does not have flexibility as the robot arm 20 as the robot arm that holds the brush B. By moving and rotating the brush B using such a robot arm, the brush B may be made to conform to the surface of the workpiece W held by the robot arm 20, which has a flexible drive mechanism, for polishing.

Figure 6 (A) shows brush B in a stationary state. As shown in the figure, brush B according to this embodiment has a cylindrical shaft portion and a number of filamentous bodies attached to the bottom surface of the shaft portion. Each filamentous body is formed in a linear, i.e., elongated, shape. The filamentous bodies are made of a material suitable for polishing the member to be polished. Experiments conducted by the inventors of this application have revealed that when the member to be polished is a magnesium alloy, deposits can be removed effectively by making the filamentous bodies out of brass.

Since each linear body is formed long and thin, it is possible for the tip of the linear body to reach steps, gaps, recesses, etc. It is also possible for the tip of the linear body to reach areas that would be difficult to polish with a plate-shaped polishing member due to the formation of burrs and other obstacles.

With the brush B rotating in this state, the robot arm 20 brings the workpiece W close and brings it into contact with the brush B, thereby starting polishing the surface of the workpiece W (step S49).

Figures 6 (B) and (C) are enlarged views that show the tip of the linear body of the rotating brush B polishing the recesses on the surface of the workpiece W, which is the member to be polished. Note that, for simplicity of explanation, the link 20L and the end effector 20L1 at the tip of the robot arm 20 that holds the workpiece W are omitted from the figure. Also, the number of linear bodies of the brush B is depicted as fewer than it actually is.

In FIG. 6B, the dashed line L1 shows the surface of the workpiece W when the reference position is on the planned path in the absence of the brush B. The solid line L2 shows the surface of the workpiece W in the presence of the brush B.

As shown by the dashed line L1, when the reference position is on the path (including the target position), the surface of the workpiece W interferes with the brush B. However, in reality, the brush B is present and is pressed against the surface of the workpiece W, making it possible to polish the workpiece W by making the brush B conform to the surface of the workpiece W.

Here, the displacement amount D1 corresponding to the distance between the dashed line L1 and the solid line L2 (i.e., the distance between the reference position on the planned path and the actual reference position) corresponds to the amount of elastic deformation of the elastic body 20DE of the multiple series elastic actuators 20D.

Therefore, a force generated based on the elastic modulus and displacement amount D1 of the elastic body 20DE acts from the workpiece W to the brush B, and a reaction force acts from the brush B to the workpiece W. For this reason, by setting the target position and path so that the force is sufficient to remove deposits on the surface of the workpiece W and not damage the surface of the workpiece W, it is possible to polish with an appropriate force.

Here, if the displacement amount D1 is too large, the surface of the workpiece W will be damaged. Therefore, as described below, a tolerance is set so that the displacement amount D1 does not become too large.

Based on a control command from the control device 10, the robot arm 20 moves the workpiece W along a path set so that the surface of the workpiece W interferes with the brush B, thereby continuing polishing by making the surface of the workpiece W follow the brush B (step S50). During this time, the control device 10 periodically obtains the magnitude of the load using a sensor provided in the series elastic actuator 20D, and performs polishing while maintaining the force acting from the brush B on the surface of the workpiece W within a substantially constant range.

Figure 6 (C) is an enlarged view showing a schematic diagram of polishing another portion of the recess on the surface of the workpiece W. Note that explanations of the dashed line L1 and the solid line L2 are omitted, as they have the same meaning as in Figure 6 (B). As shown in Figure 6 (C), the robot arm 20 changes the position and posture of the workpiece W so that the surface to be polished faces generally upward, even when polishing the same recess.

