Patent Publication Number: US-6910946-B2

Title: Polishing machine

Description:
TECHNICAL FIELD 
   The present invention relates to a polishing machine, and more particularly to a polishing machine which is capable of improving the precision of workpiece processing and its reliability by conducting a polishing process using a grinding tool at a constant pressure by means of a static pressure system and controlling the operating system of a tool carrying unit in a more stable manner. 
   BACKGROUND ART 
   Generally, a polishing process is used to polish part of the face of a casting in various shapes and patterns such as a mold, a cold forging mold and a blank mold to be as smooth as a mirror. 
   This polishing process plays the role of minimizing surface roughness after a milling or grinding process in order to make the surface smooth and maintain surface precision. 
   Equipment such as home appliances and OA (Office Automation) devices tend to have a short life cycle due to more diverse consumer demand, so the demand for molds continually increases. However, the polishing process, which is the final step of the mold manufacturing, is still conducted manually. There is designed a 6-axis multi-joint robot to automate the polishing process. However, the positioning ability of this robot is inferior to a machine tool having X, Y and Z axes, thereby inferior in precision to other finished surfaces. 
   As an example of the conventional polishing machine,  FIG. 1  shows a machine tool having a 3-directional carrying unit. In this polishing machine, a table  3  is rotatably mounted on a main body  1 , and a workpiece is fixed on the table  3 . An instruction box  5  having various control buttons installed on one side of the main body  1  for controlling the machine. The signal input via the control buttons of the instruction box  5  is transmitted to a control box  7 , which is provided on one side of the body and outputs a control signal to various operating units. 
   In addition, a pair of columns  9  are fixed to the main body  1 . A pair of the columns  9  supports a X-axis carrying unit  11  which is used for lateral movement along the X-axis as in  FIG. 1. A  Y-axis carrying unit  13  is attached to the front side of the X-axis carrying unit  11  in the shape of a cantilever. The Y-axis carrying unit  13  has the same height as the X-axis carrying unit  11 , and is used for front or back movement along the Y-direction as shown in FIG.  1 . 
   Moreover, a Z-axis carrying unit  15  used for vertical movement along the Z-axis as in  FIG. 1  is attached to one side of the Y-axis carrying unit  13 . Below the Z-axis carrying unit  15 , a grinding tool holder  19  is mounted so as to be rotatable at a predetermined angle. A grinding tool  17  is fixed to one side of the grinding tool holder  19 . 
   The conventional polishing machine constructed as above is operated as follows. 
   If a user sends a manipulating signal through the instruction box  5 , operating signals are transmitted to the X-, Y- and Z-axis carrying units  11 ,  13  and  15  respectively through the control box  7 , thereby controlling the grinding tool  17  moving it to a desired position. 
   At the same time, the grinding tool holder  19  rotates at a predetermined angle so that the grinding tool  17  may more precisely contact the workpiece fixed on table  3 . 
   If the compressed air is supplied to the grinding tool holder  19 , the polishing process of the workpiece is conducted by rotation of the grinding tool  17 . 
   In the conventional polishing machine having a configuration and operation as above, the X-axis carrying unit  11  and the Y-axis carrying unit  13  are combined in the shape of a cantilever. Thus, the Y-axis carrying unit  13  is apt to be overloaded. In particular, when the polishing process is performed on a corner of a minute curve by means of the grinding tool  17 , vibration and noise may be generated. 
   In addition, the rotation number of the grinding tool  17  should be adjusted according to materials of the tool and the mold. However, since the grinding tool  17  is rotated by the compressed air in the conventional method, the adjustment in the number of rotations of the tool  17  is not accurate, thereby failing to perform adequate polishing work. 
   Moreover, in conducting the polishing process while the rotating grinding tool  17  is in contact with the surface of the workpiece, there is required to put pressure on the surface of the workpiece at a constant pressure in order to maintain constant finish of the surface. However, since the conventional machine is not equipped with a means to maintain a stable pressure, the work reliability is lower. 
   DISCLOSURE OF INVENTION 
   The present invention has been made to overcome the above problems, and it is an object of the present invention to provide a polishing machine which is capable of reducing vibration and noise generated in the polishing process by means of controlling an operation system so that X-, Y- and Z-axis carrying units are operated in a more stable manner. 
   Another object of the present invention is to provide a polishing machine which is capable of improving processing accuracy and reliability by means of precise control of the number of rotations by the grinding tool, enabling the grinding tool to conduct the polishing process at a constant pressure. 
