Grinder and Robot

This Nonprovisional application claims priority under 35 U.S.C. § 119 on Patent Application No. 2024-092484 filed in Japan on Jun. 6, 2024, the entire contents of which are hereby incorporated by reference.

The present invention relates to a grinder and a robot.

Patent Literature 1 discloses a disc grinder including a circular grindstone (hereinafter, also referred to as “disc tool”) driven to rotate by a motor. The disc tool rotates around an output shaft via which rotation of the motor is transmitted.

The disc tool becomes worn by use. The worn disc tool needs to be replaced. However, with the disc grinder disclosed in Patent Literature 1, there is no method for detecting a worn state of the disc tool, except for making determination based on the subject view of the operator.

It is an object of an aspect of the present invention to detect a worn state of a disc tool.

In order to solve the foregoing problem, a grinder in accordance with an aspect of the present invention includes: a disc tool configured to rotate around a rotation shaft; a force sensor configured to detect a moment around the rotation shaft, the moment acting on the disc tool; and a controller, the controller carrying out a detection process of detecting a worn state of the disc tool on the basis of the moment obtained from the force sensor.

According to an aspect of the present invention, it is possible to detect a worn state of a disc tool.

The following description will discuss a grinderin accordance with an embodiment of the present invention in detail.

With reference to, the following will describe an overview of the grinder.is a schematic side view illustrating a configuration of the grinderin accordance with an embodiment of the present invention. The grinderincludes a disc tool, a force sensor, and a controller. The grindermay further include a main body, a driving motor, an inertial measurement unit (IMU), and an input device(see), and a display.

The main bodyconstitutes a main part of the grinder. For the main body, an x-axis direction (direction of an x axis) is regarded as a longitudinal direction. The main bodyhas a first end partand a second end partlocated opposite to the first end part. The first end partis an end part located on a negative direction side in the x-axis direction. The second end partis an end part located on a positive direction side in the x-axis direction.

A gripping partis provided on a side closer to the first end partof the main body. The gripping partis formed so as to have a small diameter that allows easier gripping by an operator. The gripping partmay accommodate therein the IMUand the controller. A power source buttonincluded in the input device(see) may be provided on the negative direction side of in the z-axis direction of the gripping part.

The disc toolis attached to a side closer to the second end partof the main body. More specifically, the disc toolis attached to a negative direction side in a z-axis direction of a gear accommodation partprovided on the side closer to the second end partof the main body. The gear accommodation partmay accommodate therein the driving motorand the force sensor. To the gear accommodation part, a side handle to be gripped by an operator may be attached.

The disc toolis a tool for processing, such as polishing, on a workpiece. Examples of the disc toolinclude a grindstone. The disc toolis attached to a spindlewith use of, for example, nuts. The disc toolrotates around the spindle. The spindleserves as a rotation shaft of the disc tool.

The driving motoris a motor configured to rotate the spindle. The spindleis connected to an output shaftof the driving motor.

The force sensordetects a moment around the spindle, the moment acting on the disc tool. The force sensoroutputs, to the controller, an output signal indicating the moment detected. The force sensormay detect forces acting on the disc tool. In this case, the force sensoroutputs, to the controller, an output signal indicating the force detected.

The force sensormay be attached to a flange partprotruding from an outer peripheral part of the driving motor. In a center part of the force sensor, a through holethrough which the output shaftof the driving motorand the spindleare inserted is formed.

In the present embodiment, a six-axis force sensor is used as the force sensor. The force sensordetects a force Fx in an x-axis direction, a force Fy in a y-axis direction (direction of a y axis), a force Fz in a z-axis direction (direction of a z axis), a moment Mx around an x axis, a moment My around a y axis, and a moment Mz around a z axis which act on the disc tool. Here, the x-axis direction is a direction from the first end partto the second end partof the main body. The z-axis direction is a direction parallel to an axis direction of the spindleof the disc toolwhich direction is orthogonal to the x axis. The y-axis direction is a direction orthogonal to the x axis and the z axis. The x-axis direction and the y-axis direction are directions parallel to a radial direction of the disc tool.

The IMUis an inertial measurement device configured to detect angular velocities and accelerations of the main body. More specifically, the IMUcan detect angular velocities around the x axis, around the y axis, and around the z axis of the main body. The IMUcan detect accelerations in the x-axis direction, in the y-axis direction, and in the z-axis direction of the main body. The posture of the main bodycan be detected with use of the IMU. The IMUoutputs, to the controller, an output signal indicating the detected angular velocity and an output signal indicating the detected acceleration.

The displaydisplays an image indicating a posture of the disc toolwith respect to the workpiece. Examples of the displayinclude a display panel. The displayis provided on the main body. In the present embodiment, the displayis provided on the gripping part. The displayis provided in a position visible to an operator gripping the gripping part.

The controllercontrols the parts of the grinder.

With reference to, the following will describe an example of an internal configuration of the grinder.is a block diagram illustrating one example of an internal configuration of the grinder.

