X-ray inspection equipment

Abstract

To provide an X-ray inspection device with which it is possible to obtain transmission images which are free of noise and clear, without decelerating the conveyance speed of the object to be inspected.SOLUTION: Provided is an X-ray inspection device comprising an X-ray generator that irradiates the successively conveyed object W to be inspected with an X-ray and an X-ray detector that detects the X-ray having passed through the object W being inspected, with the X-ray generator and the X-ray detector being arranged so as to face each other across a conveyance path which the object to be inspected passes through. The X-ray generator and the X-ray detector are constituted so as to be capable of reciprocating in a direction parallel to the conveyance direction of the object to be inspected, and the X-ray generator and the X-ray detector perform imaging of the object being inspected while moving in the conveyance direction from an imaging start position P1 to an imaging end position P2 at the same speed as the conveyance speed of the object W being inspected.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an X-ray inspection apparatus.

Background Art

[0002] In Patent Document 1, an X-ray generator is disposed at a predetermined height above an inspection space in the middle of a conveyance path and irradiates X-rays in the inspection space to an object to be inspected that is sequentially conveyed, and is disposed opposite to the X-ray generator in a conveyance unit. An X-ray line sensor for detecting X-rays transmitted through the object to be inspected is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the X-ray foreign object inspection apparatus described in Patent Document 1, if the exposure time to the object to be inspected is short, the obtained transmission image becomes a noisy image. Also, for example, when inspecting an object to be inspected having a relatively large thickness, if the exposure time is short, the obtained transmission image becomes an unclear image. Therefore, if the exposure time to the object to be inspected is short, the inspection accuracy cannot be improved.

[0005] On the other hand, if the exposure time is increased, a transmission image with less noise and clear can be obtained. However, in proportion to increasing the exposure time, it is necessary to slow down the conveyance speed of the object to be inspected or, in some cases, to temporarily stop it, and efficient inspection cannot be performed.

[0006] The present invention has been made in view of the circumstances described above, and aims to provide an X-ray inspection apparatus that can obtain clear transmission images with low noise without reducing the transport speed of the object to be inspected. [Means for solving the problem]

[0007] The X-ray inspection apparatus according to the present invention is By conveyor The system comprises an X-ray generator that irradiates objects to be inspected with X-rays as they are transported sequentially, and an X-ray detector that detects the X-rays that have passed through the objects to be inspected, with the transport path through which the objects to be inspected pass... , in the width direction of the conveyor An X-ray inspection apparatus in which the X-ray generator and the X-ray detector are arranged facing each other, wherein the X-ray generator and the X-ray detector They are connected to each other by movable brackets. In a direction parallel to the transport direction of the object to be inspected. as one Round-trip travel is possible. Unitized It is composed of, The movable bracket moves back and forth on a linear slider that extends in a direction parallel to the transport direction, The X-ray generator and the X-ray detector move in the transport direction from the imaging start position to the imaging end position at the same speed as the transport speed of the object to be inspected. 、 The aforementioned object to be inspected From the time when the object under inspection reaches the imaging start position until the time when the object under inspection reaches the imaging end position It is configured to perform imaging.

[0008] With this configuration, the X-ray inspection apparatus according to the present invention comprises an X-ray generator and an X-ray detector. They are connected to each other by movable brackets. In a direction parallel to the transport direction of the object being inspected. as one Round-trip travel is possible. Unitized Consists of and The moving bracket reciprocates on a linear slider that extends in a direction parallel to the transport direction, thereby moving the X-ray generator and the X-ray detector. The object to be inspected moves in the transport direction from the imaging start position to the imaging end position at a speed equal to the transport speed of the object to be inspected. From the time when the object under inspection reaches the imaging start position to the time when the object under inspection reaches the imaging end position Since imaging is performed, the exposure time can be extended without reducing the transport speed of the object under inspection, compared to a configuration in which the X-ray generator and X-ray detector are fixed for imaging. For this reason, the X-ray inspection apparatus according to the present invention can obtain a clear transmission image with less noise without reducing the transport speed of the object under inspection. Furthermore, in the X-ray inspection apparatus according to the present invention, the X-ray generator and the X-ray detector are unitized so that they can move back and forth together in a direction parallel to the transport direction, allowing the X-ray generator and the X-ray detector to move at the same speed without misalignment.

