Abstract:
The present invention relates to a method for automatic bow adjustment for a venetian blind assembly machine, said bow adjustment station comprising rollers ( 48; 104, 106 ) for guiding, bending and levelling a strip material ( 43; 112 ), and further comprising a forming section ( 36; 102 ) where mating concave and convex upper and lower form rollers ( 50; 108, 110 ) are arranged for creating a transverse curvature in the strip material, further comprises the steps of: providing levelling through means for offsetting ( 34; 100, 102 ) in order to straighten the bow of the strip material ( 43; 112 ) within a predetermined deviation on a predetermined length of strip material; measuring the deviation through optical means ( 146 ) providing a deviation signal; and adjusting the levelling by said means for offsetting ( 34; 100 ) through the deviation signal, if said measured deviation exceeds a predetermined deviation, in order to keep the deviation within said predetermined deviation. In addition, the present invention also relates to an arrangement for automatic bow adjustment for a venetian blind assembly machine. An advantage over prior art is that the bow adjustment is better controlled, the adjustments can be done with an increasing rapidity and a decreased wastage of strip material is obtained.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. patent application Ser. No. 09/541,258, filed Apr. 3, 2000, allowed, which corresponds to and claims priority to European Application No. 99201013.2, filed Apr. 2, 1999. Each of the above-identified application is hereby incorporated by reference as though fully disclosed herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a method and an arrangement for automatic bow adjustment for a venetian blind assembly machine. 
     2. Background Art 
     The production of venetian blinds of different sizes and types in venetian blind assembly machines is previously known in the art. Strip material from which venetian blinds are made is typically supplied in rolls or coils at one end of the machine. The leading end of the strip of material is fed through a levelling station, where offset rollers are positioned to receive the strip material and reversibly bend the material to remove the innate bend that results from storage in a coil condition. Subsequently, the strip material passes through a forming section where mating concave and convex upper and lower form rollers create a transverse curvature in the strip material. Further on in the line of the assembly machine, slats are punched and cut from the strip material, whereafter they are fed to a lacing station, in which the slats are fed into the gaps between the vertical cords of a venetian blind cord ladder. 
     The object of the levelling station is to remove the innate bend of the strip material that results from storage in a coiled condition and to produce substantially straight longitudinal slats for the blind. The extent of reverse bending of the strip material in the levelling station depends on parameters such as the dimensions for the blind. Different sizes of slat width and even different colours of blinds require different degree of reverse bending. Insufficient bending or over-bending of the strip material will have the result that the slats produced from the strip material have a bow in the longitudinal direction, either provided with an “upbow” curvature or a “downbow” curvature, lying outside acceptable predetermined deviations. According to the prior art production of venetian blinds, the bow adjustments have been done more or less “manually” (that is, not automatically), by trial and error. The basic adjustment, as well as the continuous adjustment during production, of the levelling station has been based on experience. During production, adjustments have been carried out continuously by visually controlling if there is a bow of the slats lying outside the predetermined deviations and thereafter manually adjusting the levelling station for such deviations. 
     The manual adjustment of the levelling station leads to a large waste of strip material, since produced slats with an unacceptable bow must be rejected and the line must be emptied of strip material. In addition, manually adjusting the process is inefficient and time consuming, as the production must be stopped and restarted during the adjustments. The manual adjustment is especially inefficient when there is a change of dimensions or colours of the slats for production of a new blind in the machine. 
     Therefore, it is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art and to achieve less wastage of the strip material. A further object is to achieve a venetian blind assembly machine, which operates more efficiently and can be easily controlled to an increasing extent with respect to what is known in the art. Yet a further purpose is to achieve an economically favourable production of venetian blinds and to minimise the drawbacks of prior art processes. 
     SUMMARY OF THE INVENTION 
     The above mentioned problem has been solved with the present invention by providing a method for automatic bow adjustment for a venetian blind assembly machine. The bow adjustment station comprises rollers for guiding, bending and levelling a strip material. Further, it comprises a forming section where mating concave and convex upper and lower form rollers are arranged for creating a transverse curvature in the strip material. In addition it includes the steps of: providing levelling through means for offsetting in order to straighten the bow of the strip material within a predetermined deviation on a predetermined length of strip material; measuring the deviation through optical means providing a deviation signal; and adjusting the levelling by said means for offsetting through the deviation signal, if said measured deviation exceeds a predetermined deviation value, in order to keep the deviation within said predetermined deviation value. 
