JP7740165B2 - Insulator manufacturing device and insulator manufacturing method - Google Patents

Description

The present invention relates to an insulator manufacturing apparatus and an insulator manufacturing method.

Generally, spark plugs used in internal combustion engines such as automobile engines have a long insulator inserted into a cylindrical metal shell, which holds the insulator in place. A center electrode, which forms a spark discharge gap opposite a ground electrode welded to the tip of the metal shell, is inserted into an axial hole formed in the insulator at the tip end, and a terminal electrode, which applies high voltage to the center electrode, is inserted at the opposite end.

Such insulators are manufactured by pressing the prepared raw material powder to form a compact with a hole that will become the axial hole, grinding the outer surface of the resulting compact to the desired insulator shape, and then firing the ground compact.

In a conventional grinding process for grinding a molded body, the molded body is supported with an insertion pin inserted from the rear end of a hole formed along the axial direction of the molded body, and is rotated by a rotation mechanism.
On the other hand, the rotating grindstone that grinds the compact has a peripheral surface formed in a shape corresponding to the outer shape of the insulator, and is rotated in the same direction by a rotation mechanism.

The compact is then brought into contact with the circumferential surface of a rotating grindstone, whereby the outer shape of the compact is ground into a shape corresponding to that of an insulator (see Patent Documents 1 and 2).
The method for manufacturing an insulator for a spar plug disclosed in Patent Document 1 includes a molding step of molding a molded body, a grinding step of grinding the molded body, and a firing step of firing the molded body.
The spark plug manufacturing method of Patent Document 2 includes a molding step, a grinding step, and a baking step, and the grinding step uses a supporting means, a pressing means, a deflection amount detecting means, and a control means.

Japanese Patent Application Laid-Open No. 2001-176637 Japanese Patent Application Laid-Open No. 2021-61106

In the manufacturing process for insulators that make up spark plugs, etc., a compact formed from raw material powder is ground into the shape corresponding to the insulator.

However, the above-mentioned Patent Documents 1 and 2 do not disclose the specific configuration of the grinding device used in the grinding process.

The present invention was made in consideration of the above, and provides an insulator manufacturing apparatus and method that can reduce grinding defects.

The insulator manufacturing device of the present invention is an insulator manufacturing device (1) that transports, processes, and removes a workpiece (4) to be inserted into an insertion pin (21), and includes a base (6), an insertion pin (21) that can be inserted into an axial hole (26) of the workpiece (4), an index table (2) on which multiple insertion pins (21, 22, 23, 24) are arranged and that can rotate relative to the base, a servo motor (8) that rotates the index table, and a workpiece engagement portion made of a material with elasticity. The grinding machine includes a rotating roller (30) that can rotate and reciprocate relative to the base, a first motor (31) that rotationally drives the rotating roller, a first drive unit (33) that can reciprocate a first motor case (37) of the first motor, a rotary grindstone (50) that can contact the outer wall of the workpiece and that can rotate and reciprocate relative to the base, a second motor (51) that rotationally drives the rotary grindstone, and a second drive unit (53) that can reciprocate a second motor case (57) of the second motor. The grinding machine employs a configuration in which the rotary grindstone, which rotates in the same direction as the workpiece that is in contact with the workpiece engaging unit and rotating, comes into contact with the rotary grindstone, which rotates in the same direction, to grind the outer wall of the workpiece into a corresponding shape.

According to the present invention, the axial hole of the workpiece is inserted into the insertion pin of the index table, and when the intermittently rotating index table is stopped and fixed in a predetermined position, a rotating roller is brought into contact with the outer wall of the workpiece, which is rotatably supported on the insertion pin, to rotate the workpiece, and a rotating grinding wheel, which rotates in the same direction as the workpiece rotation, is brought into contact with the outer wall of the workpiece from the side opposite the rotating roller, thereby grinding the outer wall of the workpiece.
The workpiece engaging portion of the rotating roller, which has an elastic margin, comes into frictional contact with the outer wall of the workpiece to rotate the workpiece, and the positions of the rotation axes of the rotating roller and the rotating grindstone are advanced or retreated to grind the workpiece.

During grinding, a molded body corresponding to the workpiece is set on the insertion pin provided at a predetermined station on the index table and brought into contact with the rotating roller, continuously applying a predetermined frictional force to the molded body. The molded body is supported in such a way that the reference part of the insertion pin abuts against the reference part while applying a rotational force that does not resist the frictional force received from the rotating grinding roller on one side. The rotating grinding roller then brings the molded body into contact with the rotating grinding roller, grinding it into a shape corresponding to the insulator.

Here, an index table refers to a rotary table that can index the position of a workpiece to a specified position with high precision.

