Abstract:
A vertical type of double disc surface grinding machine of the present invention comprises a clamp device which can clamps and holds a work like a brake disc at a correct clamping position under a stable state even when a configuration of a work upper surface is complicated. This machine is equipped with a pair of upper and lower grinding wheels, a work holding jig which is self rotatable, and said clamp device. The clamp device is equipped with a clamp unit freely rotatable through a bearing onto a clamp rod of an elevator actuator. The clamp unit is equipped with a steel ball contacting with a central concave portion of a work upper surface.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field of the Invention 
   The present invention relates to a vertical type of double disc surface grinding machine which simultaneously grinds upper and lower end surfaces of a work like a brake disc of a vehicle held by a work holding jig by means of a pair of upper and lower grinding wheels. More particularly, it relates to an improvement in a clamp device for said grinding machine which grinds the work rotated by the work holding jig. 
   2. Prior Art 
   Conventionally, the clamp device for clamping the work to the self rotatable work holding jig has been equipped with a clamp metal such as a clamp claw or a clamp arm in a manner as vertically movable, so that the work has been secured to a specified position of the work holding jig by pushing the clamp metal from upside against a proper position of a work upper surface. 
   Especially, respect to a work which is a rotating body such as a disc brake for automobile and which has a wide ground surface and provided with a specified rigidity so as no to be deflected even when it is held at its center; a center position of the work is clamped to the work holding jig and the work is self rotated together with the work holding jig so that an outer peripheral portion of the work is inserted in between the grinding wheels. 
   PROBLEMS OF THE PRIOR ART TO BE RESOLVED 
   In case where the work is ground while being rotated by the work holding jig, it is difficult to hold the work at a correct holding position under a stable state and to always keep a grinding accuracy when a configuration of work upper surface is complicated or an area to be clamped is small. 
   OBJECTS OF THE INVENTION 
   An object of the present invention is to provide a vertical type of double disc surface grinding machine which can clamp and hold a work at its correct clamp position under stable state even when a configuration of work upper surface is complicated or an area to be clamped is small. 
   SUMMARY OF THE INVENTION 
   A vertical type of double disc surface grinding machine of the present invention comprises a work holding jig including a self-rotating mechanism and a clamp device for clamping a work W from upper side against the work holding jig, in which the clamp device is equipped with a clamp unit freely rotatable around a self rotating axis center of the work holding unit through a bearing onto an elevator mechanism of an elevator actuator; i.e. a clamp rod elevated by a cylinder, and the clamp unit is equipped with a steel ball contacting with a central concave portion of work upper surface. 
   According to the above-mentioned structure, even in case of the work having the complicated configuration of upper surface or the small area to be clamped, the work can be positioned correctly within a reference receiving surface which contacts with the work W to support it and can be clamped under stable state, as compared with the clamp device equipped with the clamp metal such as the conventional clamp claw; thereby a grinding accuracy can be kept stable. 
   Since the clamp unit is fitted to the elevator member (clamp rod) rotatably around the rotating axis center of the work holding jig, there is no possibility of occurrence of slippage between the steel ball and the work during the grinding work so that the steel ball is scarcely worn out. 
   When the steel ball is so inserted in a ball retaining cylinder as to be protruding downward and pressed from above by a conical receiving recessed surface of a ball cap attached to the ball retaining cylinder in a detachable manner, maintenance procedures such as assembly and replacement of the steel ball will become easy and the steel ball itself can be cheaply available in a form of goods on the market. 
   When a stop member (stop pin) which engages with a part of the work W to restrict a rotating motion of the work W relative to the work holding jig is installed on the upper surface of the work holding jig, the rotating motion of the work holding jig can be restricted relative to the work holding jig during the grinding operation, so that the grinding accuracy can be improved still more. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of a vertical type of double disc surface grinding machine to which the the present invention is applied. 
       FIG. 2  is a vertical sectional view of a work holding jig and a work at a detaching position. 
       FIG. 3  is a vertical sectional view of a work holding jig, a work and a clamp unit at a grinding position. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is the side view of the vertical type of double disc surface grinding machine to which the present invention is applied. A pair of upper and lower opposing grinding wheels  2  &amp;  3  are housed in a body case  1 , and the upper and lower grinding wheels  2  &amp;  3  are secured to upper and lower grinding wheel shafts  4  &amp;  5  disposed on the same perpendicular axis center O 3 , respectively. The both grinding wheel shafts  4  &amp;  5  are so constructed as to be movable in vertical direction by elevator mechanisms respectively, and so connected and linked to a power transmission mechanism that these shafts are rotated in reverse directions respectively. 
   An index table  6  for supplying works is secured to an upper end of a vertical table drive shaft  7 , and this table drive shaft  7  is supported to a cylindrical support case  8  rotatably around a table rotating axis center O 1  through a bearing, and connected and linked to a drive motor through a not-shown transmission mechanism. 
   On the index table  6 , there installed a pair of work holding jigs  10  and clamp devices  12  for clamping works W on respective work holding jigs  10  from upside. 
   The both work holding jigs  10  are disposed each other around the table axis center O 1  with a phase difference of 180°, and supported to a cylindrical jig support case  15  in such a manner as movable around a self-rotating center O 2 . By a half turn of the index table  6 , a position change becomes possible between a grinding-wheel-side grinding position A 2  for grinding works and an opposing side detaching position A 1  for loading and unloading works. 
   The clamp device  12  is composed of a pair of cylinders  22  having clamp rods  21  extensible in lower side and clamp units  23  fitted to lower ends of the clamp rods  21 . Respective cylinders  22  are disposed on the same axis center as the self-rotating axis center O 2  of the work holding jig  10  respectively, and fixed to a bracket which is secured to an upper surface of the index table  6 , so that these cylinders are rotated together with the work holding jigs  10  around the table rotating axis center O 1  by the turning motion of the index table  6 . 
