Abstract:
A linear motor includes a primary part arranged as a guideway stator and at least one secondary part that is movable with respect to the primary part, the at least one secondary part having device(s) for controlling the generation of a magnetic field, causing its motion, in the primary part. It is possible to avoid costly control devices for the application of current to the stator.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a linear motor having a primary part developed as a guideway stator and at least one secondary part, as well as a method for operating a corresponding linear motor. 
       BACKGROUND INFORMATION 
       [0002]    Linear motors which work according to the synchronization principle have a primary part developed as a guideway stator on which a secondary part is situated in a freely movable manner. For the propulsion of the secondary part, a traveling magnetic field is generated which moves the secondary part, that is developed using magnets, along by magnetic reciprocal action. 
         [0003]    The generation of the traveling field in the stator windings takes place by feeding in a three-phase current of variable frequency which determines the speed of the motion. 
         [0004]    The guideway stator is subdivided into individual segments, which each have connected windings. At the connecting points of the segments current-supplying devices are situated, which respectively apply current to the connected segments, which is necessary for the motion. 
         [0005]    This form of construction requires a costly design and control of the individual current-supplying devices. 
         [0006]    For instance, in German Published Patent Application No. 39 00 511, a linear motor is described having a primary part that has stator poles arranged in series and a secondary part that is movable alongside the primary part. 
         [0007]    The coils of the guideway stator have current applied to them by power converters whose frequency and amplitude are controllable by an electronic controller which takes into account the current residence locale of the secondary part, in order to move the secondary part on the primary part. For the propulsion, segments of the primary part are supplied with current by the external control device, whereupon all the secondary parts, which are on one segment of the primary part at this time, move away uniformly. 
         [0008]    German Published Patent Application No. 199 22 441 describes a method and a device for operating a magnetic vehicle having a synchronous guideway stator linear motor. A costly, controller is described which controls the supplying of current to the individual winding sections, and with that also the propulsion of the secondary parts. Secondary parts which are located in a similarly controlled region, that can also be composed of several winding sections or segments, are in turn moved away uniformly. 
         [0009]    The suitable energizing of the coils or windings of the stator is connected with great expenditure, especially if several secondary parts are supposed to move independently of one another on a guideway stator, which can also be an extended rail system. Oppositely directed propulsion of secondary parts is not possible within one stator segment in the shown related art. 
       SUMMARY 
       [0010]    Example embodiments of the present invention provide a simple control for applying current to stator windings. 
         [0011]    A linear motor according to example embodiments of the present invention, which is particularly able to work according to the synchronization principle, has a primary part arranged as a guideway stator and at least one secondary part, that is movable with respect to the primary part, which has device(s) for controlling the generation of a magnetic field, causing its propulsion, in the primary part. It is therefore possible to avoid costly control devices associated with the guideway stator for supplying current to the stator windings. A spatially distributed magnetic alternating field that moves along the stator, the so-called traveling field, is required for the propulsion of the secondary part. 
         [0012]    A linear motor according to example embodiments of the present invention may be provided with a primary part having a number of side-by-side mounted individual coils, the individual coils being able to have current applied to them independently of one another for the generation of a magnetic field, the magnetic field causing the motion of the at least one secondary part being generated in the primary part using the application of current to the individual coils. This permits applying current only to the individual coils that are located in the immediate vicinity or within the sphere of influence of the at least one secondary part, and with that, an independent motion of the secondary parts. 
         [0013]    The at least one secondary part of a linear motor may control the generation of the magnetic field, causing its motion, in the primary part, using a control field distributed along the propulsion direction. The control field corresponds to a setpoint field and can be determined either by a control device that is located on the secondary part or can be supplied to the secondary part from the outside. It may portray spatially the drive field required for the propulsion, and is therefore an alternating field, in particular, a sinusoidal alternating field. 
         [0014]    The control field provided by the at least one secondary part of the linear motor may be locally measured when associated with a single coil, and the measured value is used as the current setpoint value for this individual coil. In the case of a magnetic control field, there is the option of assigning magnetic field sensors to the individual coils. 
         [0015]    The at least one secondary part may provide a magnetic field as the control field. This provided magnetic field can be detected in a simple manner by magnetic field sensors, such as Hall sensors, that are positioned along the primary part. The strength of the detected magnetic field is used as the current setpoint value for applying current to the individual coil. 
