Patent Publication Number: US-2005118032-A1

Title: Vaccum-generating unit

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a vacuum-generating unit capable of applying a negative pressure to a suction mechanism such as a suction pad.  
      2. Description of the Related Art  
      A vacuum supply apparatus has been hitherto utilized as a means for applying a negative pressure to a suction pad. Such a vacuum supply apparatus generally comprises: an ejector for generating a negative pressure; a vacuum port connected to and communicated with a suction mechanism such as a suction pad via a tube; a valve mechanism provided with a pressure fluid-supplying solenoid valve and a vacuum-breaking solenoid valve for feeding compressed air to the ejector and the vacuum port and cutting off the supply of the compressed air; and a vacuum switch for detecting the negative pressure generated in the vacuum port (see, for example, Japanese Laid-Open Utility Model Publication No. 61-9599).  
      In this arrangement, the ejector includes a nozzle and a diffuser which are formed as separate members respectively and which are coaxially assembled into a hole of a body respectively.  
      An explanation will be made schematically about an operation of such a conventional vacuum supply apparatus.  
      Compressed air is supplied to the ejector via the valve mechanism section to generate a negative pressure. The negative pressure generated in the ejector is applied to the suction pad via the tube connected to the vacuum port. The suction pad attracts and holds a workpiece in accordance with the action of the negative pressure generated in the suction pad. While the suction pad is attracting and holding the workpiece, a robot arm displaces the workpiece to transport the workpiece to a predetermined position.  
      Subsequently, in order to release the workpiece, compressed air (positive pressure) is supplied to the suction pad from the valve mechanism section via a passage communicated with the vacuum port, and thus an effect of the negative pressure of the suction pad is decreased and eliminated. As a result, the suction pad releases the workpiece to locate the workpiece to a desired position.  
      There has been hitherto a need to achieve a small size and a light weight as far as possible by reducing the outer diameter dimension, and to decrease the production cost by reducing the number of assembling steps. It is because, for example, when a plurality of vacuum supply apparatuses are provided in a row to construct a manifold, it is possible to obtain a solenoid valve manifold having an extremely small size and a light weight, and to effectively utilize the installation space by reducing the outer diameter dimension of the entire apparatus.  
     SUMMARY OF THE INVENTION  
      A general object of the present invention is to provide a vacuum-generating unit capable of achieving a small size and a light weight by reducing the outer diameter dimension of the entire apparatus and capable of reducing the production cost.  
      The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a perspective view illustrating a vacuum-generating unit according to an embodiment of the present invention;  
       FIG. 2  shows a side elevational view, partly cut away, taken in the axial direction of the vacuum-generating unit shown in  FIG. 1 ;  
       FIG. 3  shows a fragmental longitudinal sectional view illustrating an ejector shown in  FIG. 2 ;  
       FIG. 4  shows a fragmental side view, partly cut away, illustrating a state in which a pressure sensor is detachably installed to a tube joint;  
       FIG. 5  shows a fragmental longitudinal sectional view illustrating an ejector according to a modified embodiment of the present invention; and  
       FIG. 6  shows a fragmental longitudinal sectional view illustrating an ejector according to a comparative embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      In  FIGS. 1 and 2 , reference numeral  10  indicates a vacuum-generating unit according to an embodiment of the present invention.  
      The vacuum-generating unit  10  comprises: a main body  20  including a first block member  12 , a second block member  14 , and a third block member  16  formed of resin materials and connected to each other in the longitudinal direction; a solenoid valve assembly  26  including a pressure fluid-supplying solenoid valve  22  and a vacuum-breaking solenoid valve  24  arranged on the upper portion of the main body  20 ; an ejector  32  including a nozzle hole  28  and a diffuser hole  30  (see  FIG. 2 ) integrally formed (i.e., formed in a single component) in the third block member  16 ; and a detector  34  for detecting a negative pressure derived from a vacuum port as described later on.  
      The pressure fluid-supplying solenoid valve  22  and the vacuum-breaking solenoid valve  24  have the same components respectively, and they are closed in a normal state. The solenoid valves  22 ,  24  are not limited to the above normally closed type. The solenoid valves  22 ,  24  may be open in a normal state, self-retained, or timer-equipped, for example.  
