Abstract:
A food loaf is advanced toward a cutting device by a feed apparatus and the loaf is cut into slices, strips or cubes by the cutting device such that the loaf is fixed during the feed movement by a vacuum gripper that is advanced together with the loaf and a negative pressure is generated within an interior of a contact element of the vacuum gripper and acts upon a fixing region of the surface of the loaf in a suction region of the contact element. In order to avoid a vacuum loss, it is proposed that the suction region is divided into at least two separate partial suction regions and the interior of the contact element is accordingly divided into at least two partial interiors, wherein the partial suction regions respectively adjoin one another, are separated from by a contact line and form separate partial fixing regions.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the priority of German Patent Application Serial No. DE 10 2008 011 980.6, filed Feb. 29, 2008 pursuant to 35 U.S.C. 119(a)-(d), the subject matter of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The invention refers to a method for cutting a food, in particular, a loaf-shaped food, in which a loaf of the food is advanced toward a cutting device by means of a feed apparatus and cut into slices, strips or cubes by said cutting device. 
     The invention also refers to a cutting machine for cutting a loaf-shaped food that makes it possible to cut a loaf of the food into slices, strips or cubes and features a feed apparatus for advancing the loaf toward the cutting device during the cutting process, 
     A method and a cutting machine of the above-described type are generally known. As compared to the utilization of gripping hooks, fixing of the loaf by means of a vacuum gripper provides the advantage that the loaf itself remains undamaged because its surface is not permanently changed by the contact element of the vacuum gripper. In the known methods and cutting machines, the negative pressure is generated with the aid of so-called vacuum pumps. The negative pressure is transmitted from the vacuum pump to the interior of the contact element through a line. The contact element itself typically consists of a rubber collar of sorts that is intended to compensate for uneven areas and irregularities on the surface of the loaf due to its elastic properties in order to prevent the admission of air into the suction region of the rubber collar after the negative pressure is applied. During the cutting mode of the known machines, the vacuum pumps used typically operate continuously such that they do not have to be switched on and off between the cutting of two successive loafs, wherein the continuously operating vacuum pumps also compensate possible leaks in the region of the contact element that would allow ambient air to flow into the interior of the contact element and permanently maintain a sufficiently high negative pressure. 
     In order to solve the above-described problem, it is known to fit the contact element of the vacuum gripper with a blade that cuts into the loaf such that a seal is produced in the suction region. For example, DE 100 24 913 A1 discloses a cutting machine of the type described above, wherein the feed apparatus which comprises at least one “suction cup” that defines a negative pressure chamber, such that this negative pressure chamber is open toward the loaf. The suction cup features a blade-shaped edge that is intended to ensure a very tight connection between the suction cup and the product loaf. 
     U.S. Pat. No. 3,880,295 A also describes a cutting machine featuring a suction head with six suction regions that are arranged linearly adjacent to one another and equipped with blades that dig into the face to be fixed of a product being cut. In this case, each individual suction region is formed by an annular space between an inner blade and an outer blade extending concentric thereto. No suction region is arranged within the inner blade. The circular ring-shaped suction area of U.S. Pat. No. 3,880,295 A is thus sealed in each case towards the outside as well as towards the inside by means of a cutting edge. 
     Depending on the consistency of the surface of the loaf and the condition of the rubber collar of the contact element, however, leakage problems still occur in known vacuum grippers such that the vacuum is lost or the negative pressure is not sufficiently high for reliably fixing the loaf on the vacuum gripper. This leads to undesirable transverse displacements of the loaf during the advancing and cutting process that, in turn, result in an insufficiently accurate geometry of the produced slices, strips or cubes. 
     It would therefore be desirable and advantageous to provide an improved method for cutting a loaf-shaped food, as well as a corresponding cutting machine, in which the risk of losing or excessively reducing the vacuum in the contact element of the vacuum gripper is lowered. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a cutting method includes that the suction region is divided into at least two separate partial suction regions and the interior of the contact element is accordingly divided into at least two partial interiors, wherein the partial suction regions respectively adjoin one another and are separated from one another by a contact line and form separate partial fixing regions on the surface of the loaf. 
