Abstract:
A method and placement device are provided for moving at least two elements in and opposite to a predetermined direction. The second element is simultaneously moved by means of the first element. The first element is moved in the predetermined direction, whereas the second element is moved relative to the first element in a direction opposite to the predetermined direction and vice versa.

Description:
BACKGROUND 
     The invention relates to a method for moving at least two elements of a placement machine in, and opposite to, a predetermined direction, in which the second element is moved by means of the first element. The invention also relates to a placement machine suitable for executing such a method. 
     A conventional placement machine (and its associated method) is disclosed in international patent application WO 97/38567, in which an arm forming a first element is movable in, and opposite to, a Y direction. To the arm is attached a guide forming a second element, which guide is moved along with the arm when the latter is moved in Y-direction. In this machine, the guide is also movable in another direction that extends transverse to the predetermined direction and that is denoted an X direction. 
     The guide comprises a component placement element by means of which a component can be picked-up from a pick-up plate and subsequently can be placed on a desired position onto the substrate. For this purpose, the arm, the guide, and the component placement element are moved in common in, or opposite to, the Y-direction and the X-direction. Near to the pick-up position and the desired position on the substrate the component pick-up element is temporarily stopped to enable it to pick-up and place the component, respectively. To enable a relatively fast pick-up and placement of components, the relatively heavy arm and the component placement element are moved as fast as possible between the pick-up position and the desired position on the substrate. 
     The rapid movement of the arm and the component placement element leads to relatively large acceleration and deceleration forces. As the accuracy with which a relatively light component is picked-up or moved should be relatively high, stringent requirements must be placed on the driving and guiding of the arm. This heightened accuracy requirement presents a problem that is not only found in component placement machines, but in any placement machine with which a relatively small mass is to be moved quickly and by means of a relatively large mass. 
     SUMMARY 
     It is an object of the present invention to provide a method for moving at least two elements in which the second element can be moved comparatively accurately and quickly to a desired position by means of the first element. This object is achieved in the method according to the invention in that the first element is moved in the predetermined direction while at the same time the second element is moved relative to the first element in a direction opposite to the predetermined direction and vice versa. Accordingly, it is possible, for example, to move the first element together with the second element to a desired position in a comparatively fast manner. 
     During the movement of the first and second elements near the desired position, the second element is moved in an opposite direction to the first element. As a result, the second element undergoes a compound movement that is in a direction opposite to the predetermined direction and that is determined by the movement of the first element in the predetermined direction or vice versa. The compound movement of the second element may be comparatively small or even zero. As a result, the second element may be brought to a standstill without also bringing the first element to a relative standstill and, therefore, no large deceleration forces will be applied to the first element. 
     An embodiment of the method according to the invention is characterized in that the first element may be moved in the predetermined direction over a distance that is substantially equal to the distance over which the second element is moved in opposite direction. The resulting or compound distance over which the second element is relatively moved will then be substantially equal to zero. This makes it possible for the first element to be moved, whereas the second element remains relatively stopped. 
     A further embodiment of the method according to the invention is characterized in that the first element may be moved in the predetermined direction with a speed that is substantially equal to the speed with which the second element is moved in opposite direction. In this way, the resulting speed with which the second element is relatively moved is substantially equal to zero, whereas the speed of the first element need not be adjusted. 
     A further embodiment of the method according to the invention is characterized in that the second element may also be moved in a direction that extends transverse to the predetermined direction. In this way the second element may be moved in a plane that extends parallel to the predetermined direction and the transverse direction. 
     Yet a further embodiment of the method according to the invention is characterized in that the second element may comprise a component placement element that relative to the second element, is moved in a placement direction that extends transverse to the predetermined direction. By means of a component placement element, it is possible for a component to be moved accurately and quickly to a desired position by means of the placement machine. 
     Yet a further embodiment of the method according to the invention is characterized in that the second element may comprise an imaging device by which images may be made. By means of the imaging device it is possible to make images of a desired position to which the second element is to be moved; this imaging may be carried out while the second element is being moved. This enables the second element to be driven relative to the first element so that the second element may be accurately moved close to the desired position. 
