JP2015038930A - Component mount method and component mounting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a component mount method and a component mounting apparatus capable of increasing the productivity by performing ordinary mounting as possible for a board on which ordinary mount is possible.SOLUTION: When a carried-in board 2 arrives at a predetermined reference position, the state of the board 2 is detected and is stopped at the position. In the state that the carried-in board 2 is stooped at the reference position, when a component mounting range L is positioned in a receivable range D and when board marks 2K are positioned within a recognizable range R of a board camera 33, the board 2 is stopped at the reference position. In a state that the carried-in board 2 is stopped at the reference position, the component mounting range L is not positioned within the receivable range D, but when in a state that the carried-in board 2 is stopped at a position passing the reference position ahead by a predetermined distance d, when the component mounting range L is positioned within the receivable range D and when the board marks 2K are positioned within the recognizable range R of the board camera 33, the board 2 is stopped at the position passing the reference position ahead by a predetermined distance d.

Description

  The present invention relates to a component mounting method and a component mounting apparatus for mounting components on a substrate.

  The component mounting apparatus carries in the board by board carrying means such as a carrying conveyor, and the carried board has reached a predetermined reference position (for example, the leading portion in the advancing direction of the board has reached the detection position by the optical sensor). State) is detected and the substrate is stopped, the lower surface of the stopped substrate is supported by the receiving means, and the substrate mark for position recognition of the substrate provided at the diagonal position of the substrate is a mark recognition camera. After confirming that it is within the recognizable range of the (substrate camera), the component is mounted on the substrate by the mounting head. At this time, the substrate is in a state in which a component mounting range set as a range in which components on the substrate are mounted is supported from below by the receiving means.

  In the component mounting apparatus, generally, if the board that has been carried in is stopped at the reference position, the entire area of the component mounting range is within the allowable range where the lower surface of the board can be supported by the receiving means, and Since the board mark falls within the recognizable range of the board camera, it is possible to mount components in the entire area of the component mounting range with a single board transfer / stop operation (hereinafter referred to as such Implementation is referred to as normal implementation). In addition, since the board size is large and the parts mounting range is also large, there are boards where the parts mounting range does not fit within the acceptable range when the board that has been loaded is stopped at the reference position, For such a board, a plurality of stop positions of the board are set in the transport direction, and the board is divided by sequentially performing a plurality of mounting operations by shifting the area of the component mounting range that falls within the acceptable range. It is possible to mount components in the entire region of the component mounting range (for example, Patent Document 1).

JP 2008-27770 A

  However, even if the entire area of the component mounting range is within the receivable range and the board mark can be within the recognizable range of the board camera, and it can be normally mounted, Since the substrate is stopped at the reference position, a part of the component mounting range (rear part in the advancing direction) protrudes from the possible receiving range and is inevitably turned to divided mounting. In split mounting, the board must be transported and stopped multiple times, which increases the component mounting time required for each board and decreases productivity, and also supports multiple board stop positions. Since it is necessary to additionally provide a substrate mark at the location (see Patent Document 1), there is a problem that it takes time.

  Therefore, an object of the present invention is to provide a component actual method and a component mounting apparatus in which normal mounting can be performed as much as possible so that productivity can be improved.

  The component mounting method according to claim 1, wherein a board stop step for stopping the board by detecting a state in which the carried board has reached a predetermined reference position, and the stopped board is supported from below by a receiving means. A substrate mark recognition process for recognizing a substrate mark for position recognition of a substrate provided on a substrate received by the receiving means by a camera, and a substrate whose lower surface is supported by the receiving means, Of components mounting range set as a range where components on the board are mounted, a component that mounts components in an area located within a possible receiving range where the lower surface of the substrate can be supported by the receiving means A component mounting method including a mounting step, wherein the component mounting range is within the allowable range in a state where the board that has been loaded is stopped at the reference position in the substrate stopping step. And when the board mark is within the recognizable range of the camera, the board is stopped at the reference position, and when the board that has been loaded is stopped at the reference position, the component mounting range is Although it does not fall within the allowable range, the component mounting range is within the allowable range when stopped at a position advanced a predetermined distance from the reference position, and the board mark is recognized by the camera. When it is within the possible range, the substrate is stopped at a position advanced by the predetermined distance from the reference position.