     An advantage with the method of the present invention is that the bow adjustment is better controlled and the manual bow adjustment can be completely avoided. Thus, the adjustments can be accomplished with an increasing rapidity when there is a change of the dimensions and the colours of the strip material in the production. 
     A further advantage with the method of the present invention is that a decreased wastage of strip material is obtained. Hence, a much more cost efficient production of venetian blinds can be achieved. 
     In addition, the present invention also relates to an arrangement for automatic bow adjustment for a venetian blind assembly machine. The bow adjustment station comprises rollers for guiding, bending and levelling a strip material. Further, it comprises a forming section where mating concave and convex upper and lower form rollers are arranged for creating a transverse curvature in the strip material. In addition it includes: means for offsetting strip material, providing levelling in order to straighten the bow of the strip material within a predetermined deviation on a predetermined length of strip material; means for optically measuring the deviation, providing a deviation signal; and means for adjusting the levelling by said means for offsetting through the deviation signal, if said measured deviation exceeds a predetermined deviation value, in order to keep the deviation within said predetermined deviation value. 
     Embodiments of the present invention are described, without restricting the scope of the present invention thereto with reference to the accompanying drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic front elevation illustrating a prior art slat assembly apparatus and showing various processing stations. 
     FIG. 2 a  shows a schematic side view of a levelling and forming station in an arrangement for automatic bow adjustment according to the present invention. 
     FIG. 2 b  illustrates schematically a partial perspective view of the levelling and forming station of FIG. 2 a;    
     FIGS. 3 a  to  3   d  illustrate a levelling and forming station according to the present invention; 
     FIG. 4 illustrates schematically another partial perspective view of the levelling and forming station of FIG. 2 a;    
     FIGS. 5 a  to  5   d  illustrate a levelling and forming station according to the present invention; 
     FIG. 6 shows a schematic side view of an accumulator station in the arrangement for automatic bow adjustment according to the present invention; 
     FIG. 7 shows a principal diagram of connections for the automatic bow adjustment according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An apparatus  30  for assembling venetian blinds is illustrated in FIG.  1 . The apparatus includes a supply section  32 , means for offsetting in the form of a levelling station  34 , a forming section  36 , an accumulator station  38 , a punch and cut section  40  and a lacing section  42 . 
     Aluminium strip material  43  from which venetian blinds are made is typically supplied in rolls or coils  44 , which are stored at the supply section  32  on a rotatable shaft  46 . The leading end of the strip of material is fed through the levelling station  34 . Offset rollers  48  are positioned to receive the strip material and reversibly bend the material to remove the innate bend that results from storage in a coil condition. 
     After the levelling station  34 , the strip material passes through a forming section  36  where mating concave and convex upper and lower form rollers  50  are positioned to create a transverse curvature in the strip material. An upwardly extending accumulator chamber  52  is provided at the accumulator station  38  so that a length of strip material can be stored in a loop  54 . This storage is required to enable subsequent processing steps of the strip material to be intermittent. 
     From the accumulator station  38 , the strip material passes between idler rollers  56  and  58  which may have a surface adapted to remove any irregularities from the surface of the strip material. 
     After passing through the accumulator station  38  and idler rollers  56  and  58 , the strip is driven by drive wheels  60  and  62 , one of which can be driven by an electric motor. 
     The drive wheels  60  and  62  cause the strip material to be fed at predetermined intervals into the punch and cut section  40 , where first and second punches  66  and  68  are disposed upstream and downstream from a central cutter  70 . The cutter  70  will cut the continuous strip into individual slats  71  of the required length. The punches  66  or  68  are adapted to punch holes (not shown) in the slat material strip for the accommodation of lift cords in the finished blind. 
     Coming from the cut and punch section  40 , the strip material is fed by an outfeed drive roller  72  and outfeed backup roller  74  towards the lacing section  42 . Longitudinal movement of the slat material automatically feeds it through a plurality of a downstreamly spaced ladder lacing stations  78 . In these ladder lacing stations  78  the slat material is laced into flexible ladder supports  76  which serve to interconnect the individual slats of a blind. Downstream of the last operative lacing station  78  or combined therewith is a stop  80  against which the leading end of each slat abuts. 
     A computerised control system housed in a control unit  82  may be designed automatically to accept information and process such information depending on parameters such as the required dimensions for the finished blind. It will also be appreciated that different sizes of slat width (generally 25 mm or 16 mm) and different colours of blinds require different ladder supports. Depending on the number of ladder supports the number of lacing stations  78  that will be operative will be variable for each blind under construction. Such information is also accommodated by the computerised control system. 