     The invention is also based on a placement machine that avoids the disadvantages of the conventional machine. The placement machine according to the invention comprises at least two elements that are movable in, and opposite to, a predetermined direction. The second element is movable with the aid of the first element. Both the first element and the second element are further movable relative to each other in, and opposite to, a predetermined direction. As a result, it is possible to bring the second element to a relative standstill while the first element is moving, for example, at a constant speed, by moving the second element in the opposite direction. The second element mass to be brought to a relative standstill with this action may be comparatively small, so that comparatively small acceleration forces will occur. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below. 
         FIG. 1  is a plan view of a component placement machine according to the invention; 
         FIG. 2  is a diagrammatic representation of a placement machine according to the invention, in which the second element is located close to the desired placement position; and 
         FIG. 3  is a diagrammatic representation of the placement machine shown in  FIG. 2  in which the second element is located near a pick-up position. 
     
    
    
     DETAILED DESCRIPTION 
     In the Figures like elements carry like reference numerals. 
       FIG. 1  shows a component placement machine  1  according to the invention. The component placement machine  1  comprises an elongated frame  2  over which a substrate  3  can be moved in, and opposite to, a direction indicated by arrow P 1 . The direction indicated by arrow P 1  extends parallel to the X-direction. The component placement machine  1  further comprises two guide rails  4 ,  5  that are parallel to each other and that extend in the Y-direction, i.e., traverse to the X-direction. The guide rails  4 ,  5  are located over the frame  2 . Between the guide rails  4 ,  5  is an arm  6  that on either end comprises a guide  7 ,  8  (i.e., first element) by means of which the arm  6  is slidably supported on bearings over the guide rails  4 ,  5 . The guides  7 ,  8  each comprise a motor by which the guides  7 ,  8  are movable over the guide rails  4 ,  5  in, and opposite to, the directions indicated by the arrows P 2 , P 3 , respectively. A guide  9  is movable over the arm  6  by means of a motor in, and opposite to, the X-direction indicated by the arrow P 4 . The component placement machine  1  further comprises a number of component feeding devices  10  arranged on both sides of the frame  2  between the guide rails  4 ,  5 . 
     The component placement machine  1  described so far is known per se, for example, from international patent application WO 97/38567, which was previously discussed. For this reason, the operation of the component placement machine  1  will be concisely elucidated. Substrates  3  are moved in steps in the direction indicated by the arrow P 1  over the frame  2 . Components are positioned on the substrates  3  in the area between the guide rails  4 ,  5  by means of the component placement element. For this purpose, the guide  9  is moved over the arm  6  while at the same time the guides  7 ,  8  are moved over the guide rails  4 ,  5 , so that a desired component can be picked-up from the component feeding devices  10  by means of the component placement element. Subsequently, the component placement element is taken to a desired position above the substrate  3  via the guides  7 ,  8  after which the component is positioned in the Z direction at the desired position on the substrate by means of the component placement element. 
     The mass of the component to be placed is often less than 1 gram whereas the total mass of the guides  7 ,  8 ,  9  and the arm  6  is, for example, 65 to 80 kg. During the movement in, for example, the Y-direction, this whole mass is constantly moved to and fro between the component feeding devices  10  and the desired position on the substrate  3 . To be able to place a comparatively large number of components per time unit, the arm  6  must be moved to and fro comparatively quickly. It should also be possible to bring the arm  6  to a standstill quickly and to likewise to reset the arm  6  in motion quickly. 
     As a result of the large weight of the arm  6  compared with the weight of the component to be placed, comparatively large acceleration and deceleration forces may occur during this movement. In addition or alternatively, vibrations may occur during this movement; such vibrations must first be dampened to achieve the desired positioning accuracy; this damping takes extra time. 
     The aforementioned acceleration forces and deceleration forces and/or vibrations do not occur with a component placement machine  11  according to the present invention. The component placement machine  11  will be further explained with reference to  FIGS. 2 and 3 . The component placement machine  11  includes a guide  7  that is movable over a guide rail  4  in, and opposite to, the Y-direction indicated by the arrow P 2 . For sake of clarity, the arm  6  and the guide  9  have been omitted in  FIGS. 2 and 3 . A guide  13  (i.e., second element), which supports a component placement element  12 , can be directly moved over a guide rail  14  connected with the guide  7 . The guide rail  14  extends parallel to the guide rail  4 . The guide  13  can be moved in, and opposite to, the Y-direction, as indicated by arrow P 5 . The direction indicated by arrow P 5  extends parallel to the direction indicated by arrow P 2 . 