  The component mounting method according to claim 2 is the component mounting method according to claim 1, wherein the lower supportable range is a range in which the lower support pins constituting the lower support means can be arranged, and the recognition is possible. The range is a movable range of the camera.

  According to a third aspect of the present invention, there is provided a component mounting apparatus for supporting a substrate stopped from below by detecting a state in which the substrate that has been carried in has reached a predetermined reference position and stopping the substrate. A receiving unit; a camera for recognizing a substrate mark for position recognition of a substrate provided on the substrate received by the receiving unit; and the receiving unit based on a recognition result of the substrate mark by the camera In the component mounting range set as a range in which the component on the board is mounted on the substrate whose lower surface is supported on the substrate, the lower receiving range within which the lower surface of the substrate can be supported by the receiving means. The component mounting apparatus includes a component mounting unit that mounts a component in a region located at a position where the substrate mounting means has the component mounting range in a state where the loaded substrate is stopped at the reference position. When the substrate mark is within the receivable range and the substrate mark is within the camera recognizable range, the substrate is stopped at the reference position, and the loaded substrate is stopped at the reference position. In the state, the component mounting range does not fall within the allowable range, but when stopped at a position advanced a predetermined distance from the reference position, the component mounting range falls within the lower possible range, and When the board mark is within the recognizable range of the camera, the board is stopped at a position advanced by the predetermined distance from the reference position.

  In the present invention, when the board that has been brought in has reached a predetermined reference position to stop the board, the board that has been carried in is stopped at the reference position and the component mounting range is within the acceptable range. And when the board mark is within the recognizable range of the camera, it is stopped at the reference position, and when the board that has been loaded is stopped at the reference position, the component mounting range does not fall within the submissible range. When the component mounting range is within the receivable range and the board mark is within the recognizable range of the camera when stopped at a position advanced by a predetermined distance from the reference position, the predetermined distance is advanced from the reference position. The board is stopped at the position, and the normal mounting is performed as much as possible for the board on which the normal mounting can be performed. For this reason, the board | substrate used as the object of division | segmentation mounting can be decreased, and, thereby, productivity can be aimed at.

The perspective view of the component mounting apparatus in one embodiment of this invention (A) (b) (c) Side view of the board | substrate conveyance part with which the component mounting apparatus in one embodiment of this invention is provided. (A) (b) The top view of the conveyance conveyor and board | substrate in one embodiment of this invention BRIEF DESCRIPTION OF THE DRAWINGS (a) Perspective view (b) Top view of the receiving unit with which the component mounting apparatus in one embodiment of this invention is provided (A) (b) Operation | movement explanatory drawing of the conveyance conveyor in one embodiment of this invention The block diagram which shows the control system of the component mounting apparatus in one embodiment of this invention (A) (b) The top view of the conveyance conveyor and board | substrate in one embodiment of this invention

  Embodiments of the present invention will be described below with reference to the drawings. A component mounting apparatus 1 shown in FIG. 1 is a device that mounts a component 3 on a substrate 2, and includes a substrate transport unit 12, a component supply unit 13, and a component mounting unit 14 on a base 11. Here, for convenience of explanation, the conveyance direction (arrow A shown in FIG. 1) of the board 2 in the component mounting apparatus 1 is the X-axis direction (left-right direction as viewed from the operator OP), and the horizontal plane direction orthogonal to the X-axis direction ( The front-back direction as viewed from the operator OP) is taken as the Y-axis direction. Also, the vertical direction is the Z-axis direction.

  1 and 2A, 2B, and 2C, the substrate transport unit 12 transports the substrate 2 in the X-axis direction, and the Y-axis is located above the center of the transport conveyor 21 in the X-axis direction. A pair of flat plate-shaped substrate fixing portions 22 provided opposite to each other, a lower receiving unit 23 provided below the pair of substrate fixing portions 22 (below the conveyer 21), and raising and lowering the lower receiving unit 23 A cylinder 24 is provided.

  3A and 3B, a substrate detection sensor 25 is provided at a position where the conveyor 21 is sandwiched from both sides in the Y-axis direction. The substrate detection sensor 25 includes a light projector S1 that projects the inspection light M in the Y-axis direction and a light receiver S2 that receives the inspection light M. The substrate 2 advances from the change in the light receiving state of the inspection light M by the light receiver S2. A state in which the front end of the direction has reached the detection position (FIGS. 3A and 3B), which is the projection position of the inspection light M, is detected.