Note that the displacement amount D1 shown in FIG. 6(B) and the displacement amount D2 shown in FIG. 6(C) are not necessarily the same. For example, if burrs or the like are formed around the periphery of the surface to be polished, some of the linear bodies will not reach the surface of the workpiece W, and the force acting from the brush B to the workpiece W will be reduced. Since the robot arm 20 has a driving mechanism with flexibility on multiple axes, in such a case, it is configured to be able to move the workpiece W in a direction that reduces the displacement amount so as to compensate for the reduction in the force acting from the brush B to the workpiece W. Therefore, in that case, the displacement amount D2 will be smaller than the displacement amount D1.

Conversely, for example, depending on the direction of the surface being polished, the force acting from brush B on workpiece W increases. In such a case, robot arm 20 is configured to be able to move workpiece W in a direction that increases the amount of displacement so as to compensate for the increase in the force acting from brush B on workpiece W. Therefore, in that case, displacement amount D2 is greater than displacement amount D1.

Here, because each linear body of brush B is formed long and thin, even if the tip of some linear bodies hits the workpiece to be polished, if the force acting from brush B on workpiece W is small, it is possible to displace workpiece W so that the distance between brush B and workpiece W becomes smaller. When the distance between brush B and workpiece W becomes smaller, the force that brush B exerts on workpiece W increases, making it possible to polish workpiece W with a force that is suitable for polishing.

The control device 10 controls the robot arm 20 so that the amount of displacement falls within an allowable range and the force acting from the brush B to the workpiece W is approximately constant or within an approximately constant range (for example, within an average value ±50%). To keep the amount of displacement within the allowable range, the control device 10 periodically determines whether a displacement that exceeds the allowable range has occurred (step S51).

If the control device 10 determines that a displacement exceeding the allowable range has occurred (NO), the control device 10 generates a control command to decelerate the movement speed of the robot arm 20 and sends it to the drive unit of the robot arm 20, thereby decelerating the robot arm 20 and the workpiece W held by it (step S52).

Figure 7 is a graph to explain the deceleration operation when the tolerance range is exceeded during the tracing operation. In this graph, the horizontal axis represents time and the vertical axis represents the angle of the link 20L driven by the series elastic actuator 20D. In this graph, the target link 20L has an angle α1 at time t1 as the first target position, and an angle α2 at time t2 as the second target position, and a path P (planned trajectory) is set in which the angle changes with time and increases. The tolerance range based on the path of this link 20L is ±β1, centered on the angle of the link 20L. In this graph, the actual angle change is indicated by a solid line A.

As shown in this graph, when at time t11 the angle of link 20L falls outside the allowable range based on path P, as described above, the control device 10 reduces the rotation speed of link 20L and the movement speed of workpiece W to control the angle of link 20L to fall within the allowable range. On the other hand, between time t11 and time t2, the angle of link 20L falls within the allowable range. For this reason, the control device 10 does not perform control to move solid line A closer to path P. Therefore, even if the relative positional relationship between the workpiece W and brush B fluctuates depending on the surface shape of the workpiece W, the relative positional relationship can be maintained to follow and polishing can be continued.

Figure 8 is a schematic diagram showing how the convex surfaces (hereinafter referred to as "convex surfaces") of different types of workpieces W are polished. As with Figure 6, the end effector 20L1 and other components are omitted from the figure for the sake of simplicity. The arrow in this figure indicates the relative movement direction of the brush B with respect to the workpiece W. Conventionally, it has been difficult to move the polishing member relatively to follow such a convex surface. In addition, the relative positional relationship between the polishing member and the workpiece to be polished varies due to individual differences (including burrs) during molding, making polishing such a convex surface even more difficult.

The robot arm 20 of the polishing apparatus 100 according to this embodiment has a flexible drive mechanism, so it is possible to move the workpiece W to avoid the convex portion while compensating for fluctuations in the relative positional relationship between the convex surface of the workpiece W and the brush B. Therefore, even if a path is set according to the ideal shape of the convex portion as shown by the arrow, it is actually possible to move the workpiece W and the brush B relatively in accordance with the shape of the workpiece W and the brush B, rather than following the path. Therefore, even if the polished member has a complex surface, it is possible to polish it appropriately.

