Method and long stator linear motor for transferring a transport unit at a transfer position

Abstract

Method for transferring a transport unit of a long stator linear motor at a transfer position from a first transport section to a second transport section. On each side of the transport unit, excitation magnets are arranged to interact with driving coils, and on both sides of the transport unit, excitation-magnetic lateral forces are acting on the transport unit by an interaction of the excitation magnets with ferromagnetic components of the guide structure. Method includes supplying on at least one side of the transport unit a stator current n a driving coil to generate a lateral force-forming electromagnetic force that acts on the transport unit, so that a resulting lateral force, as a sum of the acting excitation-magnetic lateral force and of the lateral force-forming electromagnetic force, on each side of the transport unit is different to produce a steering effect on the transport unit at the transfer position.

Claims

1. A method for transferring a transport unit of a long stator linear motor at a transfer position from a first transport section, having a number of driving coils arranged on a first guide structure one behind the other in a direction of movement of the transport unit in a region of the transfer position, to a second transport section, having a number of driving coils arranged on a second guide structure one behind the other in a direction of movement of the transport unit in the region of the transfer position, wherein, on each side of the transport unit, excitation magnets are arranged to interact with driving coils in a region of the transport unit, wherein on both sides of the transport unit excitation-magnetic lateral forces are acting on the transport unit by an interaction of the excitation magnets with ferromagnetic components of the first and second guide structures, comprising: supplying on at least one side of the transport unit a stator current in at least one driving coil in the region of the transfer position that generates a lateral force-forming electromagnetic force that acts on the transport unit, so that a resulting lateral force, as a sum of the acting excitation-magnetic lateral force and of the lateral force-forming electromagnetic force, on each side of the transport unit is different to produce a steering effect on the transport unit at the transfer position.

2. The method according to claim 1, wherein the lateral force-forming electromagnetic force is produced on both sides of the transport unit.

3. The method according to claim 2, wherein the lateral force-forming electromagnetic forces produced on both sides of the transport unit are generated in a same direction.

4. The method according to claim 2, wherein lateral force-forming electromagnetic forces produced on both sides of the transport unit are generated in different directions.

5. The method according to claim 1, wherein several driving coils interact with excitation magnets on the transport unit at a same time and the stator current is supplied in at least one of the several driving coils.

6. The method according to claim 1, wherein a propulsive force acting on the transport unit is controlled with a propulsive force forming current component of the stator current and the steering effect is controlled at the transfer position with a lateral force forming current component of the stator current.

7. The method according to claim 6, wherein the propulsive force is controlled with a position controller for controlling a position of the transport unit, said position controller determines the propulsive force forming current component from a position error that is determined with a desired position and an actual position.

8. The method according to claim 6, wherein the steering effect is controlled with a steering controller, said steering controller determines the lateral force forming current component from a flux error as the difference between a desired flux and an actual flux.

9. The method according to claim 6, wherein the lateral force-forming electromagnetic force is superimposed on the propulsive force.

10. The method according to claim 9, wherein the stator current in the at least one driving coil in the region of the transfer position further generates a propulsion force-forming electromagnetic force that acts on the transport unit, which provides further steering of the transfer unit.

11. The method according to claim 10, wherein the propulsive force-forming electromagnetic force is superimposed on the propulsive force.

12. The method according to claim 5, wherein the several driving coils interact with excitation magnets on the transport unit at the same time and the stator current is supplied in only one of the several driving coils.

13. The method according to claim 5, wherein the several driving coils interact with excitation magnets on the transport unit at the same time and a stator current is supplied in all of the several driving coils.

14. The method according to claim 6, wherein the stator current in the at least one driving coil is supplied as a current vector with a lateral force-forming electromagnetic component.

15. The method according to claim 14, wherein the current vector further includes a propulsive force-forming electromagnetic component.

16. The method according to claim 15, wherein the steering effect is controlled with a steering controller that compensates for a flux error as a difference between a desired flux and an actual flux, and determines the lateral force-forming electromagnetic component of the stator current, and wherein the propulsive force is controlled with a position controller that compensates for a position error as a difference between a desired position and an actual position, and determines the propulsive force-forming electromagnetic component of the stator current.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The embodiments are explained in greater detail below with reference to FIGS. 1 to 10, which show by way of example, schematically and without limitation, advantageous embodiments of the invention. In the drawings:

(2) FIGS. 1 and 2 in each case show a transport device in the form of a long stator linear motor,

(3) FIG. 3 shows the structural and electrical layout of the long stator linear motor,

(4) FIG. 4 shows a first embodiment of a method according to the invention for transferring a transport unit at a transfer position,

(5) FIG. 5 shows the forces acting on the transport unit in this first embodiment,

(6) FIG. 6 shows a second application of a method according to the invention for transferring a transport unit at a transfer position,

(7) FIG. 7 shows the torques acting on the transport unit in a further embodiment for generating a steering effect,

(8) FIG. 8 shows a second embodiment of a method according to the invention for transferring a transport unit at a transfer position, and

(9) FIGS. 9 and 10 show a control concept for the method according to the invention.

