Patent Publication Number: US-2022229123-A1

Title: Position measuring mechanism and measuring method of linear motion system

Description:
BACKGROUND OF THE INVENTION 
     Field of Invention 
     The invention relates to position measurement technology, and more particularly to a position measuring mechanism and a measuring method of a linear motion system. 
     Related Art 
     Doubly Salient Permanent Magnet-Linear Synchronous Motor (DSPM-LSM) of discontinuous stator mainly consists of a plurality of fixed stators respectively having a plurality of coils of different phases, and one carrier or a plurality of carriers with magnet arrays, and actions of each of the carriers are controlled and corrected by feedback of a position of each of the carriers along a moving path. The above has been disclosed in patents EP3015933A1, U.S. Pat. No. 8,497,643B2, U.S. Pat. No. 8,796,959B2, EP2182627B1, US20190190366A1 and documents “Novel Force Ripple Reduction Method for a Moving-magnet Linear Synchronous Motor with a Segmented Stator”, “Cogging Force Verification by Deforming the Shape of the Outlet Edge at the Armature of a Stationary Discontinuous Armature PM-LSM”. 
     Under a premise of not requiring high-precision measurement results, the measurement system can use Hall sensors, which can reduce the complexity and costs of the position feedback measurement system. Wherein the magnet array of DSPM-LSM can be used as a measuring scale, since a distance that each of the Hall sensors can measure is less than a length of a magnet array, in order to provide position feedback information in an entire moving range of the carrier, the Hall sensors must be arranged along a moving direction of the carrier, and measuring ranges of the adjacent sensors are set to overlap each other. 
     U.S. Pat. No. 8,497,643 discloses a linear scale for obtaining a distance from a reference point, in which operation is performed by mainly using changes in magnetic flux density generated by a magnet and with sine signals and cosine signals sensed by a transducer. However, the method will reduce accuracy due to end-effects of the magnetic flux. In order to improve the precision, U.S. Pat. Nos. 8,497,643 and 6,713,902B2 further disclose the moving position or deflection direction of the first and last magnets in the magnet array. 
     U.S. Pat. No. 8,796,959B2 utilizes the previously measured shifted value between the adjacent sensors in conjunction with the positional relationship of each of the sensors, and uses a single processing unit to perform operation. In this way, the sensors, servo drivers, and processing units need to be arranged in a special digital network, but they will decrease long-term repeatability of the system due to temperature deformation and offset changes. 
     US20130229134A1 discloses a method of using position feedback in conjunction with offset of the adjacent modules and calibrating an accuracy of the measuring scale. Wherein the discretely configured linear motor system is composed of a plurality of modules, each of the modules comprises a single sensor, a stator and a drive unit, and a plurality of control units are used to control the modules and send position information. Accordingly, this method only uses the single sensor, which results in the carrier having only a single actuation direction effective, which means that when the carrier moves in an opposite direction, it will be too late for the modules to obtain a position of the carrier, as a result, an acting force of the DSPM-LMS is significantly reduced. 
     US20130037384A1 discloses an enhanced multi-position detection system applied to electromagnetic transmission, which mainly comprises a plurality of magnetic field sensors arranged at a fixed distance on an operating track for detecting positions of transmission elements on the operating track. The sensors are connected to a single processing unit. Furthermore, in order to coordinate with the position feedback detected by the sensors, the patent proposes to increase a quantity of the sensors and their functions; however, this method reduces the possibility of system modularization. Because in industrial applications, modularization of DSPM-LSM can improve the maintainability and substitutability of various components in a system; obviously, the conventional technology is still not sophisticated enough. 
     SUMMARY OF THE INVENTION 
     Therefore, a main object of the invention is to provide a position measuring mechanism and a measuring method of a linear motion system in which two sensors are respectively disposed on two sides of a stator, in addition to allowing a moving portion to perform bidirectional movement, under a premise of not increasing a quantity of the sensors, a measuring range of the sensors can be calculated based on information measured by the sensors themselves. 
     Another object of the invention is to provide a position measuring mechanism and a measuring method of a linear motion system in which measurement sections respectively measured by two sensors are combined to ensure an accuracy of position feedback, instead of the conventional technique using an operational method of combining sinusoidal and cosine signals. 
     In order to achieve the above objects, the position measuring mechanism provided by the invention comprises: a base; a moving portion capable of moving relative to the base; at least one magnet array disposed in the moving portion; a first sensing portion and a second sensing portion respectively disposed on the base at intervals for sensing a magnetic field of the magnet array; a third sensing portion having a signal unit disposed on the moving portion, and a sensitive element disposed on the base for sensing the signal unit; and a processing portion receiving sensing signals of the first sensing portion and the second sensing portion respectively, calculating a subcycle corresponding to the magnet array, and performing operation in conjunction with sensing data of the sensitive element to obtain a movement path of the moving portion, and then feeding the movement path back to a driver to adjust a movement pattern of the moving portion. 
