"ASSEMBLY LINE FOR MOTOR VEHICLE BODYWORK COMPONENTS"
The present invention relates to an assembly line for motor vehicle bodywork components.
A preferred application of the invention is in the assembly of doors of motor vehicles, to which the following description refers but without any loss of generality.
A method for assembling the doors of motor vehicles known in the prior art consists of performing a series of operations in sequence along a production line, for example a series of mounting, tacking and welding operations.
As a general rule, there is a dedicated line for each door of the motor vehicle, which means there must be the same number of lines as the number of doors of the motor vehicle .
Each of these lines usually comprises a plurality of stations in each of which at least one specific operation is performed, a plurality of handling robots configured to move the door from one station to another and, for each station, a plurality of work robots.
With reference to one specific station, the door is fed to the station by a first handling robot, it undergoes
the operations performed in the station by one or more work robots and is removed from the station by a second handling robot, which feeds it to the next station.
In this way at least one of the handling or work robots is inactive since it must wait for the robot downstream or upstream to complete its operation. This results in considerable down times in the work cycle.
In the motor vehicle industry the need is therefore felt to make production lines more efficient and cost- effective.
DISCLOSURE OF INVENTION
The purpose of the present invention is to provide a production line that overcomes the problems associated with the prior art system described above.
The above purpose is achieved with a production line as claimed in claim 1.
BRIEF DESCRIPTION OF THE DRAWINGS
In order to better understand the present invention, a non-limiting preferred embodiment thereof will now be described by way of example with reference to the accompanying drawings, in which:
figure 1 is a diagram of a layout of a production line according to the invention;
figures 2a-2d are perspective views of a station of the production line in figure 1; and
figure 3 is a graph illustrating the ratio of down times to operating times during a work cycle of the production line according to the invention.
BEST MODE FOR CARRYING OUT THE INVENTION Figure 1 shows an assembly line 1 for assembling doors
D of a motor vehicle that extends along an axis A and comprises a handling section 2 located on one side with respect to the axis A and a work section 3 located on the opposite side of the axis A with respect to the handling section 2.
The production line 1 further comprises a number of n stations P, arranged in series along the axis A, in each of which one or more operations are performed, in particular welding operations.
The handling section 2 comprises, for each station P, a handling robot 5, preferably a robot of the pick and place type, configured to transfer the doors D between the station P and the next station.
The first handling robot 5 on the line is configured to pick up a door panel D0 from a loading station (not illustrated) while the last handling robot 5 is configured to carry a finished door Dn to an unloading station (not illustrated) .
The work section 3 comprises, for each station P, one or more work robots, configured to perform a given
operation, for example welding robots 6, in said station. Each welding robot 6 comprises its own welding tip dressing station 7. All of the work robots are arranged in the work section 3 of the assembly line 1, that is to say, on the opposite side of the axis A with respect to the handling robots 5.
Each station P comprises a table 10 that is able to rotate about a vertical axis B.
Figure 2a illustrates a first preferred embodiment of the table 10.
According to this embodiment, the table 10 basically comprises a central body 11 and a pair of arms 12 borne by the central body 11 and extending radially from said body on diametrically opposite sides.
The central body 11 comprises a fixed lower part 13 and a upper part 11a made to rotate with respect to the lower part lib about a vertical axis B by an actuator 13, by means of a conventional transmission that is not illustrated. The upper part 11a is substantially a prism with an axis B, with four main faces 11c, parallel to one another in pairs, in which there are respective holes 15, facing and coaxial with one another in pairs.
Each arm 12 comprises a shaft 16 extending from an end portion 17 thereof, and housed in a respective hole 15 so as to support the arm in a cantilevered fashion.
The arms 12 are provided with a plurality of anchorage points 20, preferably holes, to permit the attachment of supporting devices 21 configured for respective doors D, for example a right door and a left door or a front door and a rear door. The anchorage points 20 are arranged on an upper surface 24 and on a lower surface 25 of the arms 12.
The functioning of the production line 1 will now be described for a general station Pn . D in indicates a general (n-th) door in the condition it is in at the end of the work process performed in the station Pn .