1 is a schematic diagram showing an insulator grinding device according to a first embodiment; 5 is an explanatory diagram showing the pressing force and crushing allowance of the rotating roller before grinding of the insulator grinding device of the first embodiment. FIG. 5 is an explanatory diagram showing the pressing force and crushing allowance of the rotating roller after grinding by the insulator grinding device of the first embodiment. FIG. 3A to 3C are explanatory diagrams illustrating the operations of the rotating roller, the rotating grindstone, and the index table of the insulator grinding device of the first embodiment. (A) An explanatory diagram of the grinding operation of the insulator grinding device of the first embodiment when the rotating roller and the rotary grindstone have retreated to their original positions, (B) An explanatory diagram of the grinding operation of the insulator grinding device of the first embodiment when the rotating roller rotates and advances to rotate the molded body, and (C) An explanatory diagram of the grinding operation of the insulator grinding device of the first embodiment when the rotating roller and the rotary grindstone rotate and advance to grind the molded body. 1A and 1B are explanatory views of the grinding operation of the insulator grinding device according to the first embodiment, illustrating the state when the rotating roller and the rotary grindstone stop rotating, the state when the rotary grindstone retreats, and the state when the rotating roller retreats. FIG. 2 is a plan view showing a mounting portion of a force sensor of the insulator grinding machine according to the first embodiment. 8 is a view showing a mounting portion of a force sensor of the insulator grinding machine according to the first embodiment, taken in the direction of arrow VIII in FIG. 7 . 9 is a view taken in the direction of the arrow IX in FIG. 8 . 6 is a graph for determining whether a ground product is good or bad based on the reaction force (N) applied to the rotating shaft of the insulator grinding device of the first embodiment. 1A is a graph showing the performance of a ground product determined from output data (N) of a force sensor associated with a bearing case of the insulator grinding device of the first embodiment. 1B is a graph showing the performance of a ground product determined from output data (N) of a force sensor associated with a bearing case of the insulator grinding device of the first embodiment. 4 is a graph showing the relationship between the pressing force of the rotating roller and the crushing allowance of the insulator grinding device of the first embodiment. FIG. FIG.

Below, a manufacturing apparatus and method for spark plug insulators according to an embodiment of the present invention will be described with reference to the drawings.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS. 1 to 14. FIG.
A first embodiment of the present invention is a manufacturing apparatus for manufacturing an insulator used in a spark plug. The manufacturing apparatus for an insulator constitutes an insulator grinding apparatus.

As shown in Figures 1, 7, 8, and 9, the insulator manufacturing apparatus 1 grinds a molded body 4, which corresponds to the workpiece to be ground. This manufacturing apparatus 1 consists of an index table 2 having insertion pins 21 that support the molded body 4, a rotating roller 30 that rotates the molded body 4 inserted onto the insertion pins 21 through frictional contact, and a rotating grindstone 50 that grinds the outer wall of the molded body 4 from the side opposite the rotating roller.

The index table 2 has a basic disk shape, and has insertion pins 21, 22, 23, and 24 fixed to the side of the table in a cantilevered manner at equal intervals on a concentric circle. The molded body 4 is inserted into the free end of the insertion pin 21.
As shown in FIG. 7, the molded body 4 has an elongated shape, a basic cylindrical shape, and an axial hole 26 formed along the central axis in the longitudinal direction.
Reference portions are provided on the inner peripheral surface and end surface of molded body 4. A large number of insertion pins 21, 22, 23, and 24 (four in this case) are arranged on an index table, and molded body 4 is set on a predetermined insertion pin (21 in this case). Insertion pins 21, 22, 23, and 24 have reference portions on their outer diameters and flange end surfaces that match molded body 4. Molded body 4 is rotatably supported with the reference portions of insertion pins 21, 22, 23, and 24 abutting against each other.

The compact 4 is rotated by the frictional force applied to the outer wall while remaining inserted into the insertion pin 21. The compact is ground while the inner reference surface of the compact 4, which serves as the grinding reference, is pressed against the outer diameter portion and flange end surface portion of the insertion pin 21.
The rotating roller 30, which comes into contact with the outer wall of the compact 4 and rotates the compact 4 by friction, is capable of switching between contact and separation with the compact 4. The compact engaging portion, which corresponds to the workpiece engaging portion formed on the outer wall of the rotating roller 30, is made of a material with a certain elasticity, and has a certain crushing margin δ when a pressing force is applied to the compact. The rotating roller 30 is rotated by a motor drive, which will be described later, with predetermined torque and rotation speed settings.

The motor 31 that drives the rotating roller 30 has a motor case 37 with a stator fixed to a fixed member 32. The fixed member 32 extends and retracts a rod 34 driven by a servo motor 33, switching the base position to a predetermined position. The servo motor 33 feeds the rotating roller 30 by setting parameters such as the pressing force and feed speed.

