Electrical contacting system for an electrophoretic dip painting plant for motor vehicle bodies

Electrical contacting system for an electrophoretic dip painting plant for motor vehicle bodies, where the bodies are guided through an electrophoretic dip paint bath by an overhead conveyor having hangers for engaging beneath the body carriers. Each conveyor hanger has at least two lower contacting devices secured thereto and each body carrier has at least four upper contacting devices secured thereto. Each upper contacting device has a protective bell open at the bottom and storing an air bubble in the submerged state. In the area of the air bubble the bell has a downwardly concave, partially circular cylindrical support and contact surface and has a horizontal cylinder axis extending transversely to the conveyance direction. At its outer side facing the guide element, two locking elements form a vertical opening therebetween to interact with a locking nose on the guide element where the locking noses pass through the openings formed by the locking elements. To ensure a secure locking of the protective bell on the lower contacting device, a system is designed where the protective bell is provided with the locking elements having a rigid axle stub coaxial to the cylinder axis of its support and contact surface. The guide element has an upwardly open guide slot parallel to the support and contact element of the lower contacting device. The side edges of this slot forming insertion curves for the axle stub which extend at an angle towards one another from top to bottom.

BACKGROUND OF THE INVENTION
 The invention relates to an electrical contacting system for an
 electrophoretic dip painting plant for motor vehicle bodies, with which
 the bodies are guided through an electrophoretic dip paint bath by means
 of an overhead conveyor. The bodies are thereby each arranged on a body
 carrier and connected to this in an adequately secure manner; the body
 carrier is a flat structure which is approximately rectangular in the plan
 view, is customarily designated as a slide or skid and often has the shape
 of a rectangular carrier frame. The overhead conveyor possesses a
 plurality of conveyor hangers which are arranged one behind the other in
 the direction of conveyance and in spaced relation to one another and
 which are suspended so as to be pivotable about upper pivot axes extending
 horizontally and transversely to the direction of conveyance and are
 designed such that two conveyor hangers following one another in the
 direction of conveyance can engage beneath a respective body carrier in
 its front and in its rear area, respectively, and support it; normally,
 the conveyor hangers have the shape of a rectangular frame with a lower
 crossbar for engaging beneath a body carrier, wherein the plane of the
 frame normally extends vertically.
 In the case of the electrophoretic dip paint bath, this is an aqueous
 suspension, from which color particles are deposited on the body submerged
 in the paint bath by way of electrophoresis when a corresponding,
 electrical difference in potential is maintained between the paint bath
 and the body. For this purpose, the bodies are connected in an
 electrically conductive manner to the metal body carriers and a
 corresponding electrical potential is applied to the conveyor hangers via
 the overhead conveyor; in addition, not only the conveyor hangers but also
 the body carriers are provided with electrical contacting devices which
 provide an electrical connection between conveyor hanger and body carrier
 when the latter is placed on two conveyor hangers. Moreover, these
 contacting devices also have the task of preventing any floating up of a
 body and thus any lifting of the body carrier from the two conveyor
 hangers supporting it when the overhead conveyor submerges the body in the
 paint bath--even if the body of a passenger vehicle is submerged in the
 paint bath with an open trunk lid, the trunk may, in the case of certain
 body shapes, not be filled by the aqueous suspension forming the paint
 bath until the load sill of the trunk dips into the paint bath and so
 without any locking of the body carrier to the conveyor hangers the trunk
 still filled with air would lead to the body carrier lifting away, in
 particular, from the conveyor hanger adjacent to the trunk.