DETAILED DESCRIPTION

(10) A transport device 1 in the form of a long stator linear motor is illustrated by way of example in FIG. 1. The transport device 1 consists of a plurality of transport sections A1 . . . A9, which are assembled into the transport device 1. This modular construction enables a very flexible design of the transport device 1, but also requires a plurality of transfer positions U1 . . . U9, at which the transport units T1 . . . Tn moving on the transport device 1 (for reasons of clarity not all of the transport units are identified by a reference numeral in FIG. 1) are transferred from one transport section A1 . . . A9 to another.

(11) The transport device 1 is configured as a long stator linear motor, in which the transport sections A1 . . . A9 each form a part of a long stator of a long stator linear motor in a manner which is known per se. Therefore a plurality of electrical driving coils are arranged in the longitudinal direction along the transport sections A1 . . . A9 in a known manner (not shown in FIG. 1 for reasons of clarity) and co-operate with excitation magnets on the transport units T1 . . . Tn (see FIG. 3). In a manner which is likewise known, by control of the electrical stator current A of the driving coils 7, 8 for each of the transport unit T1 . . . Tn a propulsive force F.sub.V is generated which moves the transport units T1 . . . Tn in the longitudinal direction along the transport sections A1 . . . A9, that is to say along the transport line. In this case each of the transport units T1 . . . Tn can be moved individually (speed, acceleration, path) and independently (apart from avoiding possible collisions) of the other transport units T1 . . . Tn. Since this basic principle of a long stator linear motor is sufficiently known, it is not discussed in greater detail here.

(12) It is likewise known for a transport section A1 . . . A9 to be composed of individual transport segments TS which in each case carry a plurality of driving coils and which in each case are controlled by an associated segment control unit 11, as is described for example in U.S. Pat. No. 6,876,107 B2 and illustrated in FIG. 9. A transport unit T1 . . . Tn located in a transport segment TS is therefore controlled by the associated segment control unit 11. Primarily this means that the segment control unit 11 controls the driving coils 7, 8 of the associated transport segment TS so that the transport unit T1 Tn is moved by the propulsive force in the desired manner (speed, acceleration) along the transport segment TS. If a transport unit T1 . . . Tn moves from a transport segment TSn into the next in transport segment TSn+1, the control of the transport unit T1 . . . Tn is also transferred in an ordered manner to the segment control unit 11.sub.n+1 of the next transport segment TSn+1. The movement of the transport unit T1 . . . Tn through the transport device 1 is monitored in a higher-level system control unit 10, which is connected to the segment control unit 11. The system control unit 10 controls the movement of the transport unit Tn through the transport device 1, for example by position presetting. The segment control units 11 then compensate for any errors between the desired value and the actual value.

(13) Several transfer positions U1 . . . U10 are also arranged along the transport line of the transport device 1. In this case different types of transfer positions U1 . . . U10 are conceivable. A switch point is provided for example at the transfer positions U2 and U7, whereas the other transfer positions U1, U3 U6, U8, U9 are designed for example as changeover points from one transport section A1 . . . A8 to another. A transition from a one-sided transport section A2 to a two-sided transport section A9 is provided for example at the transfer position U10. At the transfer position U2 (switch point) a transport unit T6 can be moved further, for example on the transport section A2 or the transport section A3. At a transfer position U1 (changeover position) a transport unit T5 is transferred from the one-sided transport section A1 to the one-sided transport section A2.

(14) A plurality of work stations S1 . . . S4, in which a manipulation takes place on the components transported by the transport unit T1 . . . Tn, can also be arranged along the transport line of the transport device 1, which is defined predominantly by the longitudinal direction of the transport section A1 . . . A8. The work station S1 can for example be configured as a feed and/or discharge station in which finished components can be removed and components to be processed are transferred to a transport unit T1 . . . Tn. Any processing steps can be carried out on the components in the work stations S2 . . . S4. In this case the transport units T1 Tn can be stopped for processing in a work station S1 . . . S4, for example in a filling station in which empty bottles are filled, or can be moved through, for example in a tempering station in which components are thermally treated, if required also at a different speed than between the work stations S1 . . . S4.

(15) Another example of a transport device 1 is illustrated in FIG. 2. Five closed transport sections A1 . . . A5 are provided here. In this case the transport sections A2 . . . A4 serve for feeding different components at the work stations S1 . . . S3. In a work station S4 of a transport section A5 these components are connected to one another or processed in some other way and are discharged from the transport device 1. A further transport section A1 serves for transferring the components from the transport sections A2, A3, A4 into the transport section A5. For this purpose transfer positions U1, U2, U3 are provided in order to transfer the transport units Tn with the different components into the transport section A1. For this purpose a transfer position U4 is provided in which the transport units Tn with the different components are transferred into the transport section A5.