   In order to accomplish the above object, there is provided a polishing machine which processes a workpiece put on a table of a main body by means of 4-directional control and has a pair of columns in the main body, the polishing machine comprising: a first carrying unit, both ends of which are fixed to a pair of the columns, the first carrying unit having a carrying block mounted thereon; a second carrying unit horizontally perpendicular to the first carrying unit and fixed to the carrying block; a third carrying unit vertically perpendicular to the second carrying unit and fixed to one end of the second carrying unit; a tool head unit mounted below the third carrying unit and inclined at a predetermined angle by a tilting unit for providing a rotational movement at a predetermined angle thereto, the tool head unit having a driving unit for rotating a grinding tool mounted to one side thereof; and a pressure adjustment unit for providing constant pressure to the grinding tool mounted to the tool head unit so that the grinding tool is in contact with the workpiece. 
   According to an aspect of the present invention, there is provided a polishing machine including a main body having a table on which a workpiece is fixed, and a tool head unit for enabling X-, Y- and Z-axis directional movements of a grinding tool for processing the workpiece on the table and capable of tilting it at a predetermined angle, the polishing machine comprising: a first carrying unit including a first housing both ends of which are fixed to each upper pair of columns, two guide rails installed on both edges of an upper surface of the first housing, a servo motor mounted to the one end of the first housing, and a ball screw rotating according to the operation of the servo motor; a carrying block mounted on the first housing to be slidable along the guide rail, the carrying block moving the tool head unit in X-axis direction by means of the ball screw; a second carrying unit fixed to an upper portion of the carrying block through a fixing plate, the second carrying unit having a driving source therein for enabling Y-axis directional movement of the tool head unit; a third carrying unit arranged vertically perpendicular to the second carrying unit and including a third housing having a driving source for enabling Z-axis directional movement of the tool head unit and an elongated portion extending downward from a lower end of the third housing; a tilting unit mounted to a lower end of the elongated portion of the third carrying unit for tilting the tool head unit to a predetermined angle; a driving unit for rotating the grinding tool mounted to the tool head unit; and a pressure adjustment unit for providing constant pressure to the grinding tool so that the grinding tool is in constant contact with the workpiece. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects, and advantages of preferred embodiments of the present invention will be more fully described in the following detailed description, taken accompanying drawings. In the drawings: 
       FIG. 1  is a perspective view showing a conventional polishing machine; 
       FIG. 2  is a perspective view showing a polishing machine according to a preferred embodiment of the present invention; 
       FIG. 3  is a front view showing a tool head unit according to a preferred embodiment of the present invention; 
       FIG. 4  is a side view showing the tool head unit according to the preferred embodiment of the present invention; 
       FIG. 5  is a sectional view showing an installed state of the tool head unit according to the preferred embodiment of the present invention; and 
       FIG. 6  shows a pneumatic circuitry of a pressure adjustment unit according to the preferred embodiment of the present invention. 
   

   BEST MODES FOR CARRYING OUT THE INVENTION 
   Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
   At first, as shown in  FIG. 2 , a polishing machine according to a preferred embodiment of the present invention includes a main body  25  configuring a support part and a table  27  mounted to the main body  25  to be rotated at a predetermined angle. A workpiece is fixed on the table  27 . 
   In addition, in the main body  25 , a control unit  29  having various operation switches and buttons manipulated by a user for controlling overall operation of the machine and a control box  31  for receiving a signal from the control unit  29  and outputting a control signal to various operating units are equipped. 
   A pair of columns  34  having a rectangular bar shape is fixed to both sides of the main body  25 . Above the columns  34 , a first carrying unit  36 , a carrying block  38  and a second carrying unit  40  are arranged in order. 
   The first carrying unit  36  for providing the X-axis direction movement of a tool head unit  46  includes a first housing  361  both ends of which are fixed to upper end of a pair of the columns  34 , two guide rails  362  mounted at both edges of the upper surface of the first housing  361 , a servo motor  366  mounted at one end of the first housing  361 , and a ball screw  364  rotated by the servo motor  366  to carry the carrying block  38  in the X-axis direction. Thus, if the ball screw  364  rotates by the servo motor  366 , the carrying block  38  on the housing  361  moves in the X-axis direction by means of the ball screw  364 . As a result, it is possible to regulate the position of the X-axis of the tool head unit  46  relative to a workpiece on the table  27 . At this time, the movement of the carrying block  38  is guided along the guide rails  362 . 
