Abstract:
A rotary cylinder for controlling operations of a chuck to be used on a lathe or the like. The rotary cylinder comprises a housing, a cylinder unit, a distributor supporting the cylinder unit in bearings fitted therein, and a seizure detecting system including a detaining mechanism for restraining the distributor from rotation relative to the housing. The seizure detecting system detects seizure between the distributor and the cylinder unit and allows the distributor to rotate relative to the housing. The distributor is capable of being fixedly held on the housing without distorting the bearings supporting the cylinder unit and of being disconnected from the housing when seizure occurs between the distributor and the cylinder unit.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a rotary cylinder device for controlling operations of a chuck to be used on a lathe or the like. 
     2. Description of the Related Art 
     Generally, a rotary cylinder device is constructed by fitting a piston axially sidably in a cylinder unit, supporting the cylinder unit for rotation in a bearing on a distributor, and fitting the distributor in an annular draining space formed in a housing. A rotary cylinder device disclosed in JP-B-63-41689 (reference 1) has a distributor positioned and held fixedly in place in an annular space with a bolt screwed in a housing so that its tip is pressed against the distributor. Another rotary cylinder device disclosed in JP-A-61-241505 (reference 2) has a distributor held fixedly in place in an annular space with a bolt screwed in a housing so that its free end part is fitted in a radial hole formed in the distributor. 
     Vibrations may be generated in those prior art rotary cylinder devices if the distributor makes a slight turning movement in a direction opposite to a direction in which the cylinder unit rotates at a high rotational speed. Therefore, the distributor is fastened to the housing with the bolt as mentioned in the references 1 and 2. In the reference 1, the bolt is pressed against a part of the distributor separated from an annular groove, such as an oil passage, formed in the distributor and hence the bolt is pressed unavoidably against a part of the distributor near the bearing. Consequently, it is possible that the bearing is distorted by pressure exerted on the distributor by the bolt. In the reference 2, if foreign matters are caught in the thin annular space between the distributor and the cylinder unit and cause seizure between the distributor and the cylinder unit, the distributor is forced to rotate together with the cylinder unit. Therefore, it is possible that the torque of the cylinder unit is transmitted through the distributor and the bolt to the housing and the housing is forced to rotate together with a high-pressure hose connected thereto. 
     Seizure between the cylinder unit and the distributor can be known from the excessive rise of load on the spindle motor of a lathe or the like. However, the excessive load that may be produced by seizure between the cylinder unit and the distributor and may be exerted on the spindle motor must be greater than a load corresponding to a cutting force necessary for machining. Therefore, the rotary cylinder device may be damaged seriously and troubles will occur before seizure between the cylinder unit and the distributor is detected. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a rotary cylinder device comprising a housing, a cylinder unit, and a distributor supporting the cylinder unit in bearings fitted therein and capable of being fixedly held on the housing without distorting the bearings supporting the cylinder unit and of being disconnected from the housing when seizure occurs between the distributor and the cylinder unit. 
     Another object of the present invention is to provide a rotary cylinder device comprising a cylinder unit, a distributor, and a seizure detecting means for detecting seizure between the cylinder unit and the distributor. 
     According to the present invention, a rotary cylinder device comprises: a cylinder unit having a distributor support member and a piston chamber therein, and a piston axially slidably fitted in the piston chamber; a distributor supported for rotation on a support part of the distributor support member; and a housing defining an annular draining space and provided with a side wall defining a bore closely receiving the distributor therein; and a detaining mechanism for restraining the distributor from rotation relative to the housing, said detaining mechanism including a protrusion provided for one of the housing and the distributor, and a recess provided in the other of the housing and the distributor and tightly receiving the protrusion, said protrusion being adapted to be forced to move out of the recess to allow the rotation of the distributor relative to the housing when a torque exceeding a threshold torque is exerted on the distributor. 
     The rotary cylinder device may further comprise a seizure detecting system capable of detecting the rotation of the distributor together with the cylinder unit due to seizure or the like. 