The bearing case 35 supporting the rotary shaft 36 of the rotary roller 30 and the force sensors 41 and 42 are connected to the motor case 37 of the motor 31 by bolts 43 and 44. When a reaction force acts on the rotary shaft 36 in the direction of arrow 45 shown in Figure 7, a reaction force acts on the force sensors 41 and 42 in the direction of arrow 47, and the force sensors 41 and 42 detect the pressing force. The rotational driving force of the motor 31 is transmitted to the rotary shaft 36.
7 to 9, the bearing case 35 and the force sensors 41, 42 are both bolted to the bracket portion of the motor 31. The force sensors 41, 42 are placed on top of the bearing case 35 and fastened (together) to the bracket with bolts 43, 44. The reaction force of the rotating shaft 36 of the rotating roller 30 is detected by the force sensors 41, 42, which are fastened together to the bolt fastening portion of the bearing case 35.

The bearing case 35 fixedly supports the rotating shaft 36 that rotatably supports the rotating roller 30, and the bearing case 35 is fastened to the bracket with four bolts 43, 44, 46, and 49. The bracket is mounted so that it can be linearly fed by an LM guide slider driven by a servo motor. The rotating roller 30, which is rotatably held on the bracket, can be moved linearly and positioned by servo motor drive as described above, by setting parameters such as pressing force and feed speed.

A motor is also mounted on one side of the bracket, with the bearing case's rotating shaft connected to the motor's output shaft. As mentioned above, the rotating roller can be rotated by the motor drive with a specified torque and rotation speed set to a specified value.

The force sensor (high-sensitivity force sensor) is fastened only to the fastening side of two of the four bolts 43, 44 on the side where compressive stress occurs in the bearing case 35. Two force sensors 41, 42 are interposed between the bearing case 35 and the bracket and are fastened together with the bolts at a predetermined torque. The reaction force (compressive stress) acting on the bearing case 35 in response to the stress of the rotating roller 30 is sensed by the two force sensors 41, 42, and the detection signal is output to an amplifier. The signal data is processed within the sensor controller, and the output (waveform) is displayed on a monitor, which is a means for displaying the output (waveform) data.

In FIG. 1, the force signals detected by the force sensors 41 and 42 are sent via the force sensor amplifier 12 to the force sensor controller 13, and then transmitted to the control device 14. The control device 14 can determine the degree of wear of the rotating roller 30 and rotary grinding wheel 50 of the manufacturing device 1 based on the data signals received from the force sensors 41 and 42.

The rod 34 that fixes the motor case 37 of the motor 31 can be extended and retracted by driving the servo motor 33. By controlling the position of the rod 34, the feed amount and return amount of the motor 31 and the rotating roller 30 can be changed, and the rotating roller 30 can be switched between pressing against and separating from the outer circumferential surface of the molded body 4.
The grinding wheel 50 is provided on the opposite side of the roller 30 with respect to the insertion pin 21. A motor 51 that rotates the grinding wheel 50 has a motor case 57 with a stator fixed to a rod 54. The rod 54 can be extended and retracted by driving a servo motor 53, which corresponds to a second drive unit, to change the motor shaft of the motor 51 to a predetermined position (a predetermined feed amount and return amount). As a result, the grinding wheel 50 advances in the feed direction shown in FIG. 1 , and when the outer surface of the grinding wheel 50 comes into contact with the outer surface of the compact 4 while rotating in the direction of arrow 56, it grinds the outer surface of the compact 4.

The grinding wheel 50 is driven by a servo motor, with a predetermined torque and rotation speed set for each type of compact particle density being processed. Similarly, the grinding wheel's feed operation is controlled by a servo motor, with pressing force and feed speed parameters set for each type of compact being processed. The control device 14 performs sequence control, and the grinding wheel 50 is fed to the grinding surface on the periphery of the compact 4, where it comes into contact and is ground into a shape corresponding to the insulator.

The servo motor 8 is driven by the sequence control of the control device 14 to rotate (position) the index table 2, and the molded body 4, which is supported by the insertion pin 21, is positioned (indexed) and stopped at the grinding position, completing preparation for grinding.
The rotating roller 30 is rotated by a motor drive with a predetermined torque and rotation speed set to predetermined values. The servo motor 33, which corresponds to the first drive unit, can rotate the rotating roller 30 by setting parameters such as pressing force and feed speed.
The control device 14 uses sequence control to feed the rotating grinding wheel 50 in accordance with the timing of its grinding operation, constantly pressing the molded body 4 with a predetermined force to apply a constant frictional force to the engagement portion of the molded body 4, while supporting the molded body 4 on the insertion pin 21 and rotating it accordingly.
The rotary grinding wheel 50 is rotated by driving a motor 51 with a predetermined torque and rotation speed set for each type of particle density of the compact 4 to be processed. Similarly, the feeding operation of the rotary grinding wheel 50 is performed by setting parameters of pressing force and feed speed for each type of compact 4 to be processed by a servo motor 53 corresponding to the second drive unit, and sequence control of the control device 14 is performed to feed the rotary grinding wheel 50 to the grinding surface on the outer periphery of the compact 4, where it comes into contact and is ground into a shape corresponding to the insulator.

