KR20110038718A - Nozzle position correction mechanism and coating device provided with the same - Google Patents

Abstract

When the nozzle 707 for discharging the liquid material and the work 708 mounted on the table 710 are moved relative to each other by the driving mechanisms 702, 703, and 704 to apply the liquid material to the surface of the work. A nozzle position correction mechanism for correcting the position of the nozzle, the adjusting portions 304, 305 and 306 for adjusting the relative position of the nozzle with respect to the drive mechanism, and a nozzle insertion hole into which the nozzle is inserted. ), And a positioning member 101 having a contact surface 106 that abuts against a tip portion of the nozzle inserted into the nozzle insertion hole. By such a configuration, the nozzle can be adjusted in a simple configuration and mechanically without requiring a special device such as a camera or a sensor.

Description

Nozzle position correction mechanism and the coating apparatus provided with the same {NOZZLE POSITION CORRECTING MECHANISM AND APPLICATION DEVICE WITH SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nozzle position correcting mechanism and a coating apparatus including the same. More specifically, the nozzle and the work mounted on the table are relatively moved by a drive mechanism to move the surface of the work. It is related with the nozzle position correction mechanism which can correct | amend the nozzle position shift according to maintenance work, when apply | coating a liquid material to this.

When performing operations, such as replenishment of liquid materials, maintenance, etc., the discharge apparatus containing a nozzle and a storage container may be detached from a coating apparatus. And when the operation | work of replenishment of liquid material, maintenance, etc. is completed, a discharge apparatus is again attached to a coating apparatus. At this time, the position of the discharge port formed in the front-end | tip of a nozzle which a discharge apparatus has is often shifted from the position before removing. If the application operation is resumed in this state, the liquid material is applied to an undesired position, and as a result, the product coated with the liquid material becomes a defective product. Therefore, in order to avoid the above situation, various mechanisms and methods for adjusting the nozzle tip position when mounting the discharge device have been proposed.

For example, Patent Document 1 discloses a coating apparatus for applying a liquid material to a substrate surface, wherein the nozzle is mounted on a syringe in which the liquid material is stored, and discharges the liquid material toward the substrate surface. The syringe which picks up and detects the height position of the tip of the nozzle and the position deviation amount from the vertical line of the nozzle tip from the captured image, and the syringe based on the height position and the position deviation amount from the position detector. Disclosed is a coating apparatus comprising a controller for correcting the position of a.

In addition, Patent Document 2, in a coating device provided with a coating nozzle and an imaging device, as a method for detecting these relative positions, the coating agent is applied to a test coating surface by the coating nozzle, and the imaging of the imaging device at that time The first position, which is the center position, is acquired, and then the imaging agent is applied to image the coating agent applied to the test coating surface, and the second position, which is the position where the center of the coating agent and the imaging center of the imaging device coincide, is obtained. And obtaining the difference in the X-axis direction and the Y-axis direction between the first position and the second position as a value indicating a relative position of the coating nozzle with respect to the imaging device. A method is disclosed.

Although the position detection apparatus used by patent document 1 or 2 is a camera, other optical instruments, for example, a laser displacement meter, a photo sensor, etc. may be used.

Reluctant to install such a special apparatus, the XYZ drive mechanism equipped with the discharge device is manually operated to move the nozzle tip to the target position such as the application position by visual observation, and to apply from the difference in the movement amount. Correction of settings such as the work start position is still performed.

Japanese Patent Application Publication No. 2000-5679 Japanese Patent Application Publication No. 2003-142816

However, in the inventions described in Patent Documents 1 and 2, in order to detect a position, a special device such as a camera or a sensor is required, and arithmetic processing and control based on the detection result are also complicated.

In addition, in the invention described in Patent Document 2, test coating must be performed for position detection, and therefore, a test coating surface needs to be separately provided.

In addition, when the position is adjusted by visual observation, the position varies depending on the operator, and the precision is limited. This task is also cumbersome and time consuming.

Accordingly, an object of the present invention is to provide a nozzle position correction mechanism capable of mechanically adjusting the position with a simple configuration and a coating device including the same without requiring a special device such as a camera or a sensor.