     The present invention resolves prior art problems by increasing the safety during the fixing process, such that at least two separate partial suction regions are created, because the vacuum in the at least one other partial suction region is still available if the vacuum in a partial suction region is lost such that at least a residual fixing force for the loaf is still available. The vacuum typically fails due to a rather singular irregularity in the surface consistency of the loaf such that the pressure in the other partial suction region remains intact if a partial suction region develops a leak. 
     The method for cutting a loaf-shaped food includes advancing the loaf of the food toward a cutting device by means of a feed apparatus for cutting into slices, strips or cubes by said cutting device, wherein during the feed movement the loaf is fixed by means of a vacuum gripper advanced together with the loaf, and wherein a negative pressure is generated within an interior of a contact element of the vacuum gripper which acts upon at least one fixing region of the surface of the loaf in at least one suction region of the contact element; and dividing the suction region into at least two separate partial suction regions and dividing the interior of the contact element accordingly into at least two partial interiors wherein the partial suction regions respectively adjoin one another, are separated from one another by a contact line and form separate partial fixing regions. 
     The strict structural separation of the individual partial interiors from one another is important for the proper function of the inventive method because two connected partial interiors would communicate with one another such that a vacuum loss in one partial interior would also lead to a corresponding vacuum loss in the other partial interior(s)—at least after brief equalization processes have taken place. For example, it is necessary to utilize two vacuum pumps, i.e., one respective vacuum pump for a partial interior or a partial suction region, if the negative pressure should be generated in this fashion. If the negative pressure is generated by means of a piston-cylinder unit, it is necessary to utilize two such piston-cylinder units or a double piston or step piston in order to separate the partial interiors from one another structurally and with respect to the pressure. 
     It is preferred that all partial fixing regions of the surface of the food that are formed by the partial suction regions are acted upon with a negative pressure of the same intensity in order to prevent irregular deformations of the loaf that propagate over its entire length up to the opposite cutting length and can lead to irregular cutting geometries at this location. 
     The partial suction regions can be shielded relative to one another particularly well if a partial fixing region formed by an inner partial suction region is acted upon with a negative pressure of a first intensity and a partial fixing region formed by an adjacent outer partial suction region that encloses the inner partial suction region is acted upon with a negative pressure of a second intensity, wherein the first negative pressure is higher than the second negative pressure. Due to these measures, high negative pressures and therefore high retaining forces can be generated in the inner partial suction region via the respective boundaries between the partial suction regions at small pressure differentials. 
     Based on a cutting machine of the initially described type, the objective of the invention is attained, according to the invention, in that the suction region is divided into at least two separate partial suction regions and the interior of the contact element is accordingly divided into at least two separate partial interiors, wherein the partial suction regions respectively adjoin one another, are separated from one another by a contact line and form separate partial fixing regions on the surface of the loaf. 
     In one preferred embodiment of the inventive cutting machine, one partial suction region is completely enclosed by another partial suction region such that the separating contact line that is in tight contact with the surface of the loaf forms a closed curve. In this case, the first partial suction region may be realized circularly and at least one other partial suction region may annularly enclose the first partial suction region. It would also be possible to realize a staggered and concentric arrangement of several outer annular partial suction regions. Alternatively, it would also be conceivable to divide an annular partial suction region into several partial suction regions by means of one or more radially extending webs. 
     An advantageous additional development of the inventive cutting machine consists of an attachment that is fixed on the vacuum gripper, wherein the contact element and the at least two partial suction regions are realized on the front side of said attachment that points in the feed direction, and wherein the attachment can be separated from the vacuum gripper and all partial suction regions extend from the attachment into the vacuum gripper in a sealed and mutually separated fashion in the mounted state of the attachment. Due to these measures, the geometry of the at least two partial suction regions can be adapted to the geometry of the loaf to be currently fixed. 