     In the situation shown in  FIG. 2 , a component  15  has already been fed from the component feeding device  10  by means of the component placement element  12 . The component  15  is to be placed at a desired position on the substrate  3 . For this purpose, the guide  7  together with the connected guide  13  is moved in the direction indicated by arrow P 2  at a comparatively high speed. As soon as the component placement element  12  comes in the neighborhood of the desired position on the substrate  3 , the guide  13  is moved, by means of a regulator, in the direction indicated by arrow P 5 , i.e., opposite to the direction indicated by arrow P 2 . The placement of the guide  13  in the direction indicated by the arrow P 5  is regulated such that the component  15  is immobile relative to the substrate  3  above the desired position on the substrate  3  at which the component is to be placed. As only the speed and movement of the comparatively light guide  13  needs to be regulated in the neighborhood of the desired position on the substrate  3 , the consequent acceleration and deceleration forces will be comparatively small. As a result, the component  15  can be placed on the substrate  3  with high accuracy, while the speed at which the total mass of the guides  7 ,  13  is moved in the direction indicated by arrow P 2  can be comparatively high. Moreover, the mass of the guides  7 ,  13  can keep moving steadily, thereby precluding attendant acceleration/deceleration forces and/or vibrations. 
       FIG. 3  shows the placement machine  11  represented in  FIG. 2  when a component  15  is being picked-up from a component feeding device  10 . The guide  7  is first moved in a direction opposite to the arrow P 2  from a position above the substrate  3  to a position located above the component feeding device  10 . Subsequently, the guide  7  is to be moved again in the direction indicated by the arrow P 2  to the position located above the substrate  3 . This reciprocating movement of the guide  7  is indicated by the arrow P 6 . To avoid comparatively high acceleration and deceleration forces and/or vibrations, in the neighborhood of the component feeding device  10 , the guide  13  is moved in the direction indicated by the arrow P 7  over the guide rail  14 . The superposed movement of the component placement element  12  is such that the component placement element  12  stands still for a moment at the desired position above the component feeding device  10 , thereby enabling the component  15  to be picked-up from the component feeding device  10 . The guide  7  can be slowed down comparatively slowly during the pick-up phase and accelerated again to be able to change direction of movement, while ensuring that there are comparatively small deceleration and acceleration forces. In contrast, the light guide  13  can undergo comparatively large decelerations and accelerations that result in comparatively small deceleration and acceleration forces, as a result of the comparatively light weight. 
     If the placement machine  11  according to the invention is used in the component placement machine  1  shown in  FIG. 1 , the guide rail  14  can be connected with the guide  9 , for example, on a side of the arm  6  facing the frame  2 .  FIG. 1  gives a diagrammatic view of such a guide rail  14  having reference numeral  14 ′. 
     The guide  7  can be moved with a speed of 2 meters per second, whereas the time needed for picking-up or placing a component may be, for example, 100 ms. As a result, the length of the guide rail  14  should be about 200 mm to enable sufficient movement of the guide  13 . 
     It is also possible to have the comparatively light guide  13  moveable in both the X and Y directions but opposite to the direction of the comparatively heavy guide. 
     It is alternatively possible to provide the guide  9  with a second guide rail  14 ″ by means of which a second component placement element  12  can be moved. In this fashion it is possible to pick-up two components at the same time (or in succession) from the component feeding devices  10  and then place them simultaneously (or in succession) on a substrate  3 . 
     It is alternatively possible to provide the guide  13  not only with a component placement element  12  but also with a camera  16  (i.e., image sensor) by means of which a pick-up position on the component feeding device  10  a desired placement position on the substrate  3  can be observed prior to picking-up and placing a component  15 , respectively. Based on the images perceived by the camera  16 , an accurate driving of the guide  13  relative to the guide rail  14  can be realized. It is also possible for the camera  16  to be installed on a separate guide that can be moved over a separate guide rail. 
     The component placement element  12 , for example, comprises a pick up tube that can be moved relative to the guide  13  in, and opposite to, the Z direction that extends transversely to the X and Y-direction. 
     Given the disclosure of the present invention, one versed in the art would appreciate that there may be other embodiments and modifications within the scope and spirit of the invention. Accordingly, all modifications attainable by one versed in the art from the present disclosure within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is to be defined as set forth in the following claims.