  4A and 4B, the lower receiving unit 23 includes a base plate 23a and a plurality of lower receiving pins 23b erected on the base plate 23a. A large number of pin insertion holes 23c are provided in a matrix on the upper surface of the base plate 23a, and each of the lower receiving pins 23b is selectively inserted into the pin insertion holes 23c and erected.

  The transport conveyor 21 transports the substrate 2 sent from the upstream side, and a position where the front end of the traveling direction of the substrate 2 is detected by the substrate detection sensor 25 (position where the detection position is reached. The position of the substrate 2). Is referred to as a reference position) (FIG. 3 (a) → FIG. 3 (b)), or a position further advanced from the reference position by a predetermined distance d (FIG. 5 (b)) as a stop position. Stop (FIG. 5 (a) → FIG. 5 (b)).

  The elevating cylinder 24 raises the lower receiving unit 23 from below the substrate 2 stopped at the stop position, and pushes up the entire substrate 2 in a state where the lower receiving pins 23b are in contact with the lower surface of the substrate 2 (FIG. 2A ) → FIG. 2 (b) → FIG. 2 (c)). As a result, both ends of the substrate 2 in the Y-axis direction are separated from the transfer conveyor 21 and are pressed against the pair of substrate fixing portions 22 from below, so that the substrate 2 is fixed at the stop position (FIG. 2C).

  In FIG. 1, the component supply unit 13 includes a plurality of parts feeders 13 a (for example, tape feeders) attached to a base 11. Each parts feeder 13a continuously supplies the parts 3 to the parts supply port 13p.

  In FIG. 1, the component mounting unit 14 includes a head moving mechanism 31 provided on the base 11 and a mounting head 32 moved by the head moving mechanism 31. The head moving mechanism 31 includes an orthogonal coordinate table provided on the base 11 and moves the mounting head 32 in the horizontal plane direction. The mounting head 32 is provided with a plurality of suction nozzles 32a extending downward.

  In FIG. 1, the mounting head 32 is provided with a board camera 33 whose imaging field of view is directed downward, and the imaging field of view is directed upward at a position between the board transport unit 12 and the component supply unit 13 on the base 11. A component camera 34 is provided. The board camera 33 recognizes (images) a pair of board marks 2K provided at each corner of the board 2 and the part camera 34 recognizes the part 3 sucked by the suction nozzle 32a. (Imaging) is performed.

  In FIG. 6, the conveyance control of the board 2 by the conveyance conveyor 21 and the stop control to the stop position are performed by the control device 40 as the control unit of the component mounting apparatus 1 performing the operation control of the conveyor drive motor 21 a that drives the conveyance conveyor 21. The pressing (fixing) operation of the both ends of the substrate 2 to the pair of substrate fixing portions 22 by the lower receiving unit 23 is performed by the control device 40 performing operation control of the elevating cylinder 24. Information on detection of the substrate 2 by the substrate detection sensor 25 is input to the control device 40.

  In FIG. 6, the supply operation of the component 3 by the component supply unit 13 is performed when the control device 40 controls the operation of each of the parts feeders 13a. The movement operation of the mounting head 32 is performed by the control device 40 controlling the operation of the head moving mechanism 31, and the control device 40 performs the lifting and lowering operation of the suction nozzle 32a included in the mounting head 32 and the rotation operation about the Z axis. The operation of the nozzle drive mechanism 32A built in 32 is controlled, and the suction operation of the component 3 by the suction nozzle 32a is performed by the control device 40 controlling the operation of the suction mechanism 32B built in the mounting head 32. The

  In FIG. 6, the imaging operation control by the substrate camera 33 and the imaging operation control by the component camera 34 are performed by the control device 40, and the image data obtained by the imaging operation of the substrate camera 33 and the image obtained by the imaging operation by the component camera 34. Image recognition of data is performed by the image recognition unit 40a of the control device 40.