     In one embodiment, the invention further comprises a plurality of measurement modules respectively including the first sensing portion, the second sensing portion and the third sensing portion, and a distance between the two adjacent measurement modules is equal to a length of the magnet array. Wherein, in order to simplify the current commutation law of a stator current, a distance between the two adjacent measurement modules is equal to a length of the magnet array. 
     Wherein the driver controls a current of the stator provided on the base, and uses a fieldbus to connect to a motion controller, so that information detected by the sensing portions is processed by a single device, thereby reducing the difficulty of identifying a position of a carrier along the movement path. 
     Another object of the invention is to provide a position measuring method to combine signals sensed by the first sensing portion and the second sensing portion in a measuring range respectively with a juncture. 
     In order to estimate an exact position of the measuring range, the invention uses subcycle information and signal amplitudes sensed by the first sensing portion and the second sensing portion for determination. 
     Wherein the measuring range is divided into a first measurement section of the first sensing portion and a second measurement section of the second sensing portion with the juncture, the first measurement section and the second measurement section are respectively configured along a movement direction of the moving portion and are adjacent to each other. 
     When the moving portion moves and displaces from right to left, a starting point of the measuring range is defined as: a signal amplitude sensed by the first sensing portion is less than a predetermined high threshold value, and a subcycle position of a signal sensed by the first sensing portion is equal to 180°; an ending point of the measuring range is defined as: a signal amplitude sensed by the second sensing portion is higher than a predetermined low threshold value, and a subcycle position of a signal sensed by the second sensing portion is equal to 180′; and when the moving portion moves and displaces from left to right, a starting point of the measuring range is defined as: a signal amplitude sensed by the first sensing portion is greater than the low threshold value, and a subcycle position of a signal sensed by the first sensing portion is equal to 180°; an ending point of the measuring range is defined as: a signal amplitude sensed by the second sensing portion is less than the low threshold value, and a subcycle position of a signal sensed by the second sensing portion is equal to 180°. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to enable the examiner to further understand the objects, features, and achieved efficacies of the invention, preferred embodiments are listed below for detailed explanation in conjunction with the drawings, wherein: 
         FIG. 1  is a schematic diagram of a preferred embodiment of the invention; 
         FIG. 2  is a schematic diagram of another embodiment of the invention showing that a quantity of measurement modules is two; 
         FIG. 3  is a schematic diagram of eight magnetic sensitive elements included in a first sensing portion and a second sensing portion in a preferred embodiment of the invention; 
         FIG. 4  is a schematic diagram of signals sensed by the first sensing portion of a preferred embodiment of the invention; 
         FIG. 5A  is a bottom view of a preferred embodiment of the invention; 
         FIG. 5B  is a side view of a preferred embodiment of the invention; 
         FIG. 6  is a schematic diagram of signal processing in a preferred embodiment of the invention in which a carrier moves from left to right to a current position; and 
         FIG. 7  is a schematic diagram of a measuring mechanism of an embodiment of the invention showing lengths, spacings and positional relationships of each of elements. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, a preferred embodiment of the invention is described in conjunction with the drawings. 
     In a measuring mechanism  10  of a linear motion system provided in a preferred embodiment of the invention, a Doubly Salient Permanent Magnet-Linear Synchronous Motor (DSPM-LSM) of discontinuous stator is taken as an example, and the measuring mechanism  10  comprises a base  20 , a moving portion  30  and a measurement module  40 . 
     As shown in  FIG. 1 , the base  20  has a predetermined length (not shown in the figure), and at least one stator  21  is disposed on the base  20  by extending along a long axial direction of the base  20 . 
     The moving portion  30  has a carrier  31  located by one side of the base  20  and separated from the stator  21  from one side of the carrier  31 , and a one-dimensional magnet array  32  composed of a plurality of magnets  321  sequentially disposed on the carrier  31 , through magnetic field interaction between the stator  21  as a primary side and the magnet array  32 , the moving portion  30  is capable of displacing along the long axial direction of the base  20 ; however, the technical content of using the stator  21  as the primary side and the moving portion  30  as a secondary side pertains to the scope of the prior art and is known by those having ordinary skill in the art to which the invention pertains, so it will not be repeat herein. 