1st invention is a nozzle position correction mechanism for correct | amending the position of the nozzle, when apply | coating a liquid material to the surface of a workpiece | work by relatively moving a nozzle which discharges a liquid material, and the workpiece mounted on the table by a drive mechanism. And an abutting surface in contact with an adjusting portion for adjusting the relative position of the nozzle with respect to the drive mechanism, a nozzle insertion hole into which the nozzle is inserted, and a tip portion of the nozzle inserted into the nozzle insertion hole. It is a nozzle position correction mechanism characterized by including the positioning member which has a surface.

2nd invention WHEREIN: In the 1st invention, the said positioning member includes the space which forms the said contact surface inside, and the said nozzle insertion hole is formed so that the one surface of the said positioning member may communicate with the said space. It is characterized by.

3rd invention WHEREIN: In 1st invention, the said positioning member includes the 1st member which has the said nozzle insertion hole, and the 2nd member joined with the said 1st member including the space which forms the said contact surface. Characterized in that provided.

In 4th invention, in the 2nd or 3rd invention, the said space comprises the window which can visually recognize the said contact surface from the outside, It is characterized by the above-mentioned.

In 5th invention, in any one of 1st-4th invention, the said positioning member is provided with two or more nozzle insertion holes of different inner diameters, It is characterized by the above-mentioned.

In 6th invention, in the invention of any one of 1st-6th, the edge part of the nozzle entrance side of the said nozzle insertion hole is formed in taper shape. It is characterized by the above-mentioned.

In the seventh invention, in any one of the first to sixth inventions, the positioning member is made of a plastic material.

The eighth invention provides a nozzle position correction mechanism according to any one of the first to seventh inventions, a discharge device having a nozzle for discharging a liquid material, a table on which a workpiece on which a liquid material is applied, a nozzle, and a work piece are mounted. It is a coating device provided with the drive mechanism and the control part which make it move relatively.

In 8th invention, in the 8th invention, the said control part grasps the position of a positioning member as a relative position with respect to the reference position of the said drive mechanism.

According to the present invention, since the positioning is mechanically performed without using a special device such as a camera or a sensor, the configuration can be simplified, and there is no variation in work accuracy by the operator.

In addition, nozzle position adjustment can be performed in a short time without complicated calculation processing or control, and setting correction of a coating operation start position etc. is also unnecessary.

1 is a perspective view schematically showing a positioning member according to the present invention.
2 is a front view of a positioning member according to the present invention.
3 is a perspective view schematically showing an adjustment mechanism according to the present invention.
4 is a three side view of the adjustment mechanism according to the present invention.
5 is a flowchart of a first correction step according to the present invention.
6 is a flowchart of a second correction step in accordance with the present invention.
7 is a perspective view schematically showing the coating apparatus according to the first embodiment.
8 is a perspective view schematically showing a positioning member according to a second embodiment.

EMBODIMENT OF THE INVENTION Below, one form for implementing this invention is demonstrated.

Positioning member

The perspective view which showed the positioning member 101 which concerns on this invention schematically is shown in FIG. 1, and a front view is shown in FIG. In the structural example of FIGS. 1 and 2, the positioning member 101 is composed of two members, the fitting member 102 and the contact member 103. The fitting member 102 has a substantially rectangular parallelepiped shape, and is formed such that the hole 104 into which the tip portion of the nozzle 707 of the discharge device 705 is inserted penetrates from the upper surface to the lower surface.

The hole 104 is formed to a diameter slightly larger than the nozzle 707 and has a depth (for example, 1/3 to 1/2 of the length of the nozzle) sufficient to correct the misalignment of the nozzle 707. .

As for the hole 104, the taper part 105 is formed in the circumference part of a nozzle entrance side. In other words, the inlet portion of the hole 104 is in the shape of a circular truncated cone, and is cylindrical in shape from the tip of the truncated cone to the outlet portion. In this way, the tapered portion 105 is formed so that the nozzle 707 is more easily inserted when the tip portion of the nozzle 707 is fitted into the hole 104 by the adjustment mechanism 301 described later. have. In addition, the fitting member 102 is preferably made of a plastic material (for example, polyether ether ketone) having excellent thermal properties (especially expansion or contraction). This is because, first, the error of nozzle position correction due to heat can be minimized by suppressing thermal expansion and contraction. Second, when the nozzle 707 is inserted into the hole 104, the nozzle 707 is inserted into the hole 104. This is because there is a possibility of damaging 707. If such a purpose can be achieved, only a part of the positioning member 101 (for example, only the fitting member 102) may be made of a plastic material.

