Abstract:
The invention pertains to a method of operating a transfer system with individual workpiece carriers driven so as to be able to travel along a path, wherein the workpiece carriers exchange information wirelessly with at least one data loading station arranged on the path. The invention is distinguished by the fact that each workpiece carrier takes on information intended for it wirelessly from the data-loading station, the information is written into a microprocessor control unit of the workpiece carrier, the written information, together with basic data present in the microprocessor, is converted into a travel and machining program for the workpiece carrier, and the workpiece carrier independently conditions its predetermined travel path on the basis of the travel and machining program, travels to corresponding machining stations and exchanges data with machining and/or positioning stations arranged on the path. Thus the advantage is achieved that a workpiece carrier is equipped with completely autonomous intelligence, which is fed to it essentially from one single data-loading station, preferably by wireless means. This permits an autonomous travel and machining operation for each workpiece carrier.

Description:
This application is a continuation-in-part of application Ser. No. 09/400,663 filed on Sep. 20, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention pertains to a method for a transfer system with workpiece carriers. Such a transfer system has, for instance, become the object of DE 195 32 281 A1. This known transfer system involves a track-guided system in which the corresponding workpiece carriers travel along the track in grooves on a plate that is constructed in a modular manner from individual plates. This known workpiece carrier features a read-write head for data transfer, with which the workpiece carrier communicates with associated individual stationary read-write heads distributed on the track. Also arranged on the known workpiece carrier are one or more distance sensors in order to permit communication of the individual workpiece carriers traveling in succession on the track. Thereby a collision of individual workpiece carriers is to be prevented, so that backed-up operation of these workpiece carriers on the transfer system is possible. 
     The disadvantage of the known transfer system is that the data-loading stations in the form of the known read-write heads are arranged distributed along the track, whereby an extraordinarily high programming and circuitry expense results. Such a read-write head is assigned to practically every machining station, which causes the disadvantage that the necessary information must first be fetched before each machining station, in order to communicate to the workpiece carrier what control processes are expected of it and what machining processes are to be carried out by the machining station. The known workpiece carriers have only a limited intelligence, because they are not freely programmable, that is to say, they must fetch the appropriate information and control commands before each machining station. It is not possible, for instance, to associate in advance a given travel behavior with a workpiece carrier over the entire track, not even, for instance, a given travel priority. The arrangement of read-write heads, moreover, presumes that the workpiece carrier is arranged directly opposite a stationary read-write head in order to guarantee a transfer of information at all. This is associated of course with the disadvantage that a prospective control of the workpiece carrier in conjunction with components of the transfer system is not possible. For instance, it is not possible for this workpiece carrier to prospectively trigger switches and other control elements on the track by wireless means so as to encounter a given constellation of the transfer system as it approaches. The arrangement of such read-write heads thus has the essential disadvantage that the workpiece carrier must be stopped for each information transfer in order to achieve a precisely opposite positioning of the workpiece carrier to guarantee the transfer of information. This prevents a rapid travel operation on the track and an information transfer of high information density. 
     The invention is thus based on the problem of refining a method for operating a transfer system with workpiece carriers, and a transfer system operating according to this method such that a separate, individual intelligence can be associated with each workpiece carrier, and thus a considerably more rapid and economical operation of the transfer system and the workpiece carriers is possible. 
     SUMMARY OF THE INVENTION 
     The core of the invention is thus that each workpiece carrier takes on information intended for it wirelessly from the data-loading station, the information is written into a microprocessor memory on the workpiece carrier, the written information, together with basic data present in the microprocessor, is converted into a travel and machining program for the workpiece carrier, and the workpiece carrier independently conditions its predetermined travel path on the basis of the travel and machining program, travels to corresponding machining stations and exchanges data with machining and/or positioning stations arranged on the path. 
     With the technical teaching provided, the essential advantage is achieved that a workpiece carrier is provided with completely autonomous intelligence which is fed to it from essentially one single data-loading station, preferably by wireless means. This permits an autonomous travel and machining operation for each workpiece carrier. It goes without saying that the present invention is not limited to the provision of a single data-loading station. It is possible, particularly in case of large transfer systems, for several data-loading stations to be distributed along the path. Of importance for the present invention, however, is that a data-loading station need not be associated with each individual machining station, as is presumed in DE 195 32 281 A1, but rather, information is fed to the workpiece carrier initially and essentially only one time, in the form of program and information data, which it retains across the entire transfer line system. 