         [0016]    This magnetic control field can be generated by transmitting coils situated on the secondary part. The shape (for instance, sinusoidal) of the control field is determined by an appropriate design and the suitable positioning of the transmitting coils. The feed force is a function of the strength of the drive field, which is determined by the amplitude of the control field. In this example embodiment, the signal processing on the secondary part only has to provide one unidimensional setpoint current value, and inject this as exciting current into the transmitting coils. This results in a drive field generated by the individual coils of the stator within the sphere of influence of the secondary part. 
         [0017]    The at least one secondary part of a linear motor may make available an electrical field as control field. An electrical field can be used to avoid in a simple manner the influence on the detection by the magnetic drive field. 
         [0018]    In an example embodiment of a linear motor, the generation of the magnetic field causing the motion may be controlled in the primary part using electromagnetic waves that are, in particular, modulated. The wavelength and/or the polarization of the electromagnetic waves may be used for the control. In this context, the sign of the setpoint current can be represented particularly by different wavelengths or directions of polarization. 
         [0019]    In a method for operating a linear motor, having a secondary part developed as a guideway stator, and at least one secondary part that is movable with respect to the primary part, the generation of a magnetic field causing the motion is controlled in the primary part by the at least one secondary part. 
         [0020]    In the method, a linear motor described herein may be used. For the control, one may use the possibilities that are described in connection with the linear motor. 
         [0021]    Further features and aspects of example embodiments of the present invention are described in more detail below with reference to the appended Figures. 
         [0022]    It goes without saying that the features indicated above, or that are yet to be clarified in the following, are usable not only in the combination specified in each instance, but also in other combinations or by themselves, without departing from the scope hereof. 
         [0023]    Hereinafter, example embodiments of the present invention and particularly its advantages will be explained in greater detail on the basis of an illustrated exemplary embodiment shown in the figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0024]      FIG. 1  is a schematic top view of a linear motor according to an example embodiment of the present invention; 
           [0025]      FIG. 2  is a schematic side view in cross section along the center axis of  FIG. 1 ; and 
           [0026]      FIG. 3  is a schematic side view of the linear motor of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION  
       [0027]    A linear motor according to an example embodiment of the present invention shown in  FIG. 1  has a primary part  100  and a secondary part  200 . Primary part  100  has two drive rails  101  and  102  that are essentially designed identically. Magnetic field sensors  120   a ,  120   b , etc. are situated on the center axis of the primary part. It should be understood that the specifically shown positioning is only to be seen as an example. 
         [0028]    Drive rail  101  has individual coils  110   a ,  110   b , etc., and drive rail  102  has individual coils  111   a ,  111   b , etc. The opposite individual coils  110   a  and  111   a ,  110   b  and  111   b , etc., are aligned coaxially with respect to magnetic field sensors  120   a ,  120   b , etc., other arrangements being also able to be selected besides this one. It should be understood that the drive rails, depending on their length, can have a plurality of individual coils and magnetic field sensors above and beyond the number shown. 
         [0029]    Each individual magnetic field sensor  120   a ,  120   b , etc., is responsible for the control of the application of current to each respective individual coil pair  110   a  and  111   a ;  110   b  and  111   b , etc. 
         [0030]    For example, magnetic field sensor  120   a  controls the application of current of individual coils  110   a  and  111   a , etc. 
         [0031]    Additional device(s) for energizing, such as amplifier circuits, current sources, etc., are provided, which are not shown in detail, however, for the sake of clarity. 
         [0032]    Secondary part  200  has travel rails  201  and  202  associated with drive rails  101  and  102 . Besides that, the secondary part has control coils  220   a  through  220   d , which enter into operative connection with magnetic field sensors  120   a ,  120   b , etc., via a generated controlled field. 
         [0033]    Travel rails  201  and  202  have individual permanent magnetic sections  210   a  through  210   e  and  211   a  through  211   e . Secondary part  200  can move freely on primary part  100  along drive rails  101  and  102 . The magnetic operative connection of drive rails  101 ,  102  with travel rails  201 ,  202  provides the feed functionality of the linear motor. The support and guidance of secondary part  200  on primary part  100  is not shown in greater detail. It can be managed, for instance, by additional magnetic rails or rollers. 
         [0034]      FIG. 2  shows a cross sectional view of the linear motor described above, along its center axis. Primary part  100  is situated underneath secondary part  200 . 
         [0035]    Magnetic field sensors  120   a  through  120   i  are situated on primary part  100 , at regular intervals. Control coils  220   a  through  220   d  are situated on primary part  200  at regular intervals. The regular spacing of the control coils does not correspond to the regular spacing of the magnetic field sensors, in this example embodiment. 