     FIGS. 2 a  to  5   d  illustrate the principle construction of a means for offsetting in the form of a levelling station  100  (generally comparable to the levelling station  34  in FIG. 1) and a forming section  102  (generally comparable to the forming section  36  in FIG. 1) in an arrangement for automatic bow adjustment according to the present invention. 
     As can be seen from FIGS. 2 a  and  2   b,  the levelling station  100  includes at least one upper roller  104  and a confronting lower roller  106 , and the forming section  102  comprises generally an upper roller  108  and a confronting lower roller  110 . All rollers serve for guiding a strip material  112  (similar to the strip material  43  of FIG.  1 ) continuously in a forward direction of the production line. However, the levelling station  100  as well as the forming section  102  may of course comprise additional rollers (not shown). The rollers  104 ,  106  of the levelling station  100  are also adapted to receive the strip material and reversibly bend the material to remove the innate bend that usually results from prolonged storage of the strip in a coiled condition. The object of the rollers  104 ,  106  is to fine-adjust the levelling of the strip material continuously, suitably without interruption of the production cycle. The positioning of the rollers  104 ,  106  is preferably adjusted automatically by an electric supply of power (not shown but conventional). The power supply is transmitted through a shaft  114  and a power transmission belt  116  in connection to a screw spindle mechanism or the like (not shown but conventional) for providing the vertical position of the rollers  104 ,  106 . The construction of said mechanism for providing the levelling, can be made in various ways well known to the person skilled in the art. For instance, the rollers  104 ,  106  can be arranged on a vertically positioned plate, which is pivotally arranged with respect to the axle of roller  108  in the forming section. 
     A particular embodiment of the mechanism for providing levelling is illustrated in FIGS. 3 a  to  3   d.  FIGS. 3 a  and  3   b  illustrate schematically rollers  104  and  106  and rollers  108  and  110  arranged on a levelling plate  105 . FIGS. 3 c  and  3   d  correspond to FIGS. 3 a  and  3   b  with added detail and roller  110  partially cut away. 
     Rollers  104  and  106  are mounted rotatably on levelling plate  105  and levelling plate  105  is rotatable about the axis of roller  108 . 
     In the absence of rollers  104  and  106 , the strip material would pass in a straight horizontal path through the apparatus as shown by the broken line P. In particular, it would be passed from a previous set of rollers or guides (not illustrated but conventional) to rollers  108  and  110 . As illustrated in FIGS. 3 a  and  3   b , by tilting the levelling plate  105 , the rollers  104  and  106  are deflected so as to move the strip material from its otherwise straight path. Thus, by deflecting the strip material around the rollers  104  and  106  in this way, the strip material may be appropriately levelled. 
     As illustrated in FIGS. 3 c  and  3   d,  the levelling plate  105  is attached to a threaded shaft  114  by means of a pivot  114   a.  The threaded shaft  114  passes through a threaded pulley wheel  115  which is rotatable by means of transmission belt  116 . Thus, by operating the transmission belt  116  to rotate the pulley wheel  115 , the threaded shaft  114  is caused to move up and down and rotate the levelling plate  105  about the axis of roller  108 . In this way, by controlling the transmission belt  116 , the levelling operation may be conducted automatically. 
     Turning now to FIG. 4, the forming section  102  is schematically illustrated. In the forming section, mating concave and convex upper  108  and lower  110  form rollers are arranged for creating a transverse curvature in the strip material  112 . The applied pressure of the rollers  108 ,  110  is preferably adjusted electrically by an electric supply of power (not shown but conventional). A shaft  118  provided with screw threads is engaged to a supporting structure (not shown but conventional). The shaft  118  is engaged by its thread in a threaded pulley wheel  119  which is rotated by a supply of power via a power transmission belt  120 . The shaft is freely rotatably mounted in a member  122 , suitably attached to the lower roller  110 , for adjusting the applied pressure by the rollers  108 ,  110 . Hence, the shaft  118  is movable in an axial and substantially vertical direction (as indicated by the arrows in FIG.  4 ). The member  122  can be an arm portion  124  attached at one end to the axle of the lower roller  110 . The other end of the arm portion  124  may be in the form of a sleeve part  126  in which the lower part of the shaft  118  is internally arranged and freely axially movable. A spring  128  is arranged on the lower part of the shaft  118 , in between the lower end  130  of the shaft and the sleeve part  126  of the arm portion  124 . The spring  128  acts on the member  122  as a prestressing force of the lower roller  110 . The shaft is arranged to move in an axial direction with rotation of the pulley wheel  119  and is restrained from rotation about its axis. Hence, when the shaft is actuated by supply of power, the lower end  130  is movable up and down, such that the spring is compressed and relaxed and the lower roller  110  provides a increasing or decreasing pressure towards the strip material  112 . Moreover, the applied pressure by the rollers  108 ,  100  also contributes to reversibly bend the strip material  112 , in addition to the levelling station  100 . Accordingly, during production, the rollers  108 ,  110  are more or less fixed in a predetermined position with pressure acting on the strip material while the rollers  104 ,  106  of the levelling station  100  are pivoted up or down for the fine adjustment of the levelling. Hence, by pivoting the levelling station  100 , the angle with which the strip material is introduced in the nip between the rollers  108 ,  110  in the forming section, will vary. Suitably, the coarse adjustment of the pressure and/or levelling towards the strip material is positioned with rollers  108 ,  110  from the start, while the fine adjustment for the levelling of the strip material is done with rollers  104 ,  106  of the levelling station. 
