JP7777951B2 - Grinding device and control method thereof - Google Patents

Description

The present invention relates to a grinding machine and its control method, and in particular to a grinding machine and its control method that can move or fix a grinding wheel rotating device with a grinding wheel attached, such as a jig grinder, in the radial direction using a linear axis, and then rotate the device itself using a separate rotating device to grind the inner or outer surface of a circle.

In a jig grinder, for example, a so-called single-column type machine grinds a workpiece (hereafter referred to as the "workpiece") by moving the workpiece placed on a table back and forth (Y-axis direction) and left and right (X-axis direction) on a slide, while moving a so-called quill, which has a grinding wheel and a high-frequency motor for rotating it attached to its bottom end, up and down (Z-axis direction). In the case of a so-called double-column type (gantry type) jig grinder, the workpiece is moved only in the X-axis direction, while the grinding wheel (spindle body) moves in the Y-axis direction. Needless to say, the names of the axes, such as X-axis, Y-axis, and Z-axis, can be interchanged depending on the machine manufacturer.

More specifically, there are two main types of grinding: The first type involves making the axis of rotation of the grinding wheel (grinding wheel shaft) eccentric (cutting into) the spindle, causing the grinding wheel to rotate about the grinding wheel shaft while the spindle continues to rotate, i.e., planetary rotation of the grinding wheel; at the same time, the quill is moved up and down to rotate the grinding wheel in a spiral, resulting in a perfectly round hole by evenly grinding the inner wall. In this case, the diameter of the hole is basically determined according to the size of the outer diameter of the grinding wheel and the degree of eccentricity of the grinding wheel spindle (amount of cutting (maximum 50 mm, for example). The other is grinding for boring non-circular holes with an inconstant curvature or for processing end portions with an inconstant curvature. In this case, so-called chopping is performed. In detail, the grinding wheel spindle is not made eccentric, or the grinding wheel is made eccentric in the opposite direction (negative direction) to the cutting by an amount equivalent to the radius of the grinding wheel so that the center of rotation of the spindle and the outer periphery of the grinding wheel coincide, and first the workpiece is moved to the processing position (grinding point) by X and Y axis feed. Then, the amount of net cutting is automatically adjusted. The grinding wheel is eccentric, i.e., chopping is performed while automatically cutting. When cutting into the workpiece surface with an inconsistent curvature, the angle of the spindle is controlled (indexed) so that the normal at the cutting point where the workpiece contacts always coincides with the cutting direction of the grinding wheel. Patent Document 1 discloses the main configuration of such a jig grinding machine. However, Patent Document 1 omits the configuration for raising and lowering the grinding wheel. Here, chopping refers to linear reciprocating motion, and the term chopping is not defined to include restrictions on the reciprocating speed used in general chopping.

Japanese Patent Application Laid-Open No. 2006-102891

In the jig grinding machine described above, depending on the selection of CNC functions and the design of the control software, for example, the grinding wheel may approach the surface beyond the range immediately after operating the override switch or changing the settings of the oscillation range, speed, or center position. Therefore, there is a need to develop software or a mechanical device that prevents the grinding wheel from colliding with the surface beyond the range of reciprocation by superimposing a command that momentarily separates the end of the grinding wheel's reciprocation range from the surface beyond the grinding surface when changing the settings of the oscillation range, speed, or center position, including the override switch, during chopping and oscillation grinding. Then, the override switch or the aforementioned setting change is applied, gradually returning the grinding wheel to its normal position over the number of reciprocations. The inventors have filed patent applications for grinding devices and control methods that meet this need (Patent Application Nos. 2018-160030 and 2019-107534).

The jig grinding machine described above has an automatic infeed device that can feed or fix the grinding wheel rotating device with a grinding wheel attached in the radial direction using a linear axis, and by rotating these devices together with a separate rotating device (a device equivalent to the main shaft described above), it is possible to grind the inner or outer surface of a circle.In addition, there are some machines where the rotation speed of the device equivalent to the separate rotating device can be freely changed by the operator using an override switch to multiply the rotation speed by the command rotation speed.
However, changing the rotation speed of a device that corresponds to another rotating device can cause overcutting due to centrifugal force, etc., and when a particularly sudden change occurs due to an override switch, etc., the overcutting is often felt. Therefore, the development of a jig grinder with a function to mitigate overcutting when such an override command is changed is desired, but there have been few effective proposals to solve this problem.

