Patent Publication Number: US-2011056901-A1

Title: Transfer apparatus and transfer method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a transfer apparatus. In particular, the present invention relates to a transfer apparatus capable of unloading an article to a predetermined position without any inclination of an arm at a time of stretching the arm. 
     2. Description of the Related Art 
     The applicant proposed to attach an optical sensor to a tip end of an arm of a slide fork or the like, for reading a mark near a support member to correct inclination of the arm. See, for example, JP 2006-219233A. However, in the case of reading the mark near the support member, areas where inclination can be detected are limited to narrow ranges immediately before a loading position and immediately before an unloading position. In other positions, inclination can only be corrected by means of an open loop control in accordance with a stored pattern. Under such circumstances, since inclination of the arm cannot be corrected sufficiently at the time of unloading the article, the article may contact a guide near the support member, and the article may be unloaded to a position shifted from an intended position. Further, since no sensor is provided for measuring a position of the article in a length direction of the arm, at the time of unloading the article, the guide may easily contact the article to cause a further shift of the unloading position of the article. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention make it possible to transfer an article while keeping a tip end of an arm horizontal, and to unload the article to a more correct position. 
     In addition, preferred embodiments of the present invention make it possible to measure inclination regardless of a position in an elevation direction of the arm, without requiring any marks or the like at the destination of transfer of the article. 
     Also, preferred embodiments of the present invention provide a specific method of unloading an article to a correct position quietly. 
     According to a preferred embodiment of the present invention, a transfer apparatus includes a tiltable base, an arm arranged to be elevated, lowered, stretched, and retracted on the base, a sensor arranged to detect inclination at a tip end of the arm, a sensor arranged to measure a position of an article on the arm, and a controller arranged to tilt the base to cancel a detected inclination and to correct a stretching amount of the arm in correspondence with a measured position of the article on the arm. 
     In this manner, by tilting the base, inclination at the tip end of the arm can be eliminated. At the time of unloading the article, collision between the arm and the guide at the unloading position due to inclination of the arm can be prevented. Further, by eliminating inclination at the tip end of the arm, the elevation distance of the arm required to load and unload the article can be shortened. Further, by measuring the position of the article on the arm, the unloading position is corrected in correspondence with the position of the article. Therefore, also in this respect, collision with the guide or the like is prevented, and the article can be unloaded to the correct position. Thus, the article can be transferred to the correct position quietly. 
     Preferably, as a sensor to detect the inclination, an inclination sensor to detect inclination of a moving element due to the gravity is provided at the tip end of the arm. In this manner, inclination at the tip end of the arm can be detected in a wide range regardless of the position in the elevation direction of the arm. Further, no marks or the like are required at the destination of the transfer of the article. 
     Further, preferably, the controller is configured to stretch the arm in correspondence with the position of the article on the arm at the time of unloading of the article, tilt the base in accordance with a stored tilt angle during stretching of the arm, and lower the arm while tilting the base in accordance with a signal from the sensor arranged to detect the inclination after stretching of the arm. During stretching of the arm, since acceleration in the horizontal direction is applied to the inclination sensor, it is difficult to correctly measure the inclination. Therefore, during this period, the base is tilted in accordance with the stored tilt angle. At the time of lowering the arm after the arm has been stretched, since only the gravity is applied to the inclination sensor, and the inclination sensor is accelerated only in the direction of gravity (vertical direction), inclination can be measured correctly. Therefore, at the time of lowering the arm, the base is tilted in accordance with the signal from the inclination sensor. In this manner, in the period from stretching of the arm, elevation of the arm, and until unloading of the article, the tip end of the arm can be kept substantially horizontal all the time so as to make it possible to unload the article to a predetermined position. 
     More preferably, the controller is configured to elevate the arm while tilting the base in accordance with a signal from the sensor arranged to detect the inclination at the time of loading of the article, and retract the arm while tilting the base in accordance with a stored tilt angle after elevation of the arm. In this manner, during the period from loading of the article until transportation of the article onto the base, the tip end of the arm can be kept substantially horizontal all the time. 
     In a preferred embodiment of the present invention, a tiltable base and an arm configured to be elevated, lowered, stretched, and retracted on the base are provided, and an article is transferred by performing by the steps of a) detecting inclination at a tip end of the arm using a sensor, and tilting the base to cancel the detected inclination, and b) measuring a position of the article on the arm, and correcting a stretching amount of the arm in accordance with the measured position of the article on the arm. 
     Preferably, the step (a) is performed at the time of elevating or lowering the arm, and the step (c) of tilting the base in accordance with a stored tilt angle is performed at the time of stretching or retracting the arm. 
     In the present specification, the description regarding the transfer apparatus is directly applicable to the transfer method, and conversely, the description regarding the transfer method is directly applicable to the description regarding the transfer apparatus. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view showing main components of a transfer apparatus according to a preferred embodiment of the present invention. 