  Here, the stop operation of the substrate 2 to the stop position by the control device 40 will be described with reference to FIGS. 3 (a) and 3 (b) and FIGS. 5 (a) and 5 (b). In the substrate 2 handled by the component mounting apparatus 1 in the present embodiment, the component mounting range L, which is set as a range in which the component 3 on the substrate 2 is mounted, mainly supports the lower surface of the substrate 2 by the support unit 23. Can be received within the allowable range D (the range in which the lower support pins 23b on the base plate 23a can be arranged; see also FIG. 4B), and each of the two provided on the substrate 2 The set of board marks 2K can be stopped so as to be within the recognizable range R of the board camera 33 defined as the movable range of the board camera 33. That is, as shown in FIGS. 3A and 3B and FIGS. 5A and 5B, the dimension in the conveyance direction (X-axis direction) of the substrate 2 in the supportable range D is the size of the supportable range. The dimension of the component mounting range L in the conveyance direction (that is, the X axis direction) of the substrate 2 is defined as the component mounting range dimension L1, and the dimension of the substrate 2 in the recognizable range R of the substrate 2 in the conveyance direction (X axis direction) Is the recognizable range dimension R1, and the distance between the two substrate marks 2K in the X-axis direction is the distance K1, the substrate 2 satisfies the size condition of “D1 ≧ L1 and R1 ≧ K1” (this size As for the board 2 that does not satisfy the condition, it is divided and mounted as will be described later.

  As described above, the possible receiving range D corresponds to the range in which the above-described pin insertion hole 23 c provided in the base plate 23 a constituting the receiving unit 23 is provided, and the coordinate system fixed to the component mounting apparatus 1. Is defined based on The recognizable range R of the board camera 33 is defined by the movement range of the mounting head 32, and this is also defined based on the coordinate system fixed to the component mounting apparatus 1. Since the two substrate marks 2K are provided at the corners of one diagonal portion of the substrate 2, the substrate 2 that satisfies the size condition of “D1 ≧ L1 and R1 ≧ K1” is expressed in “in plan view”. When the component mounting range L is stopped within the stop condition “the stop is performed so that the component mounting range L is within the acceptable range D and the two substrate marks 2K are within the recognizable range R of the substrate camera 33”. The component 3 can be mounted on the entire region within the component mounting range L by the mounting head 32.

  For the board 2 that satisfies the size condition of “D1 ≧ L1 and R1 ≧ K1”, the component mounting range L is within the acceptable range D in plan view, and the two board marks 2K are board cameras. By stopping under the stop condition of “stop within 33 recognizable range R”, component mounting can be performed on the entire region of component mounting range L by a single transport / stop operation of substrate 2. It is possible (such an implementation is called “normal implementation”). Of the substrates 2 that can be mounted normally, those that satisfy the stop condition when the substrate 2 conveyed by the conveyor 21 is stopped at the reference position (referred to as a first type) Then, the substrate 2 is stopped using the reference position as a stop position (FIG. 3A → FIG. 3B). On the other hand, when the substrate 2 transported by the transport conveyor 21 is stopped at the reference position, the above stop condition is not satisfied, but when the substrate 2 is stopped at a position advanced by a predetermined distance d (FIG. 5B) from the reference position. In the case of the type satisfying the above stop condition (second type), the substrate 2 is stopped with the position advanced by a predetermined distance d from the reference position as the stop position (FIG. 5 (a) → FIG. 5 (b)). .

  The host computer HC (FIG. 6), which is the host system of the component mounting apparatus 1, provides data about whether the board 2 is the first type or the second type for each board 2 handled by the component mounting apparatus 1. The second type substrate 2 is further stored with data on the amount of movement (the predetermined distance d) of the substrate 2 to be advanced beyond the reference position. These data are sent from the host computer HC to the control device 40 of the component mounting apparatus 1 via the communication line TL before the component mounting apparatus 1 starts mounting the component 3 on the board 2 (FIG. 6).

  The control device 40 carries and stops the board 2 based on the data sent from the host computer HC via the communication line TL when executing the part mounting work for mounting the part 3 on the board 2. That is, the transport conveyor 21 is controlled by the control device 40 to detect a state in which the loaded substrate 2 has reached a predetermined reference position and to stop the substrate 2 (substrate stop step). Specifically, for the first type of substrate 2, the transfer conveyor 21 stops the progress of the substrate 2 when it is detected that the loaded substrate 2 has reached the reference position (FIG. 3A). (FIG. 3B), for the second type of substrate 2, when it is detected that the substrate 2 has reached the reference position, the substrate 2 is further advanced by a predetermined distance d, and then the substrate 2 is advanced. Stop (FIG. 5 (a) → FIG. 5 (b)).