And the shape of the hole 104 should just be formed in accordance with the shape of the nozzle 707, It is not limited to a cylindrical shape.

The contact member 103 has a concave shape having a concave portion 108 in the center, and a contact surface whose bottom surface is in contact with a surface on which a discharge port at a tip portion of the nozzle 707 is formed. Configure 106. By forming the contact surface 106 with a gap between the contact member 103 and the fitting member 102, the nozzle 707 is fitted by the adjustment mechanism 301 described later to bring the tip of the nozzle to the contact surface. When hit, it can be confirmed by visual observation (role of window). In the structural example of FIG. 1 and FIG. 2, the above-mentioned two members 102 and 103 are fixed by fastening members, such as the screw 107, and comprise the positioning member 101. As shown in FIG. When the fitting member 102 and the contact member 103 are constituted by separate members, a liquid material adheres to the inner or outer circumference of the hole 104, or the diameter of the nozzle 707 is changed. Even if the entire positioning member 101 is not removed, only the fitting member 102 can be removed and cleaned or replaced with another component.

First of all, the two parts 102 and 103 described above do not need to be constituted by separate members, and the hole 104 into which the nozzle 707 is fitted or the contact surface 106 to which the nozzle tip abuts are formed into one member. You may form. In addition, since the recessed part 108 is not an essential structure, it does not need to be provided.

The positioning member 101 is provided at a position (a position at a specified coordinate from the reference position) relative to the reference position (for example, origin) of the drive mechanisms 702, 703, 704. For example, although the positioning member 101 is provided in the position which does not overlap with the application | coating object 708 on the table 710, you may provide wherever it is in the movable range of the nozzle 707. FIG. Since the positioning member 101 is fixedly arranged at a specific position, when the positioning member 101 adjusts the position of the nozzle 707, the position of the nozzle 707 is aligned with the position (coordinate) stored in the controller. Can be. In this case, since the relationship between the position-adjusted nozzle 707 and the application | coating position on a workpiece | work becomes as the position (coordinate) memorize | stored in the control part, the specific operation | work of an application | coating start position is also unnecessary.

Further, in the fitting member 102 of the positioning member 101, a relatively deep (long) straight hole is formed in parallel with a straight line perpendicular to the plane of the workpiece, whereby the nozzle center at the time of replacing the nozzle 707 The deviation (inclination, etc.) from the above-mentioned vertical straight line of an axis can be corrected. In the present invention, when the nozzle 707 is adjusted to a position where the tip portion of the nozzle 707 collides with the contact surface of the contact member 103, the position (from the reference plane) in the Z-axis direction of the tip portion of the nozzle 707. Height) is always the same, it is not necessary to change the setting of clearance required to apply on the workpiece. Therefore, it is easy to cope with the nonuniformity, such as the shape of the tip part of a nozzle by the kind of nozzle 707 and a manufacturing error.

Thus, by using the positioning member 101 of the present invention, the position can be easily adjusted without automatically or manually changing the application position of the nozzle 707 and the setting of the clearance with the work piece.

[Adjustment mechanism]

The perspective view which showed the adjustment mechanism 301 which concerns on this invention schematically is shown in FIG. 3, and its three side view is shown in FIG. In FIG. 4, (a) is a front view, (b) is a top view, (c) is a left side view. Here, each of the directions of the X, Y, and Z axes is the direction of the coordinate axis indicated by the symbol "302" in FIG.

As shown in FIG. 3, the adjustment mechanism 301 is provided between the discharge device 705 (shown in broken lines) and the connection member 303 mounted to the Z-axis drive mechanism 704 (shown in broken lines). have. And the adjustment mechanism 301 consists of the X direction adjustment part 304, the Y direction adjustment part 305, and the Z direction adjustment part 306, and each adjustment part 304, 305, 306 is the slide guide 307, respectively. , 308, 309 and slide members 310, 311, 312. Each slide guide 307, 308, 309 is mounted to move each slide member 310, 311, 312 in each direction indicated by an arrow in FIG. 3, whereby X, It can move in each direction of Y and Z.