     The measurement module  40  has a first sensing portion  41 , a second sensing portion  42 , a third sensing portion  43  and a processing portion  44 , wherein: 
     the first sensing portion  41  and the second sensing portion  42  are disposed on the base  20 , and are respectively located at two ends of the stator  21  corresponding to the long axial direction of the base  20 , thereby the stator  21  is interposed between the first sensing portion  41  and the second sensing portion  42 , as shown in  FIG. 3 , the first sensing portion  41  and the second sensing portion  42  respectively include eight magnetic sensitive elements (Hall sensors, H 1 ˜H 8 ) for sensing magnetic field changes of the magnet array  32 ; 
     the third sensing portion  43  comprises a signal unit  431  disposed on the carrier  31  to generate specific physical signals, and a sensitive element  432  fixed on the base  20  to sense signals generated by the signal unit  431 ; and the processing portion  44  receives sensing data of the first sensing section  41 , the second sensing section  42  and the sensitive element  432 , after performing operation to obtain position information related to the moving portion  30 , the position information is fed back to a driver  50 , and then the driver  50  performs power supply control to the stator  21 . 
     Further, when a moving stroke of the moving portion  30  exceeds a range that a single stator as a primary side is capable of acting on, a quantity of the stator  21  in the base  20  can be made to be numerous, as shown in  FIG. 2  illustrating the two stators  21  as an example, the two stators  21  are coaxially fixed on the base  20  along a long axial direction, and a quantity of the measurement module  40  increases to two to match with an increased quantity of the stators  21 , but the added measurement module  40  does not include an increase of the signal unit  431 , that is, a quantity of the signal unit  431  is the same as a quantity of the carrier  31 , and remains single. In this example, a distance between the two adjacent measurement modules  40  is equal to a length of the magnet array  32 . 
     Please refer to  FIG. 2  for another embodiment of the invention, differences between this embodiment and the previous preferred embodiment lie in a quantity of the measurement module  40  being two, the two measurement modules  40  being arranged along a movement direction of the carrier  31 , and providing position feedback along a movement path. For the convenience of control, the two measurement modules  40  can be connected to each other, and then connected by a fieldbus  61  to a motion controller  60  to handle movement control of the carrier  31  or a plurality of the carriers  31 . 
     As shown in  FIG. 3 , the eight magnetic sensitive elements (Hall sensors, H 1 ˜H 8 ) respectively included in the first sensing portion  41  or the second sensing portion  42  are arranged from left to right in sequence, and each of the magnetic sensitive elements H 1 ˜H 8  is shifted on τ/4 along a measuring axis respectively, as shown in  FIG. 7 , T is a magnetic period of the magnet array  32 , that is, a distance between the magnets  321  of a same magnetism, so that lengths of the first sensing portion  41  and the second sensing portion  42  are respectively equivalent to the two magnetic periods T, and the first magnetic sensitive element H 1  and the fifth magnetic sensitive element H 5 , the second magnetic sensitive element H 2  and the sixth magnetic sensitive element H 6 , the third magnetic sensitive element H 3  and the seventh magnetic sensitive element H 7 , the fourth magnetic sensitive element H 4  and the eighth magnetic sensitive element H 8  are respectively connected in parallel to form four groups to optimize an average feedback error to improve accuracy and sensitivity of position feedback. Signals output by the magnetic sensitive elements H 1 ˜H 8  connected in parallel in four groups are sine and cosine differential signals of Cos+, Sin+, Cos−, Sin−, as U Cos+=U cos(a), U Sin+=U sin(α), U Cos−=−U cos(α), U Sin−=−U sin(α), where α is a subcycle position (angle) calculated by the processing portion  44  according to a formula α=atan2((U Cos+−U Cos−)/(U Sin+−U Sin−)). 
     As shown in  FIG. 5A , in terms of relative position in an X-axis direction, the first sensing portion  41  is located on a left side of the stator  21 , and the second sensing portion  42  is located on a right side of the stator  21 ; and in a Y-axis direction, in addition to the first sensing portion  41  and the second sensing portion  42  locating relative to a center of the magnets  321  of the magnet array  32  as shown in  FIG. 5A , the first sensing portion  41  and the second sensing portion  42  can also be shifted along the Y-axis direction to be located on one side of the magnet array  32  (not shown in the figure). The third sensing portion  43  corresponds to one side of the magnet array  32 . 
     As shown in  FIG. 4 , during a movement of the carrier  31  moving from left to right to a current position P 1 , sine  411  amplitude  412  and cosine  413  signal in signals sensed by the first sensing portion  41  will change accordingly, wherein changes of the amplitude  412  will appear when the magnet array  32  does not cover all the magnetic sensitive elements H 1 -H 8 , that is, when the carrier  31  enters and exits a measuring range of the first sensing portion  41 , the amplitude  412  will decrease, which will cause significant interference in a first cycle and a last cycle of subcycles α 1 ,  414 , wherein amplitudes A 1 ,  412  are estimated by the following formula: 
         A =√{square root over (( U   Cos+   −U   Cos− ) 2 +( U   Sin+   −U   Sin −) 2 )},
 
