Modular conveyor system having multiple moving elements under independent control

Abstract

The modular conveyor system comprises N interconnected track sections, forming a continuous track, wherein each track section features a plurality of individually controlled coils stretching along the length thereof. Plural pallets, each having thrust producing magnets, travel independently alone the track. The track also comprises multiple linear encoder readers spaced at fixed positions therealong, and each pallet includes a linear encoder strip having a length R greater than the spacing E between the readers. Track section controllers associate the encoder strips with only one reader at any time in order to resolve the position of the pallets based on the fixed position of the readers and the relative positions of the strips in relation thereto. The section controllers also regulate and commutate the coils of the corresponding track sections in order to independently control each pallet. Communication links interface adjacent section controllers situated in adjacent track sections. The electromagnetic structure and distributed control architecture of the conveyor system enable it to independently control multiple practical pallets yet be constructed out of modular track sections, with little practical restriction on the length of the conveyor system or the number of pallets controlled thereby.

1. Apparatus for detecting the position of a moving element relative to a stationary element, said apparatus comprising:
 a plurality of linear encoder readers spaced generally along the stationary element at fixed positions relative thereto;  
 a device readable by the linear encoder readers, the readable device being mounted on the moving element and having a length which is greater than the spacing between any given pair of adjacent linear encoder readers;  
 a guide for aligning the readable device in order to interact with the linear encoder readers; and  
 circuitry, connected to each linear encoder reader, for associating the readable device with only one linear encoder reader in a state of interaction with the readable device at any time and for resolving and providing a reading of the overall position of the moving element based on the fixed position of the associated linear encoder reader and a relative position of the readable device in relation to the associated linear encoder reader;  
   wherein, in a condition where the readable device is associated with a given linear encoder reader and simultaneously begins to interact with an adjacent linear encoder reader, the circuitry is operative to switch the association of the readable device with the given linear encoder reader to the adjacent linear encoder reader once the readable device has reached a pre - specified distance through one of the given linear encoder reader and the adjacent linear encoder reader, the circuitry being operative to initialize the adjacent linear encoder reader prior to the interaction of the readable device with the adjacent linear encoder reader .  
 
     
     
       2. Apparatus according to  claim 1 , wherein the readable device is an optical strip or a magnetic strip and the linear encoder readers respectively comprise optical read heads or magnetic detectors. 
     
     
       3. Apparatus according to  claim 1 , wherein the linear encoder readers are substantially equidistantly spaced along the stationary element and the readable device has a length which is greater than the spacing between adjacent linear encoder readers and less than the spacing between three linear encoder readers. 
     
     
       4. Apparatus according to  claim 1 , wherein, in a condition where the readable device is associated with a given linear encoder reader and simultaneously begins to interact with an adjacent linear encoder reader, the circuitry is operative to switch the association of the readable device with the given linear encoder reader to the adjacent linear encoder reader once the readable device has reached a pre-specified distance through one of the given linear encoder reader and the adjacent linear encoder reader. 
     
     
       5. Apparatus according to  claim 4 , wherein the circuitry is operative to initialize the adjacent linear encoder reader prior to the interaction of the readable device with the adjacent linear encoder reader. 
     
     
       6. Apparatus according to claim  4    1 , wherein, immediately after the association of the readable device is switched to the adjacent linear encoder reader, the circuitry is operative to require the readable device to backtrack for at least a minimum distance before the association of the readable device is switched back to the given linear encoder reader, to thereby provide a hysteresis effect. 
     
     
       7. Apparatus for detecting the positions of plural moving elements relative to a stationary element, said apparatus comprising:
 a single row of linear encoder readers spaced generally along the stationary element at fixed positions relative thereto;  
 a device readable by the linear encoder readers mounted on each moving element, each readable device having a length which is greater than the spacing between any given pair of adjacent linear encoder readers;  
 a guide for aligning the readable devices in order to interact with the single row of linear encoder readers; and  
 circuitry, connected to each linear encoder reader, for associating any given readable device with only one linear encoder reader at any time and for resolving and providing a reading of the overall position of the corresponding moving element based on the fixed position of the associated linear encoder reader and a relative position of the given readable device in relation to the associated linear encoder reader;  
   wherein, in a condition where a given readable device is associated with a given linear encoder reader and simultaneously begins to interact with an adjacent linear encoder reader, the circuitry is operative to switch the association of the given readable device with the given linear encoder reader to the adjacent linear encoder reader once the given readable device has reached a pre - specified distance through one of the given linear encoder reader and the adjacent linear encoder reader .  
 
