Pick-up apparatus for retrieving and depositing a load

Apparatus for retrieving and depositing a load, in particular to and from racks, includes a pair of elongated guides in parallel relationship and a grabbing device having at least two grippers movably guided in the elongated guides for traveling in a horizontal plane in an operating direction from a ready position into an operative position in which the grippers are positioned on both sides of the load substantially parallel to the sides of the load. Each of the grippers has at least one plate-shaped gripping area, with the gripping area of one gripper confronting the gripping area of the other gripper, and with the gripping areas of the grippers extending parallel to one another. Operatively connected to the elongated guides is a force-applying unit for moving the guides in synchronism relative to one another to thereby urge the grippers against the sides of the load.

BACKGROUND OF THE INVENTION
 The present invention relates, in general, to an apparatus for retrieving
 and depositing a load, e.g. from a rack or onto a rack, and more
 particularly to a load pick-up apparatus of a type having a grabbing
 device with grippers moveably guided in parallel elongated guides for
 travel in a horizontal plane into an operative position in which the
 grippers are positioned on both sides next to confronting side walls of
 the load, and urged into engagement with the confronting side walls.
 German Pat. No. DE 196 13 707 describes an apparatus which includes
 lance-like grippers for retrieving and depositing load units, whereby the
 grippers can be moved in a horizontal plane for disposition on both sides
 next to the side walls of the load unit. The grippers are guided in
 elongated guides and pivoted in synchronism in opposite direction into a
 clamped engagement with the side walls of the load unit. After effecting
 the clamped engagement with the load unit, the load can be retrieved by
 retracting the grippers to thereby remove the load unit form the storage
 area. A depositing of the load unit for storage is effected in analogous
 fashion.
 A drawback of this conventional grabbing device is the relative small
 contact area of the grippers so that the grippers may cause damage to the
 load, in particular when cardboard boxes are involved. Moreover, the
 effective contact pressure applied by the grippers must be sufficiently
 great to ensure a safe removal and storage even when the load unit is
 charged.
 SUMMARY OF THE INVENTION
 It is thus an object of the present invention to provide an improved
 apparatus for picking up and depositing a load, obviating the afore-stated
 drawbacks.
 In particular, it is an object of the present invention to provide an
 improved load pick-up and depositing apparatus which operates at
 relatively small contact pressure while still assuring a secure retrieval
 and placement of the load, without damage to the container.
 These objects, and others which will become apparent hereinafter, are
 attained in accordance with the present invention by providing a pair of
 elongated guides in parallel disposition, and a grabbing device with at
 least two grippers which are movably guided in the guides for travel in an
 operating direction from a ready position to an operative position in
 which the grippers are disposed on both sides of the load substantially
 parallel to the sides of the load, with each gripper having at least one
 plate-shaped gripping area, with the gripping areas of both grippers
 opposing one another in parallel relationship and in substantial parallel
 relationship with respect to the side walls of the load unit, and whereby
 the elongated guides are movable in synchronism toward one another to
 thereby force the grippers into engagement against the sides of the load
 unit.
 The grabbing device according to the present invention has grippers which
 are forced in parallel alignment against the load and thus can be designed
 with a sufficiently large gripping area that enables to keep the contact
 pressure relatively small while still assuring good gripping behavior of
 the grippers. Moreover, as the synchronized movement of the grippers is
 realized via the elongated guides the load unit can be securely grabbed,
 even when the load unit is misaligned to a certain extent.
 Suitably, the gripping area of the grippers may have a roughened surface to
 realize a better force fit. The gripping action can be further enhanced,
 in particular when soft containers are involved, by providing the gripping
 area of the grippers with serrated vertical indentations.
 According to another feature of the present invention, each gripper has two
 plate-shaped vertical bearing surfaces which extend perpendicular to the
 gripping area in the direction of the opposite gripper and face away from
 one another. Thus, the load unit rests against the confronting one of the
 bearing surfaces, to thereby ensure, in particular during placement for
 storage, a secure shifting of the load unit into a proper position.
 According to still another feature of the present invention, each gripper
 has at least one further gripping area, with the bearing surfaces of each
 gripper defining in the operating direction a leading bearing surface,
 whereby one of the gripping areas is positioned in the operating direction
 ahead of the leading bearing surface. In this manner, two racks in
 confronting parallel disposition can be loaded and unloaded, without
 requiring any complex maneuvers, as it is only necessary to reverse the
 operating direction, i.e. the leading bearing surface in one operating
 direction becomes the trailing bearing surface in the other operating
 direction, and vice versa. This configuration ensures that in either
 operating direction, a bearing surface engages the load unit being
 maneuvered.