[0009] In the X-ray inspection apparatus according to the present invention, it is preferable that the X-ray generator and the X-ray detector are configured to move to the imaging completion position and then return to the imaging start position before the next object to be transported reaches the imaging start position.

[0010] With this configuration, the X-ray inspection apparatus according to the present invention returns the X-ray generator and X-ray detector to the imaging start position after they have moved to the imaging end position, before the next object to be inspected reaches the imaging start position. Therefore, the gap time between sequentially transported objects to return the X-ray generator and X-ray detector to the imaging start position in preparation for imaging the next object to be inspected.

[0011] In the X-ray inspection apparatus according to the present invention, it is preferable that the movement speed at which the X-ray generator and the X-ray detector return to the imaging start position is faster than the transport speed.

[0012] With this configuration, the X-ray inspection apparatus according to the present invention has a movement speed at which the X-ray generator and X-ray detector return to the imaging start position that is faster than the transport speed. This allows for a smaller interval between objects being transported sequentially, and increases the number of inspections per unit time.

[0013] In the X-ray inspection apparatus according to the present invention, it is preferable that the X-ray detector is configured by an area sensor.

[0014] With this configuration, the X-ray inspection apparatus according to the present invention has an X-ray detector composed of an area sensor, so a still image can be obtained without stopping the transport of the object to be inspected.

[0015] In the X-ray inspection apparatus according to the present invention, A pair of guide rails are provided at the lower part of the movable bracket, positioned opposite each other with the linear slider in between, and the movable bracket moves back and forth while being guided by the pair of guide rails. It is preferable to do so. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide an X-ray inspection apparatus that can obtain clear transmission images with low noise without reducing the transport speed of the object to be inspected. [Brief explanation of the drawing]

[0018] [Figure 1] FIG. 1 is a schematic configuration diagram of an X-ray inspection apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic perspective view of an X-ray inspection apparatus according to an embodiment of the present invention. [Figure 3] FIG. 3 is a graph showing the transition of the movement of the imaging unit of the X-ray inspection apparatus according to an embodiment of the present invention. [Figure 4] FIGS. 4(a) to (e) are diagrams showing the positional relationship between the imaging unit and the object to be inspected of the X-ray inspection apparatus according to an embodiment of the present invention in chronological order. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an X-ray inspection apparatus according to an embodiment of the present invention will be described with reference to the drawings.

[0020] (Configuration of X-ray Inspection Apparatus) As shown in FIG. 1, the X-ray inspection apparatus 1 of the present embodiment irradiates an object to be inspected W being conveyed with X-rays, and inspects for foreign matter contamination, shape, etc. in the object to be inspected W using a transmission image obtained by detecting the transmitted X-rays. It is an X-ray inspection apparatus.

[0021] In the present embodiment, as the object to be inspected W, for example, a cylindrical article such as a bottle product will be described as an example, but the object to be inspected W is not limited thereto.

[0022] The X-ray inspection apparatus 1 of the present embodiment includes a housing (not shown), an X-ray generator 10 that generates X-rays, an X-ray detector 11 that detects the X-rays transmitted through the object to be inspected W, and a control circuit 20. The X-ray generator 10, the X-ray detector 11, and the control circuit 20 are housed in a housing (not shown).

[0023] The enclosure is incorporated into a conveyor 2 that transports the object to be inspected W. The conveyor 2 is part of the production equipment for the object to be inspected W and is configured separately from the X-ray inspection device 1. Thus, the X-ray inspection device 1 is an integrated type X-ray inspection device that is incorporated into a separate conveyor 2, and is incorporated into existing conveyors that transport the object to be inspected W horizontally, such as top chain conveyors or belt conveyors.

[0024] The X-ray generator 10 and the X-ray detector 11 are positioned opposite each other in the width direction of the conveyor 2, with the transport path 3 through which the object to be inspected W passes on the conveyor 2 in between.

[0025] The X-ray generator 10 generates X-rays by irradiating an electron beam from the cathode of an X-ray tube (not shown) located inside it onto a target at the anode, and irradiates the generated X-rays radially so that the area indicated by the dashed line in Figure 1 is imaged. In this way, the X-ray generator 10 irradiates the objects to be inspected W on the conveyor belt 2 as they are sequentially transported with X-rays.