In addition, each adjustment part 304, 305, 306 is equipped with the clamp plates 313, 314, 315 and clamp screws 316, 317, 318 for fixing each adjustment part in arbitrary positions. The clamp plate 313 is provided between the slide member and the connection member, and the clamp plates 314 and 315 are provided between the two slide members. One side of the clamp plates 313, 314, and 315 is fixed with the fixing screw 319, and the other side is fixed with the clamp screws 316, 317, and 318. On the clamp screw 316, 317, 318 side of the clamp plates 313, 314, 315, an elliptical hole 320 corresponding to the moving direction is drilled. The clamp screws 316, 317, and 318 are composed of a handle portion having a large diameter and a screw portion having a small diameter, and the screw portion is inserted with a slight gap with respect to the width of the hole 320. The tip of the screw is inserted into the slide member or the connecting member with a screw.

The functions of the clamp plates 313, 314, and 315 and the clamp screws 316, 317, and 318 will be described below by taking the Z-direction adjusting unit 306 as an example. When the Z clamp screw 318 is loosened, the force that pinches the Z clamp plate 315 between the handle portion of the Z clamp screw 318 and the Y slide member 311 is loosened. The Z slide member 312 is movable. On the contrary, when the Z clamp screw 318 is tightened, the Z clamp plate 315 is sandwiched between the handle portion of the Z clamp screw 318 and the Y slide member 311 to restrict movement, thereby allowing the Z slide member 312 to be moved. Is fixed. The Z slide member 312 is movable within the range of the length of the elliptical hole 320 drilled in the Z clamp plate 315.

[Calibration Step]

The steps of correcting the position of the nozzle 707 using the positioning member 101 and the adjustment mechanism 301 will be described below. In addition, below, although the code | symbol may be attached | subjected for convenience of description, it does not demonstrate the step limited to the structure of drawing corresponding to a code | symbol.

5 shows a flowchart of the first correction step of the present invention.

First, the discharge apparatus 705 which has a nozzle is attached to the drive mechanism 702, 703, 704 of the coating device 701 via the adjustment mechanism 301 (STEP11). Here, the nozzle 707 is moved upward in the Z direction by the adjustment mechanism 301 (STEP12). This is to prevent the tip of the nozzle 707 from colliding with the positioning member 101 when the nozzle 707 is moved in the next step. Next, the nozzle 707 is moved to the position (XYZ positioning position) of the preset positioning member 101 using the drive mechanisms 702, 703, 704 (STEP13). The positioning position is not changed once set, and the adjustment and change of the position of the nozzle 707 are performed using the adjustment mechanism 301 (STEP 14 to 15). When the nozzle 707 is moved above the positioning member 101, first, the adjusting portions 304 and 305 in the X and Y directions so that the tip of the nozzle 707 fits the position of the hole 104 of the fitting member. ), The position of the tip of the nozzle 707 is finely adjusted. When this alignment is completed, the clamp screws 316 and 317 are tightened to fix the X and Y direction adjusting portions (STEP 14). Next, the nozzle 707 is inserted into the hole 104 of the fitting member using the Z direction adjusting unit 306, and lowered until the tip of the nozzle 707 strikes the contact surface 106. At this time, the tip of the nozzle 707 may be performed while visually confirming. The clamping direction 306 is fixed by tightening the clamp screw 318 at the bumped position (STEP15). The nozzle 707 is removed from the hole 104 of the fitting member to start the coating operation (STEP16).

Alternatively, the position of the nozzle 707 may be adjusted in the steps as shown below.

6 shows a flowchart of the second correction step of the present invention.

First, the discharge device 705 having the nozzle 707 is attached to the drive mechanisms 702, 703, 704 of the coating device 701 via the adjustment mechanism 301 (STEP21). Next, the nozzle 707 is moved to the X and Y positions except the Z position among the preset XYZ positioning positions using the drive mechanisms 702 and 703 (STEP22). When the nozzle moves upward of the positioning member 101, the nozzles are used by using the adjusting portions 304 and 305 in the X and Y directions so that the tip position of the nozzle 707 is aligned with the position of the hole 104 of the fitting member. The position of the tip of 707 is finely adjusted. When this alignment is completed, the clamp screws 316 and 317 are tightened to fix the X and Y direction adjusting portions (STEP 23). Next, only the movement to the Z position among the preset XYZ positioning positions is performed to the middle using the drive mechanism 704 (STEP24). The nozzle 707 inserted in the hole 104 of the fitting member to the middle in STEP24 is lowered using the Z direction adjusting part 306 until the tip of the nozzle 707 hits the contact surface 106. At this time, the tip of the nozzle 707 may be performed while visually confirming. Tighten the clamp screw 318 at the hit position to fix the Z direction adjustment part (STEP25). The nozzle 707 is removed from the hole 104 of the fitting member to start the coating operation (STEP26).