 It is also possible to provide two gripping areas ahead of and behind the
 bearing surfaces to better conform the pick-up apparatus to different
 packagings, such as plastic containers or cardboard boxes. Suitably, the
 two gripping areas are arranged in succession when viewed in the operating
 direction to thereby ensure a trouble-free operation during loading for
 storage and retrieval. In order to realize a safe grabbing of plastic
 containers as well as cardboard boxes, one of the two gripping areas has
 serrated vertical indentations and the other gripping area has a roughened
 surface. Suitably, the serrated gripping area has a thickness which is
 smaller than the thickness of the roughened gripping area. In this manner,
 different strength properties of the load units are taken into account.
 According to another feature of the present invention, the gripping area of
 each gripper may have arranged thereon at least one arbor-like projection
 which extends perpendicular to the gripping area toward the opposing
 gripper, to thereby realize a secure grabbing even when cardboard boxes
 are handled. Suitably, the arbor has a length which is greater than the
 thickness of the roughened and serrated gripping areas.
 According to yet another feature of the present invention, a synchronized
 motion of the elongated guides can be realized via an interconnecting
 spindle which is driven by a motor and has opposite ends which are
 rotatably supported in the elongated guides. Suitably, the drive for the
 spindle is operatively connected to one spindle end, while the other
 spindle end is received in a spindle nut which is securely fixed in the
 associated elongated guide. The drive may be a servomotor for cost-saving
 purposes. The contact pressure of the grippers upon the load unit may be
 restricted to a maximum value by automatically stopping operation of the
 servomotor when a predetermined motor current value is exceeded.
 A synchronized movement of the elongated guides can be realized in a simple
 manner by providing a double lever which is rotatably supported in a frame
 at a central location with respect to the elongated guides and hingedly
 connects the elongated guides to one another.

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, there is shown a
 top and side perspective view of an apparatus for retrieving and
 depositing a load, including a grabbing device, generally designated by
 reference numeral 4. In FIG. 1, the grabbing device 4 occupies a ready
 position before withdrawal of a load unit, such as container 1, from a
 rack 2. The grabbing device 4 includes two elongated guides 5 which are of
 substantial C-shaped configuration to define a longitudinal groove 5a. The
 elongated guides 5 are mounted on a frame 20 (FIG. 4) in parallel
 relationship in a horizontal plane. Each of the elongated guides 5
 accommodates in the anchoring groove 5a a gripper 6 which, for sake of
 simplicity, is shown by way of a simplified configuration to describe the
 principal mode of operation of the load retrieving and depositing
 apparatus. Both grippers 6 are guided in the elongated guides 5 for travel
 in synchronism by means of a belt drive, generally designated by reference
 numeral 3, which includes a driveshaft (not shown) extending transversely
 to the guides 5 and has a variable length in a manner known per se. The
 grippers 6 of both guides 5 oppose one another and occupy the ready
 position in FIG. 1.
 Turning now to FIG. 2, there is shown a side plan view of a novel and
 inventive gripper 6 according to the present invention for use in the
 apparatus of FIG. 1. The gripper 6 has a base plate 11 which has arranged
 thereon a total of four plate-shaped gripper areas 7, 8, 9, 10 disposed in
 a row behind one another and secured by suitable bolts 24 to the base pate
 11. Secured by bolts 25 perpendicular to the base plate 11 is a vertical
 bearing plate 12 which separates two gripping areas 7, 8 to the left
 thereof from two gripping surfaces 9, 10 to the right thereof in the
 illustration of FIG. 2. The bearing plate 12 defines two vertical bearing
 surfaces 13 which face away from one another and extend perpendicular to
 the gripping areas 7, 8, 9, 10.
 As shown in particular in FIG. 3, the gripping areas 8 and 9 which are
 positioned adjacent the bearing surfaces 13 on either side of the bearing
 plate 12 are formed with serrated vertical indentations while the gripping
 areas 7 and 10 that are further distant to the bearing plate 12 have a
 roughened surface.
 Each saw tooth of the serrated gripping areas 8, 9 has a vertical flank 14,
 which extends perpendicular to the base plate 11, and a vertical flank 15
 which extends slantingly to the base plate 11, thereby forming the
 particular configuration of each saw tooth. FIG. 3 further illustrates the
 provision of an arbor 16 on both sides of the bearing plate 12, with the
 arbors 16 of one gripper 6 extending in the direction toward the other
 opposite gripper 6.
