Abstract:
A method for driving a component placement device, the component placement device having a machine frame, component pickup units and a subframe, the first and second component pickup units configured to be movable in a direction of travel, the method comprising: moving at least one of the component pickup unit in the direction of movement relative to the subframe, the component pickup units and the subframe configured for a reactive force to be exerted on the subframe by the moving of the at least one of the component pickup units; determining a counterforce to be exerted against the subframe substantially opposite a direction of the reactive force, the counterforce determined by an auxiliary control unit, wherein the counterforce at least partially counteracts the reactive force; and applying the counterforce to the subframe substantially in the opposite direction of the reactive force by at least one drive unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Dutch Patent Application No. 2007777 filed on Nov. 11, 2011, the disclosure of which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     A component placement device is described in applicant&#39;s European patent application EP 1 937 050 A1. 
     In said known described placement device, the machine frame supports a number of subframes. Each subframe is provided with a guide, over which a component pickup unit is movable in a direction of movement parallel to the guide. Each component pickup unit is further movable relative to the subframe in a direction transversely to the direction of movement. The guides extend parallel to each other. Disposed under the component pickup units is a conveying device that extends transversely to the direction of movement for transporting substrates. Each subframe at least comprises a motor for moving the component pickup unit in the direction of movement. Components are picked up from component pickup positions by means of the component pickup unit, after which the component pickup unit is moved to a position above a desired position on the substrate, whereupon the component is placed on the desired position on the substrate. 
     SUMMARY 
     The invention relates to a component placement device comprising a machine frame and at least two component pickup units which are movable relative to at least one subframe supported by a machine frame, each component pickup unit being movable at least in a direction of movement. 
     The placement of such components must take place with the highest possible speed and accuracy. 
     To attain such a high speed, the component pickup unit is moved from the pickup position with a relatively high acceleration. In a similar manner, the component pickup unit must be quickly decelerated near the desired position on the substrate or, in other words, be moved with a relatively high negative acceleration. Such high accelerations also occur upon returning to the pickup position. Because of said accelerations, relatively large reactive forces are exerted on the subframe by the component pickup unit. Said reactive forces cause among other things, vibrations and deformations of the machine frame and other subframes supported by the machine frame, thus affecting the accuracy with which another component pickup unit can be moved to a desired position. This effect is called dynamic crosstalk, which term is understood to mean the influence of the dynamic behaviour of one component pickup unit on the positioning accuracy of another component pickup unit. 
     In order to reduce the influence of such reactive forces, it is possible to move the component pickup unit with less high accelerations. However, this will have an adverse effect on the number of components that can be moved per unit time. 
     Another possibility is to make the machine frame much heavier and stiffer, so that the reactive forces can be better absorbed. This will make the component placement device relatively costly to produce and use, however. 
     The object of the invention is to provide a component placement device and a method for controlling such a component placement device, wherein reactive forces exerted by one component placement unit will have practically no effect on the positioning accuracy of another component pickup unit. 
     This object is accomplished with the component placement unit according to the invention in that, the component placement device comprises means for determining the magnitude of a counterforce to be exerted on the subframe substantially in the direction of movement, as well as at least one drive unit for exerting the counterforce determined by said means substantially in the direction of movement on the subframe for the purpose of at least partially counteracting the reactive force exerted on the subframe by at least one component pickup unit during movement of the component pickup unit in the direction of movement relative to the subframe. 
     By actively and purposefully exerting a counterforce in the direction of movement, which direction is the opposite of the direction of the reactive force and which is preferably of the same magnitude as the reactive force, the reactive force exerted on the subframe is at least partially (and preferably substantially entirely) withstood, making it possible to prevent the occurrence of vibrations and deformations of, inter alia, the machine frame, and the transmission thereof to other subframes near the origin of the source, being the subframe, at least substantially and preferably practically entirely. As a result, the dynamic crosstalk is significantly reduced or at least practically entirely prevented. The magnitude of the counterforce to be exerted is determined either by calculation or by measurement. 
     One embodiment of the component placement device according to the invention is characterised in that the subframe is provided with a first part of the drive unit, whilst a second part of the drive unit, which cooperates with the first part of the drive unit, is mounted on an auxiliary frame that is freestanding from the machine frame. 
     The term “freestanding auxiliary frame” is understood to mean any support for a drive unit that is capable of suppressing or eliminating forces from the machine frame and from subframes supported by the machine frame, so that there will be fewer vibrations, if any. 
     Such an auxiliary frame can be formed by a wall of the building in which the component placement device is installed. Such an auxiliary frame may also be a metal construction, for example, which is disposed near the machine frame. As a result, the second part of the drive unit that is supported by the auxiliary frame will not experience any effect of the reactive force exerted on the associated subframe by the component pickup unit during movement of the component pickup unit in the direction of movement, and the force exerted on the first part by the second part can be fully utilised for counteracting the reactive force. 