         FIG. 2  is a side view showing main components of the transfer apparatus according a preferred embodiment of the present invention. 
         FIG. 3  is a block diagram showing an inclination sensor used in a preferred embodiment of the present invention. 
         FIG. 4  is a block diagram showing a controller included in a preferred embodiment of the present invention. 
         FIG. 5  is a flow chart showing a loading algorithm used in a preferred embodiment of the present invention. 
         FIG. 6  is a flow chart showing an unloading algorithm used in a preferred embodiment of the present invention. 
         FIG. 7  is a side view schematically showing a support member and an article at the time of unloading. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments for carrying out the present invention in the most preferred form will be described. The scope of the present invention shall be determined according to the understanding of a person skilled in the art based on the description of the claims in consideration of the description of the specification and techniques known in this technical field. 
       FIGS. 1 to 7  show a stacker crane  2  taken as an example of a transfer apparatus according to a preferred embodiment of the present invention. A transfer apparatus according to a preferred embodiment of the present invention may be mounted in an automatic transportation vehicle, an overhead traveling vehicle or the like, for example. Alternatively, instead of mounting the transfer apparatus in the vehicle, a body of the transfer apparatus may be attached to a tiltable base provided on a station or the like, for example. In the drawings, a reference numeral  2  denotes a stacker crane that travels on travel rails  3 . A reference numeral  4  denotes vehicle, and a reference numeral  6  denotes an elevation platform that is elevated and lowered along a mast  7 . Reference numerals  8  denote a frame, e.g., provided on front and back sides of the elevation platform  6 . Reference numerals  10  denote guided members, and each of the guided members  10  is connected to the frame  8  through a pivot central shaft  34  and a tilt shaft  36  described later. The guided members  10  are guided by the mast  7 , and elevated and lowered by elevation members  12  such as chains, belts, or ropes. Reference numerals  14  denote tilt motors arranged to control an inclination angle (tilt angle) of the elevation platform  6  relative to a horizontal plane. 
     For example, a turntable  16  is provided on the elevation platform  6 , and a pair of SCARA arms  18  are mounted on the turntable  16 . Reference numerals  19 ,  20  denote arms of the SCARA arms  18 , and reference numerals  21  to  23  denote shafts. A reference numeral  26  denotes a hand attached to distal ends of the pair of the SCARA arms  18 . Instead of the SCARA arms  18 , for example, a slide fork may be used. The turntable  16  may not be provided. The hand  26  supports the article in an area on the right side of a dotted line in  FIG. 1 . The area for supporting the article is referred to as the tip end. A reference numeral  28  denotes an inclination sensor provided at the tip end of the hand  26  to measure inclination from the horizontal plane. A reference numeral  30  denotes an article position sensor arranged to measure a position of the article on the hand  26 . For example, a laser distance sensor may be used as the article position sensor  30 . A reference numeral  32  denotes a controller of the stacker crane  2 . 
       FIG. 2  shows a tilt mechanism of the elevation platform  6 . The frame  8  is connected to the guided member  10  at one of upper and lower positions of the tilt mechanism. The frame  8  is pivotable about the pivotal shaft  34 . A tilt shaft  36  is fixed to the other of the upper and lower positions of the guided member  10 . As shown in an upper left portion in  FIG. 2 , the tilt shaft  36  is movable to the left and right within a long hole  42  provided in the frame  8 . The tilt shaft  36  is connected to a ball screw  38  attached to a tilt motor  14  through a nut  40 . In this manner, the tilt shaft  36  can move relative to the long hole  42  by the tilt motor  14 . Since the elevation platform  6  is pivotable about the pivot central shaft  34 , the elevation platform  6  can be inclined (tilted) toward the left or right in  FIG. 2 . The tilt mechanism is not limited to the mechanism shown in  FIG. 2 . For example, by supporting four corners of the elevation platform  6  by the elevation members, and by feeding the elevation members on the left and right sides of the elevation platforms  6  by different amounts, the elevation platform  6  is tilted. In the present preferred embodiment, the transfer apparatus includes the elevation platform  6 , components on the elevation platform  6  such as the SCARA arms  18 , the tilt mechanism, and the elevation mechanism of the elevation platform  6 . 