     There is thus the advantage that, because of the retention of this information, additional data transfers need no longer take place, because the workpiece carrier is so intelligent that it can travel to all machining stations independently, or pass them by, and its intelligence also suffices to condition and prepare the travel path that it is to take. In order to process the stored data, the workpiece carrier possesses a microprocessor control unit. 
     Additional advantages and refinements of the invention are the objects of the dependent claims. 
     Thus the workpiece carrier not only controls its own travel operation with respect to defined machining stations arranged stationary along the path, it also conditions the travel path provided for it. This includes, for instance, traveling on side tracks, controlling switches to travel such side tracks and the parameterization of machining stations. This is understood to mean that it contains certain information in its control program which it passes on to the machining station or possibly that it receives information from the machining stations that is intended for it or subsequent machining stations. 
     As an example here, one could mention that it obtains a certain characteristic in the information acquisition from the data-loading station, for instance, that the workpiece carrier with the workpieces on it is intended only for drill machining. A “drilling” workpiece carrier of this type now conditions the machining stations it moves to, and which are responsible for it. It then informs the machining station of, for instance, the necessary drilling depth and all other machining steps that are necessary to machine the workpiece seated on it. 
     In the next pass, the workpiece carrier can then take on other information from the dataloading station which instruct it to supply the workpiece seated on it to certain assembly processes. It can thus be programmed individually for the machining designated for it, without having to take on any additional commands along the track. 
     In the same manner, the conditioning of the track with this intelligent workpiece carrier can also take place in that, during the approach of the workpiece carrier to certain track elements, a wireless signal transmission from the track elements to the workpiece carrier and back takes place in order, for instance, to reset switches or to prepare the machining station for the fact that the workpiece carrier is arriving. In this manner, the machining station is prepared for a passthrough or a stop with the associated machining operations. 
     With the technical teaching as presented, there results for the first time the advantage that every workpiece carrier can be set up individually for a given machining, its intelligence applying for the duration of the passage through the entire transfer system. It goes without saying that such an intelligent workpiece carrier can also pass through the transfer track system several times without having to take on new information. Thus a very rapid travel operation results, because the workpiece carrier automatically controls the manner in which it travels, based on its input intelligence, without having to take on additional intelligence from the track. 
     This thus yields the additional advantage that it is now possible to machine so-called individual lot sizes with one such workpiece carrier. 
     An additional advantage of the invention lies in the fact that the workpiece carrier is constructed to be self-teaching, that is, it has a self-teaching intelligence. After taking on the information in the data-loading station, it can occur that congestion, a fault or incorrect machining takes place in one of the machining stations to be visited in the future. The workpiece carrier now present there in the faulty machining station wirelessly reports a congestion alert along the track to the successive workpiece carriers, stating more or less that the machining station cannot be visited. 
     Now when a workpiece carrier situated in the data-loading station departs, it receives a congestion alert from the workpiece carrier located ahead of it and alters its travel program such that it remains on the transfer system only for a certain distance, without colliding with the workpiece carrier situated ahead of it. Then, for instance, a wait cycle is inserted, which lasts until the machining station can again be visited. 
     The self-teaching effect can even extend so far that, in the adoption of information in the data-loading station, it is also programmed in that a certain sequence of machining steps is not necessary. In this case, the intelligent workpiece carrier can also pass through a faulty machining station without any machining taking place, and could then travel immediately to the next machining station in order to have its additional machining steps performed there. 
     Another essential advantage of the invention is that no higher-level control computer for controlling the entire travel operation is necessary, because each workpiece carrier contains its own separate intelligent sequence program for itself and behaves intelligently on the track assigned to it, that is to say, it avoids congestion, it waits and it conditions the track according to its own installed program. For instance, the computer that supplies the data-loading station with the respective control program for the workpiece carrier does not know where the respective workpiece carrier currently is located on the track. Only the control unit of the workpiece carrier itself knows that, so that a considerably simpler programming effort is provided, precisely because a higher-level control computer managing the entire track is no longer necessary. 
     The object of the present invention results not only from the objects of the individual claims, but also from the combination of the individual claims with one another. All data and characteristics disclosed in the documents, including the abstract, in particular, the spatial configuration represented in the drawings, is claimed as essential to the invention, insofar as it is novel with respect to prior art, individually or in combination. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in greater detail below on the basis of drawings representing only one mode of embodiment. In this regard, additional characteristics and advantages of the invention are seen from the drawings and the descriptions. 