It is not necessary to constantly polish the polished member and the polishing member by aligning the surface of the polished member with the polishing member. For example, a portion of the surface of the polished member may not be polished. There may also be a timing when the polished member and the polishing member separate. Furthermore, a portion of the surface may be polished using a different polishing method. Furthermore, a portion of the surface may be polished with a different tolerance range. For example, the tolerance range may be set small to increase the polishing accuracy of the surface exposed to the outside.

When it is determined that the workpiece W has reached the final target position (YES), polishing by the polishing apparatus 100 is completed (step S53).

Then, a coating material is applied to the surface of the workpiece W by an application device capable of discharging the coating material (step S54). Since magnesium alloys are prone to corrosion, applying a coating material after polishing makes it possible to improve the corrosion resistance of the workpiece W. The robot arm 20 moves the workpiece W while holding it, changing its position and posture so that it faces the nozzle of the application device, thereby making it possible to apply the coating material to the surface of the workpiece W. Note that application may be performed by the same or similar operation as during polishing, by aligning the direction in which the tip of the brush B faces (vertical direction) with the direction in which the coating material is discharged.

When application of the coating material is complete, the robot arm 20 places the workpiece W on the conveyor C2 and releases its hold on the workpiece W (step S55).

After that, any burrs and runners remaining on the workpiece W are removed using a burr removal die (step S56). Through this process, a metal die-cast product is manufactured.

As described above, the polishing apparatus 100 and polishing method according to this embodiment make it possible to effectively polish even workpieces having complex surfaces.

In this embodiment, the robot arm 20 is configured to hold the workpiece W rather than the polishing member, the brush B, so the polishing process in which an operator polishes a workpiece by pressing it against a rotating polishing member can easily be replaced with the polishing method according to this embodiment.

However, as described above, the brush B may be held by a rigid robot arm on one hand, and the workpiece may be held by a flexible robot arm on the other hand, and the brush B may be rotated to follow the workpiece W while polishing.

Furthermore, as illustrated in FIG. 2(B), the brush B may be held by the robot arm 20 shown in this embodiment, and an actuator for rotating the brush B may be mounted on an end effector or the like, so that the brush B held by the robot arm 20 can be rotated to conform to the surface of the workpiece W while polishing.

In addition, the workpiece W in this embodiment is a metal die-cast product, but is not limited to this. For example, a resin molded product may be used as the workpiece to be polished.

The present invention can be modified in various ways without departing from the spirit of the invention. For example, some components in one embodiment can be added to another embodiment within the scope of the ordinary creative ability of a person skilled in the art. Also, some components in one embodiment can be replaced with corresponding components in another embodiment.

10 Control device 10A Start position acquisition unit 10B Target position acquisition unit 10C Tolerance range acquisition unit 10D Path acquisition unit 10E Control command acquisition unit 10F Polishing member information acquisition unit 10G Polished member information acquisition unit 10H Memory unit 20 Robot arm 20A Drive unit 20C Input/output unit 20D Series elastic actuator 20DA Drive unit 20DE Elastic body 20J Joint 20L Link 20L1 End effector 30 Imaging device 40 Teaching device 50 Mold 100 Polishing device B Brush W Workpiece

Claims (16)