     Another embodiment of the component placement device according to the invention is characterised in that the first part comprises at least one permanent magnet, whilst the second part comprises at least one electrically energisable coil, or vice versa. 
     Using a permanent magnet and an electrically energisable coil that cooperates therewith, it is possible to easily generate counterforces that vary in magnitude and in time. 
     Yet another embodiment of the component placement device according to the invention is characterised in that the component placement device comprises a control unit for delivering a control signal for controlling the movement of the component pickup unit in the direction of movement, wherein the drive unit is provided with means for determining the magnitude of the counterforce to be exerted by the drive unit in dependence on the control signal. 
     Such a control signal usually comprises information on the desired movement pattern in time, for example the movement during the time that is needed for moving the component placement unit from a component pickup position to the desired position above the substrate. The movement pattern comprises three phases, for example, a first acceleration phase, a second phase with a constant high-speed and a third braking phase with a negative acceleration. During the first and the third phases, the drive unit generates a force that depends on the accelerations (decelerations) that occur and the moving mass. 
     Yet another embodiment of the component placement device according to the invention is characterised in that the component placement device is provided with a force sensor for determining the reactive force exerted on the subframe by the moving component pickup unit, wherein the drive unit is provided with means for determining the magnitude of the counterforce to be exerted by the drive unit in dependence on the reactive force exerted on the subframe in question and measured by the force sensor. 
     In this way the reactive force that occurs is measured directly and the counterforce to be exerted by the drive unit is directly known therefrom. 
     The object of the invention is achieved with the method according to the invention in that in the method for driving a component placement device comprising a machine frame and at least two component pickup units which are movable relative to at least one subframe supported by a machine frame, each component pickup unit being movable at least in a direction of movement, at least one component pickup unit is moved in the direction of movement relative to the subframe, with a reactive force being exerted on the subframe by the component pickup unit, that a counterforce to be exerted substantially in the direction of movement on the subframe is determined by means for the purpose of at least partially counteracting the reactive force, whereupon the counterforce determined by said means is exerted substantially in the direction of movement on the subframe by means of at least one drive unit. 
     Each time the component pickup unit is moved relative to the subframe, thereby exerting a reactive force on the subframe, the drive unit will exert a counterforce on the subframe. 
     Another embodiment of the method according to the invention is characterised in that the magnitude of the counterforce to be exerted is determined at least on the basis of a control signal for controlling the movement of the component pickup unit in the direction of movement. 
     From said control signal, the accelerations (decelerations) that occur can be determined, and in combination with the known weight of the moving parts, it is possible to determine therefrom the forces that will occur, and consequently the required counterforces. 
     Yet another embodiment of the method according to the invention is characterised in that the reactive force exerted on the subframe by the moving component pickup unit is measured by means of a force sensor, whereupon the magnitude of the counterforce to be exerted is determined at least in dependence on the reactive force being exerted on the subframe and measured by the force sensor. 
     Using the force sensor, the reactive force that occurs, and consequently the required counterforce, is directly determined. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in more detail with reference to the drawing, in which: 
         FIG. 1  is a schematic side view of a component placement device according to the prior art; 
         FIG. 2  is a schematic side view of a component placement device according to the invention; 
         FIGS. 3A and 3B  are a top plan view and a view in the direction indicated by arrows IIIB-IIIB, respectively, of a drive unit of the component placement device shown in  FIG. 2 ; 
         FIG. 4  is a perspective front view of an embodiment of a component placement device according to the invention; 
         FIG. 5  is a perspective, partially cutaway front view of the component placement device shown in  FIG. 3 ; 
         FIG. 6  is a perspective, partially cutaway rear view of the component placement device shown in  FIG. 3 ; 
         FIG. 7  is a partially cutaway side view of the component placement device shown in  FIG. 3 ; 
         FIG. 8  is a partially cutaway side view of the component placement device shown in  FIG. 3 , in which the subframe is tilted upwards relative to the machine frame; 