(16) In order to be able to implement a transfer position U1 . . . U10 according to the invention, it is necessary, at least in the region of the transfer position U1 . . . U10, that driving coils 7, 8 are provided on both sides of the transport unit Tn and that excitation magnets 4, 5 are arranged on both sides of the transport unit Tn as viewed in the direction of movement. The excitation magnets can be configured as permanent magnets or as electromagnets. A particularly advantageous embodiment of the long stator linear motor, at least in the region of the transfer position U, is explained with reference to FIG. 3.

(17) FIG. 3 shows a cross-section through any transport section Am and a transport unit Tn moved thereon. A transport unit Tn consists here of a main body 2 and a component receptacle 3 arranged thereon, wherein the component receptacle 3 can basically be arranged at any point on the main body 2, in particular also on the underside for suspended components. The plurality of excitation magnets 4, 5 of the long stator linear motor is arranged on the main body 2 on both sides of the transport unit Tn. The transport line of the transport device 1, or of a transport section Am, or of a transport segment TSm of a transport section Am, is formed by a stationary guide structure 6 on which the driving coils 7, 8 of the long stator linear motor are arranged. In this case the main body 2 with the permanent magnets 4, 5 arranged on both sides is arranged between the driving coils 7, 8. Thus, in each case at least one excitation magnet 4, 5 is arranged opposite a driving coil 7, 8 (or a group of driving coils) and thus interacts with the driving coil 7, 8 for generation of a propulsive force F.sub.V. Thus, the transport unit Tn is movable between the guide structures 6 and along the transport line. Naturally, other guide elements 9 (not illustrated or only indicated here for reasons of clarity), such as rollers, wheels, sliding surfaces, etc., can also be provided on the main body 2 and/or on the component receptacle 3 in order to guide the transport unit Tn along the transport line. In this case, for guiding purposes the guide elements of the transport unit Tn co-operate with the stationary guide structure 6, for example in that the guide elements 9 are supported on the guide structure 6, or slide or roll thereon. However, the guiding of the transport unit Tn can also take place at least by the provision of guide magnets.

(18) In order to move a transport unit Tn forward, it is known to supply a stator current i.sub.A1, i.sub.A2 to the driving coils 7, 8 on both sides, wherein different stator currents i.sub.A1, i.sub.A2 can also be supplied to different driving coils 7, 8. In this case it is also sufficient to supply a stator current i.sub.A1, i.sub.A2 only to the driving coils 7, 8 which can interact with the excitation magnets 4, 5 on the transport unit Tn. In order to generate a propulsive force F.sub.V acting on the transport unit Tn, a driving coil 7, 8 is supplied with a stator current IA with a propulsive force-forming current component i.sub.Aq.

(19) For the movement of the transport unit Tn, however, the driving coils 7, 8 arranged on both sides do not have to be supplied simultaneously with a stator current i.sub.A. In principle it is sufficient if the propulsive force F.sub.V acting on the transport unit Tn for movement is generated only by means of the driving coils 7, 8 on one side and the permanent magnet 4, 5 on the associated side of the transport unit Tn. On line sections of the transport line on which a large propulsive force F.sub.V is required, for example in the event of an incline, a heavy load or in regions of acceleration of the transport unit Tn, the driving coils 7, 8 can be energized on both sides (for example transport section A9 in FIG. 1), so that the propulsive force F.sub.V can be increased. Likewise it is conceivable that in certain transport sections A the guide structure 6 is only implemented on one side, or that in certain transport sections A the guide structure 6 is implemented on two sides, but is only equipped with driving coils 7, 8 on one side. This case it is also indicated in FIG. 1, in which line sections with a guide structure 6 on both sides and line sections with a guide structure 6 only on one side are indicated.

(20) A transfer position U according to the invention, in this case in the form of a switch point, such as for example the transfer position U2 in FIG. 1, between two transport sections Am, An will now be explained with reference to FIG. 4. As described above, the driving coils 7, 8 are arranged one behind the other in direction of movement along the transport sections Am, An. The transport sections Am, An consist here of transport segments TSm1, TSm2, TSm3, TSm4, TSm5 or TSn1, TSn2, TSn3, TSn4, arranged one after the other in the longitudinal direction, in each case with a plurality of driving coils 7, 8. Especially in the case of a switch point as transfer position U, in the region of the exit (or entry in the reverse direction of travel) a line section is present on which a guide structure 6 or driving coils 7, 8 can be arranged only on one side.