     
     
       8. Apparatus according to  claim 7 , wherein the readable device is an optical strip or a magnetic strip and the linear encoder readers respectively comprise optical read heads or magnetic detectors. 
     
     
       9. Apparatus according to  claim 7 , wherein the linear encoder readers are substantially equidistantly spaced along the stationary element and each readable device has a length which is greater than the spacing between adjacent linear encoder readers and less than the spacing between three linear encoder readers. 
     
     
       10. Apparatus according to  claim 7 , wherein each moving element is sized longer than its corresponding readable device in order to preclude readable devices of adjacent moving elements from interacting with the same linear encoder reader. 
     
     
       11. Apparatus according to  claim 7 , wherein, in a condition where a given readable device is associated with a given linear encoder reader and simultaneously begins to interact with an adjacent linear encoder reader, the circuitry is operative to switch the association of the given readable device with the given linear encoder reader to the adjacent linear encoder reader once the given readable device has reached a pre-specified distance through one of the given linear encoder reader and the adjacent linear encoder reader. 
     
     
       12. Apparatus according to claim  11    7 , wherein the processing circuitry is operative to initialize the adjacent linear encoder reader prior to the interaction of the given readable device with the adjacent linear encoder reader. 
     
     
       13. Apparatus according to claim  11    7 , wherein, immediately after the association of the given readable device is switched to the adjacent linear encoder reader, the circuitry requires the given readable device to backtrack for at least a minimum distance before the association of the given readable device is switched back to the given linear encoder reader, to thereby provide a hysteresis effect. 
     
     
       14. A moving- magnet type linear motor, comprising:      a plurality of moving elements traveling along a track;        a stator armature provided substantially along the entire traveling track of moving elements;        wherein each moving element travels separately and independently and comprises n permanent magnets disposed face to face with the stator armature, said magnets being arranged in alternating North and South sequence and having a pole pitch P;        wherein the stator armature comprises a plurality of individual coils arranged in a substantially continuous sequence of individual polyphase - like sets, each set comprising p overlapping coils having centers thereof spaced apart by a distance P/p, wherein p>= 2 ; and        a servocontrol system for regulating and commutating the coils so as to produce a separate moving MMF for each moving element and independently control each moving element.     
     
     
       15. A linear motor according to  claim 14 , wherein the electrical pole pitch of each coil is P. 
     
     
       16. A linear motor according to  claim 14 , wherein n= 2 . 
     
     
       17. A linear motor according to  claim 14 , wherein p= 2 . 
     
     
       18. A linear motor according to  claim 14 , wherein the stator armature comprises a yoke having a plurality of slots orientated substantially normal to the track, wherein each coil comprises two legs, and wherein each coil leg is spatially distributed over a plurality of yoke slots. 
     
     
       19. A linear motor according to  claim 18 , wherein the width of each coil leg is sized so that there are substantially no unfilled yoke slots in each polyphase- like coil set.   
     
     
       20. A linear motor according to  claim 19 , wherein the width of each coil leg is substantially equal to the width of each moving element magnet. 
     
     
       21. A linear motor according to  claim 19 , wherein there are substantially no unfilled yoke slots in an inter- coil set region.   
     
     
       22. A linear motor according to  claim 14 , wherein said servocontrol system includes a moving- element position - detecting means, comprising:      a single row of linear encoder readers spaced generally along the stator armature at fixed positions relative thereto;        a device readable by the linear encoder readers mounted on each said moving element, each readable device having a length which is greater than the spacing between any given pair of adjacent linear encoder readers;        guide means for aligning the readable devices in order to interact with the single row of linear encoder readers; and        plural processing means, for associating any given readable device with only one linear encoder reader at any time and for resolving and providing a reading of the overall position of the corresponding moving element based on the fixed position of the associated linear encoder reader and a relative position of the given readable device in relation to the associated linear encoder reader.     
     