 The gripping areas 7, 10 and the gripping areas 8, 9 have different
 thickness. More specifically, the thickness of the gripping areas 7, 10 is
 greater by about 1 millimeter than the thickness of the gripping areas 8,
 9. In the description, the term "thickness" in conjunction with the
 gripping areas 8, 9 denotes the radial distance or depth of the saw teeth
 between the tip and bottom. As shown in FIG. 3, the arbors 16 have a
 length which is greater than the thickness of the gripping areas 7, 10 by
 approximately one millimeter. Thus, the tips of the serrated gripping
 areas 8, 9 project the least into the space between the two confronting
 grippers 6. The gripping areas 7, 10 and 8, 9 of each gripper 6 extend
 also in a common vertical plane.
 By configuring the gripping areas 7, 8, 9, 10 of different thickness and by
 selecting the length of the arbors 16 accordingly, the grabbing device 4
 can be best suited to different load units, in particular when different
 materials are used for the containers 1. Thus, the serrated gripping areas
 8, 9 are effective, for example, only for cardboard boxes or the like,
 while the arbors 16, on the other hand, always contribute to the gripping
 action.
 Turning now to FIG. 4, there is shown a top plan view of the grabbing
 device 4 of FIG. 1, with the grippers 6 exhibiting again the simplified
 configuration for ease of illustration and including only one exemplified
 gripping area neighboring the bearing surfaces 13. Both elongated guides 5
 are slidably mounted on crossbars 17 which extend transversely to the
 guides 5, and interconnected by a spindle 18. One end of the spindle 18 is
 driven by a servomotor 19 and freely rotatably supported on this side to
 the associated guide 5. The other opposite end of the spindle 18 is
 rotatably mounted to a spindle nut 18a which is in fixed rotative
 engagement with the opposite guide 5. Thus, during operation of the
 servomotor 19, the guides 5 travel toward one another. In order to realize
 a synchronized displacement of the guides 5, a double lever 21 is
 pivotally mounted to the frame in the middle between the guides 5 for
 rotation about a pivot axis 26. Articulated to one end of the double lever
 21 is one end of a tie rod 22 and articulated to the other end of the
 double lever 21 is one end of a tie rod 23. The other ends of the tie rods
 22, 23 are articulated to the guides 5, respectively. The connection
 system comprised of tie rod 22--double lever 21--tie rod 23 realizes in
 conjunction with the central frame-mounted pivot point of the double lever
 21 a synchronized movement of the guides 5 toward the center and away from
 the center.
 It will be appreciated by persons skilled in the art that the spindle 18
 may certainly also be so configured as to have on one side a right-hand
 thread and on the other side a left-hand thread. In this case, the need
 for providing the double lever can be eliminated. Also, it is certainly
 within the scope of the present invention to replace the single spindle
 with two spindles having separate motors. Moreover, the provision of a
 spindle for effecting a transverse movement of the guides 5 can be
 replaced altogether by a suitable belt or chain drive. The transverse
 drive for the guides 5 may certainly also be realized in a pneumatic
 fashion.
 In FIG. 1, the grabbing device 4 is in the ready position. When desiring to
 remove a container 1 from the rack 2, the elongated guides 5 are moved by
 the servomotor 19 toward one another until the guides 5 are positioned at
 about the width of the container 1 at slight overmeasure of a few
 centimeters. Subsequently, the grippers 6 are moved in synchronism in
 direction of the container 1 into the operative end position, as shown in
 FIG. 5. In this position, the container 1 rests against the leading
 bearing surfaces 13 of the grippers 6 of the grabbing device 4, with the
 grippers 6 being so shifted as to project beyond the end face of the
 grabbing device 4 and partially into the rack 2. When the grippers 6 reach
 their end position, the elongated guides 5 are moved in synchronism toward
 one another so that the front gripping areas, i.e. gripping areas 9, 10,
 of the grippers 6 are moved toward and ultimately bear upon the
 confronting sides of the container 1. A destruction or damage of the
 container 1 is precluded when so configuring the servomotor 19 as to
 automatically stop operation when exceeding a certain motor current value
 which corresponds to a certain contact pressure. The thus grabbed
 container 1 is then pulled from the rack 2 by retracting the grippers 6,
 as shown in FIG. 6.
 In order to permit a pre-positioning of the guides 5 with respect to the
 width of the container 1 before withdrawal thereof, the width of the
 containers 1 placed in the rack compartments are inputted and stored in an
 electronic memory. Suitably, the width of the containers 1 is determined
 before the containers are placed in the rack 2. A control unit for
 controlling the movement of the guides 5 retrieves these data before
 removal of a container 1 and is used as presetting for the spacing between
 the guides 5.
 While the invention has been illustrated and described as embodied in a
 pick-up apparatus for retrieving and depositing a load, 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.