      The first to third block members  12 ,  14 ,  16  have substantially the same width respectively, and they are formed to be thin-walled (see  FIG. 1 ). The first block member  12  includes a compressed air supply port (pressure fluid supply port)  36  for supplying compressed air (positive pressure) to the ejector  32 .  
      The second block member  14  includes a first ON/OFF valve  42  in a chamber  40  therein, and the first ON/OFF valve  42  is switched from an OFF state to an ON state by applying a pilot pressure thereto. The third block member  16  includes an unillustrated second ON/OFF valve in a chamber thereof, and the second ON/OFF valve is switched from an OFF state to an ON state by applying a pilot pressure thereto.  
      The compressed air supply port  36  communicates with the inside of the chamber  40  of the second block member  14  arranged with the first ON/OFF valve  42 , via a first passage  48  having a substantially L-shaped bent form. An unillustrated second passage, which is branched from the first passage  48 , is formed to communicate with the pressure fluid-supplying solenoid valve  22 . An unillustrated third passage, which is branched from the first passage  48 , is formed to communicate with the vacuum-breaking solenoid valve  24 . An unillustrated fourth passage, which is branched from the first passage  48 , is formed to communicate with the second ON/OFF valve (not shown).  
      As shown in  FIG. 2 , a first pilot passage  58  is formed between the pressure fluid-supplying solenoid valve  22  and the first ON/OFF valve  42 . The solenoid valve  22  applies a pilot pressure to the first ON/OFF valve  42  through the first pilot passage  58  when energized to be in the ON state. A second pilot passage  60  is formed between the vacuum-breaking solenoid valve  24  and the unillustrated second ON/OFF valve. The solenoid valve  24  applies a pilot pressure to the second ON/OFF valve (not shown) through the second pilot passage  60  when energized to be in the ON state.  
      The ejector  32  is provided in the third block member  16  which is integrally formed, for example, by means of resin molding. As shown in  FIG. 3 , the ejector  32  includes the nozzle hole  28  and the diffuser hole  30 , both of which are formed in an integrated manner in the third block member  16 . The nozzle hole  28  and the diffuser hole  30  are arranged coaxially respectively. The nozzle hole  28  includes an orifice having a small diameter. On the other hand, the diffuser hole  30  includes a hole having a diameter larger than that of the nozzle hole  28  and a predetermined length in the axial direction.  
      A suction passage  64  is formed between the nozzle hole  28  and the diffuser hole  30  which constitute the ejector  32 . The suction passage  64  is communicated with a vacuum port  62  and is bent in a substantially L-shaped form. A negative pressure generated in the ejector  32  is applied to a suction mechanism such as an unillustrated suction pad connected to a tube joint  65  via a tube, for example.  
      An exit end of the diffuser hole  30  is communicated with an exhaust port (discharge port)  66  formed in the third block member  16 . The compressed air supplied to the ejector  32  is exhausted outside via a silencer  68  communicated with the exhaust port  66 .  
      When the vacuum-breaking solenoid valve  24  is in the ON state, a pilot pressure is applied to the unillustrated second ON/OFF valve. When the pilot pressure is applied, the unillustrated second ON/OFF valve becomes the ON state, and a compressed air (positive pressure) is supplied to the suction passage  64  communicated with the vacuum port  62 . Accordingly, an effect of the negative pressure is decreased and eliminated.  
      The first ON/OFF valve  42  and the unillustrated second ON/OFF valve have the same components respectively. Each of the valves includes: a valve plug  72  displaceable by a predetermined distance in a substantially horizontal direction; and a retainer  74  fixed in the chamber  40  and formed to be cylindrical so that the valve plug  72  is surrounded thereby (see  FIG. 2 ).  
      A first ring member  78  is installed to the outer circumferential surface of the valve plug  72  on one end side. The first ring member  78  is seated on a seat section  76  of the retainer  74  to close the chamber  40 . A second ring member  80  is installed to the outer circumferential surface of the valve plug  74  on the other end side. The second ring member  80  is slidable along the inner wall surface of the retainer  74 . Each of the first and second ring members  78 ,  80  is made of an elastic material such as natural rubber and synthetic rubber.  