The object of the present invention is to provide a technology for realizing a function to mitigate overcutting when an override command is changed in a grinding machine and its control method.

After extensive research into the configuration of a grinding machine and its control method that achieves an overcut mitigation function when the override command is changed, the inventors came up with the idea that such a mitigation function could be achieved by first feeding the grinding wheel rotation device on a linear axis in the radial direction away from the object to be ground and applying the override, rather than directly applying the override to the control device when the override switch is operated. Alternatively, the inventors came up with the idea that a similar mitigation function could be achieved by providing a function that automatically performs the operation of first feeding the grinding wheel rotation device on a linear axis in the radial direction away from the object to be ground and applying the override, and then gradually returning to the original coordinates, rather than directly applying the override to the control device when the override switch is operated. Furthermore, they discovered that it would be preferable to be able to change the escape direction when grinding the outside and the inside.

That is, according to a first aspect of the present invention, there is provided a grinding apparatus which has an automatic infeed device which can feed or fix a grinding wheel rotating device equipped with a grinding wheel in the radial direction on a linear axis, and which can grind the inner or outer surface of a circle by rotating the entire automatic infeed device including the grinding wheel rotating device by a separate rotating device, and which is configured so that an operator can freely change the rotation speed of the separate rotating device with an override switch, and which does not immediately apply the override to a control device when the override switch is operated, but first operates the automatic infeed device to feed the grinding wheel rotating device in the radial direction on a linear axis in a direction away from the object to be ground, and then applies the override to the rotation speed of the separate rotating device, and which is characterized in that the escape direction is changed when grinding the outer surface and when grinding the inner surface .

According to a second aspect of the present invention, there is provided a grinding apparatus having an automatic infeed device that can feed or fix a grinding wheel rotating device equipped with a grinding wheel in the radial direction on a linear axis, and further capable of grinding the inner or outer surface of a circle by rotating the entire automatic infeed device including the grinding wheel rotating device by a separate rotating device, wherein the grinding apparatus is configured so that an operator can freely change the rotation speed of the separate rotating device with an override switch, and wherein when the override switch is operated, the operation is not immediately applied to a control device, but rather the automatic infeed device is first operated to feed the grinding wheel rotating device in the radial direction on the linear axis in a direction away from the object to be ground, and then an override is applied so that the grinding apparatus gradually returns to the original coordinates over time, and wherein the grinding apparatus is characterized in that the escape direction is changed when grinding the outer surface and when grinding the inner surface .

Furthermore, according to the present invention, there is provided a grinding apparatus which has an automatic cutting device which can feed or fix a grinding wheel rotating device equipped with a grinding wheel in the radial direction using a linear axis, and which can grind the inner or outer surface of a circle by rotating the entire device including the grinding wheel rotating device and the automatic cutting device using a separate rotating device, and which is configured so that an operator can freely change the rotation speed of the separate rotating device using an override switch, the grinding apparatus comprising: a first step of determining whether a speed change will occur if an override change occurs during machining; a second step of calculating an amount of allowance addition and performing an allowance addition operation if a speed change occurs; and a third step of changing the speed and performing cutting at this changed speed, wherein the first to third steps are performed in this order .

According to the present invention, a grinding machine and its control method can achieve a function to mitigate overcutting when the override command is changed.

1 is a perspective view showing a jig grinding machine as an example of a grinding device to which the present invention is applied; 2 is a diagram for explaining the grinding device (jig grinding machine) shown in FIG. 1 together with the movement or rotation direction of each axis. FIG. 2 is an enlarged view of the U-axis feed device and the grinding wheel spindle area in the grinding machine (jig grinding machine) shown in FIG. 1. 2 is a diagram showing the relationship between the machining of a workpiece by a rotating grinding wheel in the grinding device (jig grinder) shown in FIG. 1 and the axial movements of the U-axis and Z-axis. FIG. 2 is a block diagram showing an outline of a control system of the grinding apparatus (jig grinding machine) shown in FIG. 1 . 4 is a graph showing the relationship between an override command, an actual rotation speed, and an automatic cutting position in the grinding machine and the control method thereof according to the first embodiment of the present invention. 4 is a flowchart of a control process from the start to the end of a machining process in the grinding device according to the first embodiment of the present invention.