  As described above, in the present embodiment, the transport conveyor 21 as the substrate transport means is controlled by the control device 40 to detect the state where the transported substrate 2 has reached a predetermined reference position and stop the substrate 2. When the loaded board 2 is stopped at the reference position, the component mounting range L is within the acceptable range D, and the board mark 2K is within the recognizable range R of the board camera 33. When the board 2 is stopped at the reference position, and the board 2 that has been carried in is stopped at the reference position, the component mounting range L does not fall within the acceptable range D, but at a position advanced by a predetermined distance d from the reference position. In the stopped state, when the component mounting range L is within the receivable range D and the board mark 2K is within the recognizable range R of the board camera 33, the board 2 is used as a reference. And it is adapted to stop at a position advanced put et predetermined distance d. Thereby, the board | substrate 2 which can perform normal mounting can perform normal mounting as much as possible.

  When the control device 40 stops the substrate 2 at the stop position corresponding to the type of the substrate 2 as described above, the control device 40 operates the elevating cylinder 24 to raise the lower receiving unit 23 to lift and support the substrate 2 from below. Thus, both end portions of the substrate 2 are pressed and fixed to the substrate fixing portion 22 from below. That is, the receiving unit 23 operates under the control of the control device 40 and executes a process (supporting process) for supporting the substrate 2 stopped by the transfer conveyor 21 from below.

  When the control device 40 fixes the substrate 2 as described above, the mounting head 32 is moved in the horizontal plane by the head moving mechanism 31, the substrate camera 33 is positioned above the substrate 2, and the control device 40 is provided on the substrate 2. Two substrate marks 2K are imaged. Then, the image recognition unit 40a recognizes the images of the two obtained substrate marks 2K, thereby detecting a displacement of the substrate 2 from the normal work position. That is, the substrate camera 33 is controlled by the control device 40 to execute a step of recognizing the substrate mark 2K provided on the substrate 2 received by the receiving unit 23 (substrate mark recognition step).

  When detecting the positional deviation of the substrate 2, the control device 40 controls the operation of the head moving mechanism 31 to move the mounting head 32 above the component supply unit 13 and performs the operation of supplying the component 3 to each part feeder 13 a. At the same time, the operation of the nozzle drive mechanism 32A and the suction mechanism 32B is controlled, and the part 3 is sucked and picked up by the suction nozzle 32a. Then, the mounting head 32 is moved so that the component 3 picked up by the suction nozzle 32a passes above the component camera 34, and the component 3 is imaged by the component camera 34 and the image data obtained thereby is recognized. Then, the positional deviation (suction deviation) of the component 3 with respect to the suction nozzle 32a is obtained (component recognition step).

  When the controller 40 determines the positional deviation of the component 3 with respect to the suction nozzle 32 a, the controller 40 moves the mounting head 32 so that the component 3 is positioned above the substrate 2. Then, the suction nozzle 32 a is lowered and the component 3 is mounted on the substrate 2. In other words, the component mounting unit 14 is controlled by the control device 40 and, based on the recognition result of the substrate mark 2K by the substrate camera 33, the component 3 on the substrate 2 with respect to the substrate 2 whose lower surface is supported by the receiving unit 23. A step of mounting the component 3 in an area located within a possible receiving range D in which the lower surface of the substrate 2 can be supported by the receiving unit 23 in the component mounting range L set as the mounting range ( The component mounting process) is executed.

  In the component mounting step, the control device 40 performs position correction (including rotation correction) of the suction nozzle 32a with respect to the substrate 2 so that the already-determined positional displacement of the substrate 2 and the suction displacement of the component 3 are corrected. . When the mounting of all the components 3 to be mounted on the board 2 is completed, the control device 40 operates the board transport unit 12 to carry the board 2 out of the component mounting apparatus 1.