As mentioned above, although two steps were illustrated, when the positioning member 101 and the adjustment mechanism 301 are used, it is not limited to the said two steps, It is possible also by other steps.

Hereinafter, although an Example demonstrates the detail of this invention, this invention is not limited by an Example.

Example 1

[Application device]

As shown in FIG. 7, the coating device 701 according to the present embodiment includes an X drive mechanism 702, a Y drive mechanism 703, a Z drive mechanism 704, a discharge device 705, and these. A control unit 709 for controlling the operation is provided.

The Z drive mechanism 704 is provided in the X drive mechanism 702. On the Y drive mechanism 703, a table 710 on which the application object 708 is mounted is provided. The discharge device 705 includes a storage container 706 for storing the liquid material and a nozzle 707 for discharging the liquid material at its tip. Although the combination of the storage container 706 and the nozzle 707 was shown as the discharge apparatus 705, if it has the nozzle 707, it is not limited to this, Any apparatus may be sufficient.

The adjustment mechanism 301 is provided between the Z drive mechanism 704 and the discharge device 705. At this time, the ejection apparatus 705 does not mount the adjustment mechanism 301, the Z-axis drive mechanism 704, and the ejection apparatus 705 in series in the Y direction, but the ejection apparatus 705 is the site | part of the X direction of the adjustment mechanism 301 [Example For example, the slide member 312 is preferably disposed. Thereby, operation with respect to the adjustment mechanism 301 can be performed easily. Further, by providing the discharge device 705 in the X direction of the adjustment mechanism 301, the distance from the X-axis drive mechanism 702 is shortened, so that the discharge device 705 and the adjustment mechanism 301 are serially in the Y direction. The load which deflects the Z-axis drive mechanism 704 can be reduced more than when arrange | positioned.

The positioning member 101 is provided at a position which does not overlap the application object 708 on the table 710. In this embodiment, although the positioning member 101 is provided on the table 710, it is not necessary to necessarily provide it on the table 710, and may be provided wherever it exists in the movable range of the nozzle 707. FIG. In addition, when installing on the table 710, the contact member 103 may be integrally provided with the table 710, and only the fitting member 102 may be detachable. According to any installation method, the positioning member 101 is a position relatively positioned relative to the reference position (for example, the origin, etc.) of the drive mechanisms 702, 703, 704 (the position at the designated coordinates from the reference position). It is installed in). In order to ensure the reproducibility of the mounting position when replacing or the like, it is preferable to process the mounting surface with good accuracy, and to provide a positioning pin or the like not shown.

At the time of application | coating operation, the prepared discharge apparatus 705 is first installed in the application apparatus 701. FIG. Thereafter, the position of the nozzle 707 is adjusted in the manner as described above. Then, the application object 708 is mounted on the table 710 and fixed. Next, it moves below the nozzle 707 and application | coating is started. When application | coating is complete | finished, the table 710 and the discharge apparatus 705 are moved to the standby position by each drive mechanism 702, 703, 704, and the application | coating operation | work to one application | coated object 708 is complete | finished. In the case where the application operation is continued for the plurality of application objects 708, the above-described operation is repeated by exchanging the application object 708 that has already been applied with the application object 708 that is not applied. In addition, when the discharge apparatus 705 is detached and mounted in order to refill the liquid material or to replace the nozzle 707, the above-described nozzle position adjustment is performed and the above-described operation is resumed.

Example 2

[Configuration example in which a plurality of holes are formed in the positioning member]

In Example 1, although there was only one hole 104 into which the nozzle of the positioning member 101 is fitted, a plurality of holes 805 having different inner diameters in order to correspond to a plurality of types of nozzle diameters in which use is assumed. To 809). The structural example is shown in FIG.