First, to facilitate understanding of the present invention, a grinding machine to which the present invention is applicable will be described with reference to the drawings. FIG. 1 is a perspective view showing an example of a grinding machine to which the present invention is applicable. FIG. 2 is a diagram illustrating the grinding machine along with the movement or rotation direction of each axis. The U-axis feeder can move linearly along the Z-axis and rotate around the Z-axis (referred to as the C-axis) relative to the head. The U-axis feeder can move the grinding wheel shaft linearly in the U-axis direction. Each axis may be a combination of multiple parallel axes. FIG. 3 is an enlarged view of the U-axis feeder and the grinding wheel shaft area in the grinding machine (jig grinder). FIG. 4 is a diagram illustrating the relationship between the machining of the workpiece by the rotating grinding wheel in the grinding machine (jig grinder) and the axial movement of the U-axis and Z-axis. As shown in FIG. 1, the grinding machine 10 to which the present invention is applicable has a table feeder 36 and a table 30 supported on a bed 12 via rails 16 for movement in the Y-axis direction (front-to-back direction). The column 14 is fixed to the bed 12, but relative motion can be imparted between the column 14 and the feed device 36 in the direction along the rail 16. A motor for moving the feed device 36 (not shown) is disposed at the rear of the bed 12, and this motor moves the table feed device 36 back and forth along the rail 16 via a ball screw (not shown) or other means. A head 18 is supported on the column 14 so as to be movable (liftable) in the W-axis direction. A grinding wheel spindle 20 is provided at the tip of the head 18, and a grinding wheel 100 (see FIG. 3) is attached to the tip of the grinding wheel spindle 20. A head lift motor (not shown) is disposed above the column 14, and this motor lifts and lowers the head 18 via a ball screw (not shown). A grinding wheel spindle rotation motor (C motor 302 in FIG. 5) is disposed inside or at the rear of the head 18, and this motor rotates the grinding wheel spindle 20. An encoder (not shown) constituting a measuring means is attached to the head lift motor. The other linear and rotary axes, excluding the grinding wheel spindle, are equipped with encoders and motors (not shown) to calculate and control the feed or rotation amount. The data output from these encoders is used to calculate the amount of lift of the head 18 and the amount of cutting into the workpiece (see Figure 4), which will be described later. The Z-axis is provided parallel to the W-axis, allowing Z-axis movement to be imparted without interfering with the W-axis head movement, C-axis rotation, or U-axis linear movement.

As mentioned earlier, the Y-axis feed device 36 is mounted on the bed 12 via rails 16. This Y-axis feed device 36 is configured to be able to move linearly back and forth in the Y-axis direction along the direction of the rails 16. The table 30 is supported on the Y-axis feed device 36 via rails (not shown). This table 30 is configured to be able to move linearly left and right (X-axis direction) relative to the Y-axis feed device 36. A workpiece (not shown) is removably mounted and fixed on its upper surface. Naturally, a motor for moving the Y-axis feed device 36 is provided on the bed 12, and this motor moves the Y-axis feed device 36 along the rails 16 via a ball screw (not shown) or the like. The table 30 similarly moves on the Y-axis feed device 36 via a motor and ball screw (not shown) or the like. While the grinding wheel spindle 20 is rotated by the grinding wheel spindle rotation motor, the head 18 (grinding wheel spindle 20) is lowered by the head elevation motor, bringing the grinding wheel 100 attached to the tip of the grinding wheel spindle 20 into contact with the surface of the workpiece on the table 30. The table 30 is freely movable in the X and Y directions by the two motors mentioned above. This allows the grinding wheel 100 to grind the surface of the workpiece. The grinding device 10 is equipped with various operation switches or similar input devices, and is configured so that the operator can change their state during operation. It also has an AE (acoustic emission) sensor (not shown) on the workpiece side as a means for detecting contact between the grinding wheel 100 and the workpiece. When the AE sensor detects contact between the workpiece and the grinding wheel 100, it displays this to the operator or sends a skip signal to stop the feeding of the grinding wheel 100.