 DE-40 41 211-C1 discloses an electrophoretic dip painting plant of the type
 described above. In the known construction, the conveyor hangers have the
 shape of rectangular frames with a plane of the frame normally extending
 vertically and the body carriers have the shape of rectangular frames with
 a plane of the frames extending horizontally over the greatest portion of
 the path of conveyance. Two lower contacting devices are secured to the
 lower crossbar of each conveyor hanger and these consist essentially of a
 support and contact pin projecting vertically upwards and a rail-like
 guide element arranged next to the pin transversely to the direction of
 conveyance and likewise projecting vertically upwards. Two upper
 contacting devices are secured to each of the two longitudinal frame legs
 of the body carrier, namely one in the front and one in the rear area of
 the body carrier; each of these contacting devices has a metal protective
 bell which is open to the bottom, may be placed from above onto the
 support and contact pin of one of the lower contacting devices and
 encloses and stores a bubble of air when it dips into the paint bath from
 above. The protective bell has two side walls and a circular cylindrical
 circumferential wall which connects these side walls to one another and
 forms with the inner side of its upper area a support and contact surface,
 against which the associated support and contact pin abuts when the body
 carrier is borne by two conveyor hangers. The bubble of air ensures a good
 electrical contact between the contact surface of the protective bell and
 the upper end of the support and contact pin--color is applied not only to
 the body but also to all the areas of the body carrier coming into contact
 with the paint bath and the upper contacting devices secured to it. Two
 rib-like locking elements projecting from the side wall of the protective
 bell facing the guide element of the associated, lower contacting device
 are secured to this side wall and these locking elements--in a view of
 this side wall--extend downwards at an angle and towards one another,
 wherein their lower ends are arranged at a transverse distance from one
 another so that they form an opening between them, and wherein the angle
 bisector of the angle formed by the two locking elements extends through
 the cylinder axis of the circumferential wall of the protective bell.
 These two locking elements interact with a locking nose, which is secured
 to the guide element of the lower contacting device, is approximately of a
 saw tooth shape in the side view and may be pushed through between the two
 locking elements from below with a horizontally extending body carrier and
 vertically extending conveyor hanger, but prevent any lifting of the
 protective bell from the lower contacting device as soon as--when seen
 transversely to the direction of conveyance and horizontally--the angle
 formed by the plane of the frame of the conveyor hanger and the plane of
 the frame of the body carrier deviates from 90.degree. by more than a
 specific angle. Since--as is apparent from FIG. 1 of DE-40 41 211-C1--the
 overhead conveyor submerges the body carriers in the paint bath at an
 angle and also guides them out of the paint bath again at an angle,
 wherein the plane of the frame of the guide hangers still extends at least
 approximately vertically even in this case, such angular deviations occur
 not only during the submergence of the bodies into the paint bath but also
 during the guidance of the bodies out of the paint bath.
 It has been shown in practice that the construction resulting from DE-40 41
 211-C1 cannot ensure a reliable locking of the body carrier on the
 conveyor hangers, namely during the submergence of the bodies into the
 paint bath: In this respect, the conveyor hanger adjacent to the trunk of
 the body and the body carrier can be pivoted relative to one another such
 that the angle bisector of the V-shaped configuration formed by the two
 locking elements of a protective bell forms with the plane of the frame of
 the conveyor hanger a relatively small, acute angle of up to, for example,
 approximately 12.degree.. This can result in the protective bell
 disengaging at the lower contacting device when the protective bell moves
 relative to the support and contact pin of the lower contacting device,
 during the course of the relative movement between body carrier and
 conveyor hanger, such that the contact pin does not constantly extend in a
 plane of diameter of the circular cylindrical circumferential wall of the
 protective bell. Such a disengaging of protective bells of the body
 carriers at the lower contacting devices of the conveyor hangers can,
 however, have extremely disadvantageous consequences--once the bodies are
 completely submerged in the paint bath, the body carriers are again
 lowered onto the conveyor hangers, and in this respect protective bells
 which have previously become disengaged can come to rest adjacent to the
 associated support and contact pins.
 SUMMARY OF THE INVENTION
 The object underlying the invention was, therefore, to improve electrical
 contacting systems of the type such as those resulting from DE-40 41
 211-C1 such that the malfunctioning described in the above cannot occur.