The torque and rotation speed of the rotating roller 30 are set arbitrarily according to the particle density of the compact 4 to be applied. The friction force acting on the engagement portion of the high-density compact is set appropriately.
The frictional force acting on the compact 4 can be constantly absorbed by the deflection of the rotating roller 30, and the frictional force acting on the engaging portion of the compact 4 can be kept constant.
When the rotating roller 30 is adapted to perform grinding operations according to the particle density of the molded body 4 being loaded, the operating pattern, such as the thrust and speed of the servo motor feed, is set arbitrarily to maintain a constant pressing force of the rotating roller 30 on the engagement portion of the molded body 4.

The compact 4 is ground while maintaining the relationship F1>F2 between the pressing force F1 of the rotating roller 30 and the pressing force F2 of the grinding wheel 50 during grinding. The compact 4 is nearly perfectly round, allowing grinding within the tolerance of the diameter dimension, improving production efficiency.
The feed amount of the grinding wheel 50 by the servo motor 53 can be corrected for each station, thereby preventing the mounting errors of the insertion pins 21, 22, 23, and 24 from being accumulated in the grinding dimensions of the compact 4.

The rotary grindstone 50 is driven by a servo motor 53 to control the rotary feed operation by setting predetermined numerical conditions such as torque, rotation speed, feed, etc. for each type of particle density of the compact.
The grinding wheel 50 is fed to the grinding surface on the outer periphery of the compact 4 and brought into contact with it to grind it into a shape corresponding to the insulator. The pressing force of the grinding wheel 50 during grinding is stabilized to keep the friction force constant.
To compensate for mounting errors and variations in the insertion pins 21, 22, 23, and 24 of the index table 2, the feed amount of the servo motor 8 is corrected for each station. This prevents the mounting errors of the insertion pins 21, 22, 23, and 24 from accumulating in the grinding dimensions.

During this grinding process, the compact 4 set on a penetration pin provided at a predetermined station on the index table 2 is brought into contact with the rotating roller 30, continuously applying a predetermined frictional force to the compact 4, and the compact 4 is supported so that its reference portion abuts against the reference portion of the penetration pin 21 while applying a rotational force that does not resist the frictional force from the rotating grindstone 50 on one side. The rotating grindstone 50 is then brought into contact with the compact 4 to grind it into a shape corresponding to the insulator. The insulator grinding device of this embodiment is expected to increase productivity.

1, 5A, and 7 show the state before grinding. In this initial state, the index table 2 is stopped, and the insertion pin 21 is inserted into the axial hole 26 of the compact 4. The upper surface of the inner wall of the axial hole 26 of the compact 4 is in contact with the upper surface 211 of the insertion pin 21.
When compact 4 is rotated by contact friction with rotating roller 30 from the initial state before grinding, as shown in Fig. 2, the outer surface of rotating roller 30 rotating in the direction of arrow 39 presses against the outer surface of compact 4, causing compact 4 to rotate in the direction of arrow 40 due to frictional force, and the center line of the rotation axis of compact 4 is pressed by rotating roller 30, moving the center line of the rotation axis of compact 4 toward rotary grindstone 50 (to the right in Fig. 2) from the position shown in Fig. 5(A). The allowance δ of rotating roller 30 at this time is defined as the pressing force F1 against the compact.

Next, during grinding, as shown in Figure 3, servo motor 53 is driven to extend rod 54 to the left in Figure 2, and the outer surface of grinding wheel 50, rotating in the direction of arrow 47, comes into contact with and presses against the outer surface of compact 4 from the counter-rotating roller 30 side. The pressing force of grinding wheel 50 against the compact at this time is F2. The crushing allowance δ of roller 30 shown in Figure 3 is maintained constant, similar to the state shown in Figure 2 before grinding. The pressing force is maintained so that F1 > F2, as shown in Figure 3.

Next, the relationship between the pressing force of the rotating roller during grinding and the crushing allowance will be described with reference to Fig. 12. Basically, the magnitude of the crushing allowance δ is proportional to the magnitude of the pressing force N1. For example, the pressing force is set so that the crushing allowance falls within the range of region 48 shown in Fig. 12.
Next, the relationship between the pressing force of the rotating roller and the crushing margin will be described.
Figure 2 shows the relative positions of the compact, rotating roller, and grinding wheel before grinding, and Figure 3 shows the relative positions of the compact, rotating roller, and grinding wheel during grinding. The compression allowance δ of the rotating roller is kept constant before and during grinding.