         FIG. 9  is a cross-sectional view in the direction indicated by arrows VIII-VIII in  FIG. 6  of the drive unit of the component placement device according to the invention. Like parts are indicated by the same numerals in the figures. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a schematic side view of a component placement device  1  according to the prior art, which comprises a machine frame  2 , a subframe  3  supported by the machine frame  2  and a component pickup unit  4  which is movable relative to the subframe  3 . The component pickup unit  4  is movable at least in a direction of movement indicated by arrow P 1  and in the opposite direction. The machine frame  2  comprises a support part  5  and upright parts  6  disposed on either side of the support part  5 . The support part  5  is supported on a base  8  via support legs  7 . Supported on the support part  5 , between the upright parts  6 , is a conveying device (not shown) for conveying substrates  9  in a direction transversely to the plane of the drawing. The component pickup unit  4  is movable in a usual manner, as for example known from EP 1 937 050 A1, from a component pickup position (not shown) to a desired position above the substrate  9  for picking up, moving and subsequently positioning the picked-up component on the substrate  9 . The movement of the component pickup unit  4  relative to the subframe  3  takes place by means of a motor which is controlled by a control unit for moving the component pickup unit  4  with the desired accelerations and at the desired speeds. Upon acceleration of the component pickup unit  4  in the direction indicated by arrow P 1 , the motor exerts a force F 1  in the direction indicated by arrow P 1  on the component pickup unit  4 . This results in a reactive force F 2  of the component pickup unit  4  on the subframe  3 , which reactive force F 2  is equal in magnitude to the force F 1  but opposite in direction thereto. Said reactive force F 2  is exerted on the upright part  6  via the subframe  3 , as a result of which the upright part  6  will bend elastically in the direction indicated by arrow P 2 . The bent shape is illustrated in dotted lines. The degree of bending is shown on an enlarged scale for the sake of clarity. The deformation of the part  6  causes the subframe  3  to move in the opposite direction of arrow P 1 . The varying reactive forces F 2  will cause vibrations. Once the reactive force F 2  decreases, the part  6  will bend back. Because the reactive force F 2  will decrease to zero when the component pickup unit  4  is stopped for picking up or placing a component, the vibrations will dampen out and the vibrations and movements in the machine frame caused by the reactive force F 2  will have practically no effect on the accuracy during placement of the component by means of the stationary component pickup unit  4 . 
     If, however, a second subframe  3  is present on the machine frame  2  next to the first subframe  3 , which second subframe  3  is also provided with a second component pickup unit  4  that is movable relative to the second subframe  3 , the deformations and vibrations in the machine frame  2  caused by the reactive force F 2  will interfere with an accurate placement of a component by means of said second component pickup unit  4 , since said deformations and vibrations affect, via the loop  10  (illustrated in dotted lines), the relative positions of the parts present in the loop  10 . As a result, accurate placement of a component by means of the component pickup unit  4  of the second subframe with a degree of accuracy of less than 15 micron or less is not possible. It also stands to reason that the reactive forces that occur during movement of the component pickup unit  4  over the second subframe will have a negative effect on the placement accuracy of the component pickup unit  4  of the first subframe. 
       FIG. 2  is a schematic side view of a component placement device  21  according to the invention, which is different from the component placement device  1  shown in  FIG. 1  in that it comprise an auxiliary frame  22  in addition to a machine frame  2 , a subframe  3 , a component pickup unit  4 , a support part  5  and parts  6 . The auxiliary frame  22  comprises sections  23  positioned under the support part  5 , which are supported on the support legs  7  of the machine frame  2 . The auxiliary frame  22  further comprises uprights  24  extending parallel to the parts  6  and a girder  25  disposed between ends of the uprights  24 . Since the connection between the machine frame  2  and the auxiliary frame  22  is spaced from the loop  10  by a relatively large distance, forces that occur near the component pickup unit  4  are not noticeably transmitted to the auxiliary frame  22 , and vice versa. The auxiliary frame  22  is made of a metal, for example. 
     The component placement device  21  is further provided with a drive unit  26 , which is shown on a larger scale in  FIGS. 3A and 3B . The drive unit  26  comprises a first part connected to the end  27  of the subframe  3 , which comprises two spaced-apart blocks  28 ,  29  provided with permanent magnets  30 ,  31 . The magnets  30  of the blocks  28 ,  29  are positioned opposite each other and have the same polarization. The magnets  31  of the blocks  28 ,  29  are positioned opposite each other and have the same polarization but which is the opposite of that of the magnets  30 . The polarisation directions extend in a direction parallel to the conveying direction of the substrate  9 . The drive unit  26  further comprises a second part, which is provided with an electrically energisable coil  32  that is connected to the girder  25 , a left-hand part of which is disposed between the magnets  30  and a right-hand part of which is disposed between the magnets  31 . 