(21) A transport unit Tn is moved along the transport line, in this case initially the transport section Am. For this purpose, in the region of the transport unit Tn, that is to say in the region in which the excitation magnets 4, 5 of the transport unit Tn and driving coils 7, 8 can interact, the driving coils 7, 8 are supplied with a stator current i.sub.A, wherein the stator currents i.sub.A1, i.sub.A2 of these driving coils 7, 8 do not have to be the same. This is ensured by the associated segment control unit 11.sub.mi (see FIG. 9). The stator current i.sub.A1, i.sub.A2, or the propulsive force-forming components i.sub.Aq1, i.sub.Aq2 of the driving coils 7, 8, in co-operation with the excitation magnets 4, 5, generates the propulsive force F.sub.V acting on the transport unit Tn.

(22) The excitation-magnetic lateral forces F.sub.PMS1, F.sub.PMS2 always act on the transport unit Tn on both sides of the excitation magnets because of the co-operation of the excitation magnets 4, 5 of the transport unit Tn with ferromagnetic components of the guide structure 6. The excitation-magnetic lateral forces F.sub.PMS1, F.sub.PMS2 acting on both sides of the transport unit Tn are of equal magnitude and opposing directions in the normal case, with the same air gap, the same construction of the guide structure 6 on both sides, etc., so that the vectorial sum of the acting excitation-magnetic lateral forces F.sub.PMS1, F.sub.PMS2 is zero. In the ideal case the transport unit Tn is therefore free of lateral forces.

(23) The basis of the present invention is that the magnetic flux or the magnetic field between the transport unit Tn and the driving coils 7, 8 or the guide structure 6, which in the normal case is produced by the permanent magnets 4, 5, is influenced in a targeted manner in order to introduce a steering effect L into the transport unit Tn. For this purpose the current vector, which is responsible for the magnetic field, of the stator current i.sub.A of at least one driving coil 7, 8 is modified so that a propulsive force-forming and/or lateral force-forming electromagnetic force component is produced, which is superimposed on the propulsive force F.sub.V. In this case the objective is generally that the acting propulsive force F.sub.V, and thus the movement of the transport unit Tn, is not influenced.

(24) In a first embodiment of the invention, by means of the stator current i.sub.A, or the magnetic flux emanating therefrom (the magnetic flux and the stator current i.sub.A should be considered to be equivalent), not only the propulsive force F.sub.V required for the movement of the transport unit Tn is generated, but also a lateral force-forming electromagnetic force component F.sub.EMS, also referred to in the following as an electromagnetic lateral force, is generated. For this purpose a stator current i.sub.A is supplied to a driving coil 7, 8 co-operating with the transport unit Tn which, in addition to the propulsive force-forming electromagnetic force component which effects the propulsive force F.sub.V, produces also a force component transversely thereto, that is to say in the lateral direction. Thus, the electromagnetic lateral force F.sub.EMS is superimposed on the propulsive force F.sub.V. In this case the components .sub.d of the introduced electromagnetic field which produce the lateral force serve in practice to weaken or strengthen the acting excitation-magnetic field. Thus the transport unit Tn is acted on by the resulting lateral forces F1, F2, which are in each case produced as the sum of the acting excitation-magnetic lateral force F.sub.PMS and, if present, the electromagnetic lateral force F.sub.EMS on each side of the transport unit Tn, that is to say F.sub.1=F.sub.PMS1=F.sub.EMS1 and F.sub.2=F.sub.PMS2+F.sub.EMS2 (see FIG. 5).

(25) Wherever no electromagnetic lateral force F.sub.EMS is required, that is to say for example outside a transfer position U, the current vector of the stator currents i.sub.A1, i.sub.A2supplied to the driving coils 7, 8 is preferably controlled so that the vectorial sum of the resulting lateral forces F.sub.1, F.sub.2 is zero. In the ideal case this means that the electromagnetic lateral forces F.sub.EMS1, F.sub.EMS2 are equal to zero. Thus, in these regions a maximum efficiency of the movement of the transport unit Tn is achieved, since all of the energy flows into the generation of the propulsive force F.sub.V.

(26) In addition, in the entry region of the transfer position U (FIG. 4 above) the stator currents i.sub.A1, i.sub.A2 are preferably supplied on both sides so that the vectorial sum of the resulting lateral forces F.sub.1, F.sub.2, or the electromagnetic lateral forces F.sub.EMS1, F.sub.EMS2, is zero. The resulting lateral forces F.sub.1, F.sub.2, which are therefore reduced to the excitation-magnetic lateral forces F.sub.PMS1, F.sub.PMS2, are therefore of the same magnitude and in opposing directions in the entry region of the transfer position U in the normal case and thus cancel each other out.