       FIG. 3  shows structure of the inclination sensor  28 . A reference numeral  43  denotes a power supply, and reference numerals  44  to  46  denote resistors. Among the resistors  44  to  46 , the voltage of the resistor  46  is outputted. A reference numeral  48  denotes a coil, a reference numeral  49  denotes a yoke made of magnetic material, a reference numeral  50  denotes a rotor made of magnetic material. When the coil  48  is energized, the rotor  50  is induced to be in alignment with the yoke  49 . A shield plate  51  is attached to the rotor  50  in the direction of gravity. When the inclination sensor  28  is inclined, due to gravity, the shield plate  51  and the rotor  50  move together to the left or right. Reference numerals  52 ,  53  denote LEDs, and reference numerals  54 ,  55  denote phototransistors. Photodiodes or the like may be used instead of the phototransistors. When the inclination sensor  28  is inclined, the shield plate  51  is tilted, and light from one of the LEDs  52 ,  53  is interrupted. When the light is interrupted, resistance of one of the phototransistors  54 ,  55  is increased, and electrical current flows through the coil  48  and the resistor  46 . By the electrical current flowing through the coil  48 , inclination of the rotor  50  and the shield plate  51  is eliminated, and a feedback for the inclination by the gravity of the shield plate  51  is provided. As a result, the electrical current flowing through the resistor  46  becomes substantially proportional to the inclination angle of the inclination sensor  28 . The inclination sensor  28  is not limited to a sensor arranged to detect inclination of the pendulum (shield plate  51 ) due to gravity. Alternatively, a sensor having a moving element moving along a circular arc route in a vertical plane, and detecting the position of the moving element may be adopted. It is desirable to damp vibration of the moving element by providing a feedback to cancel inclination of the moving element, specifically by energizing the coil  48  and attracting the moving element by the yoke  49 . 
       FIG. 4  shows a controller  32  of the stacker crane  4 . A travel controller  56  controls travel of the vehicle, and uses data of a position of the vehicle in a traveling direction, measured by a linear scale  57 . An elevation controller  58  uses height data of the elevation platform  6 , e.g., measured by a linear scale  59  to elevate or lower the elevation platform  6 , and thus, elevate or lower the arms. Further, the elevation controller  58  elevates or lowers the elevation platform  6  to cancel (offset) the change at the position of the tip end of the arm due to vibration. Any type of sensor can be used for measuring the position of the vehicle in the travel direction and the position in the height direction. At the time of stretching or retracting the SCARA arms  18 , the elevation controller  58  implements damping control by elevating or lowering the elevation platform  6 , e.g., in accordance with data in a damping control pattern memory  60  to damp vibration at the tip end of the hand. The damping control reduces vibration caused by, e.g., tilt control by a tilt motor, stretching and retraction of SCARA arms, and the change in the load by the transfer of the article. The tilt controller  62  implements tilt control to keep the tip end of the hand horizontal using a signal from the inclination sensor  28 . At the time of stretching or retracting the arms, since acceleration is applied to the inclination sensor  28  in the horizontal direction, it is difficult to obtain data of the correct inclination angle. Therefore, the tilt is corrected in accordance with a pattern stored in a memory  63  for each of the cases where any article is present and no article is present. A turntable controller  64  controls a turntable based on a signal from an angle sensor such as an encoder  65 . An arm controller  66  stretches and retracts the SCARA arms based on a signal from the article position sensor  30  to determine the stretching amount of the arms at the time of unloading the article. 
       FIG. 5  shows control at the time of loading an article. During stretching of the arms, since acceleration in the horizontal direction is applied, it is difficult to obtain correct data from the inclination sensor. Therefore, tilt control of the elevation platform is implemented in accordance with a pattern stored in a memory, and inclination at the tip end of the arms is eliminated. Further, since the tip end of the arms is vibrated in a vertical direction as a result of tilt control and stretching of the arms, damping control in the elevation direction is implemented by elevating or lowering the elevation platform for damping vibration at the tip end of the arms. 
     After the end of stretching of the arms, the arms are elevated by elevating the elevation platform. As shown on the right side of  FIG. 5 , elevation of the arms occur in a segment L 1  having a large elevating speed, a segment L 2  having a small elevating speed for loading an article from a support member, and a segment L 3  having a large elevating speed after the segment L 2 . In the segments L 1  to L 3 , since no acceleration is applied in the horizontal direction, by determining an inclination angle using the inclination sensor to implement feedback control of the tilt shaft, inclination is corrected to keep the tip end of the arms (tip end of the hand) horizontal. By operation of the tilt shaft and the change in the load due to transfer of the article, vibration occurs at the tip end of the arms. Therefore, the elevation platform is elevated or lowered to cancel the vibration. 
     Also at the time of retracting the arms, since acceleration in the horizontal direction is applied, it is difficult to accurately determine the inclination angle by the inclination sensor. Therefore, the tilt shaft is controlled in accordance with a pattern stored in the memory. The stored pattern for the tilt control in the case where any article is present is different from the stored pattern in the case where no article is present. Further, the stored pattern at the time of stretching the arms is different from the stored pattern at the time of retracting the arms. As the stored pattern, a tilt angle is stored for every stretching amount of the arms. The elevation platform is elevated or lowered to cancel vibration at the tip end of the arms due to the control of the tilt shaft and retraction of the arms. 