During grinding using this manufacturing equipment, the reaction force acting on the rotating shaft 36 in the direction of arrow 45 shown in Figure 7 is detected by force sensors 41 and 42 due to the balance between the pressing force of the rotary grindstone 50 and the pressing force of the rotating roller 30. The time progression of the reaction force acting on the rotating shaft 36 is detected, for example, as shown in Figure 10. The reaction force acting on the rotating shaft 36 detected by this detection means is determined by the judgment means to be within the distribution range of pass-quality compacts when the reaction force N value in Figure 10 is, for example, between 11 and 28. For example, if the N value is less than 11, the judgment means determines that the compact is not being held down enough by the rotating roller and is prone to slippage, and if the N value exceeds 28, the judgment means determines that the pressing force is too strong and there is a risk of scratches such as streaks or cracks. If a product is determined to be pass-quality, the equipment is inspected.

The manufacturing equipment's judgment means constantly detects the reaction force on the rotating shaft 36. For example, as shown in Figure 11 (A), when the reaction force is within a specified range indicated by the reference numeral 54 in a specified grinding process area, it is judged that there is no abnormality in the quality of the compact, and the process continues. For example, as shown in Figure 11 (B), when the detected reaction force is an undersized value indicated by the reference numeral 55, it is judged to be an abnormality, prompting an inspection to determine when it is time to replace the rotating roller or grinding wheel.

When the grinding process is completed and the rotating roller 30 and grindstone 50 are retracted relative to the compact 4, the index table 2 shown in Figure 1 is rotated in the direction of arrow 7, and the compact 4 is removed from the insertion pin 21 at a position rotated approximately 180 degrees from the position shown in Figure 1 and transported to the next process.

The control device 14 drives the servo motor 8 using sequence control to rotate (position) the index table 2, and then positions (indexes) and stops the compact 4, which is supported on the insertion pin 21, at the grinding position, completing preparations for grinding. The control device 14 uses sequence control to advance the rotating roller 30 in accordance with the timing of the grinding operation of the rotary grindstone 50, and the rotating roller 30 constantly presses the compact 4 with a predetermined force, continuously applying a constant frictional force to the engagement portion of the compact 4, while supporting the compact 4 on the insertion pin 21 and rotating it accordingly. The control device 14 controls the advancement and rotation of the rotating roller 30, as well as the advancement and rotation of the rotary grindstone 50.

An example of the grinding operation of the insulator grinding device of this embodiment will be described with reference to Figures 4 and 5(A) to 6(F). Here, an example of the operation of the rotating roller 30, the rotary grindstone 50, and the index table 2 will be described. In Figure 4, the circled numbers indicate the ordinal numbers of the processes.
<First step>
In the initial state, the index table 2 is stopped, and the rotary roller 30 and the rotary grindstone 50 are in their original positions at the retreat ends of their respective return positions shown in FIGS.

<Second process>
As shown in Figure 5(B), the rotating roller 30 advances and rotates in the direction of the arrow due to the extension of the rod 34 driven by the servo motor 33. The compact 4 follows the rotating roller 30 and begins to rotate due to frictional contact with the rotating roller 30. The pressing force F1 of the rotating roller is maintained at 20 N or more. Meanwhile, the rotary grindstone 50 follows the rotating roller 30 and begins to advance.
<3rd process>
The rotating roller 30 continues to rotate and advance as shown in Figure 5(C). The pressing force F1 of the rotating roller 30 is maintained at 20 N or more. The rotating grindstone 50 rotates in the same direction as the rotation of the compact 4, and starts grinding when it comes into contact with the outer wall of the compact 4.
The relationship F1 (pressing force of the rotating roller 30)>F2 (pressing force of the rotary grindstone 50) is maintained until grinding of the compact 4 is completed.

<4th step>
When grinding of the compact is completed, the rotating roller 30 and the rotary grindstone 50 start to stop rotating, as shown in FIG. 6(D).
<5th step>
When the grindstone 50 stops rotating, it completes its retreat as shown in FIG. 6(E).
<6th step>
When the rotation roller 30 has completed the stopping operation, it completes the retreating movement as shown in FIG. 6(F).

<7th step>
When the grinding wheel 50 has finished retracting, the index table 2, which had been stopped until then, starts rotating in the direction of the arrow 7 shown in Figure 1. This completes the preparation for removing and setting the compacts 4, and outputs a signal. This completes one cycle.
The output data of the determination means shown in Figure 10 shows the transition of the reaction force acting on the rotating shaft 36 during grinding, and a product is determined to be non-defective when the reaction force is in the range of 11 to 28 N. If the pressing force of the rotating roller against the compact is excessive, streaks, scratches, or cracks are likely to occur at the contact point between the rotating roller and the compact. Furthermore, if the pressing force of the rotating roller is too small, slippage occurs between the rotating roller and the compact.