      When the first ON/OFF valve  42  is in the OFF state, the supply of the compressed air to the ejector  32  is stopped. When the first ON/OFF valve  42  is in the ON state, the compressed air is supplied to the ejector  32 .  
      The detector  34  includes a pressure sensor  82  for detecting the negative pressure to be applied to the suction pad via an unillustrated communication passage communicated with the suction passage  64 . As shown in  FIG. 4 , the pressure sensor  82  is detachably installed to a tube joint  84  connected to the third block member  16  by the aid of a screw portion. A detection signal outputted from the pressure sensor  82  is transmitted, for example, to an unillustrated external controller via a lead wire  86 .  
      In this arrangement, since the pressure sensor  82  is detachably installed by the aid of the tube joint  84 , it is possible to achieve a small size and a light weight of the entire apparatus as compared with an arrangement in which an unillustrated vacuum switch is installed. An operator can arbitrarily select a pressure sensor  82  corresponding to a negative pressure range of the negative pressure derived from the vacuum port  62 . Further, it is possible to conveniently replace with another pressure sensor  82 .  
      As shown in  FIG. 2 , a flow rate-adjusting screw  88  for adjusting a flow rate of a pressure fluid (i.e., pilot pressure) for breaking the vacuum is provided between the pressure fluid-supplying solenoid valve  22  and the vacuum-breaking solenoid valve  24 . When a knob  88   a  of the flow rate-adjusting screw  88  is gripped and rotated in a predetermined direction, a tapered portion  88   b,  which faces the passage  60 , can be displaced in the vertical direction by screwing the screw  88  with respect to a cylinder  90  to adjust the flow rate of the pressure fluid flowing through the passage  60 .  
      The vacuum-generating unit  10  according to the embodiment of the present invention is basically constructed as described above. Next, its operations, functions, and effects will be explained. It is assumed that each of the pressure fluid-supplying solenoid valve  22  and the vacuum-breaking solenoid valve  24  is in the OFF state in the initial state.  
      Compressed air supplied from an unillustrated compressed air supply source is introduced into the first passage  48  via the compressed air supply port  36 . The compressed air introduced into the first passage  48  is supplied into the chamber  40  of the first ON/OFF valve  42  communicated with the first passage  48 . The valve plug  72  is displaced in the leftward direction in  FIG. 2  under the action of the compressed air, but the first ON/OFF valve  42  is still in the OFF state.  
      In the above state, the unillustrated controller outputs an ON signal to the pressure fluid-supplying solenoid valve  22  to start a pressure fluid-supplying operation. In this situation, the vacuum-breaking solenoid valve  24  is still in the OFF state.  
      When the pressure fluid-supplying solenoid valve  22  becomes the ON state, a pilot pressure is applied to the first ON/OFF valve  42  via the first pilot passage  58 . The valve plug  72  is displaced in the rightward direction in  FIG. 2  under the pilot pressure, so that the first ON/OFF valve  42  becomes the ON state. When the first ON/OFF valve  42  is in the ON state, then the compressed air introduced into the first passage  48  passes through the first ON/OFF valve  42 , and the compressed air is supplied to the ejector  32 .  
      In the ejector  32 , the compressed air is jetted from the nozzle hole  28  toward the diffuser hole  30  to generate a negative pressure. The negative pressure is applied to the unillustrated suction pad via the suction passage  64  and the tube connected to the vacuum port  62 .  
      Therefore, the suction pad makes contact with the workpiece in accordance with the operation of the unillustrated robot arm. When the suction pad attracts and contacts the workpiece under the negative pressure, the negative pressure is further raised. The negative pressure is detected by the pressure sensor  82  of the detector  34 . A detection signal is transmitted from the pressure sensor  82  to the unillustrated controller. When the controller receives the detection signal from the pressure sensor  82 , it is confirmed that the suction pad reliably attracts and holds the workpiece.  
      Next, an explanation will be made about a situation in which the negative pressure of the suction pad is shut off to separate the workpiece therefrom at a predetermined position after moving the workpiece by a predetermined distance.  