The cycle is described starting from an initial condition in which the door D in (for example a right door) is on the arm 12 of the table 10 located in the work section 3 in the station Pn, at the end of the work process, and a subsequent door i+i,ri-i (for example a left door) has been loaded onto the arm 12 of the station Pn located in the handling section 2. In a first step, the table 10 rotates so as to place the door D in in the handling section 2 and the door D ;+ι;η_ι in the work section 3, in a position facing the work robots 6.
In a second step, the work robots 6 perform the operations for which they are designed on the door D i+ln_1; meanwhile, in the handling section 2 the handling robot 5 picks up the door D in and transfers it to the next station P-n+ir and the handling robot 5 in the station Pn- moves a
subsequent door D t+2,n-i onto the table 10 of the station Pn .
The two steps are performed cyclically: as soon as the work on the door D i+ln_1 is finished (this door is now indicated as D i+ln) , the table 10 rotates, to move the door D i+2,n-i into the work station 3. While this door is being processed, the door D i+ln is transferred to the station Pn+1 , and a new door D ;+3;n_i is loaded onto the table 10.
In figure 6 the times of the various operations in the work cycle are shown in a graph. As described previously, the work cycle comprises a work step with a duration of Tt and a rotation step with a duration of T2, which follow one another in alternating order with a period T, or cycle time, equal to the sum of Tt and T2.
The work step, with a duration of Tt comprises the operation of transferring the doors between one station and the other and the welding operations, performed in parallel. The time Tt is conveniently comprised between 10 and 20 s and is preferably approximately 15 s.
The rotation step, with a duration of T2, is the "down time" of the work cycle in which both the welding robots 6 and the handling robots 5 are inactive. Conveniently, this time T2, is less than 5 s and, even more preferably, is approximately 4 s.
Conveniently, the door assembly cycle is temporarily interrupted every n cycle times, for example every 12 cycle
times, to perform a tip dressing operation on the welding tools .
This dressing operation is performed simultaneously for all of the welding robots, in the respective dressing stations 7 of each one, and has a duration of between 10 and 15 s, and preferably of approximately 12 s. If performed every 12 cycle times, the dressing step, considered in relation to the single cycle time, thus results in an extremely short additional down time of around 1 s .
The total down time is thus a small percentage of the cycle time T (for example 5 seconds out of a total of 19) .
Figure 2b shows a first alternative embodiment of the table 10 with respect to that shown in figure 2a.
According to this embodiment the table 10 comprises four arms 12a, 12b, arranged crosswise and borne by the respective faces 11c as previously described. The arms 12a, which are opposite one another, are provided with supporting devices 21a for a first door model (for example the front doors, or the right or left doors of a vehicle model) .
Likewise, the arms 12b, which are opposite one another, are provided with supporting devices 21b for a second door model (for example the front doors, or the right or left doors of a vehicle model) . According to this
embodiment, the vehicle model can be changed in real-time, simply by using either one or the other pairs of arms 12a or 12b each time.
Figure 2c illustrates a second alternative embodiment of the table 10 in which, compared to the embodiment in figure 2b, two opposite arms, for example the arms 12a, are provided with two supporting devices 21a, 21c fixed respectively to the upper surface 24 and to the lower surface 25. A second actuator 22, preferably an electric motor, is configured to allow the arms 12a to rotate about a common axis C.
In this way, by combining the rotation of the table 10 and of the arms 12a it is possible to manage the production of three different vehicle models.
Figure 2d shows a third alternative embodiment in which all of the four arms 12a, 12b each carry two supporting devices 21, one on the upper surface 24 and one on the lower surface 25.
Thus, by combining the rotation of the table 10 and of the arms 12a, 12b it is possible to manage the production of four different vehicle models.
The advantages of an assembly line according to the present invention are apparent from the above description.
The use of a rotating table 10, combined with the arrangement of the work and handling robots on opposite
sides of each station, means that work and handling operations can be performed parallelly on the doors. This results in a drastic reduction in down times, which only occur during the rotation of the table 10.
Since more work time is available, the number of work robots can be reduced compared to a conventional assembly line to perform the same operations, with a subsequent reduction in production costs and the space taken up by the line .
The work cycle time is further optimised by dressing all the welding tips at the same time.
Lastly it is clear that modifications and variations may be made to the line 1 without departing from the scope of the present invention, as set forth in the claims.