     wherein A is an amplitude, and Cos+, Sin+, Cos−, Sin− are sine and cosine differential signals respectively. 
     Similarly, sine amplitude and cosine signal in sensing signals output by the second sensing portion  42  also have the same situation as that of the first sensing portion  41 . 
     As shown in  FIG. 7 , the stator  21  is disposed in a space pattern of interposing between the first sensing portion  41  and the second sensing portion  42 , a length L 21  of the stator  21  is smaller than a separation distance L 40  between the first sensing portion  41  and the second sensing portion  42 , a length of the separation distance L 40  is an integral multiple of the magnetic period T, and must have a length of at least four magnetic periods τ to provide a sensing overlapping area  401  of the first sensing portion  41  and the second sensing portion  42  as shown in  FIG. 6 , and when signals of the first sensing portion  41  and the second sensing portion  42  are combined, signals of cycles  402   a ,  402   b  with lower accuracy are excluded. A length L 1  of a measuring scale is an integral multiple of the magnetic period τ and is determined by the following formula 1: 
         L 1= L 40+(4+ n )τ,
 
     wherein n is a natural number containing 0 (formula 1). 
     In this example, a length of the magnet array  32  is equal to the length L 1  of the measuring scale. 
     As shown in  FIG. 6 , the third sensing portion  43  is located in the overlapping area  401  to provide a unique and distinct juncture  433  as a signal juncture of the first sensing portion  41  and the second sensing portion  42 . In order to ensure a correctness of the juncture  433 , it is required to make a length L 431  of the signal unit  431  less than two magnetic periods τ as shown in  FIG. 7 , and to be determined by positions of a signal  435  of the signal unit  431  and the subcycle  414  of the first sensing portion  41  located at 180°, and in order to avoid influence by the cycles  402   a ,  402   b  with lower accuracy, a disposing position of the third sensing portion  43  is limited. For example, when a length of the magnetic sensitive elements H 1 ˜H 8  is two magnetic periods τ, the signal unit  431  can be located in third and fourth overlapping periods in the overlapping area  401  of the first sensing portion  41  and the second sensing portion  42 . 
     As shown in  FIG. 6 , the third sensing portion  43  is used to generate a unique and distinct zero point  434  in the overlapping area  401 , and a position of the zero point  434  is defined by the signal unit  431  and the subcycle  414  of the first sensing portion  41 , wherein the subcycle  414  of the first sensing portion  41  is equal to a threshold value α 10 , for example, the threshold value α 10  shown in  FIG. 6  is zero, and therefore, the length L 431  of the signal unit  431  needs to satisfy formula 2: 
       (π−α10)*(τ/2π)&lt; L 431&lt;2τ−[(π−α10)*(τ/2π)]  (formula 2).
 