The positioning member 801 shown in FIG. 8 is comprised by two members, the fitting member 802 and the contact member 803 similarly to Example 1. FIG. In the fitting member 802, a hole 805 into which the nozzle used most is fitted is formed in the center. On the right side, holes 806 and 807 having a larger diameter than the center hole 805 are formed, and on the left side, holes 808 and 809 having a diameter smaller than the central hole 805 are formed. In each of the holes 805 to 809, a tapered portion 810 as described above is formed to match the diameter of the hole. By forming the plurality of types of holes 805 to 809 in this manner, it is possible to cope with a change in the liquid material and a change in the amount of the desired coating without replacing the positioning member 801. Moreover, what is necessary is just to form the hole into which the nozzle is fitted, if the nozzle diameter to be used is predetermined previously. The contact surface 804 formed in the contact member 803 is formed corresponding to the number of holes 805 to 809.

[Industry availability]

This invention can be implemented in the various apparatus which discharges a liquid material from a nozzle.

As an example, not only the air type that applies the compressed air to the liquid material in the storage container having a nozzle at the tip for a desired time, but also, for example, a flat tubing mechanism or a rotary tubing mechanism. A tubing type having a plunger type, a plunger type sliding a plunger to move and discharge the plunger to a desired amount in close contact with an inner surface of a storage container having a nozzle at the tip, a screw type for discharging a liquid material by rotation of a screw, and a liquid to which a desired pressure is applied. The present invention can also be applied to a valve type for controlling the material to be discharged by opening and closing the valve, and a jet type device for impinging the valve body on the valve seat to discharge the liquid material from the nozzle tip.

101: positioning member 102: fitting member (first member)
103: contact member (second member) 104: hole (nozzle insertion hole)
105: taper portion 106: contact surface
107: screw 108: recess (space)
301: adjustment mechanism 302: coordinate axis
303: connection member 304: X direction adjusting portion
305: Y direction adjustment unit 306: Z direction adjustment unit
307: X Slide Guide 308: Y Slide Guide
309: Z slide guide 310: X slide member
311: Y slide member 312: Z slide member
313: X clamp plate 314: Y clamp plate
315: Z clamp plate 316: X clamp screw
317: Y clamp screw 318: Z clamp screw
319: set screw 320: oval hole
701: coating device 702: X drive mechanism
703: Y drive mechanism 704: Z drive mechanism
705: discharge device 706: storage container (syringe)
707: nozzle 708: coating object
709: control unit 710: table
801: positioning member 802: fitting member
803: contact member 804: contact surface
805: central hole 806, 807: large diameter hole
808 and 809: small diameter holes 810: tapered portion

Claims (9)

A nozzle position correcting mechanism for correcting the position of the nozzle when the liquid material is applied to the surface of the workpiece by relatively moving the nozzle mounted on the table and the nozzle for discharging the liquid material. )as,
An adjusting unit for adjusting the relative position of the nozzle with respect to the drive mechanism;
A nozzle insertion hole into which the nozzle is inserted; And
Positioning member which has a contact surface which contacts the front-end | tip part of the nozzle inserted into the said nozzle insertion hole.
Nozzle position correction mechanism comprising a. The method of claim 1,
The positioning member includes a space that forms the contact surface therein, and the nozzle insertion hole is formed to communicate one surface of the positioning member with the space. The method of claim 1,
The positioning member includes a first member having the nozzle insertion hole and a second member including a space for forming the contact surface, and a second member joined to the first member. The method according to claim 2 or 3,
The said space is a nozzle position correction mechanism which comprises the window which can visually recognize the said contact surface from the exterior. The method according to any one of claims 1 to 4,
A nozzle position correction mechanism, wherein a plurality of nozzle insertion holes having different inner diameters are formed in the positioning member. The method according to any one of claims 1 to 5,
An end position of the nozzle insertion hole of the nozzle insertion hole is formed in a tapered shape, the nozzle position correction mechanism. The method according to any one of claims 1 to 6,
The positioning member is made of a plastic material. The nozzle position correction mechanism in any one of Claims 1-7;
A discharge device having a nozzle for discharging a liquid material;
A table for mounting a workpiece to which the liquid material is applied;
A drive mechanism for relatively moving said nozzle and said workpiece; And
Control
Applicator comprising a. The method of claim 8,
The said control part grasps the position of a positioning member as a relative position with respect to the reference position of the said drive mechanism.

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