     The above and other objects, features and advantages of the present invention will become more apparent from the following description taken in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal sectional view of a rotary cylinder in a preferred embodiment of the present invention; 
     FIG. 2 is an enlarged sectional view taken on line II—II in FIG. 1; 
     FIG. 3 is a partly sectional front view of the rotary cylinder of FIG. 1 as mounted on a spindle; 
     FIG. 4 is a front view of a pin, explaining a detaining mechanism and a seizing detecting system in a modification; 
     FIG. 5 is a sectional view of a detaining mechanism and a seizing detecting system in another modification; 
     FIG. 6 is a sectional view of a detaining mechanism in a third modification; 
     FIG. 7 is a sectional view of a detaining mechanism in a fourth modification; and 
     FIG. 8 is a sectional view of a detaining mechanism in a fifth modification. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1 illustrating a rotary cylinder  1  in a preferred embodiment of the present invention, the rotary cylinder  1  has a cylinder unit  2  constructed by attaching a cup-shaped rod cover  4  to a distributor support shaft  3  so as to cover the front end surface  3   a  of the distributor support shaft  3  and to define a cylindrical piston chamber  5 . A piston  6  is axially slidably fitted in the piston chamber  5  of the cylinder unit  2 . The piston  6  divides the piston chamber  5  into a front pressure chamber  5   a  and a rear pressure chamber  5   b . The piston  6  is restrained from rotation relative to the cylinder unit  2  by a pin  7  fixed thereto. A reduced rear part  3   b  of the distributor shaft  3  is supported in a pair of bearings  8  fitted in a front and a rear end part of a distributor  9 . The front bearing  8  fitted in the front end part of the distributor  9  is retained in place by the rear end surface  3   c  of the distributor shaft  3 , and the rear bearing  8  fitted in the rear end part of the distributor  9  is retained in place by an end cap  10  attached to the rear end surface  3   d  of the distributor shaft  3 . The cylindrical distributor  9  is fitted in a cylindrical draining bore  11   a  formed in a housing  11 , for rotation relative to the housing  11 . The rear end surface  9   a  of the distributor  9  is in contact with an inner flange 11 b  formed in a rear end part of the housing  11 . The housing  11  is provided with a seizure detecting system  12 , which will be described later, for detecting seizure between the cylinder unit  2  and the distributor  9 . As shown in FIG. 2, the seizure detecting system  12  has a detecting device  13  engaged with the distributor  9  to restrain the distributor  9  from rotation. 
     The distributor  9  is provided in its outer circumference with a first outer annular groove  14   a  and a second outer annular groove  14   b  for supplying a fluid into the front pressure chamber  5   a  and the rear pressure chamber  5   b , respectively. The outer annular grooves  14   a  and  14   b  are connected to a pair of ports, not shown formed in the housing  11  at positions axially and circumferentially separated from each other, respectively. The ports are connected by hoses, not shown, to a fluid source, not shown. The distributor  9  is provided in its inner circumference with a first inner annular groove  15   a  and a second inner annular groove  15   b , the first inner annular groove  15   a  is connected by a passage  16  formed in the distributor shaft  3  and a passage  17  formed in the rod cover  4  to the front pressure chamber  5   a . The second inner annular groove  15   b  is connected by a passage  18  formed in the distributor shaft  3  to the rear pressure chamber  5   b.    
     The piston  6  has a hollow piston rod  6   a  having an internally threaded front end part. As shown in FIG. 3, a connecting pipe  20  coaxial with a spindle  19  included in a machine tool is screwed in the internally threaded front end part of the piston rod  6   a . The connecting pipe  20  is connected to a chuck  21  attached to the front end of the spindle  19 . The piston  6  is reciprocated by the pressure of the fluid supplied into the cylindrical piston chamber  5  to operate jaws  21   a  included in the chuck  21 . The rear end of the spindle  19  is connected to the front end of the rod cover  4  by an adapter  22  so that the cylinder unit  2  rotates together with the spindle  19  and the chuck  21 . 
