Patent Publication Number: US-2007102479-A1

Title: Control system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is a National Stage application of International Application No. PCT/JP2005/010354, filed on Jun. 6, 2005, which claims priority of Japanese application number 2004-177675, filed on Jun. 16, 2004. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a control system for controlling, by pneumatic pressure, a work machine for changing the attitude of an object to be welded or the like, during welding by an automatic assembly device, such as a welding robot.  
      2. Description of the Prior Art  
      In general, in an automatic assembly device, such as an automatic welding device, the workpiece, namely, the object to be welded, is held by a holding device and welding is carried out automatically at prescribed locations by a welding robot. In this welding operation, if it is necessary to perform welding at prescribed locations about the perimeter of the workpiece, for example, then a rotating table holding the workpiece, provided on the holding device side, rotates through a prescribed angle, in such a manner that the welding locations are always positioned on the upper side so that a downward-facing welding operation can be carried out.  
      The holding device of this kind is operated in conjunction with the welding robot, and more specifically, control data for the rotating table on the holding device side is input to the operating program for the welding robot. Consequently, the welding robot and the holding device are mutually connected by a plurality of control wires.  
      Therefore, it is necessary to lay a plurality of control wires between the welding robot and the holding device, although a workpiece holding device which makes this troublesome laying work unnecessary has been proposed.  
      This workpiece holding device uses an electric motor which rotates a workpiece holding body and a casing provided with a plurality of holes through which the welding torch of a welding robot can be inserted. Optical sensors which are capable of detecting the welding torch are provided inside each of the holes. When a prescribed optical sensor is actuated due to the welding torch being inserted into a particular hole, then the electric motor is controlled in such a manner that the workpiece holding body is rotated through a prescribed angle (see, for example, Japanese Patent Laid-open No. 2000-288786).  
     SUMMARY OF THE INVENTION  
      According to the composition described above, the workpiece holding body is rotated to a prescribed angle in accordance with the position of the hole into which the welding torch is inserted. However, since optical sensors are used in order to detect the welding torch, there is a risk that incorrect operation may occur because spatter which flies inside the holes during welding could be mistakenly detected as a welding torch. Furthermore, since the rotating table driven by the electric motor needs to be controlled, the control mechanism becomes complicated and costs increase.  
      Therefore, it is an object of the present invention to provide a control system which prevents incorrect operation due to spattering arising in the course of welding, and furthermore, in which the control mechanism can be simplified.  
      The control system according to the present invention is a control system in which an operating member of an automatic assembly device is capable of controlling another work machine, wherein detecting members for detecting the operating member are provided at a plurality of locations on the main body of the device. A plurality of air supply tubes are provided, with one end thereof being connected to an air source and the other end thereof supplying operating air to the other work machine. Electromagnetic opening and closing valves are provided respectively at an intermediate position in the air supply tubes. A control unit is provided for inputting detection signals from the detecting members and outputting control signals to the electromagnetic opening and closing valves provided in the air supply tubes. The detecting members are respectively constituted by a plurality of non-contact type detectors capable of detecting the operating member in at least two different locations. The control unit outputs a prescribed control signal only when detection signals from the respective detectors of the detecting member are obtained simultaneously.  
      Furthermore, the time period during which detection signals are obtained simultaneously from the respective detectors of the detecting member is at least 0.5 seconds.  
      Moreover, the control unit comprises a time period setting unit for setting the time period during which the detection signals for outputting a control signal are obtained simultaneously.  
      Furthermore, the time period set by the time period setting unit is at least 0.5 seconds.  
      Moreover, the detectors in the respective detecting members are disposed inside hole sections.  
      Furthermore, optical sensors are used as the detectors.  
      According to the configuration of the control system described above, it is possible to operate a work machine via detecting members provided on the main body of the control system, in accordance with the operating member, and it is possible to prevent spatter that arises during welding from being mistakenly detected as the operating member. Moreover, since the work machine is operated by operating air, when a pneumatic pressure cylinder is used, for example, the position can be registered (controlled) at the ends of the stroke of the piston forming the drive member of the cylinder. Therefore, the composition of the control unit can be simplified and consequently costs can be reduced, as compared with the case where the angle of rotation is controlled by an electric motor or the like. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view schematically showing a general composition of a welding robot and a workpiece attitude changing device, and a control system for the same, according to an embodiment of the present invention.  