     
       23. A linear motor according to  claim 22 , wherein the servocontrol system comprises:
   a trajectory generator providing a position set point signal for each moving element;        a position compensator, connected to the moving - element position - detecting means and the trajectory generator, providing a position error minimizing signal for each moving element; and        a commutation controller, connected to the moving - element position - detecting means and the position compensator, for determining which of the coils are situated underneath each moving element and providing a current set point signal for those coils in accordance with the position error minimizing signal associated with each moving element; and        current control loop means, connected to the commutation controller, for regulating the coils in accordance with the current set point signals.     
     
     
       24. A linear motor according to  claim 23 , wherein said trajectory generator provides means to avoid collisions between adjacent moving elements. 
     
     
       25. A modular conveyor system, comprising:
   n interconnected track sections, forming a substantially continuous track, wherein each track section comprises a stator armature having a plurality of individually controllable coils disposed substantially along the entire length of the track section;        a plurality of moving elements traveling separately and independently along the continuous track, each moving element having at least two thrust producing magnets arranged in alternating North and South sequence and disposed face to face with the stator armatures of the track sections;        n track section controllers, one per track section, for regulating and commutating the coils of the corresponding stator armature in order to produce a separate moving MMF for each moving element located in the corresponding track section and independently control each moving element located therein; and        communication means for interfacing the section controllers of adjacent track sections, wherein a given section controller is operative to utilize the communication means in order to transfer a servo responsibility for resolving the position of a given moving element to an adjacent section controller when the given moving element straddles the corresponding track sections, and wherein each of the given and adjacent section controller pair provides at least one coil regulating signal to the other of said pair in the event any portion of the magnets of the given moving element spans any portion of at least one coil situated in the track section corresponding to the other of said pair, provided that the responsibility for resolving the position of the given moving element has not yet been transferred to the other of said pair.     
     
     
       26. A modular conveyor system according to  claim 25 , wherein the communication means comprises a peer- to - peer network.   
     
     
       27. A modular conveyor system according to  claim 25 , further comprising a central controller connected to each of the section controllers for initializing the section controllers. 
     
     
       28. A modular conveyor system according to  claim 25 , further comprising at least one station controller directly connected to at least one of the section controllers, wherein the at least one station controller provides movement commands to the at least one section controller in respect of at least one of the moving elements located in the corresponding track section. 
     
     
       29. A modular conveyor system according to  claim 25 , wherein:
   the magnets of each moving elements have a pole pitch P;        the electrical pole pitch of each of the coils is P; and        the coils of each track section stator armature are arranged in a substantially contiguous sequence of individual polyphase - like sets, each set comprising p overlapping coils having centers thereof spaced apart by a distance P/p, where p>= 2 , and wherein coils associated with one track section do not overlap onto an adjacent track section.     
     
     
       30. A modular conveyor system according to  claim 25 , wherein:
   each track section comprises a single row of linear encoder readers spaced at fixed positions there along;        each moving element includes a device readable by the linear encoder readers mounted thereon, each readable device having a length which is greater than the spacing between any given pair of adjacent linear encoder readers; and        each section controller provides a moving - element position - detection processing means for associating any given readable device of a moving element located in the corresponding track section with only one linear encoder reader located therein at any time and for resolving the position of the corresponding moving element based on the fixed position of the associated linear encoder reader and a relative position of the given readable device in relation to the associated linear encoder reader.     
     
     
       31. A modular conveyor system according to  claim 30 , wherein each moving element is sized longer than its corresponding readable device in order to preclude readable devices of adjacent moving elements from interacting with the same linear encoder reader. 
     
     
       32. A modular conveyor system according to  claim 30 , wherein, immediately after the association of the given readable device is switched to the adjacent linear encoder reader, the position- detecting processing means is operative to require the given readable device to backtrack for at least a minimum distance before the association of the given readable device is switched back to the given linear encoder reader, to thereby provide a hysteresis effect.   
     
     
       33. A modular conveyor system according to  claim 30 , wherein each section controller comprises:
   a trajectory generator providing a position set point signal for each moving element located in the corresponding track section;        a position compensator, connected to the moving - element position - detecting processing means and the trajectory generator, providing a position error minimizing signal for each such moving element; and        a commutation controller, connected to the moving - element position - detecting processing means and the position compensator, for determining which of the coils in the corresponding track section are situated underneath each such moving element and for providing a current set point signal for such coils in accordance with the position error minimizing signal associated with each such moving element; and        current control loop means, connected to the commutation controller, for regulating the coils located in the corresponding track section in accordance with the current set point signals.     
     