[0026] The X-ray detector 11 comprises a photodiode (not shown) and a plurality of X-ray detection elements (not shown) consisting of scintillators provided on the photodiode. The X-ray detector 11 is composed of an area sensor in which the X-ray detection elements are arranged in a planar manner in the transport direction and in a direction perpendicular to this transport direction.

[0027] The X-ray detector 11 captures a transmission image of the X-rays that have passed through the object W being irradiated with X-rays from the X-ray generator 10 onto the object W on the transport path 3. Specifically, the X-rays are converted into an optical signal by the scintillator of the X-ray detection element, and this optical signal is converted into an electrical signal by a photodiode. Further processing such as noise reduction is then applied to generate a transmission image of the density distribution based on the amount of X-ray transmission.

[0028] The control circuit 20 is connected to the display unit 12, the setting operation unit 13, and the drive unit 14.

[0029] The display unit 12 consists of a flat-panel display or the like, and is configured to output information to the user. The display unit 12 displays images such as inspection results from the control circuit 20.

[0030] Furthermore, the display unit 12 displays the pass / fail judgment result of the inspected object W using characters or symbols such as "OK" or "NG". The display unit 12 also displays statistical values ​​such as the total number of inspected items, the number of good items, and the total number of NG items.

[0031] The display content and display mode of the display unit 12 are determined based on default settings or requests made by predetermined key operations from the setting operation unit 13.

[0032] The setting operation unit 13 is used to input various parameters and other settings to the control circuit 20. The setting operation unit 13 consists of multiple keys and switches operated by the user, and is used to input various parameters and other settings to the control circuit 20 and to select the operating mode.

[0033] In this embodiment, the display unit 12 and the setting operation unit 13 are integrated as a touch panel display and are located on the upper front of a housing (not shown).

[0034] The drive unit 14 is configured as a drive source that moves the imaging unit 30 (described later) back and forth in a direction parallel to the transport direction of the object W under inspection, and consists of an actuator such as a motor.

[0035] The control circuit 20 includes an X-ray image storage unit 21, an image processing unit 22, a determination unit 23, and a control unit 25.

[0036] The X-ray image storage unit 21 is configured to store the X-ray images received from the X-ray detector 11.

[0037] The image processing unit 22 applies various image processing algorithms to the X-ray image read from the X-ray image storage unit 21 to perform image processing. Here, the image processing algorithm consists of a combination of multiple image processing filters.

[0038] The determination unit 23 performs image processing on the X-ray image processed by the image processing unit 22 to distinguish between the object to be inspected W and foreign matter, determine whether or not foreign matter is present, and also determines whether the shape of the object to be inspected W is good or bad.

[0039] The control unit 25 has a CPU and memory that serves as a storage area or work area for the control program, and controls the entire X-ray inspection apparatus 1. The control contents of the control unit 25 include control of the display content and display format of the display unit 12.

[0040] Furthermore, the control unit 25 controls the drive of the drive unit 14. By controlling the drive of the drive unit 14, the control unit 25 controls the reciprocating movement of the imaging unit 30.

[0041] (Imaging unit) As shown in Figure 2, in the X-ray inspection apparatus 1 of this embodiment, the X-ray generator 10 and the X-ray detector 11 are connected to each other by a movable bracket 31, and are unitized so that they can reciprocate in a direction parallel to the transport direction B of the object to be inspected W.

[0042] In this embodiment, the imaging unit 30 is composed of an X-ray generator 10, an X-ray detector 11, and a movable bracket 31.

[0043] The movable bracket 31 is configured to reciprocate on a linear slider 32 that extends in a direction parallel to the transport direction B of the object W to be inspected. The reciprocating movement of the movable bracket 31 is achieved by the drive unit 14.

[0044] A pair of guide rails 33 and 34 are provided at the bottom of the movable bracket 31, positioned opposite each other in a direction perpendicular to the transport direction B, with the linear slider 32 in between. The movable bracket 31 moves back and forth while being guided by the pair of guide rails 33 and 34.

[0045] As a result, the X-ray generator 10 and the X-ray detector 11 move back and forth between the imaging start position (the position shown in Figure 4(a)) and the imaging end position (the position shown in Figure 4(b)).