According to this embodiment, it is possible to reduce grinding defects such as cracks and chips that occur when grinding a molded body corresponding to a workpiece into an insulator shape, such as variations in the grinding dimensions of the molded body, such as outer diameter or ellipse, and differences in the shape and particle density of the molded body to be applied.
Furthermore, according to this embodiment, the output data (N) of the force sensor acting on the bearing case can be used to determine the quality of the grinding process.
11(A), when the reaction force on the rotating shaft is, for example, 20 N within a predetermined time range indicated by the reference numeral 54, the compact is ground into a perfect circle and is determined to have the normal outer diameter. After that, the rotating grindstone moves back while the rotating roller remains in contact with the compact, and then the rotating roller moves back and is reset to zero.
11(B), when the reaction force acting on the rotating shaft is, for example, 5 N within a predetermined time range indicated by the reference numeral 55, the pressing force of the rotating roller or the rotating grindstone is determined to be too small, and a judgment is made to prompt an inspection of the timing of replacement of the rotating roller or the rotating grindstone. If the pressing force of the rotating roller or the rotating grindstone is insufficient, the outer shape of the compact may become oval, the outer diameter of the body may become excessively large, or the rotating roller or the rotating grindstone may reach the end of its life.

Next, this embodiment will be described in comparison with comparative examples 1, 2, and 3.
(Comparative Form 1)
Comparative Example 1 is an example where there is an error in the positional accuracy of the insertion pin mounting holes. Specifically, if the machining accuracy of each of the insertion pin mounting holes of the index table is uneven, grinding defects are likely to occur. For example, as shown in Figure 13, if the center position of insertion pin 21 is eccentric by distance X or distance -X with respect to the index table, grinding defects of molded body 401 are likely to occur.
In contrast to this, in this embodiment, as described above, for example as shown in Figure 10 or Figure 11, the transition data of the reaction force acting on the rotating shaft 36 during grinding can be detected, and the quality of the molded body can be determined by a judgment means, thereby reducing grinding defects.

(Comparative Example 2)
In comparative form 2, when there is misalignment of the insertion pin, for example, as shown in Fig. 14(A), the misalignment of the insertion pin 21 is eccentric by a distance X in the positive direction, which tends to result in grinding defects like the molded body 402. For example, as shown in Fig. 14(B), the misalignment is eccentric by a distance X in the negative direction, which tends to result in grinding defects like the molded body 403.
In contrast to this, in this embodiment, as described above, for example as shown in Figure 10 or Figure 11, the transition data of the reaction force acting on the rotating shaft 36 during grinding can be detected, and the quality of the molded body can be determined by a judgment means, thereby reducing grinding defects.

(Comparative Example 3)
Comparative Example 3 is an insulator manufacturing apparatus that uses a rotating roller and a rotary grindstone, and is a manufacturing apparatus that does not have a force sensor on the bearing case that supports the rotating shaft of the rotating roller. Various issues in the grinding process that uses this manufacturing apparatus to grind insulators (molded bodies formed from raw material powder) that make up spark plugs, etc. will be described in the following items (1) to (10).

(1) The insulator manufacturing apparatus according to Comparative Example 3 has the following problems when drawing high density type molded bodies.
When the frictional force decreases due to wear of the rotating roller, when the crushing allowance of the forward end fixed rotating roller becomes excessive, or when the frictional force becomes excessive or too small due to wear of the rotating grinding wheel, the outer diameter of the molded body may become excessive, or the cross-sectional shape may become elliptical, resulting in poor grinding, or the molded body may be prone to cracks or chips.
(2) When grinding a compact, the rotating roller applies a certain frictional force to the engaging portion of the compact, causing the compact to continue to rotate in the opposite direction to the rotating roller, while the rotating grindstone is brought into contact with the grinding portion of the compact to grind the compact. If the insertion pins of the index table are misaligned, the cross-sectional outer or inner wall shape of the compact will become elliptical, resulting in poor grinding.

(3) The grinding reference for the molded body is obtained by the rotating roller applying a certain frictional force to the outer peripheral engagement portion of the molded body, and at that time pressing the reference surface of the molded body against the outer diameter portion and flange end surface portion, which are the reference of the insertion pin.The forward end of the rotating roller is fixed, and the change in the reduction in the outer diameter of the molded body due to the grinding process is absorbed by the elasticity of the rotating roller.
For this reason, the frictional force caused by the pressing force of the rotating grinding wheel changes depending on the progress of grinding, but it is difficult for the elasticity of the rotating roller to absorb the change in the reduction in the outer diameter of the molded body, and since the forward position of the servo motor for one of the rotating grinding wheels is also set to a predetermined position, it is difficult to perform grinding while maintaining the frictional force caused by the pressing force of the rotating roller within a constant range.
Therefore, the frictional force acting on the engaging portion of the compact due to the pressing force of the rotating roller is reduced, and the compact is likely to succumb to the frictional force acting on the compact from the pressing force of the grindstone.
In this state, even if the molded body is pressed against the grinding reference of the insertion pin by the pressing force of the rotating roller, the molded body cannot be brought into contact with the grinding reference of the insertion pin, and grinding will be carried out with a gap remaining between the molded body and the insertion pin, which means that the processing of the molded body will end with it remaining oval or with a large diameter, making it easy for grinding defects to occur.