As described above, the machine tool (grinding device) 10 shown in Figure 1 is a CNC-controlled machine tool (grinding device) capable of simultaneous control of at least three axes: X, Y, and Z. It also has a drive axis (rotational axis or linear drive axis) whose axial direction is parallel to the rotational axis, the grinding wheel spindle 20. Specifically, the machine tool (grinding device) 10 has a U-axis feed device 40 below the head 18. This U-axis feed device 40 is a linear feed mechanism including the grinding wheel spindle 20 and the disk body 27 above it. It is a device that linearly moves the grinding wheel spindle 20 and the disk body 27 above it within a predetermined stroke range depending on the angular position of the C-axis at that time, and the direction of this linear movement is defined as the U-axis (direction). In other words, in the machine tool (grinding device) 10 shown in Figure 1, the head 18 can move linearly (up and down) in the Z-axis direction. To distinguish it from the Z-axis, this is referred to as the W-axis feed device. Furthermore, the U-axis feed device 40 can move linearly along the Z-axis and rotate around the Z-axis (referred to as the C-axis) relative to the head 18. The U-axis feed device 40 can move the grinding wheel spindle 20 linearly in the U-axis direction. To explain the drive axis control of the machine tool (grinding device) 10 more specifically with reference to Figures 2 and 3, in the machine tool (grinding device) 10, the U-axis linear feed mechanism is mounted on the rotating side of the C-axis. A feed command for the grinding wheel spindle (U-axis) can move the U-axis feed device 40 linearly along the U-axis. A rotation command for the C-axis rotates the center of the grinding wheel spindle. Furthermore, this C-axis device can move linearly in the vertical direction using the Z-axis device.

Figure 5 is a block diagram showing an outline of the control system of the jig grinding machine shown in Figure 1. The jig grinding machine of the present invention has, as its control system, a control device 300, an input/output device 310, each axis motor 320 and its respective motor driver 330, a grinding wheel rotation motor 102A, and a grinding wheel motor inverter 102inv. The control device 300 has a computer numerical control (CNC) 302, a programmable controller 304, and an I/O (input/output) module 306. The control system of the jig grinding machine of the present invention also has, as input/output devices 310, a keyboard, various switches, a temperature sensor, etc., as well as a tool setter related to skip signals, an AE sensor, etc.

Here, we will explain the problems with the conventional example once again. The jig grinder 10 shown in Figures 1 to 5, as clearly illustrated in Figure 3 in particular, is a grinding machine that can grind the inner or outer surface of a circle (cylindrical in consideration of thickness) to be ground by rotating a grinding wheel rotation device 102 (which of course includes a grinding wheel rotation motor 102A, a grinding wheel motor inverter 102inv [see Figure 5], etc., but only the portion of this device that can be inserted into the machining chamber) with a grinding wheel 100 attached, using a separate rotation device (C-axis rotation device) 106 (which of course includes a C motor for C-axis rotation, a C-axis motor drive [see Figure 5], etc.) to freely change the rotation speed of the device corresponding to the separate rotation device (C-axis rotation device) 106 by using an override switch to freely change the magnification of the rotation speed relative to the commanded rotation speed. However, if the rotation speed of the device equivalent to the other rotating device (C-axis rotating device) 106 is changed, its mass may cause overcutting due to centrifugal force, etc. In particular, there is a risk that overcutting may be felt when there is a sudden change, such as when the override command is changed.

Therefore, in the grinding apparatus and control method thereof according to an embodiment of the present invention, when the override switch is operated, instead of applying it directly to the control device 300 (see Figure 5), the grinding wheel rotation device 102 is first moved radially along the linear axis (U-axis) in a direction away from the object to be ground, and the override is applied. That is, the grinding apparatus 10 according to an embodiment of the present invention has an automatic infeed device 104 that can feed or fix a grinding wheel rotation device 102, to which a grinding wheel 100 is attached, in the radial direction on a linear axis (U-axis), and further, the entire automatic infeed device 104, including the grinding wheel rotation device 102, is rotated by a separate rotation device (C-axis rotation device) 106, thereby grinding the inner or outer surface of a circle (cylindrical when considering the thickness) to be ground. The grinding apparatus is configured so that the rotation speed of the separate rotation device (C-axis rotation device) 106 can be freely changed by an operator using an override switch, and is characterized in that, when the override switch is operated, the operation is not immediately applied to the control device 300 (see FIG. 5 ), but rather the automatic infeed device 104 is first operated to feed the grinding wheel rotation device 102 in the radial direction on the linear axis (U-axis) in a direction away from the grinding object, and then the override of the rotation speed of the separate rotation device (C-axis rotation device) 106 is applied. Furthermore, in the grinding apparatus 10, rather than immediately applying the override switch to the control device 300 (see FIG. 5), the automatic infeed device 104 may be operated to feed the grinding wheel rotating device 102 radially along the linear axis (U-axis) away from the workpiece, and then an override of the rotational speed of another rotating device (c-axis rotating device) 106 may be applied, gradually returning the grinding wheel to the original coordinates (target coordinates under CNC control) over time. In addition, in the grinding apparatus 10, the escape direction may be changed between grinding the outside of the workpiece (e.g., when machining the outer peripheral surface) and grinding the inside of the workpiece (e.g., when machining the inner peripheral surface). Figure 6 is a graph showing the relationship between (a) the override command, (b) the automatic infeed position, and (c) the actual rotational speed in a grinding apparatus and a control method thereof according to an embodiment of the present invention. In the grinding machine and control method according to an embodiment of the present invention, as shown in Figure 6(a), when the override switch is operated, instead of immediately applying the override (to the control device 300 (see Figure 5)), as shown by the dashed line in Figure 6(b), the automatic cutting position by the automatic cutting device 104 is temporarily moved radially away from the object to be ground, and then gradually returned to the original commanded position (coordinates). As a result, the actual rotational speed also catches up with a corresponding delay, as shown in Figure 6(c).