         [0036]    The subdivisions between permanent magnet sections  210   a  through  210   e  and  211   a  through  211   e  ( FIGS. 1 and 3 ) may be aligned along the centers of control coils  220   a  through  220   d.    
         [0037]    Secondary part  200  has a control device  230  which is connected to control coils  220   a  through  220   d  via a connection  240 , especially a cable, and which is able to apply current to the control coils. 
         [0038]    In the figure shown, the control coils have current applied to them whose direction is indicated both by the arrow in control unit  230  and by the arrow on connection  240 . In this current direction, control coils  220   a  and  220   c  form a magnetic north pole at their lower side, and control coils  220   b  and  220   d  form a magnetic south pole at their lower side. 
         [0039]    Between control coils  220   a  through  220   e  a magnetic alternating field is created which is designated as control field  250 . The spatial distribution of control field  250  is specified by the geometry and the situation of control coils  220   a  through  220   d . The amplitude of magnetic control field  250  is specified by the amplitude of the current which the control coils have applied to them. The control unit controls the amplitude of the current through the control coils. 
         [0040]    Control field  250 , which is shown by the field lines in the figure, enters into operative connection with magnetic field  120   a ,  120   b , etc. The intensity of the magnetic field recorded in the magnetic field sensors is a function of the distance of the magnetic field sensors from control coils  220   a  through  220   d.    
         [0041]    In this example, magnetic field sensors  120   c  and  120   f  are permeated by strong magnetic fields, substantially vertically from top to bottom, whereas magnetic field sensors  120   d ,  120   e ,  120   g  and  120   h  are permeated by weaker magnetic fields, slantwise from bottom to top. The respectively recorded magnetic field strength in the vertical direction (or rather, the vertical component of the field) is used for controlling the application of current to the associated individual coils  110   a ,  110   b , etc., as well as  111   a ,  111   b , etc. Because of the sinusoidal development of the control field, a corresponding sinusoidal development of the drive field is achieved. 
         [0042]      FIG. 3  shows a side view of the example embodiment. Travel rail  201  of secondary part  200  is adjacent to drive rail  101  of primary part  100 . 
         [0043]    Drive rail  101  has individual coils  110   a  through  110   h , whose respective current application is controlled by magnetic field sensors  120   a  through  120   h  (not shown in  FIG. 3 ). Travel rail  201  is made up of permanent magnet sections  210   a  through  210   e.    
         [0044]    Sections  210   a ,  210   c  and  210   e  may have identical magnetic polarity, which is opposite to the polarity of sections  210   b  and  210   e . In the example shown, sections  210   a ,  210   c ,  210   e  have a magnetic north pole, whereas sections  210   b  and  210   d  have a magnetic south pole. The magnetic field that starts from sections  210   a  through  210   e  is designated here as a permanent field. 
         [0045]    The application of current to individual coils  110   a  through  110   h  is controlled by magnetic field sensors  120   a  through  120   h , according to the manner shown in  FIG. 2  and described. According to that, individual coils  110   a  through  110   h  have current applied to them in such a way that coils  110   c ,  110   f  develop a magnetic north pole field and coils  110   b ,  110   d ,  110   e ,  110   h  develop a magnetic south pole field of different strengths, and, in the overall picture, a substantially sinusoidal magnetic drive field or traveling field is created. 
         [0046]    The operative connection of the magnetic drive field with the permanent field sets secondary part  200  in the motion indicated by arrow A, with respect to primary part  110 . The control field is moved along with the secondary part. The motion of the control field leads to a propulsion of the drive field, also along direction A, whereby, in turn, the secondary part is moved further. 
         [0047]    The feed force (acceleration) of the secondary part is a function of the strength of the drive field, which is specified by the strength of the current applied to individual coils  110   a  through  110   h . As was explained, this current strength is specified by the strength of the control field, which depends on the current given off by control device  230  to control coils  220   a  through  220   d . A change in the speed of motion can consequently be provided in a simple manner by a change in the current that is output by control unit  230 . 
         [0048]    A change in the direction of motion can be provided in the same manner, by a simple change in the current direction by control coils  220   a  through  220   d . Using such a change in the current direction, the polarity of the control field, and thus the polarity of the drive field, reverse themselves. Since the polarity of the permanent field is maintained, there is a resultant change in the direction of motion. 
         [0049]    It should be understood that in the figures shown, only an example embodiment of the linear motor is shown. Besides that, any other specific embodiment is possible, particularly due to a different positioning of the drive rails, positioning of the individual coils, positioning of the travel rails, construction and positioning of the control coils, positioning of the magnetic field sensors, etc., without leaving the scope hereof.