 To accomplish the set object, the invention proceeds on the basis of an
 electrical contacting system for an electrophoretic dip painting plant for
 motor vehicle bodies, with which the bodies are guided through an
 electrophoretic dip paint bath by means of an overhead conveyor which has
 conveyor hangers for engaging beneath body carriers each supporting one
 body and being placeable on two respective conveyor hangers, these hangers
 being arranged one behind the other in the direction of conveyance and
 being pivotable about upper pivot axes extending horizontally and
 transversely to the direction of conveyance, wherein the contacting system
 has for each conveyor hanger at least two lower contacting devices secured
 thereto as well as for each body carrier at least four upper contacting
 devices secured thereto and adapted to be placed on the lower contacting
 devices, each lower contacting device has a support and contact element
 pointing upwards as well as a guide element arranged next to this element
 transversely to the direction of conveyance and likewise pointing upwards
 and each upper contacting device has a protective bell open at the bottom
 and storing a bubble of air in the submerged state, the protective bell
 having in the area of the bubble of air a downwardly concave, partially
 circular cylindrical support and contact surface adapted to be placed on a
 support and contact element and having an approximately horizontal
 cylinder axis extending transversely to the direction of conveyance as
 well as on its outer side facing the guide element two locking elements
 forming a vertical opening between them for interacting with a locking
 nose on the guide element in order to make passage of the locking noses
 through the openings formed by the locking elements of the protective
 bells possible during placement of a body carrier on two conveyor hangers
 and to prevent any lifting of the protective bells away from the lower
 contacting devices during the inclined submergence of a body into the
 paint bath.
 In accordance with the invention, such a contacting system is designed such
 that the protective bell has at its outer side provided with the locking
 elements a rigid axle stub coaxial to the cylinder axis of its support and
 contact surface and the guide element has for a lateral guidance of the
 axle stub an upwardly open guide slot which is parallel to the support and
 contact element of the lower contacting device and the side edges of which
 form in the upper area of the guide slot insertion curves for the axle
 stub which extend at an incline from top to bottom towards one another.
 When in the above and in the following a vertical opening between the
 locking elements of a protective bell is mentioned, it goes without saying
 that this opening is, of course, vertically aligned only when the body
 carrier is in the horizontal but not after any pivoting of the body
 carrier.
 As for the rest, reference is made to DE-40 41 211-C1 with respect to the
 operation of the electrophoretic dip painting plant as well as the design
 and functioning of the contacting system and the content of this
 publication is also intended to be made the subject matter of the present
 application.
 The inventive contacting system results in the following, advantageous
 functioning:
 Due to the fact that the axle stub of the protective bell cannot deflect to
 the side, i.e. in the direction of conveyance or contrary to the direction
 of conveyance, as a result of its engagement in the guide slot of the
 guide element of the lower contacting device and, consequently, it is
 ensured that the axis of the axle stub always intersects the longitudinal
 axis of the support and contact element of the lower contacting device, it
 is also ensured that the support and contact element which is preferably
 pin-like is always located in a plane of diameter of the circular
 cylindrical support and contact surface of the protective bell or rather
 always abuts against the respectively highest location of the support and
 contact surface when protective bell and lower contacting device are
 pivoted relative to one another; consequently, the two locking elements
 arranged on the protective bell and, with them, the opening formed by them
 and the locking nose arranged on the lower contacting device may only be
 pivoted relative to one another but not displaced laterally in relation to
 one another and so with a corresponding dimensioning and arrangement of
 the opening and the locking nose the protective bell is already locked on
 the lower contacting device even with relatively small pivot angles. It is
 thus the basic principle of the invention to fix the rotational or rather
 pivot axis of the protective bell in relation to the lower contacting
 device not in longitudinal direction of the guide slot of the contacting
 device but transversely to this longitudinal direction so that even a body
 still partially filled with air cannot lead to any disengaging of the
 protective bell at the lower contacting device when the body is submerged
 into the paint bath along a path extending at an angle. The insertion
 curves for the axle stub provided in the upper end region of the guide
 slot represent an additional, advantageous feature which ensures that the
 axle stub is lowered into the guide slot when a body carrier is placed on
 two conveyor hangers, even if its width in its area serving for the
 transverse or rather lateral guidance of the axle stub is only
 insignificantly larger than the diameter of the axle stub--without these
 insertion curves careful attention would have to be paid during the
 placement of a body carrier on the conveyor hangers that body carrier and
 conveyor hanger are positioned exactly relative to one another.