     
       34. A modular conveyor system according to  claim 30 , wherein, in a condition where a readable device is associated with a first linear encoder reader in a first track section and simultaneously begins to interact with a second, adjacent linear encoder in a second, adjacent track section, the section controller corresponding to the first track section transfers the servo responsibility for resolving the position of the corresponding moving element to the section controller associated with the second, adjacent track section once the readable device has reached a pre- specified distance through one of the first and second linear encoder readers.   
     
     
       35. A modular conveyor system according to  claim 34 , wherein the coil regulating signals include:
 ( a )  the measured position of the given moving element, and      ( b )  one of:  
 ( i )  the position error minimizing signal, and    
 ( ii )  the current set point signals for the spanned coils.   
   
     
     
       36. A modular conveyor system according to  claim 25 , wherein the given section controller is operative to transfer static data concerning the straddling moving element to the adjacent section controller prior to the transfer of the servo responsibility for resolving the position of the straddling moving element. 
     
     
       37. A modular conveyor system according to  claim 36 , wherein the given section controller is operative to transfer dynamic or memory based servocontrol data concerning the straddling moving element to the adjacent section controller substantially simultaneously with the transfer of the servo responsibility for resolving the position of the straddling moving element. 
     
     
       38. A modular conveyor system according to  claim 25 , wherein the given section controller is operative to bi- directionally transfer static, dynamic or memory - based data to an external device via a dedicated communication port, independent of any other section controller.   
     
     
       39. A modular conveyor system, comprising:
   n interconnected track sections, forming a substantially continuous track, wherein each track section comprises a stator armature having a plurality of individually controlled coils disposed substantially along the entire length of the track section, and wherein each track section comprises a plurality of linear encoder readers spaced at fixed positions there along;        a plurality of moving elements traveling separately and independently along the continuous track, each moving element having a plurality of thrust producing magnets arranged in alternating North and South sequence and disposed face to face with the stator armatures of the track sections, each moving element including a linear encoder strip having a length greater than the spacing between any given pair of adjacent linear encoder readers, the length of each moving element being sized to prevent linear encoder strips from adjacent moving elements to interact with the same linear encoder readers;        n track section controllers, one per track section, each section controller providing:    ( a )  position - detection processing means for associating any given linear encoder strip of any moving element located in the corresponding track section with only one linear encoder reader located therein at any time and for resolving the position of such moving element based on the fixed position of the associated linear encode reader and a relative position of the given linear encoder strip in relation to the associated linear encoder reader, and      ( b )  servo means, connected to the position - detection processing means, for regulating and commutating the coils of the corresponding stator armature in order to produce a separate moving MMF for each moving element located in the corresponding track section to thereby independently control each such moving element; and          communication means for interfacing the section controllers of adjacent track sections, wherein a given section controller is operative to utilize the communication means in order to transfer a responsibility of resolving the position of a given moving element to an adjacent section controller when the given moving element straddles the corresponding track sections, and wherein each of the given and adjacent section controller pair provides at least one coil regulating signal to the other of said pair in the event any portion of the magnets of the given moving element spans any portion of at least one coil situated in the track section corresponding to the other of said pair, provided that the responsibility for resolving the position of the given moving element has not yet been transferred to the other of said pair.     
     
     
       40. A modular conveyor system according to  claim 39 , wherein said servo means comprises:
   a trajectory generator providing a position set point signal for each moving element located in the corresponding track section;        a position compensator, connected to the trajectory generator, providing a position error minimizing signal for each such moving element;        a commutation controller, connected to the position compensator, for determining which coils located in the corresponding track section are situated underneath each such moving element and providing a current set point signal for such coils in accordance with the position error minimizing signal associated with each such moving element; and        current control loop means, connected to the commutation controller, for regulating the coils in accordance with the current set point signals.     
     
     
       41. A modular conveyor system according to  claim 40 , wherein said coil regulating signals include:
 ( a )  the measured position of the given moving element, and      ( b )  one of:  
 ( i )  the position error minimizing signal in respect of the given moving element, and    
 ( ii )  at least the current set point signal in respect of each such spanned coil.   
   