      The unillustrated controller transmits an OFF signal to the pressure fluid-supplying solenoid valve  22 . As a result, the solenoid valve  22  becomes the OFF state, and thus the first ON/OFF valve  42  becomes the OFF state. Accordingly, the supply of the compressed air to the ejector  32  is stopped, and thus the application of the negative pressure from the vacuum port  62  to the suction pad is stopped.  
      On the other hand, the unillustrated controller transmits an ON signal to the vacuum-breaking solenoid valve  24  so that the solenoid valve  24  is in the ON state. When the solenoid valve  24  is in the ON state, a pilot pressure is applied to the unillustrated second ON/OFF valve via the second pilot passage  60 . The valve plug  72  of the second ON/OFF valve is displaced under the pilot pressure, and the second ON/OFF valve becomes the ON state. When the second ON/OFF valve is in the ON state, the compressed air introduced into the first passage  48  is supplied to the vacuum port  62  through the second ON/OFF valve. As a result, the compressed air supplied from the compressed air supply port  36  passes through the vacuum port  62 , and the compressed air is supplied to the suction pad. The suction pad stops attracting the workpiece and separates the workpiece therefrom.  
      When the suction pad separates the workpiece therefrom, the pressure of the suction pad changes the negative pressure to an atmospheric pressure. The pressure sensor  82  detects the atmospheric pressure and transmits a detection signal to the unillustrated controller to indicate the fact that the workpiece is separated. When the controller receives the detection signal, it is confirmed that the suction pad separates the workpiece therefrom. Thus, it is possible to reliably separate the workpiece from the suction pad.  
      In the embodiment of the present invention, the nozzle hole  28  and the diffuser hole  30  are integrally formed or formed in a single component, for example, by using a mold for molding resin, in the third block member  16  of the main body  20 . Accordingly, it is possible to realize a small size and a light weight of the entire apparatus. Therefore, it is possible to effectively utilize the space in which the vacuum-generating unit  10  is installed.  
      It is a matter of course that a plurality of the vacuum-generating units  10  according to the embodiment of the present invention are connected in a row to construct a manifold.  
      Next, an explanation will be made while making comparison between an ejector  100  according to a modified embodiment of the present invention shown in  FIG. 5  and an ejector  200  concerning a comparative embodiment shown in  FIG. 6 .  
      In the ejector  100  according to the modified embodiment, a nozzle hole  104  and a diffuser hole  106  are formed coaxially in an integrated manner in a single block member  102  composed of a resin material. A suction port  108  is formed between the nozzle hole  104  and the diffuser hole  106 . A supply port  110  for supplying a pressure fluid to the nozzle hole  104  is formed on one side of the block member  102 . A discharge port  112  for discharging the pressure fluid derived from the diffuser hole  106  is formed on the opposite side of the block member  102 .  
      The ejector  200  concerning the comparative embodiment comprises two members of a block member  203  having a diffuser hole  202  formed therein, and a nozzle  210  formed with a nozzle hole  208  and connected to the block member  203  in an air-tight manner by the aid of an O-ring  206  in an opening  204  of the block member  203 . A supply port  212  and the nozzle hole  208  are formed integrally in the nozzle  210 . The nozzle  210  is inserted into the opening  204  of the block member  203  by the aid of a screw portion  214 .  
      The block member  203  is formed with a suction port  216  which is communicated with the opening  204 , and a discharge port  218  which is communicated with the diffuser hole  202  respectively.  
      Therefore, in the ejector  100  according to the modified embodiment, the nozzle  210  and the O-ring  206  are unnecessary as compared with the ejector  200  concerning the comparative embodiment. The ejector  100  according to the modified embodiment can be constructed by only the single block member  102 . Therefore, the number of parts is reduced, and it is unnecessary to perform the operation for assembling the nozzle  210  to the block member  203 . As a result, the ejector  100  according to the modified embodiment makes it possible to reduce the production cost by reducing the number of parts and reducing the number of assembling steps.  
      While the invention has been particularly shown and described with reference to preferred embodiments, it will be understood that variations and modifications can be effected thereto by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.