       FIG. 2  is horizontal cross-sectional view showing the structure of a holding table of the workpiece attitude changing device.  
       FIG. 3  is a block diagram showing the general composition of the control system.  
       FIG. 4  is a partially cutaway side view showing the general composition of a safety device in the control system.  
       FIG. 5  is a perspective view showing the composition of a detecting member in the control system. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Below, a control system according to an embodiment of the present invention is described in detail with reference to  FIG. 1  to  FIG. 5 .  
      The description in this embodiment relates to a control system which controls an attitude changing device capable of changing the attitude of a workpiece, which is an object to be welded by a welding robot  1 , which is one example of an automatic assembly device.  
      As shown in  FIG. 1 , welding robot  1  has, for example, a multi-jointed robot arm  2 , and a welding torch (one example of an operating member)  3  is attached to the front end of robot arm  2 . At a position corresponding to welding robot  1 , there are provided: an attitude changing device (one example of a work machine)  4  which holds the workpiece W that is to be welded as well as changing the attitude thereof; an article attachment device (one example of a work machine)  5  in which another component W′ is set; and a control system  6  for controlling the aforementioned attitude changing device  4  and article attachment device  5  by welding torch  3  of welding robot  1 .  
      Attitude changing device  4  comprises a rotational actuator  11  having a rotating shaft section which is driven in rotation by pneumatic pressure, and a holding table  12  for holding a workpiece W, provided on the rotating shaft section of rotational actuator  11 .  
      As shown in  FIG. 2 , the rotational actuator  11  comprises: a casing  22  in which two air cylinder chambers  21  ( 21 A and  21 B) extending in a prescribed direction are formed mutually in parallel; a rotational output shaft (rotational shaft section)  23 , provided rotatably via a bearing between the two cylinder chambers  21  at an intermediate position in the lengthwise direction thereof (stroke) and having pinion teeth  23   a  formed on the peripheral surface thereof; and a pair of pistons  24 , disposed movably in the lengthwise direction inside the respective cylinder chambers  21  and formed with rack teeth  24   a  which intermesh with the pinion teeth  23   a  of the rotational output shaft  23 . Air inlet/outlets  25  are formed in casing  22  in positions corresponding to one end of the respective cylinder chambers  21 , and holding table  12  is fixed to the upper end sections of the rotational output shaft  23 .  
      Therefore, by moving the two pistons  24  in mutually opposite directions by supplying or expelling air (pressurized air) via the respective air inlet/outlets  25 , it is possible to cause rotational output shaft  23 , in other words, holding table  12 , to rotate in a forward or reverse direction.  
      As shown in  FIG. 1 , a standard single-rod type pneumatic pressure cylinder  26  is used as article attachment device  5 , and serves to register a component W′ in position with respect to the workpiece W, by moving the component W′, when attaching the component W′ onto the workpiece W, for instance. Furthermore, first and second position detectors (for example, magnetic sensors)  29  ( 29 A and  29 B) for detecting that piston section  28   a  of piston rod  28  is positioned at the end of the stroke are provided inside cylinder chamber  27  of pneumatic pressure cylinder  26 .  
      Rotational actuator  11  and pneumatic pressure cylinder  26  are operated by means of air pressure, and therefore, the respective pistons (drive members) are registered in position (controlled) at the respective stroke end positions. Consequently, the composition of the control unit can be simplified in comparison with a case where the angle of rotation achieved by an electric motor, or the like, is controlled.  
      Furthermore, as shown in  FIG. 1  and  FIG. 3 , control system  6  comprises: a plurality of detecting members  33  disposed respectively inside hole sections  32  ( 32 A to  32 F) formed at a plurality of locations, for example, six locations, in the upper part of a vertically-oriented box-shaped casing  31  forming the main body of the device, (the detecting members being provided in the same number as the hole sections); a plurality of (for example, six) air supply tubes  37  (being one example of an air supply conduit), provided inside casing  31 , one end of each air supply tube being connected to a joining tube section  36  connected to an air source (for example, an air compressor)  34 , and the other ends thereof being connected to air supply apertures (more specifically, couplings, or the like)  35  provided in a plurality of (for example, six) locations on the outer surface of casing  31 ; electromagnetic opening and closing valves  38  provided at an intermediate point of each of air supply tubes  37 ; and a control circuit unit (one example of a control unit)  39  for inputting detection signals from detecting members  33  and outputting an opening or closing signal (a prescribed control signal, also called an operating signal) to electromagnetic opening and closing valves  38 . The other end of joining tube section  36  is connected to a connection aperture  40 , such as a coupling, and air source  34  is connected to connection aperture  40  via an air connection tube  41 .  