     FIGS. 5 a  to  5   d  illustrate the forming section in greater detail. 
     As illustrated in FIGS. 5 a  and  5   b,  lower roller  110  is rotatable on arm portion  124  about a pivot  124   a  on the levelling plate. In this way, as illustrated in FIGS. 5 a  and  5   b,  lower roller  110  may be pivoted towards and away from upper roller  108 . 
     Referring to FIGS. 5 c  and  5   d  (in which the roller  110  is illustrated partially cut away), it will be seen that the arm portion  124  has a sleeve part  126  through which the shaft  118  extends. A spring  128  is positioned around the shaft  118  and is sandwiched between the sleeve part  126  and the lower end  130  of the shaft  118 . Thus, by moving the shaft  118  upwardly as illustrated in FIGS. 5 c  and  5   d,  the spring  128  is compressed so as to create additional pressure on sleeve part  126 , thereby urging roller  110  to pivot about pivot  124   a  and create additional pressure between the rollers  108  and  110 . 
     Thus, by varying the position of the shaft  118 , the pressure between the rollers  108  and  110  can be varied according to the strip material being used. 
     As illustrated, the shaft  118  has a threaded portion  118   a  at at least one end. In particular, the threaded portion  118   a  engages with a threaded pulley wheel  119  such that rotation of the pulley wheel  119  causes shaft  118  to move up or down as illustrated in FIGS. 5 c  and  5   d.  Furthermore, a transmission belt  120  is provided to drive the pulley  119 . Thus, by operating the transmission belt  120 , the apparatus is able automatically to adjust the pressure provided between the upper and lower rollers  108  and  110  for forming the strip material appropriately. 
     As illustrated in FIG. 6, in a subsequent stage, after the forming section, an accumulator station  140  (similar to the accumulator station  38  of FIG. 1) is suitably provided for in the arrangement for automatic bow adjustment according to the present invention. An accumulator chamber  142  (similar to the accumulator chamber  52  of FIG.  1 ), being upwardly extended, is provided at the accumulator station  140  so that a length of strip material  112  can be accumulated in a loop  144 . This storage is required to enable subsequent processing steps of the strip material  112  to be intermittent. Optical means  146  is preferably arranged at the wall  148  of the accumulator chamber  142 . The optical means is connected to a computerised control system via power and control cable  147 . The optical means  146  can be a laser, ultraviolet or infrared operating means, or photoelectric sensors. The optical means is preferably a laser. In addition, there may also be supporting means  150 ,  152  for guiding and fixing the strip material  112  in the accumulator chamber  142 . Consequently, the supporting means  150 ,  152  can also be in connection with the computerised control system via power and control cables  151 ,  153 . As explained above with reference to FIGS. 2 a  to  3   d,  levelling is provided through means for offsetting at the levelling station  100  in order to straighten the bow of the strip material within a predetermined deviation on a predetermined length of strip material. However, by the use of the optical means  146  at the accumulator station, deviations are continuously measured, during the movement of the strip material, through optical means  146 . The optical means  146  provides a deviation signal, which is registered and treated in a computer. The levelling by said means for offsetting  100  is adjusted through the deviation signal, if said measured deviation exceeds a predetermined deviation, in order to keep the deviation within said predetermined deviation. The optical means should preferably be able to measure deviations of, for example, ±0.2 mm along a certain length of the strip material, i.e. within a range between 400 mm and 1200 mm. 