(27) In the transfer region (middle of FIG. 4) of the transfer position U the stator currents i.sub.A1, i.sub.A2 which are supplied to the driving coils 7, 8 are now changed so that resulting lateral forces F.sub.1, F.sub.2 which differ in magnitude are produced on both sides of the transport unit Tn from weakening or strengthening of the permanent magnetic field. Since the magnetic flux is a function of the stator current vector i.sub.A, the magnetic flux component .sub.d responsible for the lateral force can be changed by changing of the current vector of the stator current i.sub.A on one side, or also on both sides, of the transport unit Tn, in order to generate the electromagnetic lateral force F.sub.EMS1, F.sub.EMS2 on at least one side. The magnetic flux is preferably changed so that the electromagnetic lateral forces F.sub.EMS1, F.sub.EMS2 on both sides of the transport unit Tn are directed in the same direction (FIG. 5). It is also possible to change the magnetic flux iv so that the electromagnetic lateral forces F.sub.EMS1, F.sub.EMS2 have different directions on both sides of the transport unit Tn, but these would partially cancel each other out, which would ultimately be associated with higher losses. If a plurality of driving coils 7, 8 simultaneously interact with the transport unit Tn, which is normally the case, then the magnetic flux of one of the acting driving coils 7, 8, or a plurality of the acting driving coils 7, 8 or also all of the acting driving coils 7, 8 can be changed. Likewise it is conceivable to generate an electromagnetic lateral force F.sub.EMS1, F.sub.EMS2 only on one side of the transport unit Tn. In this case only the generated resultant of the forces acting on the transport unit Tn is crucial.

(28) In the middle of FIG. 4, for example, the stator current i.sub.A1 of the driving coils 7 of the transport section Am, in the region of which the transport unit Tn is located, is controlled so that an electromagnetic lateral force F.sub.EMS1=f(i.sub.A1) is produced in one direction. On the opposite side the stator current i.sub.A2 of the driving coils 8 of the transport section Am, in the region of which the transport unit Tn is located, is controlled so that due to the magnetic flux component .sub.d an electromagnetic lateral force F.sub.EMS2=f(i.sub.A2) is produced in the same direction. Thus the lateral force F.sub.1 acting on one side is increased and the lateral force F.sub.2 acting on the other side is simultaneously decreased. However, it may be sufficient to generate an electromagnetic lateral force F.sub.EMS only on one side. Thus the transport unit Tn experiences a steering force F.sub.L resulting from the vectorial sum of the two lateral forces F.sub.1, F.sub.2, that is to say F.sub.L=F.sub.1+F.sub.2. In the illustrated exemplary embodiment the resulting steering force F.sub.L guides the transport unit Tn along the transport section Am, whereby the transport unit Tn is moved further straight ahead in the exit region of the transfer position U (bottom of FIG. 4).

(29) In this case the field weakening takes place on the side of the transport unit Tn along which the transport unit Tn is not to be moved further, in this instance on the driving coils 8. The field strengthening takes place on the side on which the transport unit Tn is to be moved further, in this instance on the driving coils 7.

(30) Thus it is obvious that, by control of the stator currents i.sub.A in the region of the transfer position, a steering force F.sub.L in one of the two lateral directions can be generated as a steering effect L which guides the transport unit Tn along the desired transport section Am or An. Hereby, however, it is possible to define not only the direction but in particular also the magnitude of this steering force F.sub.L any time during the movement of the transport unit Tn. This steering force F.sub.L can also be variable over time and can also be adapted to the respective transport unit Tn and also to the current movement. For example, a transport unit Tn laden with a heavier load or moving more quickly may require a higher steering force F.sub.L than an empty or slow-moving transport unit Tn.

(31) The stator currents i.sub.A1, i.sub.A2 of the driving coils 7, 8 are preferably controlled so that the propulsive force F.sub.V, required or predetermined by the higher-level system control unit 10 (FIG. 9) is maintained. Thus the advancing movement of the transport unit Tn remains unaffected by the generation of the steering effect L in the transfer position U. For example, in the exit region of the transfer position U (bottom of FIG. 4), at which only the driving coils 7 of one side are active, this may also mean that the q-component of the stator current i.sub.A1 which produces the propulsive force F.sub.V must be simultaneously increased in order to maintain the propulsive force F.sub.V. However, the propulsive force F.sub.V is generally set in any case by the position control of the transport unit Tn and therefore it is normally not necessary to intervene in this control of the propulsive force F.sub.V in the transfer position U.

(32) At the entry of the transport unit Tn into the transfer position U the active control of the lateral force-forming current components i.sub.Ad1, i.sub.Ad2 of the stator currents i.sub.A1, i.sub.A2 is started. It is not absolutely necessary that electromagnetic lateral forces F.sub.EMS1, F.sub.EMS2 are already generated at the entry on both sides of the transport unit Tn. However, the electromagnetic lateral forces F.sub.EMS1, F.sub.EMS2 must be controlled in the transfer region by the stator currents i.sub.A1, i.sub.A2 at any time so that the required steering force F.sub.L is produced in the desired direction and with the required magnitude. In order to ensure a defined position of the transport unit Tn over the entire length of the transfer position U it is, however, advantageous if the electromagnetic lateral forces F.sub.EMS1, F.sub.EMS2 are actively controlled on both sides along the entire length of the transfer position U.