      The respective air supply apertures  35  ( 35 A to  35 F) are connected to the respective work machines, in sets of two, for example, and in the present embodiment, they are connected respectively via air connection tubes  42  and  43 , to two air inlet/outlets  25  of rotational actuator  11  of attitude changing device  4 , and pneumatic pressure cylinder  26  of article attachment device  5 . Of course, it is also possible to connect another pneumatic pressure-type work machine to the remaining set of air supply apertures  35  ( 35 E and  35 F).  
      Moreover, control system  6  is provided with a safety device  51  in order to halt the welding work by welding robot  1 , if the air pressure supplied from a connection aperture  40  (or an air supply aperture  35 ) falls for some reason or other, or if a problem such as a breakdown occurs in any one of the work machines, such as article attachment device  5 , and the device halts during operation, or if the power supply in control system  6  is interrupted.  
      As shown in  FIG. 1 ,  FIG. 3  and  FIG. 4 , safety device  51  comprises: a raising and lowering body  52  having an inverted L-shaped cross-section in which the vertical section  52   b  is disposed in line with the side face of casing  31  in such a manner that the horizontal section  52   a  is able to rise and fall at a position on the upper surface of the casing  31 ; a raising and lowering device, such as a pneumatic raising and lowering cylinder  53 , which raises and lowers the raising and lowering body  52  through a prescribed height; and an operating circuit section  54  which operates the pneumatic pressure cylinder  53 . Furthermore, hole sections  55  having the same diameter and the same position as the hole sections  32  formed in casing  31  are formed in the horizontal section  52   a  of the raising and lowering body  52 .  
      A single-rod type cylinder with an in-built spring, for example, is used as pneumatic pressure cylinder  53 , and when the rod section of the piston rod of the cylinder is caused to project and raises up raising and lowering body  52 , the horizontal movement of welding torch  3  is impeded by hole section  55 , and hence a safety switch provided in welding robot  1  (for example, a switch using a sensor capable of detecting the occurrence of vibrations in the welding torch) is activated and welding robot  1  is halted. The amount by which raising and lowering body  52  is raised is greater than the path of movement of the front end of welding torch  3 , and therefore, welding torch  3  always abuts against the side of raising and lowering body  52  if it is shifted to the next operation while raising and lowering body  52  is raised.  
      As shown in  FIG. 4 , pneumatic pressure cylinder  53  comprises a tubular cylinder main body  62  having a cylinder chamber  61 ; a piston rod  63 , disposed inside the cylinder chamber  61 , of which rod section  63   a  projects externally; and a spring body  64 , disposed inside the piston side portion  61   a  of cylinder chamber  61 , for impelling piston rod  63  towards the exterior (a coil spring is used for spring body  64 , and when the pneumatic pressure is released, for example, the piston rod is caused to project by the force of the spring). Furthermore, the air supply aperture  65  of the rod side region  61   b  of the cylinder chamber  61  is connected via an air introduction tube  66  to an intermediate portion of the joining tube section  36 .  
      Therefore, in a state where air is supplied normally from air source  34 , pneumatic pressure is supplied to the interior of rod side cylinder chamber  61   b  and the piston rod  63  is drawn in against the resistance of spring body  64 , but if there ceases to be pneumatic pressure from air source  34 , then the force of the spring causes rod section  63   a  of piston rod  63  to project, thereby lifting raising and lowering body  52 . If robot arm  2  of welding robot  1  is moved in this state, then welding torch  3  makes contact with (abuts against) the perimeter edge of hole section  55  of raising and lowering body  52 , and therefore safety device  51  in welding robot  1  activates and the robot halts.  
      Next, operating circuit unit  54  will be described.  