A step of setting a path of a reference position of a robot arm having a flexible drive mechanism such that a polishing member and a polished member interfere with each other;
setting an allowable range within which a deceleration operation of the robot arm is executed when a reference position of the robot arm deviates from the path, based on the path;
and polishing the surface of the workpiece by rotating the polishing member held by the robot arm so as to conform to the surface of the workpiece ,
The polished member is a metal die-cast product.
Polishing method. A step of setting a path of a reference position of a robot arm having a flexible drive mechanism such that a polishing member and a polished member interfere with each other;
setting an allowable range within which a deceleration operation of the robot arm is executed when a reference position of the robot arm deviates from the path, based on the path;
and polishing the surface of the workpiece held by the robot arm by following the rotating polishing member ,
The polished member is a metal die-cast product.
Polishing method. The step is carried out while maintaining the force acting from the polishing member on the surface of the workpiece within a substantially constant range.
The polishing method according to claim 1 or 2. The polished member is made of a magnesium alloy.
The polishing method according to claim 1 . The polishing member is made of brass.
The polishing method according to claim 1 . The polishing method according to any one of claims 1 to 5, wherein the robot arm has multiple drive shafts, and each of the multiple drive shafts is equipped with a series elastic actuator as the flexible drive mechanism. The polishing method according to any one of claims 1 to 6, further comprising a step of applying a coating material to the surface of the polished member using the robot arm after the polishing step. The polishing method according to any one of claims 1 to 7, wherein the polishing member is a buff or a brush. performing a metal die casting;
and performing the polishing method according to claim 1 or 2 using the metal die-cast product formed in the above step as the polished member. The method for manufacturing a metal die-cast product according to claim 9, further comprising a step of removing burrs and runners from the metal die-cast product formed by the metal die-casting. a robot arm having a flexible drive mechanism and configured to be able to hold a polishing member;
A path of a reference position of the robot arm is set so that the polishing member and the workpiece interfere with each other;
setting an allowable range within which a deceleration operation of the robot arm is executed when a reference position of the robot arm deviates from the path based on the path;
The polishing member is configured to polish the surface of the workpiece while rotating, and the polishing member is configured to conform to the surface of the workpiece ,
The polished member is a metal die-cast product.
Polishing equipment. a robot arm having a flexible drive mechanism and configured to be capable of holding a member to be polished;
A path of a reference position of the robot arm is set so that the polishing member and the polished member interfere with each other;
setting an allowable range within which a deceleration operation of the robot arm is executed when a reference position of the robot arm deviates from the path based on the path;
The surface of the workpiece is polished by following the rotating polishing member ,
The polished member is a metal die-cast product.
Polishing equipment. A control device for controlling a robot arm having a flexible drive mechanism and a holding mechanism capable of holding a polishing member,
setting a path of a reference position of the robot arm such that the polishing member and the workpiece interfere with each other;
setting an allowable range within which a deceleration operation of the robot arm is executed when a reference position of the robot arm deviates from the path, based on the path;
a step of rotating the polishing member by using the robot arm to conform to the surface of the workpiece;
is configured to be executable ,
The polished member is a metal die-cast product.
Control device. A control device for controlling a robot arm having a flexible drive mechanism and a holding mechanism capable of holding a member to be polished,
Setting a path of a reference position of the robot arm such that a polishing member and the polished member interfere with each other;
setting an allowable range within which a deceleration operation of the robot arm is executed when a reference position of the robot arm deviates from the path, based on the path;
using the robot arm to polish the surface of the workpiece by following the rotating polishing member;
is configured to be executable,
The polished member is a metal die-cast product.
Control device. A step of setting a path of a reference position of a robot arm having a flexible drive mechanism such that a polishing member and a polished member interfere with each other;
setting an allowable range within which a deceleration operation of the robot arm is executed when a reference position of the robot arm deviates from the path, based on the path;
a step of polishing the surface of a workpiece by rotating the polishing member using the robot arm having a holding mechanism capable of holding the polishing member, and aligning the polishing member with the surface of a workpiece;
generating control instructions for operating the robot arm by a computer to perform the steps of :
The polished member is a metal die-cast product.
Computer program. A step of setting a path of a reference position of a robot arm having a flexible drive mechanism such that a polishing member and a polished member interfere with each other;
setting an allowable range within which a deceleration operation of the robot arm is executed when a reference position of the robot arm deviates from the path, based on the path;
a step of polishing the surface of the member to be polished by using the robot arm having a holding mechanism capable of holding the member to be polished so as to follow a rotating polishing member;
generating control instructions for operating the robot arm by a computer to perform the steps of :
The polished member is a metal die-cast product.
Computer program.

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