The controllerincludes a processor, a primary memory, a secondary memory, and an input/output IF, as illustrated in. The processor, the primary memory, the secondary memory, and the input/output IFare connected with each other via a bus. Examples of a device usable as the controllerinclude a workstation.

The secondary memorystores a control program P. The processorloads, on the primary memory, the control program P stored in the secondary memory. The processorthen carries out processes included in a process method M(described later) in accordance with instructions included in the control program P loaded on the primary memory.

Examples of a device usable as the processorinclude a central processing unit (CPU). Examples of a device usable as the primary memoryinclude a semiconductor random access memory (RAM). Examples of a device usable as the secondary memoryinclude a hard disk drive (HDD).

The input/output IFis an interface for communicating with the force sensor, the IMU, the input device, the display, and an inverter. Examples of the input/output IFinclude a universal serial bus (USB), an advanced technology attachment (ATA), a small computer system interface (SCSI), serial communication, and the like.

The input deviceis a device that can receive an input from the operator. The input devicemay be constituted by, for example, a button, a switch, a touch panel, or the like. In the present embodiment, the input deviceincludes the power source buttonand a selection button. The selection buttonis a button for inputting tool information of the disc tool. An operation of the selection buttonby the operator causes the tool information of a new disc toolattached to the grinderto be inputted. The tool information includes at least one of outer diameter information of an unworn disc toolwhich has not been used, and type information of the disc tool.

The grindermay further include the inverter. The invertercontrols a rotation speed of the driving motor. The inverteris one example of a rotation speed controlling device. The controllercarries out pulse width modulation (PWM) control over the inverter. Specifically, the controllersets a duty ratio, and outputs, via the input/output IF, a PWM signal generated on the basis of the set duty ratio, to the inverter. The invertercontrols current supplied to the driving motorby applying voltage generated on the basis of the inputted PWM signal to the driving motor. The voltage applied by the inverteris controlled, thereby controlling the rotation speed of the driving motor.

Next, with reference to, the following will describe one example of a process method Mcarried out by the controller.is a flowchart illustrating one example of the process method Mcarried out by the controller.

First, the processorcarries out an obtaining process S. In the obtaining process S, the processorobtains, via the input/output IF, an output signal outputted from the force sensor.

Subsequently, the processorcarries out a detection process S. In the detection process S, the processordetects a worn state of the disc toolon the basis of the moment Mz obtained from the force sensor. In the detection process S, the processorcalculates an outer diameter of the disc toolas the worn state of the disc tool. In the detection process S, the processormay calculate a thickness of the disc toolas the worn state of the disc tool.

With reference to, the following will describe one example of detection of a worn state of the disc tool.is a schematic view for explaining one example of a worn state of the disc tool.is a view of the disc toolas seen from an axial direction of the spindle. The outer diameter Dof the disc toolillustrated by the reference numeralinis greater than the outer diameter Dof the disc toolillustrated by the reference numeralin. When the disc toolis used, the disc toolbecomes worn. For example, when the disc toolis used, the outer diameter of the disc toolmay be reduced.

The moment Mz acting on the disc toolis proportional to the size of the outer diameter of the disc tool. A smaller outer diameter of the disc toolleads to a smaller moment Mz acting on the disc tool. For example, the moment Mz acting on the disc toolillustrated by the reference numeralinis smaller than the moment Mz acting on the disc toolillustrated by the reference numeralin. The processordetects a worn state of the disc toolby calculating an outer diameter of the disc toolon the basis of the moment Mz.

Subsequently, the processorcarries out a rotation speed controlling process S. In the rotation speed controlling process S, the processorcontrols the inverteron the basis of the moment Mz obtained from the force sensorso that the rotation speed of the driving motorbecomes a target value corresponding to the outer diameter of the disc tool.

In the rotation speed controlling process S, the processormay control the inverterso as to make a circumferential velocity of the disc toolconstant. In the rotation speed controlling process S, the processorcontrols the inverterso as to prevent the circumferential velocity of the disc toolfrom exceeding a limit velocity (hereinafter, referred to as “maximum operational circumferential velocity”) within which the disc toolcan be safely used. The maximum operational circumferential velocity is set by, for example, Ordinance on Industrial Safety and Health.

Next, the processorcarries out a notification process S. In the notification process S, the processorcarries out notification to prompt the operator to replace the disc toolin a case where the moment Mz obtained from the force sensorbecomes less than a threshold. In the notification process S, the processorcarries out the notification to the operator by, for example, causing the displayto display a display screen that prompts replacement of the disc tool. In this case, the processorgenerates a display screen to be displayed on the display. In the notification process S, the processormay be configured to carry out the notification to the operator by, for example, outputting an alert sound or a voice with use of an output device, such as a speaker.