(33) At the exit of the transport unit Tn from the transfer position U (bottom of FIG. 4) the air gap between the untraveled transport section An and the transport unit Tn is simultaneously increased. As a result the excitation-magnetic lateral force F.sub.PMS2 on this transport section An is substantially reduced, which assists the guiding of the transport unit Tn along the desired transport section Am. In particular this reduction of the excitation-magnetic lateral force F.sub.PMS2 could be sufficient in order to move the transport unit Tn in the exit region along the desired transport section Am. The driving coils 8 at the exit of the transfer position U would also no longer have to be actively controlled in order to generate an electromagnetic lateral force F.sub.EMS.

(34) However, the transfer position U does not have to be implemented as a switch point, but may also be implemented as a transfer from one transport section Am to another transport section An, such as for example the transfer position U1 in FIG. 1, where for example a transition from a two-sided transport section (driving coils on both sides) to a one-sided transport section (driving coils on one side) takes place. Such a situation is explained for example with reference to FIG. 6. In this case the entry, the transfer position and the exit can be controlled as in the case of a switch point according to FIG. 4. At the exit (bottom of FIG. 6) the excitation-magnetic lateral force F.sub.PMS2 on the transport section An is also reduced without active control of the lateral force-forming current component i.sub.Ad2 of the stator current i.sub.A2. On the opposite side of the transport section Am the electromagnetic lateral force F.sub.EMS1 can be maintained for guiding purposes (for example if the excitation-magnetic guiding alone is not reliably sufficient). This means that in this case it would be sufficient in principle if the electromagnetic lateral force F.sub.EMS is controlled on only one side in the region of the entry (top of FIG. 6) or the transfer region (middle of FIG. 6). It is not absolutely necessary to control the electromagnetic lateral forces F.sub.EMS1, F.sub.EMS2 simultaneously on both sides. The procedure could be similar in the case of a transition from a one-sided transport section to a two-sided transport section.

(35) Thus with the driving coils 7, 8 provided for the propulsion of the transport unit Tn the respective magnetic flux .sub.1, .sub.2 can be controlled in a transfer position U on both sides of the transport unit Tn by means of defining stator currents i.sub.A1, i.sub.A2, in order to generate a steering effect L which guides the transport unit Tn along one of the two transport sections Am, An in the transfer position. In this case the propulsive force F.sub.V can be maintained unchanged. This inventive idea can also be used in yet another advantageous way. This is explained with reference to FIG. 7.

(36) As already described in detail above, in the transfer position U two transport sections Am, An meet one another. By the supply of the stator currents i.sub.A1, i.sub.A2 the driving coils 7, 8 in co-operation with the excitation magnets 4, 5 on both sides of the transport line generate propulsive force-forming electromagnetic force components F.sub.EMV1, F.sub.EMV2, which add up to the total propulsive force F.sub.V of the transport unit Tn, that is to say F.sub.V=F.sub.EMV1+F.sub.EMV2. If the propulsive force-forming electromagnetic force components F.sub.EMV1, F.sub.EMV2 are of the same magnitude, the transport unit Tn is torque-free about a vertical axis of the transport unit Tn, on the assumption that it is constructed symmetrically about the longitudinal axis in the direction of movement. However, if the propulsive force-forming electromagnetic force components F.sub.EMV1, F.sub.EMV2 are of different magnitudes, a steering torque M.sub.L acts on the transport unit Tn about the vertical axis, as illustrated in FIG. 7. This steering torque M.sub.L can now likewise be used as a steering effect L for guiding the transport unit Tn along a desired transport section A.

(37) The propulsive force F.sub.V is normally controlled by means of the position s of the transport unit Tn along the transport line, so that the transport unit Tn is at the set position at any time. Thus the current speed and the acceleration of the transport unit Tn is also controlled indirectly.