     The movement of the component pickup unit  4  relative to the subframe  3  takes place by means of a motor which is controlled by a control unit  33  for moving the component pickup unit  4  with the desired accelerations and at the desired speeds. Upon acceleration of the component pickup unit  4  in the direction indicated by arrow P 1 , the motor exerts a force F 1  in the direction indicated by arrow P 1  on the component pickup unit  4 . This results in a reactive force F 2  from the component pickup unit  4  on the subframe  3 , which reactive force F 2  is equal in magnitude to the force F 1  but opposite in direction thereto. At the same time, the control unit  33  sends the control signal to an auxiliary control unit  34 , in which the reactive force F 2  to be expected is calculated on the basis of an acceleration-time profile in the control signal and the known moving mass. On the basis of said reactive force F 2  to be expected, an electric current is led to the coil  32  by means of the auxiliary control unit  34 , which current will generate a counterforce in the drive unit  26  which is equal in magnitude to the reactive force F 2  to be expected but which direction is the same direction as the force F 1 . The forces F 1 , F 2  and the force generated by the drive unit  26  are preferably in line with each other. In this way the forces generated by the drive unit are prevented from introducing a torque. The reactive force F 2  exerted on the subframe  3  will be opposed and eliminated by the counterforce generated by the drive unit  26 . Since no resulting force is exerted on the subframe  3 , no vibrations and deformations will occur in the component placement device  21 . Thus the movement of the component pickup unit  4  relative to the subframe  3  will not affect the accuracy with which a component can be placed on a substrate  9  by means of an adjacent component pickup unit  4 . In  FIG. 2 , dotted lines illustrate the deformations experienced by the auxiliary frame  22  as a result of the forces exerted thereon. Since the auxiliary frame  22  is freestanding, said forces will not be transmitted to the machine frame  5 , and said deformations and the accompanying vibrations will not affect the placement accuracy of the component pickup unit  4 . 
       FIGS. 4-9  show various views of an embodiment of a component placement device  41  according to the invention, which comprises a machine frame  42 , a conveying device  43  for substrates  44 , which is supported by the machine frame  42 , and three subframes  45 , which each comprise two guides  46  disposed side by side. A component pickup unit  47 , which conveying device  43  is provided with a nozzle  147 , among other parts, by means of which a component can be picked up, is movable over each guide  46 . The component placement device  41  comprises, at a front side thereof, a number of component supplying devices  48 , which are accommodated in exchangeable holders  49 . The component placement device  41  is further provided with an auxiliary frame  50 , which comprises two sections  51  positioned under the machine frame, two uprights  52  extending transversely thereto, which are disposed at the rear side of the component placement device  41 , and a girder  53  extending between the uprights  52 . The sections  51  are connected to the machine frame  55  via legs  54 . Because of the relatively large distance between the legs  54  and the component pickup unit  47 , such an arrangement of auxiliary frame  50  can nevertheless be regarded as freestanding. Each subframe  45  is provided with permanent magnets  54  near the girder  53 , in line with each guide  46 , which magnets are disposed between coil blocks  55  connected to the girder  53 . The permanent magnets  54  are connected to the subframe  45  via a connecting section  56 . 
     The operation of the drive unit made up of the permanent magnets  54  and the coil blocks  55  is comparable to that of the drive unit  26  described with reference to  FIGS. 2 ,  3 A,  3 B. Each subframe  45  has two drive units  57  associated therewith, by means of which first and second drive unit  57  a counterforce is generated for eliminating the reactive force from the first and the second component pickup unit  47 , respectively, being moved over the first and the second guide  46 , respectively. 
     In order to make it possible to gain access to the space under the subframes  45 , for example for carrying out maintenance work, each subframe  45  can be pivoted in a direction indicated by arrow P 3  about a pivot axis  58  located near the girder  53 . This pivoted position of the subframe  45  is shown in  FIG. 8 , in which the permanent magnets  54  are shown to have been swung out from their position between the coil blocks  55 . 
     It is noted that six guides extend parallel to each other in the component placement device  41  shown in  FIGS. 4-9 , which guides are each provided with a component pickup unit  47 . In use, a component is placed on a substrate  9 , for example by a first one of the six component pickup units  47 , whilst the other five component pickup units  47  are moved at relatively high accelerations. The use of the drive units  57 , which exert forces on the subframes  45  for counteracting reactive forces being exerted on the subframes  45  by the moving component pickup units  47 , significantly reduces or altogether prevents the occurrence of vibrations and deformations, as a result of which the components can be accurately placed on the substrate by the first component pickup unit  47 , in which regard a degree of accuracy of less than 10-15 micron can be realised. 
     The directions of movement of the various component pickup units  47  may also extend transversely to each other or include a different angle with each other. 
     If the component pickup unit  47  is also movable in a further direction of movement extending transversely to the direction of movement, it is also possible to provide the component placement device with drive units for generating counterforces in said further direction of movement. 
     It is also possible to use other combinations of magnets and coils, such as Lorentz actuators, for the drive unit. Also hydraulic drive units are possible.