     Shown are: 
     FIG. 1, a transfer system according to the invention, schematized and in a plan view; 
     FIG. 2, a representation of a switch of the transfer system; 
     FIG. 3, a workpiece carrier in use on a short section of the transfer system (viewed in perspective from below); 
     FIG. 4, a plan view onto the workpiece carrier of FIG. 3; 
     FIG. 5, a bottom view of the workpiece carrier of FIG. 3; and 
     FIG. 6, the signal transmission processes between the data-loading station and between individual workpiece carriers, schematized. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The transfer system according to the invention consists of a rail system  1 , which consists, in the present embodiment, of an outer rail  2  and an inner rail  3 . Connecting bars  15  are also provided in the system in order to guarantee a spacing between the respective outer rail  2  and inner rail  3  that is true to gauge. It goes without saying that the invention is not limited to the proposed rail system  1 ; alternatively, only one rail could be present and the workpiece carrier  6  could be arranged either upright on or suspended from this rail system  1 . 
     In the example shown, there are additionally one or more middle rails  4 ,  5  arranged between the outer rail  2  and the inner rail  3 . The arrangement of middle rails  4 ,  5  has the advantage that workpiece carriers of different gauge can also travel on the transfer system. 
     The transfer system of FIG. 1 thus comprises a main travel track  7  formed by the rail system  1 , constructed in essence as an oval rail platform, and a secondary travel track  8 , which branches off from the main travel track  7  via switches  10   a ,  10   b.    
     By means of the secondary travel track  8  a work station can be isolated, in which case, for instance, a hand machining station can be set up, which is subject to different accident-prevention regulations than, for instance, the automatic machining operations at the other machining stations of the workpiece carrier in the area of the main travel track  7 . 
     According to FIGS. 1 and 2, the secondary travel tack  8  is connected to the main travel track  7  via switches  10   a ,  10   b , where such a switch in the area of the separating inner rail  3  between main travel track  7  and secondary travel track  8  comprising a switch blade  11  driven so as to pivot on a pivot axis  14 , engaging at its front end with the respective inner rail  3  and able to pivot in the direction of arrow  13  from one functional position up to an edge  12  in the other functional position. In this manner, the switch  10   a  can be shifted such that, in the example, the workpiece carrier  6   i  passes through the main travel track  7  in the direction of arrow  9 . In the other functional position of the switch  10   a , it is shifted such that the workpiece carrier, in the example the workpiece carrier  6   h , passes through the secondary travel track  8  in the direction of arrow  9   a . The switch  10   b  arranged on the outside is controlled correspondingly. 
     All together, a number of workpiece carriers  6   a - 6   h  are arranged so as to be able to move on the rail system  1 , and each workpiece carrier  6  has its own intelligent control unit. 
     In the vicinity of the rail system  1 , there are a series of machining stations, also designated as positioning stations  16 ,  16   a ,  16   b  below. As a rule, each machining station coincides with a positioning station. The term “positioning station” is understood to mean that in the area of this positioning station, the workpiece carrier situated there is held in place by positioning jaws  24 ,  25  in order to guarantee a very precise fixation of the workpiece carrier in the area of the rail system. In this manner, high-precision machining processes can be performed by machining stations, not shown in detail, on the workpieces arranged on the workpiece carrier. 
     Each positioning station  16 ,  16   a ,  16   b  is marked by input- and output-side sensors  17 ,  18  which control the entry and exit operations at the respective positioning station  16 . 
     A transceiver unit  28  that communicates with a transceiver unit  29  arranged on the workpiece carrier  6 d is arranged in the area  52  of a first data-loading station  27 . The supply of data, information and programs necessary for the operation of the workpiece carrier from the data-loading station  27  to the respective workpiece carrier  6 , which give the workpiece carrier an intelligence of its own, is accomplished by way of this wireless interface, implemented, for instance, by infrared transmission. 
     After receipt of the data, the workpiece carrier  6   d  signs off from the data-loading station  27  and makes a connection with the sensor  17 , which reports to it that it has just left the area of the data-loading station  27 . 
     By way of the associated transceiver unit  28 , the data-loading station  27  sends to the transceiver unit  29  of the next workpiece carrier  6   e  a signal in such a manner as to announce that the data-loading station  27  is now free the workpiece carrier  6   e  may enter. 