(38) As is known, the propulsive force-forming electromagnetic force components F.sub.EMV1, F.sub.EMV2 result directly from the propulsive force-forming component i.sub.Aq1, i.sub.Aq2 of the respective introduced stator current i.sub.A1, i.sub.A2 by multiplication by a known force constant K.sub.f. Without restricting the generality it is assumed hereafter that the electrical components of the long stator linear motor are configured to be the same on both sides, so that the force constant K.sub.f is also of the same magnitude on both sides. This results in the propulsive force-forming electromagnetic force components F.sub.EMV1, F.sub.EMV2 to.sub.FEMV1=K.sub.f.Math.i.sub.Aq1 and F.sub.EMV2=K.sub.f.Math.i.sub.Aq2. The propulsive force-forming component i.sub.Aq1, i.sub.Aq2 of the respective introduced stator current i.sub.A1, i.sub.A2 are controlled in a controller by means of the position error E of the transport unit Tn, in order to generate the required propulsive force F.sub.V. In this case the position error E is given as the difference between a desired position s.sub.soll and an actual position s.sub.ist, E=s.sub.solls.sub.ist. In this case the actual position s.sub.ist is detected by known means. Thus F.sub.EMVj=K.sub.f.Math.i.sub.Aqj=K.sub.f.Math.K.Math.E=K.sub.f.Math.K (s.sub.j,solls.sub.j,ist) generally applies, with a control constant K. When it is also considered that the actual positions of the transport unit Tn must be the same on both sides, that is to say s.sub.1,ist=s.sub.2,ist, then it follows that F.sub.EMV1F.sub.EMV2=K.sub.f.Math.K.Math.(s.sub.1,solls.sub.2,soll).

(39) If the desired positions of the two sides of the transport unit Tn are modified in each case by a modification factor s.sub.1, s.sub.2, that is to say (s.sub.1,soll+s.sub.1 and s.sub.2,soll+s.sub.2), then a desired steering torque M.sub.L can be set by means of the modification factor. With the assumption s.sub.1,soll=s.sub.2,soll this then results in F.sub.EMV1F.sub.EMV2=K.sub.f.Math.K.Math.(s.sub.1s.sub.2) and the steering torque M.sub.L=(F.sub.EMV1F.sub.EMV2).Math.x=K.sub.f.Math.K.Math.(s.sub.1s.sub.2).Math.x.

(40) In a preferred embodiment the modification factor s/2 is added on one side and subtracted on the other side, resulting directly in the relationship F.sub.EMV1F.sub.EMV2=K.sub.f.Math.K.Math.(s.sub.1,solls.sub.2,soll+s). In this case the assumption s.sub.1,soll=s.sub.2,soll can be made again, since it is interveneb by means of the modification factor s and the result is F.sub.EMV1F.sub.EMV2=K.sub.f.Math.K.Math.s. If the distance between the centers of the two air gaps is designated by 2 (FIG. 7), the steering torque follows directly from M.sub.L=(F.sub.EMV1F.sub.EMV2).Math.x=K.sub.f.Math.K.Math.s.Math.x.

(41) The propulsive force F.sub.V of the transport unit Tn is controlled by the position control in the form of the desired position presetting s.sub.1,soll, s.sub.2,soll. By setting the modification factor s, or the modification factors s.sub.1, s.sub.2, propulsive force-forming electromagnetic force components F.sub.EMV1=K.sub.f.Math.K s/2 and F.sub.EMV2=K.sub.f.Math.K s/2 or F.sub.EMV1=K.sub.f.Math.K s.sub.1 and F.sub.EMV2=K.sub.f.Math.K s.sub.2 are generated which are superimposed on the original propulsive force-forming electromagnetic force components by the position control in the form of the desired position presetting s.sub.1,soll, s.sub.2soll and thus also on the propulsive force F.sub.V and which generate a desired steering torque M.sub.L. In this case it is naturally sufficient that a propulsive force-forming electromagnetic force component F.sub.EMV1, F.sub.EMV2 is superimposed on only one side in order to generate a steering torque M.sub.L.

(42) By the use of a modification factor s/2 it can be ensured in a simple manner that the propulsive force F.sub.V as the sum of the two propulsive force-forming electromagnetic force components F.sub.EMV1, F.sub.EMV2 is not influenced. Thus then the forward movement of the transport unit Tn is not influenced by the introduction of a steering torque M.sub.L.

(43) The steering torque M.sub.L can now be used as a steering effect L in a transfer position U in order to move the transport unit Tn along a desired transport section A, as is explained with reference to FIG. 8. A switch point is again shown there as a transfer position U. In the entry (top of FIG. 8) the propulsive force-forming electromagnetic force components F.sub.EMV1, F.sub.EMV2 are adjusted to the same value, resulting in s=0 and M.sub.L=0. In the transfer region (middle of FIG. 8), by setting the modification factors s.sub.1, s.sub.2 steering torque M.sub.L is generated as described above, leading to the transport unit Tn being guided along the transport section Am and moved further along the transport section Am. In the exit region of the transfer position (bottom of FIG. 8) the transport unit Tn can then be driven only on one side and moved further (as in FIG. 8), or a drive can be provided on both sides.

(44) Naturally the method using the steering force F.sub.L and the method using the steering torque ML can also be combined, as indicated in FIG. 8.