 It should also be emphasized that it is not critical when, for example, the
 support and contact elements adjacent to a trunk still filled with air
 lift away form the support and contact surfaces of the protective bells
 associated with these contact elements when the body is submerged into the
 paint bath along a path extending at an angle since the electrical
 connection between overhead conveyor and body is always still ensured by
 the other protective bells and lower contacting devices--it is only
 important for the protective bells adjacent to the area of the body still
 filled with air to remain locked on the lower contacting devices
 associated with them and not be able to disengage from them.
 The inventive contacting system preferably has one or several features of
 the known contacting system resulting from DE-40 41 211 C1. As already
 mentioned, the support and contact elements of the lower contacting
 devices are expediently of a pin-type configuration; in principle, it is,
 however, only important, as a result of the pivot axis of the protective
 bell fixed in transverse direction, for the upper end of the contact
 element to always be located opposite the respectively highest point of
 the contact surface of the protective bell during a pivoting of protective
 bell and lower contacting device relative to one another. Furthermore, the
 simplest way is to design the guide elements of the lower contacting
 devices as rail-like uprights, even if the guide elements can, in
 principle, be of a different configuration; like the state of the art, it
 may, however, be expedient to provide the guide elements at the top with
 an inclined insertion surface for the protective bells--such an inclined
 insertion surface is arranged on the side of the guide element facing the
 protective bell and extends (when seen in the direction of conveyance) at
 an angle from bottom to top and outwards (i.e. the upper end of the
 inclined insertion surface has a greater transverse distance from the
 protective bell than the lower end of the inclined insertion surface). To
 provide a good electrical contact as well as to avoid excessive wear and
 tear, it is, in addition, advantageous to design the upper end of the
 contact element in a ball shape.
 To ensure a secure locking of the protective bell on the lower contacting
 device even after relatively small pivoting angles, and independently of
 the pivoting direction, a preferred embodiment of the inventive contacting
 device is designed such that the locking elements have approximately flat
 locking surfaces which face the axis of the axle stub and the planes of
 which extend approximately parallel to the axis of the axle stub and form
 with one another an angle having an angle bisector extending through the
 axis of the axle stub.
 Tests by the applicant with the inventive contacting system have shown that
 it is recommendable to design this such that--when seen from above with a
 horizontally extending body carrier--the width of the opening formed by
 the locking elements of the protective bell is greater than the maximum
 width of the locking nose only to such an extent that during pivoting of
 the protective bell and, with it, the longitudinal central axis of the
 opening in relation to the longitudinal central axis of the guide slot
 through approximately 8.degree., preferably more than approximately
 10.degree., the locking elements already prevent any passage of the
 locking nose through the opening.
 So that the locking noses of the lower contacting devices can pass through
 the openings formed by the locking elements of the protective bells
 without further ado when a body carrier is placed on the conveyor hangers,
 it is recommended to provide corresponding, inclined slide-on surfaces on
 the locking elements and/or on the locking noses, where applicable also
 inclined slide-on surfaces for the purpose of enabling the lower edges of
 the protective bells to be lowered to easily pass the locking noses. For
 this purpose, the following features of preferred embodiments of the
 inventive contacting system are recommended: The locking nose has (when
 seen from the side) an end face sloping upwards and to the rear;
 furthermore, the locking nose can (when seen from above) have side
 surfaces extending at an incline upwards towards one another. It is,
 finally, favorable for the locking function when the locking nose (when
 seen from the front) has a flat lower side which extends transversely to
 the guide slot.
 So that the system is not statically overdefined, preferred embodiments of
 the inventive contacting system are characterized by the fact that when
 the contact element is supported on the contact surface of the protective
 bell the axle stub does not abut either on the locking nose or on the end
 of the guide slot, which may easily be achieved by way of a corresponding
 dimensioning of the length of the guide slot and a corresponding
 arrangement of the locking nose on the guide element.