Figure 7 is a flowchart of the control process from start to finish in the grinding machine of this embodiment. Specifically, the grinding machine of this embodiment starts the machining process (S701), checks whether an override switch operation or other override change occurs during machining, and determines whether a speed change will occur (S703). If a speed change occurs (YES in S703), the amount of clearance added to the remaining clearance amount at that time is calculated (S704), the clearance direction is determined (S705), the clearance addition operation is performed (S706), and the speed is changed (S707). Cutting is performed at this changed speed, and it is determined whether the grinding wheel rotation has ended (S708). If the grinding wheel rotation has ended (YES in S708), the machining process ends (S709). On the other hand, if the grinding wheel rotation has not ended (NO in S708), the process returns to S702. Furthermore, if the determination in S703 above shows that there is no change in speed (NO in S703), a release damping operation is performed (S710) and the process proceeds to S708.

The amount of overcut (radius change Δr) corresponding to a change in rotation speed is generally defined by the following equation (1): c(u) may be a constant, or it may be defined as a function related to the U-axis coordinate depending on the configuration of the automatic cutting device 104. In this case, the relationship between the U-axis coordinate and the radius change Δr for a constant R and ω may be investigated in advance, and the relationship may be defined using polynomial approximation or a table.

10 Jig grinding machine (grinding device), 100 Grinding wheel, 102 Grinding wheel rotation device, 104 Automatic cutting device, 106 Another rotation device (C-axis rotation device), 300 Control device, W Workpiece,

Claims (3)

A grinding machine that has an automatic infeed device that can feed or fix a grinding wheel rotating device with a grinding wheel attached in the radial direction on a linear axis, and can further rotate the entire automatic infeed device, including the grinding wheel rotating device, on a separate rotating device to grind the inner or outer surface of a circle. The grinding machine is configured so that the operator can freely change the rotation speed of the separate rotating device with an override switch. When the override switch is operated, rather than immediately applying the control signal, the automatic infeed device is first operated to feed the grinding wheel rotating device in the radial direction on a linear axis away from the object to be ground, and then the rotation speed override of the separate rotating device is applied. This grinding machine is characterized by changing the escape direction when grinding the outside and when grinding the inside. A grinding machine that has an automatic cutting device that can feed or fix a grinding wheel rotating device with a grinding wheel attached in the radial direction on a linear axis, and can further rotate the entire automatic cutting device, including the grinding wheel rotating device, on a separate rotating device to grind the inner or outer surface of a circle. The grinding machine is configured so that the rotation speed of the separate rotating device can be freely changed by the operator using an override switch. When the override switch is operated, rather than immediately applying the control device, the automatic cutting device is first operated to feed the grinding wheel rotating device in the radial direction on a linear axis away from the object to be ground, and then an override is applied to gradually return it to the original coordinates over time. This grinding machine is characterized by changing the escape direction when grinding the outside and when grinding the inside. A grinding machine that has an automatic cutting device that can feed or fix a grinding wheel rotating device with a grinding wheel attached in the radial direction using a linear axis, and can grind the inner or outer surfaces of a circle by rotating the entire device including the grinding wheel rotating device and the automatic cutting device using a separate rotating device, and is configured so that the operator can freely change the rotation speed of the separate rotating device using an override switch, and has a control method for a grinding machine that has a first step of determining whether a speed change will occur if an override change occurs during processing, a second step of calculating an amount of allowance addition and performing an allowance addition operation if a speed change occurs, and a third step of changing the speed and performing cutting at this changed speed, characterized in that the first to third steps are performed in this order.