(45) The application of a sufficient steering force F.sub.L and/or of a sufficient steering torque M.sub.L naturally is in principle necessary only until the guide elements of the transport unit Tn, for example rollers, wheels, sliding surfaces, magnetic bearings, or the like, act reliably on the desired transport section A. Thus a defined position of the transport unit Tn is ensured and the active control of the driving coils 7, 8 for application of the steering effect L (steering force F.sub.L and/or steering torque M.sub.L) can be ended.

(46) The control concept for the transport device 1 and thus also for the transfer position U according to the invention will now be explained with reference to FIGS. 9 and 10.

(47) A higher-level control unit 10 is responsible for the movement of the transport units Tn in the long stator linear motor along the transport line. Thus the control unit 10 controls the movement of the transport units Tn, for example by the setting of desired position values s.sub.soll, and thus also controls the speed and acceleration of the transport units Tn. Likewise the higher-level control unit 10 is also responsible for guiding the transport unit Tn along the transport device 1 and thus also for steering the transport units Tn in transfer positions U. Thus the control unit 10 also controls the steering effect L acting on the transport unit Tn, for example by setting of desired values of the magnetic flux .sub.soll, and thus determines the transport line along which the transport units Tn move in the transport device 1. For each of the moving transport units Tn the higher-level control unit 10 sets corresponding desired values for the position s.sub.soll and the magnetic flux .sub.soll.

(48) A segment control unit 11n, 11.sub.n+1, which controls the driving coils 7, 8 of the respective transport segment TSn, TSn+1 individually with a stator current i.sub.A, is associated with each transport segment TSn, TSn+1, or generally with a group of driving coils 7, 8 or also with each driving coil 7, 8, of a transport section An. A separate segment control unit 11n, 11.sub.n+1 can of course be provided for the driving coils 7, 8 on each side, wherein the segment control units 11.sub.n, 11.sub.n+1 on each side can also be connected to one another by means of a data line and can exchange data with one another. Each segment control unit 11.sub.n, 11.sub.n+1 generates from the desired value settings for the position s.sub.soll and the magnetic flux .sub.soll a stator current i.sub.A which is supplied to the driving coils 7, 8. Preferably only the driving coils 7, 8 which interact with the transport unit Tn, or the excitation coils 4, 5 thereof, are controlled. The stator current i.sub.A is a current vector (current space vector) which comprises a propulsive force-forming component i.sub.Aq for generating the propulsive force F.sub.V and which causes a magnetic flux . In the transfer position U modified propulsive force-forming electromagnetic force components F.sub.EMV1, F.sub.EMV2 and/or lateral force-forming electromagnetic force components F.sub.EMS1, F.sub.EMS2 which cause the required steering effect L can be introduced by means of the current vectors i.sub.A1, i.sub.A2. Thus in co-operation with the excitation magnets 4, 5 of the transport unit Tn, as described, at any time the stator current vector i.sub.A generates the desired action on the transport unit Tn, in particular a propulsive force F.sub.V and potentially a steering effect L (steering force F.sub.L and/or steering torque M.sub.L).

(49) In a segment control unit 11, a steering controller RL for controlling the steering effect L and a position controller RP for controlling the position s are implemented for each driving coil 7, 8, as illustrated in FIG. 10. The control of the steering effect L is preferably active only in one transfer position U and takes place for example on the basis of the magnetic flux and a desired flux .sub.soll is set as described above. In general only the propulsive force F.sub.V is controlled outside a transfer position U. The current actual flux .sub.ist is measured or estimated by means of a suitable observer and is compared with the desired flux .sub.soll. In a transfer position U the steering controller RL compensates for the flux difference or the flux error e.sub.=.sub.ist in order to generate the desired steering effect L. For this purpose any suitable controller can be used. To this end the steering controller RL calculates for the controlled driving coil 7, 8 a lateral force-forming current component i.sub.Ad of the stator current i.sub.A and potentially also a modification factor s or s/2 (if a steering torque M.sub.L is also used as steering effect). The position controller RP compensates for a position error e.sub.s which results from the set desired position s.sub.soll and the current actual position s.sub.ist. The actual position s.sub.ist can be measured or can also be determined in some other suitable manner, for example again by a control engineering observer. At least in a transfer position U, when the steering torque M.sub.L is used as a steering effect L, the position error e.sub.s also includes the modification factor s. Thus the position error e.sub.s results for example as e.sub.s=s.sub.solls.sub.ist [s/2]. Any suitable controller can be used to compensate for the position error e.sub.s. For position control the position controller RP determines for the controlled driving coil 7, 8 a propulsive force-forming current component i.sub.Aq of the stator current i.sub.A. Thus both components of the stator current i.sub.A are present and the set stator current i.sub.A can be supplied to the controlled system, in this case the transport device 1 or the designated parts, in particular the controlled driving coil 7, 8.