 Additional features, advantages and details of the invention result from
 the attached claims and/or from the following description as well as the
 attached drawings of a particularly advantageous embodiment of the
 inventive contacting system, wherein this has been illustrated in the
 drawings and is described in the following only insofar as this is
 necessary for understanding the present invention with knowledge of DE-40
 41 211-C1.

DETAILED DESCRIPTION OF THE INVENTION
 In FIG. 1, part of a lower crossbar 10 of a conveyor hanger of an overhead
 conveyor is indicated; this conveyor hanger is intended to have the shape
 of a rectangular frame consisting of a hollow, square steel section,
 wherein the plane of the frame normally extends vertically and at right
 angles to the direction of conveyance of the overhead conveyor and is
 intended to extend parallel to the plane of drawing in FIG. 1.
 Furthermore, a longitudinal frame leg 12 of a body carrier in the form of
 a rectangular body support frame is indicated in FIG. 1, namely in cross
 section; this support frame is welded together from portions of a hollow,
 square steel section, the plane of the frame extends in the normal case
 horizontally and at right angles to the plane of drawing of FIG. 1, and
 the longitudinal frame leg 12 is intended to be the right-hand
 longitudinal frame leg of the body support frame in accordance with FIG.
 1.
 The direction of conveyance of the overhead conveyor is intended to extend
 at right angles to the plane of drawing of FIG. 1 and is indicated in FIG.
 2 by the arrow F; with respect to further details of the overhead
 conveyor, reference is made for the sake of simplicity to FIGS. 1 and 2 of
 DE-40 41 211-C1 and its description.
 FIG. 5 shows an overview of the overhead conveyor system. The overhead
 conveyor 5 is shown traveling in the direction indicated by arrows 27.
 Conveyor hangers 7 engage beneath body carriers 3 for conveying motor
 vehicle bodies 1 through an aqueous suspension 12 wherein color particles
 are deposited on the bodies 1 by electrophoresis.
 An upper contacting device designated as a whole as 14 is securely
 attached, e.g. by welding, to the longitudinal frame leg 12, and a lower
 contacting device designated as a whole as 16 is secured to the lower
 crossbar 10. The lower contacting device essentially consists of a base
 plate 18 secured to the crossbar 10, a rail-like guide upright 20 which
 projects vertically upwards and is welded to the base plate, a contact pin
 22 welded to the base plate and projecting vertically upwards and a
 reinforcing web 24 which is connected by welding not only to the base
 plate 18 but also to the guide upright 20 and the contact pin 22. Base
 plate, guide upright, contact pin and reinforcing web consist of steel, a
 contact member 26 secured to the upper end of the contact pin 22
 expediently of copper, wherein the contact member is of a spherical design
 at the top. A central longitudinal axis of the contact pin has been
 designated as 22a; this extends at right angles to the base plate 18 and
 through the center of the spherical upper side of the contact member 26.
 The upper contacting device 14 has a protective bell 30 made of steel which
 is hollow inside and open at the bottom and has two side walls 32 and 34
 as well as a circumferential wall 36; the latter has a circular
 cylindrical wall area 36a which extends over a circumferential angle of
 more than 180.degree. and the cylinder axis of which has been designated
 as 38. The inner side of the wall area 36a forms a circular cylindrical
 support and contact surface 40 which is coaxial to the cylinder axis 38
 and with which the protective bell 30 can be supported on the contact
 member 26 and thus on the contact pin 22. An attachment plate 41 made of
 steel is welded to the side wall 34 of the protective bell 30 facing away
 from the lower contact device 16 and this plate has, for its part, been
 secured to the longitudinal frame leg 12 by welding.
 In accordance with the invention, an axle stub 42 is secured to the side
 wall 32 of the protective bell 30 facing the guide upright 20 and the axis
 of this axle stub coincides with the cylinder axis 38; furthermore, two
 locking bars 44 and 46 serving as locking elements and illustrated in FIG.