     During said measuring of the strip material  112 , it is essential that the strip material is substantially straight and properly aligned. Preferably, the strip material  112  is in a fixed position during the measurement of the optical means  146 . For the purpose of holding the strip material  112  in position for said measuring, supporting means  150 ,  152  can be attached to the accumulator chamber  142 . The supporting means  150 ,  152  are preferably attached to said accumulator chamber of said accumulator station, each on one of an upstream and downstream side of said means for optical measurement  146 . It is suitable to hold the strip material and to make the measurements with the optical means  146  simultaneously when a slat is lifted in the lacing station  78 , when a new blind is set-up or during a cut  70  and/or punch  66 ,  68  operation on the strip material  43 ,  112  since the forward movement of the strip material  112  then is shortly interrupted anyway. 
     As illustrated by FIG. 7, a schematic principal block diagram  400  for an embodiment of the automatic bow adjustment according to the present invention is depicted. An operator panel  410  and a bar code reader  415  provides a Man Machine Interface (MMI) for the Venetian blind machine, i.e., means for parameter setting of the machine such as with parameters for the specific strip material  43 ,  112  in use through means for offsetting  34 ,  100 ,  102  in order to straighten the bow of the strip material  43 ,  112  within a predetermined deviation on a predetermined length of strip material. 
     A PC control system  420  for the parameter setting is governed by a kernel  430  connected to digital  440  and analogue  450  I/O interfaces, respectively, for control of means  100 ,  102  regarding i.a. bow adjustment via signals emanating from the means for optical measurement  146 . 
     Switches  442  and  444  are connected to the digital interface  440  for On/Off control of the setting of motor means M 1  and M 2 , respectively, in a slat profiling unit  460 . Motors M 1  and M 2  are preferably of the type stepper, servo or the like motors. 
     The motor M 1  provides a coarse adjustment transmitted via the power transmission belt  120 , which is also connected to an axis (not shown) of the motor M 1 , in a manner known by those skilled in the art. M 1  is connected to an input of the I/O interface  450  through a weight indicator  470  providing a position signal, for example inputted as pressure in kilogram, for the coarse adjustment of rollers  110 ,  108 . 
     The motor M 2  is connected to an axis  114  via its axis (not shown), in a manner known by those skilled in the art, via the power transmission belt  116 . M 2  provides the fine adjustment for levelling in accordance with the present invention through the axis  114  connected to the levelling station  100  in a known manner for those skilled in the art. Means  146  for optical measurement of deviation in bending of the strip material transmits its signals picked up to the PC control system  420  which outputs control signals to the motor M 2  in accordance with the measured deviation, thus compensating the bow to be within a predetermined deviation, for example, ±0.2 mm. The device  480 , indicated as a field regulator in FIG. 7, inputs a value for deviations to the control system  420 , used to make necessary calculations and determinations for regulation via M 2  etc. 
     It is easily understood that deviations within two tenths of a mm are hard, if not impossible, to cope with using methods and arrangements presently known to a person skilled in the art to which the present invention pertains, mainly ocular inspection. But with the optical means for measurement and the method according to the present invention, such deviations are possible to op-hold, with for example a laser measurement device in co-ordination with other measures claimed in the attached set of claims. 
     The strip accumulator unit  490  comprises a rectifier  495  for input of a trigger signal to the control system  420  for trigging the measurement period of an optical means during for example cutting of the strip material. 
     Further, by providing the optical means after the levelling station  100  and the forming section  102  at the accumulator station  38 ,  140  said deviation signal is used as a feedback signal, thus inhibiting time periods for control measurement of said bow and unnecessary loss of strip material compared with possible feed-forward measurements by placing the optical means before station  100  and/or section  102 . 
     It is possible to arrange the optical means, e.g. the preferred laser measurements, before the means for offsetting (and in addition, possibly have means for controlling the deviation after the forming section without using a feed-back signal). If the laser measurements are made before the means for offsetting (i.e. even before the levelling station, there will be no feedback signal, but rather feed-forward measurements). However, the most preferred arrangement is still after the forming section as stated in claims  2  and  6 . 
     It is thus believed that the operation and construction of the present invention will be apparent from the foregoing description. The term comprising when used in this description or the appended claims should not be construed in an exclusive or exhaustive sense but rather in an inclusive sense. Features which are not specifically described or claimed may be additionally included in the structure according to the present invention without deviating from its scope. While the method and arrangement illustrated or described has been characterized as being preferred it will be obvious that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined in the attached claims. It is particularly within the scope of the present invention that any adjusted settings of the bow adjusting means may be electronically saved for future retrieval and re-use.