     As indicated in FIG. 2, the seizure detecting system  12  comprises a part of the housing  11  provided with a radial through hole  11   c , a steel ball  23  put in the radial through hole  11   c , a detecting rod  24  axially movably inserted in the radial through hole  11   c  so that an enlarged inner end  24   a  thereof is in contact with the steel ball  23 , a bracket  26  fastened to the housing  11  with bolts  27  so as to cover the radial through hole  11   c , a spring  29  disposed between the bracket  27  and the inner end  24   a  of the detecting rod  24  in the radial through hole  11   c  so as to press the steel ball  23  (protrusion) through the rod  24  against the distributor  9 , a part of the distributor  9  provided with a recess  9   b  receiving a part of the steel ball  23  therein to form a linking device  28  for restraining the rotation of the housing  11  and the distributor  9  relative to each other, and a switch  25  held on the bracket  26  so as to be operated by the detecting rod  24 . 
     An outer end part of the detecting rod  24  projects through a hole formed in the bracket  26  from the outer surface of the bracket  26 . If an excessive torque is exerted on the distributor  9 , the steel ball  23  is forced to move out of the recess  9   b  to allow the distributor  9  to rotate relative to the housing  11 , and the detecting rod  24  is pushed radially outward by the steel ball  23  so that the outer end  24   b  of the detecting rod  24  is pressed against the actuator of the switch  25  to close the switch  25 . Then, a detection signal is transmitted through the switch  25 . 
     When the distributor  9  is turned from a predetermined position (FIG. 2) relative to the housing  11 , the steel ball  9  is forced to move out of the recess  9   b  formed in the distributor  9 , and the switch detects the movement of the outer end  24   b  of the detecting rod  24 . The detecting device  13  having the steel ball  23  and the detecting rod  24  may be substituted by a single pin-shaped detecting member  13  shown in FIG.  4 . 
     FIG. 5 shows a seizure detecting system in a modification. In the seizure detecting system shown in FIG. 5, a steel ball  23  is put radially movably in a radial hole  9   c  formed in the distributor  9 , the steel ball  23  is biased radially outward by a spring  30  disposed in the radial hole  9   c  on the inner side of the steel ball  23 , the steel ball  23  is kept in the radial hole  9   c  by a retaining protrusion  31 , and the detecting device  13  is inserted in a through hole  11   c  formed in the housing  11  and is pressed against the steel ball  23  by a spring  34 . If the distributor  9  is turned from the predetermined position relative to the housing  11 , the steel ball  23  is forced to sink into the radial hole  9   c  and the detecting device  13  is moved radially inward. 
     The cylinder unit  2  of the rotary cylinder  1  is driven for rotation at a high rotational speed by a spindle motor, not shown, included in a lathe or the like. If foreign matters are caught in an annular space T between the distributor  9  and the reduced rear part  3   b  of the cylinder unit  2 , seizure between the distributor  9  and the cylinder unit  2  occurs. The torque of the cylinder unit  2  tries to rotate all the components of the rotary cylinder  1 . The distributor  9  is restrained from rotation relative to the housing  11  by the steel ball  23  received in the recess  9   b  formed in the distributor  9 . However, the steel ball  23  is forced to move out of the recess  9   c  to allow the distributor  9  to rotate relative to the housing  11  if an excessive torque greater than a threshold is exerted on the housing  11 . Consequently, the steel ball  23  pushes the detecting rod  24  radially outward, the detecting rod  24  closes the switch  25 , a stop signal is transmitted through the switch  25  to a controller  32  for controlling the spindle motor, not shown, and the controller  32  provides a stop signal to stop the spindle motor. Thus, the seizure detecting system  12  detects quickly seizure between the cylinder unit  2  and the distributor  9  and stops the rotation of the cylinder unit  2  to limit the breakage of the rotary cylinder  1  to the least unavoidable extent. When the steel ball  23  is forced to move out of the recess  9   c  formed in the distributor  9  to move the detecting rod  24  radially outward in the through hole  11   c  formed in the housing  11 , the distributor  9  is released from the housing  11 . Consequently, the housing remains stationary even if the distributor  9  rotate together with the cylinder unit  2 , and hence it is possible to avoid the danger of the high-pressure hoses connected to the housing  11  being flung around. Since the distributor  9  is restrained from rotation by a circumferential force acting between the steel ball  23  and the surface of the recess  9   b , any radial pressure is not exerted on the bearings  8  and hence the bearings  8  are not distorted. 