The threshold used in the notification process Sis a value determined in advance on the basis of a factor such as the type, the outer diameter, or a circumferential velocity of the disc tool. The threshold may be a value set in accordance with tool information of the disc toolinputted via the selection buttonof the input device. That is, the threshold may be set in accordance with the outer diameter information and/or the type information of the disc toolinputted with use of the selection buttonof the input device.

The notification that prompts replacement of the disc toolis not limited to a configuration in which a display screen is displayed on the display. For example, in the notification process S, the processormay carry out the notification to the operator by ringing an alarm. In the notification process S, the processoronly needs to be configured to carry out the notification to the operator in an acoustic and/or visual manner.

As described above, the fact that the grinderincludes the force sensorenables detection of the moment Mz around a rotation shaft of the spindleof the disc tool. This enables detection of a worn state of the disc tool.

Typically, a smaller outer diameter of the disc toolleads to a lower circumferential velocity of the disc tool. The controllercarrying out the rotation speed controlling process Senables control of the rotation speed of the driving motorin accordance with the worn state of the disc tooldetected with use of the moment Mz obtained from the force sensor. This makes it possible to make the circumferential velocity of the disc toolconstant. It is also possible to carry out control so as to prevent the circumferential velocity of the disc toolfrom exceeding the maximum operational circumferential velocity.

The controllercarrying out the notification process Senables the operator to recognize a timing for replacing the disc tool. This also enables the operator to set the replacement timing corresponding to at least one of the outer diameter information and the type information of the disc toolby inputting the tool information of the disc toolthrough the operation of the selection button. This enables replacement of the disc toolat the replacement timing corresponding to the outer diameter and/or the type of the disc tool.

In the embodiment described above, the output shaftof the driving motorand the spindle, which serves as a rotation shaft of the disc tool, are configured to be parallel shafts, but this configuration should not be construed as a limitation. The output shaftand the spindlemay be intersecting shafts. In this case, the force sensormay be attached to a retaining member that retains the spindle. Further, the driving motormay be disposed inside the gripping part.

In the embodiment above, the grinderis configured to include the IMU, but this configuration should not be construed as a limitation. The grindermay include an angular velocity sensor that can detect at least one of angular velocities around the x axis, around the y axis, and around the z axis. The grindermay include an acceleration sensor that can detect at least one of accelerations in the x-axis direction, in the y-axis direction, and in the z-axis direction.

In the embodiment above, the grinderis configured to include the display, but this configuration should not be construed as a limitation. The main bodyof the grindermay be provided with an indicator, e.g., an LED lump or the like. In this case, in the notification process S, the processormay light the indicator in order to prompt the operator to replace the disc tool. A configuration is also possible in which an external display is connected to the grinder. In this case, in the notification process S, the processor may output a visual signal indicating generated displaying image to the external display to cause the display to display the displaying image that prompts replacement of the disc tool.

In the embodiment above, the input deviceis configured to include the selection button, but this configuration should not be construed as a limitation. The input devicemay include an initialization button instead of the selection button. A configuration is possible in which when the disc toolis replaced with a new one, the operator presses the initialization button, so that the rotation speed of the driving motoris initialized. In this case, the threshold used in the notification process Smay be a value obtained by decreasing, by a predetermined percentage, a value of the moment Mz detected in the first processing after pressing the initialization button.

In the embodiment above, a configuration is employed in which the inverteris used to control the rotation speed of the driving motor, but this configuration should not be construed as a limitation. A device including a triac element may be employed as the rotation speed controlling device configured to control the rotation speed of the driving motor. In this case, the rotation speed controlling device is phase-controlled. The rotation speed controlling device may apply voltage generated on the basis of phase control to the driving motor.

In the embodiment above, the grinderis described as a grinder gripped by an operator, but this configuration should not be construed as a limitation. The grinderdescribed above may be attached to a robot. In this case, the controllerfunctions as a device configured to control operation of a robot including the grinder. The controllerthat controls the robot may carry out a replacement process of causing the robot to replace the disc tool, on the basis of the worn state of the disc tooldetected. More specifically, in a case where the controllerdetermines that the worn state of the disc tooldetected in the detection process Sshows that the disc toolis worn to a degree to which the disc toolneeds to be replaced, the controllercarries out the replacement process. In the replacement process, the controllercauses the robot to replace the disc tool. According to such a configuration, in a case where the controllerdetects that the disc toolhas been worn to a degree to which the replacement is needed, control by the controllercauses the robot to automatically replace the disc tool. This enables reduction in the man-hour for the operator by an amount needed to replace the disc tool.

Aspects of the present invention can also be expressed as follows:

A grinder in accordance with Aspect 1 of the present invention includes: a disc tool configured to rotate around a rotation shaft; a force sensor configured to detect a moment around the rotation shaft, the moment acting on the disc tool; and a controller, the controller carrying out a detection process of detecting a worn state of the disc tool on the basis of the moment obtained from the force sensor.

According to the configuration of Aspect 1, the fact that the grinder includes the force sensor enables detection of a moment around a rotation shaft of the disc tool. This enables detection of a worn state of the disc tool.