     The workpiece carrier  6   d , traveling out of the area  52  of the data-loading station  27  in the direction of arrow  30 , is now located on the track behind a workpiece carrier  6   c  situated in front of it. The latter is in turn waiting to enter a positioning station  16 , in which the workpiece carrier  6   b  is firmly positioned and is currently being subjected, for instance, to machining. The machining of the workpieces can also be accomplished, for instance, through a cutout  26  or an opening in the carrier plate  32  of the workpiece carrier (see FIG.  5 ). 
     In front of the workpiece carrier  6   b  in the direction of travel lies an additional workpiece carrier  6   a , and in front of the latter yet another workpiece carrier  6 . 
     Arranged on each workpiece carrier  6 - 6   h  there is also a transmitter  21 , with which the former can condition the travel track by, for instance, making contact with various devices on the travel track. For instance, the workpiece carrier  6  makes contact with a stationary receiver  22  in the area of the switch  10   a  by way of a signal  23 . The receiver  22  is coupled to a device that determines whether the main or the secondary travel track  7 ,  8  is to be taken and triggers the switches accordingly. 
     The program stored in the workpiece carrier  6  now informs the receiver  22  that the workpiece carrier is to take the secondary travel track  8 . The device connected to the receiver  22  correspondingly shifts the switch blade  11  in the switch  10   a  in the direction of the secondary track. 
     Every workpiece carrier additionally carries a switch that interacts with stationary coding pins in the track. Thus, a switch  20  that is being actuated by a coding pin  19  arranged in the vicinity of the switch  10   a  is shown in the workpiece carrier  6 . The coding pin  19  actuates the switch  20  in order to turn on the transmitter  21  only if the workpiece carrier  6  is facing a travel situation that necessitates a conditioning of the travel track. That is to say, the transceiver units on the workpiece carrier  6 , and possibly even just a lone sender, transmit only if it is necessary and desired. This also serves to conserve energy. Other program sequences can also be initiated by the switch  20 . For instance, coding pins  19  of this type can also be arranged in front of a curve to inform the workpiece carrier that it must reduce its speed in the curve. These are thus stationary coding devices that communicate certain information which influences its travel operation to the workpiece carrier. Of course, wireless coding devices can also be employed instead of such mechanical coding devices. 
     According to FIGS. 3-5, the workpiece carrier consists, in essence, of a carrier plate  32  with a central cutout  26 , through which appropriate tools can extend during the machining of the workpiece in order to permit a flexible machining of the workpiece seated on the workpiece carrier. 
     On the bottom of the carrier plate  32  (FIG.  5 ), various functional units are arranged. It is immediately recognizable that this is a three-wheel workpiece carrier, with a drive motor  36  that is flanged onto a drive wheel  37  and powers the drive wheel  37 . The latter is arranged on a wheel block  43  together with the drive motor  36 , which wheel block  43  is seated on the rail so it can be pivoted about a vertical axis (perpendicular to the carrier plate  32 ) and thus steered. Another wheel block  44 , which can likewise be pivoted about a vertical axis, is present for the co-rotating wheel  38 . 
     The steering motions of these wheel blocks  43 , 44  are accomplished by virtue of the fact that each wheel block  43 ,  44  is connected to a pair of guide rollers  41 , which engages in a groove  42  arranged roughly in the middle of the respective rail  2 ,  3 . 
     On the opposite side, there is only a co-rotating wheel  39  arranged on a wheel block  31 , which is not constructed so as to be steerable. 
     Also arranged on the bottom of the carrier plate  32  on corresponding blocks are outward directed positioning rollers  40 , which interact with associated retaining elements in the respective positioning station  16 ,  16   a ,  16   b  in order to guarantee a firm fixation of the workpiece carrier in the respective positioning station. 
     Also present is an energy accumulator  35 , which can consist of a battery or some other energy accumulator. Instead of batteries, it is preferred here to use so-called Gold-Caps, which are high-capacitance capacitors that are capable of storing a sufficient amount of energy that a continuous travel operation of up to 3 min is possible on the track. For a length of the rail system of roughly 10-15 m, such Gold-Caps suffice to guarantee passing through an entire round without the necessity of an intermediate charge. 
     Also present is an energy transfer unit  33  which guarantees that the energy can be transferred wirelessly from the data-loading station  27  to the energy accumulator  35 . The energy transfer can take place by, for instance, inductive means. 
     Also present is a microprocessor  34 , with which various volatile and/or nonvolatile memories can be associated. Basic data can be programmed for each workpiece carrier in these memories, EEPROMs for instance. The microprocessor  34  then queries this EEPROM and modifies its fixed stored travel program, taking into account the data stored in the EEPROM. 