 2 are secured to the side wall 32, only one of these bars, the locking bar
 44, being illustrated in FIG. 1. At their sides facing the cylinder axis
 38, the locking bars 44, 46 each form a flat locking surface 44a and 46a,
 respectively, which extends parallel to the cylinder axis 38; the two
 locking surfaces form with one another an acute angle, the angle bisector
 50 of which extends through the cylinder axis 38, and between the lower
 ends of the locking bars 44, 46 there is an opening 52, through which a
 locking nose 54 welded to the guide upright 20 can pass in the direction
 of the angle bisector 50 when the angle bisector 50 extends at least
 approximately parallel to the longitudinal axis 22a of the contact pin 22
 and thus at right angles to the base plate 18 of the lower contacting
 device 16.
 The locking nose 54 has a flat lower side 54a extending parallel to the
 base plate 18, a sloped end face 54b and two inclined side surfaces 54c
 and 54d. The two side surfaces extending at an angle facilitate the
 passage of the locking nose 54 through the opening 52 when the protective
 bell 30 is lowered onto the contact pin 22 from above, and during this
 procedure the sloped end face 54b promotes the passing of the locking nose
 54 through the lower edge of the side wall 32 of the protective bell 30.
 The guide upright 20 is provided with a guide slot 70 which opens upwards
 and the side edges of which form in the upper area of the guide slot
 insertion curves 70a and 70b which ensure during the lowering of the upper
 contacting device 14 onto the lower contacting device 16 that the axle
 stub 42 enters the guide slot 70. Beneath the insertion curves 70a, 70b,
 the width or breadth of the guide slot 70 is only very slightly greater
 than the diameter of the axle stub 42.
 The longitudinal central axis of the guide slot 70 extends, in accordance
 with the invention, parallel to the longitudinal axis 22a of the contact
 pin 22 in such a manner that when looking at the lower contacting device
 16 in longitudinal direction of the lower crossbar 10 of the conveyor
 hanger the two axes are congruent.
 In accordance with the invention, the various elements of the contacting
 system are arranged and dimensioned as follows:
 When the angle bisector 50 extends parallel to the longitudinal axis 22a of
 the contact pin 22 and thus parallel to the longitudinal central axis of
 the guide slot 70, the locking nose 54 can pass in vertical direction
 through the opening 52 during the lowering of the upper contacting device
 14 onto the lower contacting device 16.
 When the circular cylindrical wall area 36a of the protective bell 30
 touches the contact member 26 during the course of the lowering of the
 upper contacting device 14 and is supported on it, the axle stub 42 is
 still located above the lower end of the guide slot 70 and above the
 locking nose 54.
 If the protective bell 30 is pivoted about the cylinder axis 38, one of the
 locking bars 44, 46 in cooperation with the locking nose 54 prevents the
 axle stub 42 lifting out of the guide slot 70 as soon as the pivot angle
 is greater than, for example, 10.degree. because the locking nose 54 can
 then no longer pass through the opening 52.
 If the axle stub 42 is located beneath the insertion curves 70a, 70b in the
 guide slot 70, the cylinder axis 38 intersects the longitudinal axis 22a
 of the contact pin 22 at least almost.
 The locking nose 54 projects from the guide upright 20 to such an extent
 that it engages in the space between the two locking bars 44 and 46 once
 the upper contacting device 14 has been placed on the lower contacting
 device 16.
 Finally, in accordance with the invention, the guide upright 20 has in the
 area of its upper end an inclined insertion surface 20a which extends at
 an angle from top to bottom in the direction towards the space between
 guide upright 20 and contact pin 22 and facilitates introduction of the
 side wall 32 of the protective bell 30 into this space during the lowering
 of the upper contacting device 14.
 The present disclosure relates to the subject matter disclosed in German
 Application No. 198 39 725.9 of Sep. 1, 1998, the entire specification of
 which is incorporated herein by reference.