[0046] Specifically, the X-ray generator 10 and the X-ray detector 11 are configured to move in the transport direction B from the imaging start position to the imaging end position at the same speed as the transport speed of the object W to be inspected, while imaging the object W to be inspected.

[0047] The X-ray generator 10 and X-ray detector 11 are configured to move to the imaging end position and then return to the imaging start position before the next object to be inspected W reaches the imaging start position. In this case, it is desirable that the movement speed of the X-ray generator 10 and X-ray detector 11 returning to the imaging start position is faster than the transport speed of the object to be inspected W. In other words, it is desirable that the movement speed of the X-ray generator 10 and X-ray detector 11 in the direction opposite to the transport direction B is faster than the movement speed in the transport direction B. This makes it possible to reduce the interval between sequentially transported objects to be inspected W, and to increase the number of objects to be inspected W per unit time.

[0048] (Transition of the imaging unit's movement) Next, the transition of movement of the imaging unit 30 will be described with reference to Figures 3 and 4.

[0049] In Figure 3, the dashed line shows the transition of movement of the object under inspection W, and the solid line shows the transition of movement of the imaging unit 30. In Figure 3, the transition of movement of the imaging unit 30 is explained using the example of the object under inspection W1, which is transported first, and the object under inspection W2, which is transported next, among the objects under inspection W that are transported sequentially. In Figure 3, P1 indicates the imaging start position, and P2 indicates the imaging end position.

[0050] Figures 4(a) to 4(e) show the positional relationship between the imaging unit 30 and the object under inspection W at each time from time t0 to time t4 shown in Figure 3, with Figure 4(a) corresponding to time t0, Figure 4(b) to time t1, Figure 4(c) to time t2, Figure 4(d) to time t3, and Figure 4(e) to time t4, respectively.

[0051] As shown in Figure 3, when the object under inspection W1 reaches the imaging start position P1 at time t0, the imaging unit 30 starts imaging the object under inspection W1 while moving toward the imaging end position P2 at a speed equal to the transport speed of the object under inspection W1, following the object under inspection W1. In other words, as shown in Figure 4(a), at the moment when the center of the transport direction of the object under inspection W1 coincides with the imaging axis A perpendicular to the imaging plane of the X-ray detector 11, the X-ray generator 10 and the X-ray detector 11 start imaging the object under inspection W1 and begin following the object under inspection W1.

[0052] Subsequently, imaging of the object W1 is performed while the object W1 and the imaging unit 30 move at a constant speed until imaging of the object W1 is completed, that is, until the object W1 reaches the imaging completion position P2.

[0053] Next, when the object under inspection W1 and the imaging unit 30 reach the imaging completion position P2 (the position shown in Figure 4(b)) at time t1, imaging of the object under inspection W1 is completed, and the imaging unit 30 begins to return to the imaging start position P1. Specifically, the control unit 25 starts the reverse drive of the drive unit 14.

[0054] At this point, the imaging unit 30 slightly overshoots the imaging end position P2 in the transport direction B, then reverses its direction of movement at that position (the position shown in Figure 4(c)) and begins to return to the imaging start position P1.

[0055] At time t2, as the imaging unit 30 begins to return to the imaging start position P1, a positive acceleration is applied to the imaging unit 30. In other words, the imaging unit 30 accelerates and moves from the position shown in Figure 4(c) towards the imaging start position P1.

[0056] Next, at time t3, the acceleration applied to the imaging unit 30 is switched from positive to negative. That is, the drive unit 14 is controlled by the control unit 25 so that the imaging unit 30, which was moving with positive acceleration, is given negative acceleration at time t3, and it begins to decelerate.

[0057] Time t3 is, for example, the timing when the imaging unit 30 reaches half the distance it has traveled, i.e., the midpoint between the imaging start position P1 and the imaging end position P2 (the position shown in Figure 4(d)), and can also be defined as t3 = (t2 + t4) / 2. Note that the timing for switching between positive and negative acceleration applied to the imaging unit 30 is not limited to the timing described above, but may be changed as appropriate according to the specifications of the imaging unit 30 and the drive unit 14.

