Method and arrangement for assembly of component parts, preferably for motor vehicles
BACKGROUND OF THE INVENTION 
     It has been known for a long time to assemble automobiles in so-called assembly lines to achieve, on the one hand, a maximum of finished pieces and, on the other hand, a uniform quality, so that replacement parts are interchangeable in each automobile. The characteristic feature of such assembly lines is that a moving track moves at a predetermined rate along the line, so that the parts being assembled are brought with each timed movement from one work station to another, until at the end of the line a completely assembled vehicle rolls off the track. The intervals during which the track is moved are of critical importance for the division of assembly work, because at each of the work stations the required work must be completed within this interval. This work can only be performed by people. So in this assembly system, people are made into integral parts of a machine. This situation is understandably unfavourable in many respects, not to mention the psychological considerations. 
     Therefore, it has been a goal for a long time to find a way of assembling motor vehicles which avoids these disadvantages, while achieving at least equal capacity and quality. 
     Until now the technical world has made the assumption that the track in such an assembly line must be an inseparable functional entity and therefore the work rate along the whole length of the line must be uniform. 
     The inventor of the present invention had the boldness to break through this thinking barrier and to look for a solution by turning away from previous systems. 
     According to the invention, the solution lies fundamentally in the idea of dividing up the previously connected track into a plurality of individual cars, and to steer said cars along the assembly line according to a principal so that as is required they are either driven along the assembly line or are shunted off to adjacent stations and from there back to the line. This eliminates the strict work rate during assembly and people are removed as component parts of the machine, now making possible cooperation between more people in groups where previously each worker had to complete his always unvarying hand movements in practical isolation. People are no longer component parts of the machine; rather, they have individually or preferably in a group the ability to make decisions and have responsibility. Furthermore, the cases of absenteeism will not be as troublesome as they were previously. But in regard to capacity and quality, the invention also has considerable advantages. Up to now if a major error occurred at any of the work stations, the entire line had to be shut down until the error was corrected. For this reason, it is usual to allow minor assembly errors, which can be corrected later, to pass to the end of the line. In order to correct these errors afterwards, subsequently assembled parts must often be disassembled. Such minor errors occur often, making the assembly appreciably more time-consuming and costly. 
     SUMMARY OF THE INVENTION 
     In the invention such disadvantages are avoided, because it is not necessary to hold to a strict work rate. 
     According to the invention, in the assembly of the units a method is used in which each unit or parts of the unit are placed and transported on individual motor-driven transport cars. Movement of the cars is individually controlled as to direction and speed with the help of signals from at least one control wire connected with a control center and running in the direction of the line. 
     An apparatus for assembly of units transported along an assembly line is characterized according to the invention by a plurality of cars steered along the line, said cars being provided with a suspension means for the units, at least one motor-driven wheel steered by a steering device, at least two additional wheels, and at least one signal receiver for control of the car; and by at least one control wire running along the assembly line and working in conjunction with the signal receiver of the car. 
     A transport car useable for the apparatus is characterized by being provided in the area of the front and rear ends with at least one drivable wheel which is steerable by means of a steering device and at least one additional pivotable wheel. When moving in the longitudinal direction of the car, at least one of the driven wheels serves to steer the car according to its angular setting. When moving transversely to its longitudinal direction, the steering of the car is effected by the driven wheels being set in a running position essentially transversely to the longitudinal direction of the car, at least one of these wheels being controlled as to its speed of rotation. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The invention will be described in more detail with reference to the accompanying drawings, in which FIG. 1 shows an assembly hall for automobiles with two different assembly lines and transport cars, one for bodies and the other for chassis and body-chassis; 
     FIG. 2 a view similar to FIG. 1 of another part of the body line; 
     FIG. 3 an alternative embodiment of a body car and a chassis car usable in the method according to the invention; 
     FIG. 4 a schematic plane view of one end of the cars shown in FIGS. 1-3. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT FOR THE PREFERRED PRACTICE OF THE METHOD 
     FIG. 1 shows a portion of an assembly arrangement for automobiles which on an upper level has an assembly line for bodies and on a lower level has a line for chassis and body-chassis. An electric wire 1 runs along the upper as well as the lower line, which wire is preferably embedded in a rubber mat. Driverless transport cars 2 and 3 are moved along the wire on each level, the cars 2 on the upper level carrying bodies and the cars 3 on the lower level carrying chassis as well as both the bodies and chassis. The FIGURE illustrates how a body from the upper level with the help of an elevator arrangement generally designated by 4 is placed on a car 3, which already carries a chassis. Farther along the line, there is another elevator arrangement 5 with the help of which the chassis is lifted up towards the body. 