      Operating circuit unit  54  actuates safety device  51  in cases where a problem has occurred in a work machine, such as article attachment device  5 , or where the air pressure has fallen or the power supply to control system  6  has been interrupted. Operating circuit unit  54  activates safety device  51  on the basis of a signal from first and second position detectors  29 A and  29 B which detect the end of the stroke of piston rod  28  provided in pneumatic pressure cylinder  26 , or by detecting a fall in the pneumatic pressure, or an interruption in the power supply.  
      Therefore, an open tube (or pipe)  67  for allowing the air to escape into the atmosphere is provided at an intermediate position of air introduction pipe  66 , and furthermore, an electromagnetically actuated three-way switching valve  68  is provided in the connection section of open tube  67 . Moreover, three-way switching valve  68  supplies pneumatic pressure to pneumatic pressure cylinder  26  when power is supplied to control system  6 . However, as described above, if a problem occurs in the work machine, for example, or if the pneumatic pressure falls, or if there is a power cut which causes an interruption in the power supply, then pneumatic pressure cylinder  26  connects to open tube (or pipe)  67 .  
      In the electrical control circuit (not illustrated) for controlling three-way switching valve  68 , if piston rod  28  of pneumatic pressure cylinder  26  is halted during operation, then the detection signals from two position detectors  29 A and  29 B are interrupted for a prescribed time period or longer. When this situation is detected, safety device  51  is operated.  
      More specifically, if the time period during which a detection signal from position detectors  29 A and  29 B has not been detected has exceeded a set time period according to a timer, then three-way switching valve  68  is connected to open tube (or pipe)  67  (in other words, the command to three-way switching valve  68  is removed), and the pneumatic pressure is released from raising and lowering pneumatic pressure cylinder  53 .  
      Furthermore, in electrical control circuit, if a detection signal is input from pressure switch  69  provided at an intermediate point of joining tube section  36  (which is set to output a detection signal if the pressure becomes equal to or less than 0.3 MPa, for example), and if a power supply is no longer being supplied to control system  6 , then the command to three-way switching valve  68  is removed and pneumatic pressure cylinder  26  connects automatically to open tube (or pipe)  67  and the pneumatic pressure falls to atmospheric pressure.  
      Consequently, if a problem has occurred in a work machine or in the air delivery tube system, or if there has been a power interruption due to a fault in the electrical system, then safety device  51  activates and the operation of welding robot  1  is halted.  
      Furthermore, as shown in  FIG. 5  (in which the raising and lowering body is not illustrated), the respective detecting members  33  comprise two sets (or three or more sets) of optical sensors (one example of a detector)  71 A and  71 B disposed in positions mutually separated by a prescribed height “h” in the axial direction of hole section  32  (for example, positions mutually separated by approximately several centimeters). Of course, optical sensors  71 A and  71 B respectively have a light emitting unit  72  and a light receiving unit  73  provided on the inner wall faces of hole sections  32 .  
      Moreover, the set time period can be adjusted in such a manner that a confirmation signal can be obtained which confirms that welding torch  3  has been detected, if the time period during which welding torch  3  is detected simultaneously by two respective optical sensors  71 A and  71 B in a detecting member  33 . In other words, the time period during which the detection signals from the two optical sensors  71 A and  71 B are mutually overlapping is equal to a prescribed set time period (for example, approximately 0.5 seconds to several seconds).  
      More specifically, control system  6  comprises: a time period detection unit  81  which inputs the detection signals detected by optical sensors  71 A and  71 B in respective detecting members  33 , determines whether or not the time period during which both detection signals are detected is equal to or greater than a prescribed set time period, and outputs a confirmation signal indicating that the welding torch is present, if this time period is equal to or exceeds the set time period; and a control signal output unit  82  which inputs this confirmation signal and outputs an operating signal (a prescribed control signal) indicating an angle corresponding to detecting member  33  relating to that confirmation signal, to the electromagnetic opening and closing valve  38  which operates rotational actuator  11 . Furthermore, control system  6  also comprises a set time period adjusting unit (or time period setting unit)  83  which is able to adjust, externally, the set time period during which the detection signals are detected simultaneously by time period detecting unit  81  described above. Time period detecting unit  81  judges which of the detecting members  33  has supplied the detection signals.  
      Stated in general terms, control system  6  has a function of changing (controlling) the attitude of the workpiece W held by holding table  12  by outputting a rotational operating signal to rotational actuator  11  in accordance with the detection signals from detection members  33 . Furthermore, control system  6  also has a function of controlling the pneumatic pressure cylinder  26  of article attachment device  5 .  