[0058] Next, the decelerating imaging unit 30 slightly overshoots the imaging start position P1 in the opposite direction to the transport direction B, and then decelerates at time t4. At this point, the direction of movement reverses, and it begins moving towards the imaging end position P2. At this time, as shown in Figure 4(e), the object to be inspected W2 has not yet reached the imaging start position P1.

[0059] Subsequently, when the object under inspection W2 reaches the imaging start position P1 at time t5, the imaging unit 30 moves toward the imaging end position P2 at a speed equal to the transport speed of the object under inspection W2, following the object under inspection W2, and begins imaging the object under inspection W2. From this point onward, the process is the same as for the object under inspection W1.

[0060] In this manner, the drive unit 14 is controlled by the control unit 25 so that the X-ray generator 10 and the X-ray detector 11 periodically repeat reciprocating movements.

[0061] (Effects and Benefits) As described above, in this embodiment, the X-ray inspection apparatus is configured such that the X-ray generator 10 and the X-ray detector 11 can reciprocate in a direction parallel to the transport direction B of the object to be inspected W, and imaging of the object to be inspected W is performed while moving in the transport direction B from the imaging start position P1 to the imaging end position P2 at the same speed as the transport speed of the object to be inspected W. Therefore, compared to a configuration in which the X-ray generator 10 and the X-ray detector 11 are fixed for imaging, the exposure time can be extended without reducing the transport speed of the object to be inspected W. For this reason, the X-ray inspection apparatus in this embodiment can obtain a clear transmission image with less noise without reducing the transport speed of the object to be inspected W.

[0062] In this case, if the transport of the object to be inspected W is stopped each time it is exposed in order to extend the exposure time, for example, if the object to be inspected W is a container filled with liquid, the liquid surface will shake each time it is stopped, and transport cannot be started again until the shaking of the liquid surface subsides. For this reason, it is not possible to increase the number of objects to be inspected W per unit time.

[0063] Since the X-ray inspection apparatus according to this embodiment does not require stopping the transport of the object to be inspected W, the liquid level fluctuations described above do not occur, and the number of objects to be inspected W per unit time can be increased.

[0064] Furthermore, as described above, the X-ray inspection apparatus according to this embodiment obtains a clear transmission image with less noise by ensuring a long exposure time by moving the X-ray generator 10 and the X-ray detector 11 back and forth. Therefore, it is not necessary to increase the current or voltage of the X-ray source of the X-ray generator 10 to irradiate with high-power X-rays, and the output of the X-ray source can be reduced. Moreover, by reducing the output of the X-ray source, the X-ray generator 10 can be made smaller.

[0065] Furthermore, in this embodiment, the X-ray inspection apparatus returns the X-ray generator 10 and X-ray detector 11 to the imaging start position P1 after they have moved to the imaging end position P2, before the next object to be inspected W reaches the imaging start position P1. Therefore, the gap time between sequentially transported objects to be inspected W can be used to return the X-ray generator 10 and X-ray detector 11 to the imaging start position P1 in preparation for imaging the next object to be inspected W.

[0066] Furthermore, in this embodiment, the X-ray inspection apparatus has a movement speed at which the X-ray generator 10 and the X-ray detector 11 return to the imaging start position P1 that is faster than the transport speed of the object to be inspected W. Therefore, the interval between sequentially transported objects to be inspected W can be reduced, and the number of inspections per unit time can be increased.

[0067] Furthermore, since the X-ray inspection apparatus according to this embodiment is configured with an area sensor as the X-ray detector 11, a still image can be obtained without stopping the transport of the object to be inspected W.

[0068] Furthermore, in this embodiment, the X-ray inspection apparatus is unitized so that the X-ray generator 10 and the X-ray detector 11 can move together in a direction parallel to the transport direction B, allowing the X-ray generator 10 and the X-ray detector 11 to move at the same speed without misalignment.

[0069] (modified version) In this embodiment, an example has been described in which the X-ray inspection apparatus according to the present invention is applied to a horizontal irradiation type X-ray inspection apparatus in which the X-ray generator 10 and the X-ray detector 11 are arranged facing each other in a horizontal direction perpendicular to the transport direction of the object to be inspected W, with the transport path 3 in between. However, it may also be applied to an X-ray inspection apparatus of the type in which the X-ray generator 10 and the X-ray detector 11 are arranged facing each other in a vertical direction with the transport path 3 in between.