     
     
       42. A modular conveyor system according to  claim 39 , wherein, in a condition where an aforesaid linear encoder strip is associated with a first linear encoder reader in a first track section and simultaneously begins to interact with a second, adjacent linear encoder in a second, adjacent track section, the section controller corresponding to the first track section transfers the responsibility for resolving the position of the corresponding moving element to the section controller associated with the second, adjacent track section once the linear encoder strip has reached a pre- specified distance through one of the first and second linear encoder readers.   
     
     
       43. A modular conveyor system according to  claim 39 , wherein the given section controller is operative to transfer static data concerning the straddling moving element to the adjacent section controller prior to the transfer of the responsibility for resolving the position of the straddling moving element. 
     
     
       44. A modular conveyor system according to  claim 39 , wherein the given section controller is operative to transfer dynamic or memory based servocontrol data concerning the straddling moving element to the adjacent section controller substantially simultaneously with the transfer of the responsibility for resolving the position of the straddling moving element. 
     
     
       45. A modular conveyor system according to  claim 39 , wherein the given section controller is operative to bi- directionally transfer static, dynamic or memory - based data to an external device via a dedicated communication port, independent of any other section controller.   
     
     
       46. A modular conveyor system, comprising:
   a plurality of interconnectable track sections, each track section having a respective track section controller for regulating and commutating a plurality of individually controllable coils disposed along the length of its respective track section to provide a separate moving magneto - motive force to any one of a plurality of separately and independently moving elements traveling along the track section, each track section controller including bidirectional communication means for interfacing with section controllers of adjacent track sections to transfer servo responsibility for a given moving element to an adjacent track section controller, and including position detecting means for detecting the position of each moving element traveling thereon.     
     
     
       47. Apparatus for detecting the position of moving elements relative to a stationary element in a conveyor system, comprising:
   a plurality of position detecting sensors spaced generally along the stationary element at fixed positions relative thereto;        position - indicating means mounted on said moving elements detectable by said sensors; and        circuitry connected to each position detecting sensor for resolving and providing readings of the position of each moving element;      
       
         said conveyor system comprising:  
         
           a track;  
         
         
           a plurality of said moving elements traveling separately and independently along said track, wherein said conveyor system comprises:  
           
             said track, formed from n interconnected track sections, forming a substantially continuous track, wherein each track section comprises a stator armature having a plurality of individually controllable coils disposed substantially along the entire length of the track section;  
           
           
             said moving elements each having at least two thrust producing magnets arranged in alternating North and South sequence and disposed face to face with the stator armatures of the track sections;  
           
           
             n track section controllers, one per track section, for regulating and commutating the coils of the corresponding stator armature in order to produce a separate moving MMF for each moving element located in the corresponding track section and independently control each moving element located therein; and  
           
           
             communication means for interfacing the section controllers of adjacent track sections, wherein a given section controller is operative to utilize the communication means in order to transfer a servo responsibility for resolving the position of a given moving element to an adjacent section controller when the given moving element straddles the corresponding track sections, and wherein each of the given and adjacent section controller pair provides at least one coil regulating signal to the other of said pair in the event any portion of the magnets of the given moving element spans any portion of at least one coil situated in the track section corresponding to the other of said pair, provided that the responsibility for resolving the position of the given moving element has not yet been transferred to the other of said pair. 
           
         
       
     
     
       48. Apparatus for detecting the position of moving elements relative to a stationary element, in combination with a moving- magnet type linear motor, said apparatus comprising:      a plurality of position detecting sensors spaced generally along the stationary element at fixed positions relative thereto;        position - indicating means mounted on said moving elements detectable by said sensors; and        circuitry connected to each position detecting sensor for resolving and providing readings of the position of each moving element;      
       
         said linear motor comprising:  
         
           a stator armature provided substantially along the entire traveling track of moving elements;  
         
         
           wherein each moving element travels separately and independently and comprises n permanent magnets disposed face to face with the stator armature, said magnets being arranged in alternating North and South sequence and having a pole pitch P;  
         
           wherein the stator armature comprises a plurality of individual coils arranged in a substantially contiguous sequence of individual polyphase - like sets, each set comprising p overlapping coils having centers thereof spaced apart by a distance P/p, where p>= 2 ; and    
         
           a servocontrol system for regulating and commutating the coils so as to produce a separate moving MMF for each moving element and independently control each moving element.