     As shown in  FIG. 7 , an offset distance (Ls) (not shown in the figure) of the sensitive element  432  is less than one magnetic period τ. A position of the sensitive element  432  is determined by the following formula, relative to an interval length L 13  of the first subcycle  414  of the first sensing portion  41 , the interval length L 13  is: 
     
       
         
           
             
               
                 
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     an offset distance Lf (not shown in the figure) of the signal unit  431  is less than half of a length L 431  of the signal unit  431 , and a distance L 211  between the signal unit  431  and the first magnetic period τ of the magnet array  32  is determined by the following formula 4: 
     
       
         
           
             
               
                 
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     For example, in  FIG. 6 , the offset distance Ls of the sensitive element  432  is ¼ magnetic period τ, and the offset distance Lf of the signal unit  431  approaches zero. 
     In addition, the invention is capable of calculating a measuring range  403  of the measurement module  40  according to an action pattern of the moving portion  30 . In  FIG. 6 , when the carrier  31  moves from left to right in a displacement, a starting point  241  and an ending point  242  of the measuring range  403  of the measurement module  40  are defined according to the following formula 5, wherein Alowth is a low threshold value  249 , for example Alowth is 25% of a rated amplitude, and Ahighth is a high threshold value  248 , for example, Ahighth is 75% of a rated amplitude. Therefore, the processing portion  44  calculates the amplitudes A 1 ,  412  and the subcycles α 1 ,  414  of the first sensing portion  41 , and amplitudes A 2 ,  421  and subcycles α 2 ,  422  of the second sensing portion  42 , which means that the amplitudes A 1 ,  412  of the first sensing portion  41  are greater than the low threshold value  249 , positions of the subcycles α 1 ,  414  of the first sensing portion  41  equal to 180°, the amplitudes A 2 ,  421  of the second sensing portion  42  are lower than the high threshold value  248 , and positions of the subcycles α 2 ,  422  of the second sensing portion  42  are 180°. 
     
       
         
           
             
               
                 
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     When the carrier  31  moves from right to left in a displacement, the starting point  241  and the ending point  242  of the measuring range  403  of the measurement module  40  are defined according to the following formula 6, which means that the amplitudes A 1 ,  412  of the first sensing portion  41  are smaller than the high threshold value  248 , positions of the subcycles α 1 ,  414  of the first sensing portion  41  equal to 180°, the amplitudes A 2 ,  421  of the second sensing portion  42  are higher than the low threshold value  249 , and positions of the subcycles α 2 ,  422  of the second sensing portion  42  are 180°. 
     
       
         
           
             
               
                 
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     Furthermore, when the carrier  31  enters the measuring range  403 , the processing portion  44  feeds back calculated position information of the moving portion  30  to the driver  50 , and then the driver  50  is used to control the stator  21  to perform current commutation. In this example, as shown in  FIG. 7 , a separation distance L 25  between the first sensing portion  41  and the stator  21  is adjusted so that each of the magnetic sensitive elements H 1 ˜H 8  of the first sensing portion  41  are in phase with a coil of the stator  21 , thereby simplifying a power supply control mode of the stator  21 . 
     The measuring range  403  is further divided into a first measuring range  217  and a second measuring range  227  based on the juncture  433  as a reference, wherein when the carrier  31  is located on a left side of the juncture  433 , the carrier  31  is located in the first measuring range  217 , and then the subcycle  414  of the first sensing portion  41  is used to calculate a position of the moving portion  30 , and the position is fed back; when the carrier  31  is located on a right side of the juncture  433 , the carrier  31  is located in the second measuring range  227 , and then the subcycle  422  of the second sensing portion  42  is used to calculate a position of the moving portion  30 , and the position is fed back. 
     In  FIG. 7 , in order to make the two adjacent measurement modules  40  have an overlapping area, a separation distance L 11  between the first sensing portions  41  of each of the measurement modules  40  is equal to the length L 1  of the magnet array  32 . 
     Furthermore, as shown in  FIG. 7 , the two magnet arrays  32  are taken as an example, the two magnet arrays  32  are coaxially fixed on the carrier  31  along a long axial direction, in order to ensure a correctness of the calculated starting point  241  and ending point  242 , a minimum spacing  1010  between the two adjacent magnet arrays  32  is equal to a length L 2  of the first sensing portion  41 , and equivalent to the two magnetic periods τ. In this example, at least one spacer  111 ,  112  is disposed between the two adjacent magnet arrays  32 , and the minimum spacing  1010  is provided by a length of the at least one spacer  111 ,  112 . 
     It is to be understood that the above description is only preferred embodiments of the present invention and is not used to limit the present invention, and changes in accordance with the concepts of the present invention may be made without departing from the spirit of the present invention, for example, the equivalent effects produced by various transformations, variations, modifications and applications made to the configurations or arrangements shall still fall within the scope covered by the appended claims of the present invention.