     The invention is described in greater detail below with reference to one embodiment of a vacuum gripper of a cutting machine that is illustrated in the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which: 
         FIG. 1  is an elevational side view of a vacuum gripper according to the present invention; 
         FIG. 2  shows a perspective representation of a vacuum gripper in the form of an oblique front view; 
         FIG. 3  shows a perspective representation of the vacuum gripper according to  FIG. 2  in the form of an oblique rear view; 
         FIG. 4  shows a rear elevational view of the vacuum gripper according to  FIGS. 1 to 3 ; 
         FIG. 5   a  shows a longitudinal section through the vacuum gripper in a starting position along the line V-V in  FIG. 4 ; 
         FIG. 5   b  shows a representation analogous to  FIG. 5   a  in a negative pressure position; 
         FIG. 6  shows a perspective representation of a gripping device that comprises a base frame and three vacuum grippers according to  FIGS. 1 to 5  supported therein; 
         FIG. 7  shows a side view of the gripping device according to  FIG. 6 , and 
         FIG. 8  shows a top view of the gripping device according to  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. 
     Turning now to the drawing, and in particular to  FIG. 1  to  FIG. 5   b , there is shown a vacuum gripper  1  consisting of two coaxially arranged piston-cylinder units  2  and  3  that are coupled to one another by means of a common piston rod  4  and separated from one another by a partition wall  5 , in which the piston rod  4  is supported in a sliding and sealed fashion. 
     The vacuum gripper  1  has a front side  6 , to which a product string  7  illustrated in a dashed manner in  FIG. 3 , for example in the form of a pork sausage, is fixed by means of a vacuum in a manner, which will be described in more detail hereinbelow. On the opposite end, the vacuum gripper  1  has a rear side  8 , on which it can be fixed on a base frame  45  of a gripping device that is illustrated in  FIGS. 6 to 8  and described in greater detail below with the aid of a slot-shaped recess  9 . The mounting is furthermore achieved with two groove-shaped recesses  10  in an outside surface  11  of the vacuum gripper  1 . 
     Adjacent to the partition wall  5 , the vacuum gripper  1  features a front section  12  that is formed by the piston-cylinder unit  2  and serves for generating the negative pressure for fixing the loaf  7 . The oppositely arranged rear section  14  is essentially formed by another piston-cylinder unit  3  that serves for driving a piston  28  of the piston-cylinder unit  2  situated in the front section  12 . 
     According to  FIG. 5   a , the piston-cylinder unit  3  serving as the drive for generating the negative pressure, consists of a cylinder liner  16  and a piston  18  that is supported in the interior  17  thereof in a displaceable and sealed fashion and divides the interior  17  into a first work chamber  19  that faces the partition wall  5  and a second work chamber  20  that is situated on the other side of the piston  18 . The work chamber  19  can be acted upon with compressed air through a channel  21  that consists of several sections and is initially situated in a connection piece  22  inserted into the partition wall  5  and then in the partition wall  5  itself. In the partition wall  5 , as well as in the connection piece  22 , the channel features two sections that extend orthogonal to one another such that the complete channel  21  has the shape of a L. The second work chamber  20  extending in an attachment  24  of the rear section  14  via a channel  23 . It also extends in a rear connection piece  25 . 
     The piston-cylinder unit  2  that serves for generating the negative pressure for fixing the loaf  7  is situated on the opposite side of the partition wall  5  coaxial to the piston-cylinder unit  3 —referred to a common axis  26 . The piston-cylinder unit  2  also consists essentially of a cylinder liner  27 , in which a piston  28  is supported in a sliding and sealed fashion. The piston  28  of the piston-cylinder unit  2  and the piston  18  of the piston-cylinder unit  3  have the same diameter and the same stroke due to the coupling by means of the piston rod  4 . 