     In the present preferred embodiment, the inclination angle at the tip end of the arms can be measured over the entire range at the time of elevating and lowering the arms. However, in the case of reading marks of the support member using an optical sensor, the tilt angle can be detected only in narrow segments. Therefore, in the other segments, since feedback control cannot be implemented in a manner to eliminate the inclination angle, the arms and the article may contact at a line not on a plane, or the article after loading may contact the support member. 
       FIG. 6  shows control of unloading an article. At the time of loading the article by the arms, or at the time of unloading the article from the arms, based on the distance to the article measured by the article position sensor, the stretching amount of the arms is corrected. Thus, in  FIG. 7 , the article  72  can be unloaded to a predetermined position of a support member  70  in a length direction. The tip end is inclined due to stretching of the arms. However, since acceleration is applied in the horizontal direction, it is difficult to determine the inclination angle using the inclination sensor. Therefore, the inclination angle is corrected in accordance with a stored pattern in the memory. In the elevation controller, damping control is implemented by elevating or lowering the elevation platform to cancel vibration at the tip end of the arms. The damping control may be omitted. 
     At the time of unloading the article by lowering the elevation platform to lower the arms, as in the case of  FIG. 5 , different lowering speeds are used in the three segments L 1 , L 2 , and L 3 . In each segment, feedback control of the tilt shaft is implemented based on the inclination angle determined by the inclination sensor. Through the feedback control, the tip end of the arms is kept horizontal. Damping control is implemented by the elevation controller to cancel the vibration by operation of the tilt shaft and the vibration at the tip end of the arms due to transfer of the article. At the time of retracting the arms, inclination is corrected in accordance with the stored pattern for the case of retracting the arms without any article. Thus, the tilt shaft is controlled, and vibration control is implemented to cancel vibration at the tip end of the arms. 
     In  FIG. 7 , the reference numeral  70  denotes the support member, and a reference numeral  71  denotes a guide such as a ball like roller. At the time of unloading the article  72 , when the arms are not present at predetermined positions, the arms are guided by the guide  71 . For example, the article  72  is a case of a flat panel such as a liquid crystal panel or a plasma panel. However, any article can be the target of transfer in the embodiment. Since the article position sensor  30  measures the distance to article  72  on the hand  26 , the article can be unloaded to a predetermined position of the support member  70  in the depth direction. In particular, when the article  72  is moved repeatedly in a warehouse, positional deviation of the article  72  relative to the hand  26  is accumulated to cause a large cumulative deviation (error). However, in the present preferred embodiment, since the positional deviation is eliminated each time unloading of the article is carried out, the positional deviation is not accumulated. Further, since the inclination sensor  28  measures inclination at the tip end of the hand  26 , and eliminates inclination by operating the tilt shaft, the article  72  does not collide with components such as the guide  71 . Therefore, the article  72  can be unloaded to a correct position without applying impact or the like to the article  72 . Further, the unloading position of the article  72  can be kept correctly. 
     In the present preferred embodiment, though the laser distance sensor is used as the article position sensor  30 , any sensor can be used as long as it can measure the distance to the article  72 . The position of the article position sensor  30  is not limited to the rear end of the hand  26 . Though the inclination sensor  28  is provided at the tip end of the hand  26  (portion for supporting the load of the article  72 ), the inclination angle based on the elevation platform may be measured, e.g., using a camera provided in the elevation platform. In the present preferred embodiment, damping control is implemented at the time of retracting the arms without having any article after unloading and at the time of stretching the arms without having any article before loading. However, the damping control for the arms without having any article may be omitted. Further, the damping control may entirely be omitted. 
     DESCRIPTION OF THE NUMERALS 
     
         
         
           
               2 : stacker crane 
               3 : travel rail 
               4 : vehicle 
               6 : elevation platform 
               7 : mast 
               8 : frame 
               10 : guided member 
               12 : elevation member 
               14 : tilt motor 
               16 : turntable 
               18 : SCARA arm 
               19 ,  20 : arm 
               21  to  23 : shaft 
               26 : hand 
               28 : inclination sensor 
               30 : position sensor for articles 
               32 : controller 
               34 : pivotal shaft 
               36 : tilt shaft 
               38 : ball screw 
               40 : nut 
               42 : long hole 
               43 : power supply 
               44  to  46 : resistor 
               48 : coil 
               49 : yoke 
               50 : rotor 
               51 : shield plate 
               52 ,  53 : LED 
               54 ,  55 : phototransistor 
               56 : travel controller 
               57 ,  59 : linear scale 
               58 : elevation controller 
               60 : damping control pattern memory 
               62 : tilt controller 
               63 : memory 
               64 : turntable controller 
               65 : encoder 
               66 : arm controller 
               70 : support member 
               71 : guide 
               72 : article 
           
         
       
    
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.