(4) When using an index table for transport, it is common for some machining errors and variations to occur in the position of each mounting hole for the insertion pin, which is specific to the index table. Such errors and variations in part machining can cause misalignment of the coordinates of each indexing station for the grinding reference of the insertion pin. Because the forward end of the rotating roller is fixed, as mentioned above, errors and variations in the mounting position of the grinding reference for the insertion pin accumulate as errors when the compact is ground, and since this variation cannot be corrected or adjusted, the compact is prone to grinding defects, such as oval shapes or large diameters, which still contain these errors.

(5) In recent years, there has been a trend toward smaller spark plugs and smaller diameters due to factors such as an increase in the area occupied by intake and exhaust valves in the combustion chamber as a result of the increased power output of internal combustion engines. This has created a demand for smaller insulators as well. To achieve this smaller size and smaller diameter insulators, the molding density has been increased (fine grain size, increased pressure), and the thickness from the outer periphery of the insulator to the axial hole has been reduced to reduce the diameter of the insulator.
Such high density type compacts have improved molding density compared to conventional density types, and therefore have larger frictional forces and grinding resistance, resulting in poorer grindability.

When such high-density compacts are pulled and ground using conventional insulator grinding equipment, the frictional force and grinding resistance are greater than with conventional density types, so the pressing force on the rotating grindstone must be increased, which inevitably results in additional frictional force pushing the compact back toward the rotating roller during grinding.

(6) When grinding a high-density compact with the forward end of the rotating roller fixed, if the frictional force acting on the engaging portion of the compact due to the pressing force of the rotating roller decreases, the compact is likely to succumb to the frictional force acting on the compact from the pressing force of the grinding wheel. As a result, the compact cannot be pressed against the grinding reference of the insertion pin to bring the compact into contact with the grinding reference of the insertion pin, and grinding is carried out with a gap between the compact and the insertion pin. This means that the processing of the compact ends with an oval or large diameter, further increasing the frequency of grinding defects.

(7) If the pressing force of the rotating roller is set strong to match the grinding resistance of a high-density type molded body, excessive force will be applied to the rotating roller engagement part of the molded body, making it easy for grinding defects to occur, such as scratches on the rotating roller engagement part of the molded body.
(8) If the pressing force of the grinding wheel is set strong to match the grinding resistance of a high-density type compact, and the thickness of the compact from its outer surface to its shaft hole is thin, the frictional force of the grinding wheel becomes excessive, which can easily cause grinding defects such as cracks or chips on the grinding surface of the compact.
(9) With high-density compacts, it is inevitable that the frequency of wear of the rotating rollers and grinding wheels will increase in proportion to the increase in molding density. However, if worn rollers and grinding wheels that have passed the replacement period continue to be used for grinding, the frictional force and grinding resistance acting on the compact will decrease significantly, making it impossible to grind the compact, and the resulting grinding defects will be oval or of a large diameter.

(10) Since it is difficult to estimate the frequency of wear of the rotating rollers and grinding wheels due to grinding processing, the replacement intervals for the rotating rollers and grinding wheels are set relatively early, which results in poor production efficiency.
In this embodiment, the problems (1) to (10) described above can be solved.

(Other embodiments)
Although the present embodiment shows an example in which four insertion pins are provided, the present invention does not limit the number of insertion pins provided on the index table.
The number of force sensors of the present invention is not limited to the number used in this embodiment.
As described above, the present invention is not limited to the above-described embodiment, and can be implemented in various forms without departing from the spirit and scope of the present invention.

The insulator manufacturing apparatus of the present invention performs the operations of setting, transporting, processing, and removing the workpiece on the insertion pin through the feeding operation of the first motor case by the first drive unit, the feeding operation of the motor case by the second drive unit, the rotation of the rotating roller and the rotary grindstone, the returning operation of the first motor case by the first drive unit, the returning operation of the second motor case by the second drive unit, and the intermittent rotation of the index table.

The insulator manufacturing apparatus of the present invention is equipped with a control device (14) that controls the rotation speed and torque of the rotating roller, the rotation speed and torque of the rotary grindstone, the feed thrust and speed of the first servo motor, and the thrust and speed of the second servo motor.