     Another piston rod  30  that leads to a piston  31  connected thereto is situated on the side of the piston  28  that lies opposite of the piston rod  4 . The piston  31  is situated in a section of the cylinder liner  27  in which this liner has a reduced diameter relative to the piston  28  and a work chamber  32  corresponding thereto. The unit consisting of the pistons  28  and  31  (as well as the piston rod  30 ) therefore represents a step piston that is supported in a correspondingly stepped bore of the cylinder liner  27  in an axially displaceable fashion. 
     The front side  6  of the vacuum gripper  1  is provided with a closed circular outer blade  33 , the wall thickness of which is significantly reduced in comparison with the remaining wall thickness of the cylinder liner  27 , wherein the transition from the blade  33  to the remaining wall of the cylinder liner  27  is realized in the form of a radial step  34 . The front side  6  of the vacuum gripper  1  is furthermore provided with an inner blade  35  that is also realized circularly and extends concentric to the outer blade  33 . In comparison with the front edge of the outer blade  33 , the front edge of the inner blade  35  is slightly set back. The inside diameter in the region of the inner blade  35  corresponds to the diameter of the front piston  31  of smaller diameter. The two blades  33  and  35  forms a contact element  29  of the vacuum gripper  1  together with the cylinder liner  27 . 
     The circular cross section formed by the inner blade  35  defines an inner partial suction region  36 . The annular region that lays between the inner suction region  36  and the outer blade  33  defines an outer partial suction region  37 . Both partial suction regions  36 ,  37  jointly form the entire effective suction region of the vacuum gripper  1 . The outer partial suction region  37  is connected to a right work chamber  39  defined by the piston  28  by means of two bores  38  that are offset relative to one another by 180°. The right work chamber  39  and the bores  38  define steps  60  in the cylinder liner  27 . 
     From the starting position illustrated in  FIG. 5   a , in which both blades  33  and  35  are spaced apart from the end of the loaf  7 , the vacuum gripper  1  is moved toward the loaf  7 , the opposite front end of which is supported on a conventional cutting device, e.g., in the form of a rotatably driven cut-off knife  70 . The approach of the vacuum gripper  1  takes place with a sufficiently high force and to such an extent that the both blades  33  and  35  penetrate into the loaf  7 —as shown in  FIG. 5   b . Due to the rounded shape of the end of the loaf  7 , the inner blade  35  penetrates deeper than the outer blade  33 . The penetrating movement then becomes increasingly difficult and also stops once the loaf  7  is supported in the region of the radial step  34  of the vacuum gripper  1  with its face, wherein this is, however, not yet the case in  FIG. 5   b.    
     After the two blades  33  and  35  have penetrated into the material of the loaf  7  and thus sealed the two suction regions  36  and  37 , the right work chamber  20  of the piston-cylinder unit  3  is acted upon with compressed air such that the two pistons  28  and  31  are displaced toward the left into the position illustrated in  FIG. 5   b . The work chamber  39  that is situated to the right of the piston  28  and a first partial interior  41 ′, as well as a second partial interior  41  that corresponds to the inner partial suction region  36  and is situated in the section of the cylinder liner  27  of reduced diameter, are significantly increased in this fashion such that a negative pressure is generated in the two partial suction regions  36 ,  37  and reliably fixes the loaf  7  on the vacuum gripper  1 . The partial interiors  41 ,  41 ′ are separated from one another by a contact line K formed by the inner blade  35 . 
     Due to the very effective seal between the partial suction regions  36  and  37  produced by the blades  33  and  35 , a single retraction of the pistons  28  and  31 , provides for a single negative pressure generation that suffices for permanently ensuring a sufficiently high retaining force. Since the inner partial suction region  36  is completely enclosed by the outer partial suction region  37  and the pressure differential between the two regions therefore is small or ideally zero, the inner partial suction region  36 , in particular, is hardly at risk of a vacuum loss. Even if air is admitted into the outer partial suction region  37  past the outer blade  33 , a sufficiently high negative pressure is still maintained in the inner partial suction region  36  as long as the inner blade  35  produces an adequate seal. 