[0070] Furthermore, although the X-ray inspection apparatus according to this embodiment is configured to have one set of X-ray generator 10 and X-ray detector 11, it may also be configured to have two or more sets of X-ray generator 10 and X-ray detector 11. In this case, it is preferable to unitize these two or more sets of X-ray generator 10 and X-ray detector 11 so that they can be moved as a single unit.

[0071] Furthermore, in the X-ray inspection apparatus according to this embodiment, the X-ray generator 10 and the X-ray detector 11 are configured to be unitized and reciprocate as a single unit. However, the apparatus is not limited to this configuration, and the X-ray generator 10 and the X-ray detector 11 may be configured to be reciprocate independently. In this case, the control unit 25 synchronizes the movement of the X-ray generator 10 and the movement of the X-ray detector 11.

[0072] While embodiments of the present invention have been disclosed, it will be apparent to those skilled in the art that modifications can be made without departing from the scope of the invention. All such modifications and equivalents are intended to be included in the following claims. [Explanation of Symbols]

[0073] 1. X-ray inspection device 2 Conveyor 3. Conveyor path 10 X-ray generator 11 X-ray detectors 12 Display section 13. Setting Operation Unit 14 Drive Unit 20 Control circuits 21 X-ray image storage unit 22 Image Processing Unit 23 Judgment section 25 Control Unit 30 imaging units 31 Moving bracket 32 Linear Sliders 33, 34 Guide rails W, W1, W2 Test object P1 Imaging start position P2 imaging end position

Claims

1. An X-ray generator (10) that irradiates an object to be inspected (W) which is sequentially transported by a conveyor (2), The system includes an X-ray detector (11) that detects the X-rays that have passed through the object to be inspected, An X-ray inspection apparatus in which the X-ray generator and the X-ray detector are arranged so as to face each other in the width direction of the conveyor, with the transport path (3) through which the object to be inspected passes, The X-ray generator and the X-ray detector are connected to each other by a movable bracket (31), thereby forming a unit that can reciprocate as a single unit in a direction parallel to the transport direction of the object to be inspected. An X-ray inspection apparatus in which the moving bracket reciprocates on a linear slider (32) extending in a direction parallel to the transport direction, so that the X-ray generator and the X-ray detector move in the transport direction from the imaging start position (P1) to the imaging end position (P2) at the same speed as the transport speed of the object to be inspected, and imaging is performed from the time (t0) when the object to be inspected reaches the imaging start position until the time (t1) when the object to be inspected reaches the imaging end position.

2. The X-ray inspection apparatus according to claim 1, characterized in that the X-ray generator and the X-ray detector are configured to move to the imaging completion position and then return to the imaging start position before the next object to be transported reaches the imaging start position.

3. The X-ray inspection apparatus according to claim 1 or claim 2, characterized in that the speed at which the X-ray generator and the X-ray detector return to the imaging start position is faster than the transport speed.

4. The X-ray inspection apparatus according to claim 1 or 2, characterized in that the X-ray detector is configured by an area sensor.

5. The X-ray inspection apparatus according to claim 3, characterized in that the X-ray detector is composed of an area sensor.

6. A pair of guide rails (33, 34) are provided at the lower part of the movable bracket, arranged to face each other with the linear slider in between. The X-ray inspection apparatus according to claim 1 or 2, characterized in that the movable bracket moves back and forth while being guided by the pair of guide rails.

7. A pair of guide rails (33, 34) are provided at the lower part of the movable bracket, arranged to face each other with the linear slider in between. The X-ray inspection apparatus according to claim 3, characterized in that the movable bracket moves back and forth while being guided by the pair of guide rails.

8. A pair of guide rails (33, 34) are provided at the lower part of the movable bracket, arranged to face each other with the linear slider in between. The X-ray inspection apparatus according to claim 4, characterized in that the movable bracket moves back and forth while being guided by the pair of guide rails.

9. A pair of guide rails (33, 34) are provided at the lower part of the movable bracket, arranged to face each other with the linear slider in between. The X-ray inspection apparatus according to claim 5, characterized in that the movable bracket moves back and forth while being guided by the pair of guide rails.

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