  Of the above-mentioned size conditions of “D1 ≧ L1 and R1 ≧ K1”, for the board 2 that does not satisfy at least the condition of “D1 ≧ L1”, the component mounting range can be achieved by one transport / stop operation of the board 2. Component mounting cannot be performed on the entire area L (that is, normal mounting cannot be performed), and it is necessary to perform split mounting. In the two-part split mounting, a pair of additional board marks 2Ka is additionally provided on the board 2 so that the two board marks 2K are within the recognizable range R of the board camera 33 at the first mounting. 2 is stopped, the board 2 is stopped so that the two additional board marks 2Ka are within the recognizable range R of the board camera 33 at the time of the second mounting, and the region of the component mounting range L that falls within the substitutable range D The two mounting operations are sequentially executed while shifting (FIG. 7 (a) → FIG. 7 (b)).

  As described above, in the present embodiment, when the substrate 2 that has been loaded reaches the predetermined reference position and the substrate 2 is stopped, the substrate 2 that has been loaded is stopped at the reference position. When the component mounting range L is within the acceptable range D and the board mark 2K is within the recognizable range R of the board camera 33, the board 2 is stopped at the reference position, In the state of being stopped at the reference position, the component mounting range L does not fall within the allowable range D. However, when the component mounting range L is stopped at a position advanced by a predetermined distance d from the reference position, the component mounting range L is within the allowable range D. If the board mark 2K is within the recognizable range R of the board camera 33, the board 2 is stopped at a position advanced by a predetermined distance d from the reference position. So that as much as possible perform normal mounting for the substrate 2 capable of performing mounting. For this reason, the board | substrate 2 used as the object of division | segmentation mounting can be decreased, and improvement of productivity can be aimed at by this.

  Provided are a component mounting method and a component mounting apparatus that can improve productivity by performing normal mounting as much as possible on a substrate on which normal mounting can be performed.

DESCRIPTION OF SYMBOLS 1 Component mounting apparatus 2 Board | substrate 3 Component 2K Board | substrate mark 14 Component mounting part 21 Conveyor (board | substrate conveyance means)
23 Underlay unit (underlay means)
33 Substrate camera (camera)
D Acceptable range L Component mounting range R Recognizable range d Predetermined distance

Claims (3)

A substrate stopping step of detecting a state where the loaded substrate has reached a predetermined reference position and stopping the substrate;
A receiving step of supporting the stopped substrate from below by a receiving means;
A substrate mark recognition step of recognizing with a camera a substrate mark for position recognition of a substrate provided on the substrate received by the receiving means;
Of the component mounting range set as a range in which components on the substrate are mounted on the substrate whose lower surface is supported by the lower receiving device, the lower receiving device capable of supporting the lower surface of the substrate by the lower receiving device. A component mounting method including a component mounting step of mounting a component in an area located within a possible range,
In the substrate stopping step, the component mounting range is within the receivable range and the substrate mark is within the recognizable range of the camera in a state where the board that has been loaded is stopped at the reference position. When the circuit board is stopped, the board is stopped at the reference position, and in the state where the board that has been loaded is stopped at the reference position, the component mounting range does not fall within the supportable range, but advances by a predetermined distance from the reference position. When the component mounting range is within the receivable range and the board mark is within the recognizable range of the camera, the board is moved from the reference position to the predetermined position. A component mounting method characterized by stopping at a position advanced by a distance.   The component mounting method according to claim 1, wherein the lower supportable range is a range in which a lower support pin constituting the lower receiving means can be arranged, and the recognizable range is a movable range of the camera. . A substrate transfer means for detecting a state where the loaded substrate has reached a predetermined reference position and stopping the substrate;
Receiving means for supporting the substrate stopped by the substrate conveying means from below;
A camera for recognizing a substrate mark for position recognition of a substrate provided on the substrate received by the receiving means;
Based on the recognition result of the board mark by the camera, the lower receiving portion of the component mounting range set as a range in which components on the board are mounted on the substrate whose lower surface is supported by the receiving means. A component mounting apparatus comprising a component mounting portion that mounts a component in a region located within a possible receiving range capable of supporting the lower surface of the substrate by means,
The board conveying means is configured such that the loaded board is stopped at the reference position, the component mounting range is within the receivable range, and the board mark is within the recognizable range of the camera. When the circuit board is stopped, the board is stopped at the reference position, and in the state where the board that has been loaded is stopped at the reference position, the component mounting range does not fall within the supportable range, but advances by a predetermined distance from the reference position. When the component mounting range is within the receivable range and the board mark is within the recognizable range of the camera, the board is moved from the reference position to the predetermined position. A component mounting apparatus characterized by stopping at a position advanced by a distance.

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