      In the foregoing composition, if the attitude of the workpiece W is to be changed when carrying out a prescribed welding task with respect to a workpiece W situated on holding table  12 , for example, then welding torch  3  of welding robot  1  is inserted into hole section  32  ( 32 A) where first detecting member  33 A, which issues the command to change the attitude in a prescribed direction, is located.  
      Upon so doing, a detection signal for welding torch  3  is input to control circuit unit  39  from two optical sensors  71 A and  71 B of first detecting member  33 A disposed inside hole section  32 A.  
      In control circuit unit  39 , the detection signals from two optical sensors  71 A and  71 B are input to time period detection unit  81 , which only outputs a confirmation signal indicating that welding torch  3  is present, to control signal output unit  82 , if both of the detection signals are detected simultaneously for a set time period or longer. Thereupon, control signal output unit  82  outputs a signal corresponding to the position of detecting member  33  in question, in other words, an operating signal (prescribed control signal) which causes holding table  12  to rotate through a prescribed angle, to rotational actuator  11 .  
      If spatter flies into hole section  32  and the splatter happens to be detected by two optical sensors  71 A and  71 B as it passes through the center of hole section  32 , then since two optical sensors  71 A and  71 B are separated from each other, the detection signals from two optical sensors  71 A and  71 B will not be detected simultaneously. Therefore, a confirmation signal is not output from the time period detection unit  81  of control circuit unit  39 , and consequently, there is no risk of incorrect operation due to spattering.  
      In this way, by simply introducing welding torch  3  into a hole section  32  formed in a casing  31 , the attitude of the workpiece W is changed automatically, via detecting members  33 . More specifically, when it becomes necessary to change the attitude of the workpiece W, an instruction to that effect can be supplied to attitude changing device  4  or article attachment device  5 , in accordance with the operational tasks carried out by the welding robot. Furthermore, it is possible to prevent spattering generated during welding from being detected mistakenly as welding torch  3 .  
      Furthermore, rotational actuator  11  and pneumatic pressure cylinder  26  described above are operated by air pressure (an operating pneumatic pressure), and therefore they are registered in position (controlled) at the respective stroke ends of the piston, which means that the composition of the control unit can be simplified, and costs can be reduced, in comparison with a case where the angle of rotation achieved by an electric motor, or the like, must be controlled.  
      Moreover, since safety device  51  is provided, then even if there is a problem in control system  6 , the welding work (operational task) performed by welding robot  1  is halted, and therefore work safety can be ensured.  
      In order to achieve a more reliable confirmation that welding torch  3  is present by the detecting members  33 , set time period adjusting unit  83  of control system  6  should set the time period during which the detection signals are simultaneously detected, to a long period.  
      In the embodiment described above, an optical sensor is used as a detecting member for detecting a welding torch, but it is also possible to use a proximity sensor, or the like, for example. Besides locating the sensors in the hole sections, it is also possible to locate detecting members respectively at appropriate positions inside a box-shaped container, without forming hole sections and without providing partitions.  
      Furthermore, the embodiment described above relates to such a case that is applicable to welding work by a welding robot, but the present invention may of course be applied to other assembly tasks, apart from welding.  
      Moreover, the embodiment described above relates to such a case where six detecting members are provided, but it is possible to increase or reduce the number of detecting members, appropriately, in accordance with the increase or decrease in the number of tasks performed with respect to the workpiece, for example.  
      Furthermore, the embodiment described above relates to such a case where the rotational axis of the holding table is disposed in the vertical direction, but the rotational axis is not limited to being vertical, and it may also be disposed at an oblique angle with respect to the vertical plane, or naturally, in a horizontal direction, depending on the attitude during welding.  
     INDUSTRIAL APPLICABILITY  
      The control system according to the present invention is valuable for controlling a workpiece attitude changing device by a welding torch in a welding robot device; and furthermore, it is also valuable for controlling a work machine, when changing the attitude of a component, or moving a component, by means of a work arm in an article assembly robot device.  
      What has been described above are preferred aspects of the present invention. It is of course not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, combinations, modifications, and variations that fall within the spirit and scope of the appended claims.