     Although the distributor  9  is restrained from rotation relative to the housing  11  by the steel ball  23  or the detecting member  13  (FIG. 4) in this embodiment, the distributor  9  may be restrained from rotation relative to the housing  11  by a detaining mechanism separate from the seizure detecting system  12 . The seizure detecting system  12  may detect the rotation of the distributor  9  from the predetermined angular position by attaching an indicator, such as a reflector or a magnet, to a predetermined position on, for example, the circumference of the distributor  9 , and sensing the movement of the indicator by a sensor, such as a proximity switch, attached to the housing  11  instead of detecting the same by the radial movement of the detecting device  13 . 
     Referring to FIG. 6 showing a detaining mechanism in a modification, a bolt  52  is screwed in the housing  11  so that its end part  52   a  projects from the inner circumference of the housing  11  into a recess  9   e  of a predetermined depth formed in the outer circumference of the distributor  9 . A neck  52   c  is formed in a part of the bolt  52  corresponding to the boundary between the inner circumference of the housing  11  and the outer circumference of the distributor  9 , i.e., a part between the end part  52   a  and a threaded part  52   b  of the bolt  52 , by forming an annular groove  54  in the same part. The diameter of the neck  52   c  is determined so that the neck  52   c  is sheared off when a breaking torque slightly smaller than a torque that will be exerted on the distributor  9  when seizure is caused between the distributor  9  and the reduced rear part  3   b  of the distributor shaft  3  of the cylinder unit  2  by foreign matters caught in the annular space T between the reduced rear part  3   b  of the distributor shaft and the distributor  9  is exerted on the distributor  9 . 
     When a torque exceeding the breakage torque is exerted on the distributor  9 , the neck  52   c  of the bolt  52  is sheared off and the end part  52   a  of the bolt  52  is separated from the threaded part  52   b . Consequently, the distributor  9  is allowed to rotate relative to the housing  11 , the housing  11  remains stationary and hence the high-pressure hoses connected to the housing  11  are not flung around. 
     The distributor  9  is provided with the recess  9   e  in this modification, a seizure detecting system in another modification, a bolt  52  having an end part  52   a , a threaded part  52   b , and a neck  52   c  formed between the end part  52   a  and the threaded part  52   b  may be attached to the distributor  9  so that the end part  52   a  projects from the outer circumference of the distributor  9  into a recess  9   e  formed in the housing  11 . 
     As shown in FIG. 7, a pin  60 , such as a taper pin, having an outer end part and an inner end part, and provided with a through hole  60   a  perpendicular to the axis of the pin  60  in a part thereof between the outer and the inner end part may be driven into a through hole formed in the housing  11  so that the through hole  60   a  is located on the boundary between the distributor  9  and the housing  11  and the inner end part is fitted in a hole  9   e  formed in the distributor  9 . 
     As shown in FIG. 8, a pin  60 A having an inner end part and an outer end part, and provided with a neck  62   c  may be used instead of the pin  60  shown in FIG.  7 . The pin  60 A is driven into the through hole formed in the housing  11  so that the neck  60   c  is located on the boundary between the distributor  9  and the housing  11  and the inner end part is fitted in the hole  9   e  formed in the distributor  9 . 
     As is apparent from the foregoing description, according to the present invention, the distributor is restrained from rotation relative to the housing by putting a protrusion projecting radially inward from the housing in the recess formed in the: distributor, while the distributor is allowed to rotate relative to the housing when a torque exceeding the predetermined threshold torque is exerted on the distributor. Therefore, the distortion of the bearing fitted in the distributor can be prevented, the housing can be kept stationary even if an excessive torque is exerted on the distributor due to seizure between the cylinder unit and the distributor, and the accidental flinging of the high-pressure hoses connected to the housing can be avoided. 
     The rotation of the distributor together with the cylinder unit due to seizure or the like can be detected and rotation of the cylinder unit can be stopped upon the detection of the rotation of the distributor, so that the breakage of the rotating cylinder can be limited to the least unavoidable extent. Since the rotation of the distributor relative to the housing is detected through the detection of the radial movement of the detecting device, the rotation of the distributor relative to the housing can be easily and surely detected and the rotation of the housing is prevented. 
     Although the invention has been described in its preferred forms with a certain degree of particularity, obviously many changes and variations are possible therein. It is therefore to be understood that the present invention may be practiced otherwise than as specifically described herein without departing from the scope and spirit thereof.