     Each of the cars 2, 3 has a frame 6 with means for carrying various parts of a car, as will be described later. The cars are in principal constructed identically at both ends and in FIG. 4 one end of a car is shown schematically, which contains a drive wheel 7 with a drive motor 8, steering motor 9, batteries 10 and a traversing wheel 11. 
     The drive wheel 7 can be turned with the help of the steering motor 9 for driving in the desired direction. The steering motor 9 receives steering orders either from an electronic control unit (not shown) dependent on the sensed position relative to the control wire 1, or directly from manual operating means (not shown) coupled to the driving and steering motors of the car. The control unit as well as the manual operating means can consist of electronic devices which are known per se. The other end of the car differs from that described above essentially only in that the drive wheel 7 is placed on the opposite side so that both of the car&#39;s drive wheels are diagonally arranged. Both of the traversing wheels 11 are freely turnably journalled and automatically assume the correct alignment. The drive wheels 7 are adjustable and lockable at 90° to the longitudinal direction of the car to enable the car to be moved transversely. Steering is effected by the difference in rotational speed between the wheels. Of the two drive wheels 7, only one is variably adjustable within a definite angle, preferably between a position for driving straight forward and a position for driving transversely, while the other wheel 7 can only be set in one or the other of these two positions. FIG. 2 shows how the cars are driven both longitudinally and transversely. 
     The control units in the respective cars are programmed so that all of the cars can be controlled synchronically along the wire, at the same time as the control of individual cars is made possible. This can be achieved by methods which are known per se in electronics, for example by a certain frequency in the electric wire giving a definite control order to one car, while the other cars remain unaffected. For example, certain or individual cars can be given the instruction to move away from the main line onto a &#34;siding&#34;, as is shown in FIG. 2, for example. Furthermore, the control unit can be programmed so that by an impulse a car can be given the instruction to deviate transversely completely away from the control wire and drive a certain distance from the line before it stops, whereafter the operation can be taken over by an assembler who with the help of the manual control means can drive the car to the appropriate storage place. 
     The control wire can furthermore be divided into a plurality of sections, of which, for example, some can be made dead and some live, so as to only affect cars within a certain section. In general, one can by exploiting known technique per se within electronic control and data engineering, achieve a number of variational possibilities for controlling the cars collectively as well as individually from a control center via an electric wire. 
     To the frame 6 of the car 2, two transverse rails 12 are attached, which are designed to support trundles 13 which are rotatably journalled on two longitudinal support beams 14 which are connected to each other. They are designed to be attached to a body, preferably on its ordinary lifting bracket. As FIG. 2 shows, especially the bodies can, by the use of the described contruction, be transported either in the normal position or in a tipped position. In tipping, the support beams 14 are coupled to a stationary tipping device (generally designated by 15), whereby one pair of trundles 13 rolls on the rails 12 to an end position in which the support beams are fixed with the help of beams 16 disposed on the car 2. 
     The cars 3 have, as do the cars 2, transverse rails 12, but these are disposed on racks 17 so as to be able to be raised and lowered to achieve an elevated placement of the body (see FIG. 1). On a level under the rails 12 on both of the racks 17, there is a fixture 18 for a chassis which can be raised and lowered. The moving of the fixture vertically is done with the help of the outer stationary elevator arrangement 5 while the movement of the rails is controlled by hydraulic cylinders 19 connected to the respective racks 17. 
     During assembly, the body is thus moved from the cars 2 to the cars 3 for assembly with the chassis. Thereafter the two assembled units are moved back to the car 2. 
     As is evident from the Figures, the frame 6 on the cars 2 and 3 is in the form of a platform which can be used as a work platform by the assemblers. 
     In FIG. 3, an alternative embodiment of the cars is shown which can be used in the method according to the invention. A car 20 carries a body which can be raised and lowered. The car 20 consists of a forward and a rear member 21 and 22 respectively, which are provided with wheels, and which are connected to each other by means of a frame member 23. In the open space between the members 21 and 22 a chassis car 24 is driven for assembling of the body and chassis, whereafter the chassis car is driven away. 
     The cars described are provided with touch sensitive means which activate an emergency brake. These means (not shown) can be arranged around the cars in such a way that only those means are activated which face forward when the car is moving. Also, a resilient bumper 25 can appropriately be arranged. Distance detecting means can also be disposed on each car, by means of which a certain distance between the cars can be maintained. 
     It will of course be appreciated that many modifications can be made within the scope of this invention provided that they can meet with the functional necessities of the invention.