     The inner partial suction region  36  acts upon an inner partial fixing region  42  on the surface of the loaf  7  and the outer partial suction region  37  accordingly acts upon an outer partial fixing region  43  on the surface of the loaf  7 . The surfaces of both partial fixing areas  42 ,  43  add up to the total effective fixing region. 
     The negative pressures adjusting in the partial suction regions  36  and  37  after a stroke of the driving piston  18  can be influenced with the selection of the diameter of the pistons  28  and  31 , the diameter of the piston rod  4  and the diameter and number of bores  38 . In this case, it is sensible to choose the negative pressure being generated in the inner partial suction region  36  higher than that in the outer partial suction region  37  because the inner partial suction region  36  is arranged such that it is “protected” by the outer partial suction region  37 . 
     After the loaf  7  has been fixed by activating the vacuum gripper, the loaf  7  can be fed to the cutting device together with the vacuum gripper  1  while slices are successively cut off the front end of the loaf  7 . The feed movement is interrupted shortly before the outer blade  33  reaches the effective range of the cut-off knife of the cutting device. A reliable ejection of the remainder of the loaf  7  that still adheres to the vacuum gripper  1  is achieved in that the pistons  28  and  31  are not only retracted into the starting position illustrated in  FIG. 5   a  by subjecting the work chamber  20  to pressure via the connection piece  25 , but further toward the right by an additional stroke  44  (see  FIG. 5   a ) until the piston  28  contacts a step  60  in the cylinder liner  27  resulting from the abrupt change in diameter. This not only causes the pressure in the two partial suction regions  36  and  37  to return to the initial level, i.e., to zero, but also a certain excess pressure to be generated in the two partial suction regions  36  and  37  that actively transports the remainder of the loaf  7  outward, wherein the friction occurring in the region of the blades  33  and  35  needs to be overcome. Subsequently, the pistons  18 ,  28  and  31  are returned into the starting position illustrated in  FIG. 5   a  without the front side  6  of the vacuum gripper contacting a loaf  7  to be cut next in a sealing fashion, i.e., the suction regions  36  and  37  are still under atmospheric pressure. Subsequently, the next gripping and cutting cycle can begin by contacting a new loaf  7 . 
     According to  FIG. 6 , three vacuum grippers  1  of the type described with reference to  FIGS. 1 to 5   b  are arranged adjacent to one another in a parallel fashion in a base frame  45  of a gripping device  46 . The crossbars  47  to  49  that form the base frame  45  together with lateral sections  50  and  51  fix the vacuum grippers  1  in the base frame  45  by means of the recesses  9  and  10  illustrated in  FIGS. 1 to 3 . 
     The connection pieces  25  and  22  of the respective rear piston-cylinder unit  3  that serve for actuating the front piston-cylinder units  2  for generating the negative pressure are respectively connected in parallel by means of compressed air pipes  52  and  53  such that the negative pressure for the fixing process is always simultaneously generated or neutralized for three adjacently arranged loaves  7  and the residual remains are ejected. 
     The base frame  45  of the gripping device  46  is known and an identical embodiment thereof serves for accommodating classic, purely mechanical grippers, in which a gripping hook penetrates into the rear end of the loaf  7  with its gripping tines due to a pneumatic actuation, wherein the gripping tines are retracted from the remainder after the cutting process is completed, namely also by means of a pneumatic actuation. Consequently, the existing base frame  45  and the compressed air connections arranged thereon can be used for the vacuum grippers  1 , as well as for mechanical grippers with gripping tines that are not illustrated in the figures. 
     While the invention has been illustrated and described as embodied in a loaf cutting method and apparatus, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.