     A transfer of information between the data-loading station  27  and two workpiece carriers  6   d  and  6   e  arranged some distance apart will be described on the basis of FIG.  6 . 
     The data-loading station  27  has transceiver unit  28  that is capable of carrying out the signal transmission  48   a  to a transceiver unit  29  on the workpiece carrier  6   d . Thus the data necessary for the microprocessor  34  is programmed into the workpiece carrier  6   d  by way of this air interface  46   a.    
     On the workpiece carriers  6   d ,  6   e  a transceiver unit  47  is also present, which communicates wirelessly via a signal  49  with the adjacent workpiece carrier  6   e . In this way, it is assured, for example, that a certain minimum distance  45  between the workpiece carriers  6   d ,  6   e  is always maintained, by a spacing regulation taking place via the information exchange. 
     Arranged in a stationary position on the data-loading station  27  and on each of the positioning stations  16  is an additional sensor  18 , which communicates via the signal transmission  50  to the entering workpiece carrier  6   e  when it is allowed to enter, that is to say, when the data-loading station  27  or the positioning station  16  is free. Every workpiece carrier also has a another transceiver unit  48 , which is arranged at the front in the direction of travel and can preferably coincide with the transceiver unit  47 , which guarantees a forward signal transmission  49  and communicates with the respective adjacent other workpiece carrier situated towards the front, in order again to be able to maintain the forward spacing  45  in the travel direction. 
     This transceiver unit  48  additionally reserves the station to be visited for itself, that is to say, the sensor  18  is appropriately addressed and then responds appropriately and either releases the station  16   b  for the workpiece carrier or not. Behind the station  16   b  in the direction of travel an additional stationary sensor is arranged with a transceiver device  17 , which accomplishes the signal transmission  51  to the workpiece carrier  6   d . The signal transmission  51  takes place with the transceiver unit  47  arranged on the workpiece carrier, which confirms that the workpiece carrier is permitted to leave the respective positioning station  16   b  and, by way of this air interface, signals are exchanged which guarantee a release the travel operation and allow the next workpiece carrier, situated behind it, to enter. 
     The range of the individual transceiver units is dimensioned such that essentially only the respective adjacent and associated transceiver units can be addressed, in order to avoid interference and to not have to expend any great effort to encode the signals. 
     Altogether, it can thus be stated that, by associating an individual intelligence, a faster and more secure travel operation is guaranteed, because the workpiece carriers can communicate with one another without the necessity of any intervention by a control computer. 
     Simple, individual control programs are programmed into the individual workpiece carriers with the data-loading station  27 , which can take place quickly and with little effort. Thus, a high degree of flexibility for new variants is possible, that is to say reprogramming can be undertaken very quickly, because only one individual control program need be input into each individual workpiece carrier. A conditioning of the travel track, a programming of all switches and other things of this kind need not take place from a (no longer present) central control computer. 
     Legend to the drawings 
       1  Rail system 
       2  Outer rail 
       3  Inner rail 
       4  Middle rail 
       5  Middle rail 
       6  Workpiece carrier a-h 
       7  Main travel track 
       8  Secondary travel track 
       9  Direction of arrow  9   a    
       10  Switch  10   a,b    
       11  Switch blade 
       12  Edge 
       13  Direction of arrow 
       14  Pivot axis 
       15  Connecting bar 
       16  Positioning station a, b 
       17  Sensor 
       18  Sensor 
       19  Coding pin 
       20  Switch 
       21  Transmitter 
       22  Receiver 
       23  Direction of arrow 
       24  Positioning jaw 
       25  Positioning jaw 
       26  Opening 
       27  Data-loading station 
       28  Transceiver unit 
       29  Transceiver unit 
       30  Direction of arrow 
       31  Wheel block 
       32  Carrier plate 
       33  Energy transfer unit 
       34  Microprocessor 
       35  Energy accumulator 
       36  Drive motor 
       37  Drive motor 
       38  Wheel 
       39  Wheel 
       40  Positioning roller 
       41  Guide roller 
       42  Groove 
       43  Wheel block 
       44  Wheel block 
       45  Distance 
       46  Signal transmission unit  46   a,b    
       47  Transceiver unit 
       48  Transceiver unit 
       49  Signal transmission 
       50  Signal transmission 
       51  Signal transmission 
       52  Area