The insulator manufacturing apparatus of the present invention may be configured to include highly sensitive force sensors (41, 42) for detecting stress generated in the rotary bearing case (35) of the rotary roller, thereby making it possible to determine the quality of grinding and the timing for replacing the rotary roller or rotary grindstone.
A highly sensitive force sensor senses the reaction force (compressive stress) applied to the bearing case during grinding, and the output (waveform) data can be used to check the quality of the compact and determine when to replace the rotating rollers or grinding wheels due to wear. By stabilizing the pressing force during grinding, it is easy to keep the friction force constant, and by not applying excessive pressing force to the compact, it prevents cracking or chipping of the compact. In addition, the output (waveform) data can be used to check the quality (quality) of the grinding of the compact and to determine when to replace the rotating rollers or grinding wheels.

The insulator manufacturing method of the present invention is a method for manufacturing insulators for spark plugs, and includes the steps of: rotating and advancing a rotating roller (30) toward a workpiece (4) rotatably supported on an insertion pin (21) of an index table (2); rotating and advancing a rotary grindstone (50) toward the workpiece; starting grinding of the workpiece with the rotary grindstone contacting the rotating workpiece due to frictional force caused by contact between the rotating roller and the workpiece; stopping the rotation of the rotating roller and the rotary grindstone after grinding of the workpiece is completed; retracting the rotary grindstone; retracting the rotating roller; and intermittently rotating the index table.

1 Insulator manufacturing device 2 Index table 4 Molded body (work)
6 Base 8 Servo motor 14 Control device 21, 22, 23, 24 Insertion pin 26 Shaft hole 30 Rotation roller 33 Servo motor (first driving unit)
35 Bearing case 36 Rotating shaft 38 Work engagement portion 41, 42 Force sensor (high sensitivity force sensor)
50 Rotating grindstone 53 Servo motor (second driving unit)

Claims (8)

An insulator manufacturing device (1) that conveys, processes, and removes a work (4) to be inserted into an insertion pin (21),
A substrate (6),
an insertion pin (21) that can be inserted into a shaft hole of the workpiece (4);
an index table (2) on which a plurality of the insertion pins (21, 22, 23, 24) are arranged and which is rotatable relative to the base;
a servo motor (8) for rotating the index table;
a rotating roller (30) having a work engaging portion (38) made of a material having an elasticity and capable of rotating and reciprocating relative to the base;
a first motor (31) for driving the rotary roller;
a first drive unit (33) capable of reciprocating a first motor case (37) of the first motor;
a rotary grindstone (50) that can contact the outer wall of the workpiece and that can rotate and reciprocate relative to the base;
a second motor (51) for rotating the grindstone;
a second drive unit (53) capable of reciprocating a second motor case (57) of the second motor,
The insulator manufacturing device grinds the outer wall of the workpiece into a corresponding shape by bringing the rotating grindstone, which rotates in the same direction as the workpiece that is in contact with the workpiece engaging portion and rotating. 2. The insulator manufacturing device according to claim 1, wherein the operations of setting, transporting, processing, and removing a workpiece on the insertion pin are performed by the feeding operation of the first motor case by the first drive unit, the feeding operation of the second motor case by the second drive unit, the rotation operation of the rotating roller and the rotary grindstone, the returning operation of the first motor case by the first drive unit, the returning operation of the second motor case by the second drive unit, and the intermittent rotation operation of the index table.
The insulator manufacturing apparatus of claim 2, further comprising a control device (14) that controls the rotation speed and torque of the rotating roller, the rotation speed and torque of the rotary grindstone, the feed thrust and speed of the first drive unit, and the thrust and speed of the second drive unit. The insulator manufacturing apparatus of claim 3, wherein the pressing force of the rotating roller against the workpiece is F1 and the pressing force of the rotating grindstone against the workpiece is F2, and the relationship F1 > F2 is maintained. The insulator manufacturing apparatus of claim 4 is equipped with force sensors (41, 42) that detect stress generated in the bearing case (35) that rotatably supports the rotating shaft (36) of the rotating roller. The insulator manufacturing apparatus of claim 5 is equipped with a means for inputting the output signal of the force sensor and displaying the output data while the workpiece is being ground. The insulator manufacturing apparatus of claim 2, further comprising a plurality of the insertion pins cantilevered and fixed concentrically on one side of the index table. A method for manufacturing a spark plug insulator, comprising:
a step of rotating and advancing a rotary roller (30) toward a workpiece (4) rotatably supported on an insertion pin (21) of an index table (2);
A process in which a grinding wheel (50) rotates and advances toward a workpiece;
a step of starting grinding of the workpiece by the rotating grindstone contacting the rotating roller and the workpiece rotating due to frictional force;
a step of stopping the rotation of the rotary roller and the rotary grindstone after grinding of the workpiece is completed;
a step of the grindstone retracting;
the rotating roller retracting;
and a step of intermittently rotating the index table.