     FIG. 2  is the enlarged vertical sectional view of the work holding jig  10  and the work W at the detaching position A 1 . The work comprises a disc brake for a vehicle, and is composed of a hub  26  integrally having a flange  26   a  and an annular disc  27  secured to the flange  26   a . Both upper and lower end faces of the disc  27  is subjected to the surface grinding operation. 
   A self-rotating shaft  30  is supported rotatably in a jig support case  15  though a bearing  29 . The work holding jig  10  is secured to an upper end face of the self-rotating shaft  30  on the same axis center as the self-rotating axis center O 2 . The bottom end of the self-rotating shaft  30  is connected and linked to a drive motor through a not-shown gear transmission mechanism. 
   The work holding jig  10  is formed into an annular shape. An annular positioning piece  28  is fixed on top of the jig  10  in a coaxial manner. An annular work reference surface  32 , with which a lower surface of the flange  26   a  of the work W contacts, is formed protrusively toward upside. An inner peripheral surface  31  of the positioning piece  28  is set to a size fitting with the hub  26  of the work W. The work holding jig  10  is provided with an upward projecting stop pin  37  for restricting a rotating movement of the work W relative to the work holding jig  10 . The stop pin  37  is inserted into a rod insertion hole  40  formed on the work holding jig  10  in such a manner as movable in vertical direction and urged toward upside by a spring  42 , so as to stop the rotating movement of the work W relative to the work holding jig  10  when its upper end portion engages with a fitting bolt  45  or the flange  26   a  of the work W. 
     FIG. 3  is the enlarged vertical sectional view of the clamp unit  23  and the work holding jig  10  at the grinding position A 2 . The clamp unit  23  is equipped with a steel ball  46  which contacts with a peripheral edge of a central hole of the work W from upside, a ball retaining cylinder  47  which fits with and supports the steel ball  46  protrusively toward downside, a ball cap  48  which has a conical receiving recessed face  48   a  contacting with an upper face of the steel ball  46 , a bearing holder  51  which is supported rotatably around the self-rotating axis center O 2  through the bearing  50  by the bottom portion of the clamp rod  21 , and a lower cover  52  which is secured to a lower surface of the bearing holder  51 . The steel ball  46 , the ball retaining cylinder  47 , the ball cap  48  and the bearing holder  51  are all arranged on the same axis center as the self-rotating center O 2  of the work holding jig  10 . 
   An inner peripheral surface of a lower half of the ball retaining cylinder  47  is formed into a small-diameter tapered shape at its lower part. The steel ball  46  is held by said tapered portion in a manner as protrusively toward downside. The ball cap  48  fits in the ball cylinder  47  from upside. The steel ball  46  is connected to the lower cover  52  together with the ball retaining cylinder  47  in a manner a protrusive toward downside. 
   (Function) 
   In  FIG. 1 , paying attention to an operation at the detaching position A 1 ; the clamp unit  23  is moved upward, the work W is placed on the work holding jig  10 , and the clamp rod  21  is moved downward, thereby the clamp unit  23  is clamped onto an upper central position of the work W. 
   In  FIG. 2 , at the time of loading the work, the hub  26  of the work W fits in the inner peripheral surface  31  of the positioning piece  28 , a lower face of the flange  26   a  contacts with the annular reference receiving surface  32  of the positioning piece  28 , and the stop pin  37  is positioned at a location deviated from the fitting bolt  45  in a peripheral direction. When the clamp unit  23  is moved downward under this state, the steel ball  23  contacts forcedly with a top edge P of an inner peripheral face (central hole) of the hub  26 , so that the work W is positioned at a predetermined position as illustrated in FIG.  3 . 
   Since a portion pressurized by the steel ball  46  is limited within the reference receiving surface  32 , the work is positioned stably and correctly when it is clamped. 
   After completion of the clamping operation at the detaching position A 1  of  FIG. 1 , the operating position is changed to the grinding position A 2  when the index table  6  is moved by a half-turn. 
   In  FIG. 3 , the grinding wheels  2  &amp;  3  are retracted upward and downward respectively during the position changing operation. After completion of the position changing operation, the work holding jig  10  is self rotated to cause rotation of the work W around the self-rotating axis center O 2  and a distance between the upper and lower grinding wheels  2  &amp;  3  is decreased, thereby the upper and lower end faces are simultaneously subjected to the surface grinding. 
   The steel ball  46  is also rotated together with the work W around the self-rotating axis center O 2  during the grinding operation, however, the entire of the clamp unit  23  is rotated around the self-rotating axis center O 2  relative to the clamp rod  21  because the clamp unit  23  is supported against the clamp rod  21  through the bearing  50 . In other words, a slippage does not occur between the steel ball  46  and the work W so that a slippage does not occur between the steel ball  46  and the conical receiving face  48   a  too. Therefore, a worn-out of the steel ball  46  is controlled. 
   Since the work W is stopped in its rotation relative to the work holding jig  10  by the stop pin  45 , there is no possibility of rotation of the work W relative to the work holding jig  10  caused by a grinding resistance. 
   After completion of the grinding operation of the work W, the upper and lower grinding wheels  2  &amp;  3  are retracted from the upper and lower end faces of the work W upward and downward respectively. The self rotation of the work holding jig  17  is stopped, and the position is changed to the detaching position A 1  of  FIG. 1  by the half turn of the index table  6 . Then, the clamp unit  23  is moved upward. 
   Other Embodiment 
   
       
       (1) In place of the elevator actuator utilizing the cylinder having the clamp rod of  FIG. 1 , another actuators of pinion rack type and rocking lever type etc. utilizing motors for their power sources may be used.