   On the other hand, the second carrying unit  40  for moving the tool head unit  46  in Y-axis direction includes a second housing  404  fixed to an upper portion of the carrying block  38  through a fixing plate  382 . In addition, though not shown in the figure, a ball screw similar to the ball screw  364  of the first carrying unit  36  is mounted below the second housing  404 , and a driving unit for rotating the ball screw like the servo motor  366  of the first carrying unit  36  is equipped in the second housing  404  in order to regulate the Y-axis directional movement of the tool head unit  46 . Thus, the second carrying unit  40  may regulate the Y-axis directional position of the tool head unit  46  against the workpiece on the table  27 . 
   A third housing  426  configuring a third carrying unit  42  is mounted to one side of the second carrying unit  40 . Though not shown in the figure, a ball screw similar to the ball screw  364  of the first carrying unit  36  is mounted below the third housing  426 , and a driving unit for rotating the ball screw like the servo motor  366  of the first carrying unit  36  is equipped in the third housing  426  in order to regulate the Z-axis directional movement of the tool head unit  46 . Thus, the second carrying unit  40  may regulate the Z-axis directional position of a grinding tool  64  against the workpiece on the table  27 . 
   As shown in  FIG. 5 , a tilting unit  44  for tilting the grinding tool  64  relative to the workpiece is mounted at a lower end of an elongated portion  428  which is elongated downward from a lower end of the third housing  426 . The tilting unit  44  has a tilting servo motor  43  for driving the tool head unit  46  through a driving axis  45  and a driven axis  47 . The driven axis  47  engaged with the driving axis  45  is fixed to the base  48  of the tool head unit  46 . This driven axis  47  transmits the rotational force of the tilting servo motor  43  supplied through the driving axis  45  toward the tool head unit  46  so that the grinding tool  64  mounted at the lower end of the tool head unit  46  may be tilted. 
   The driven axis  47  is mounted to one side of the base  48  fixed to one side of the tilting unit  44  through a connection block  49 . The tool head unit  46  is mounted to the other side of the base  48 . 
   As shown in  FIGS. 3 and 4 , the tool head unit  46  is provided with a tool-rotating servo motor  50  for rotating the grinding tool  46 . One end of this servo motor  50  is fixed to one side of a fixing bracket  52 . A driving pulley  54  mounted to a rotary shaft of the servo motor  50  is positioned to the other side of the fixing bracket  52  fixed to the base  48 . 
   In addition, a driven pulley  56  is positioned to the other side of the fixing bracket  52 , being spaced apart form the driving pulley  54 . The driving pulley  54  and the driven pulley  56  are wound by a belt  58 . Thus, the rotational force of the servo motor  50  is transmitted to the driven pulley  56  through the driving pulley  54  and the belt  58 . 
   A connection rod  57  is mounted to the other side of the fixing bracket  52 . The rotational force of the driven pulley  56  is transmitted to the grinding tool  64  through a rectangular spindle  60 . As shown in  FIG. 5 , the connection rod  57  has a rectangular groove which one end of the rectangular spindle  60  having a rectangular section is inserted into. Thus, the rectangular spindle  60  is capable of transmitting the rotational force from the servo motor  50  and at the same time is capable of sliding in a longitudinal direction along an inner surface of the connection rod  57 . 
   The rotational force of the driven pulley  56  transmitted through the rectangular spindle  60  is then transmitted to a rotary shaft  63  through a connection portion  61 . The connection portion  61  has rectangular grooves at both sides, respectively. Among them, one end of the spindle  60  is inserted into the rectangular groove formed on one end of the connection portion  61 , while one end of the rotary shaft  63  is inserted into the rectangular groove formed on the other end. The grinding tool  64  is coupled to the lower end of the rotary shaft  63 . As described above, since the connection portion  61  has the rectangular grooves at both ends, the spindle  60  and the rotary shaft  63  coupled to both ends of the connection portion  61  can transmit the rotational force from the servo motor  50  and at the same time can slide in a longitudinal direction along the inner surface of the connection portion  61 . 
   In such a configuration, if the rotary shaft  63  rotates by the rotational force transmitted from the servo motor  50  through the driving pulley  54 , the belt  58 , the driven pulley  56 , the connection rod  57  and the connection portion  61 , the grinding tool  64  coupled to the lower end of the rotary shaft  63  also rotates and conducts the polishing process for the workpiece fixed on the table  32 . 
   On the other hand, as shown in  FIG. 3 , a through hole  64  is formed in the center of the fixing bracket  52 . To both sides of the through hole  64 , attached is a hollow plate  68  of a disk shape having a threaded fixing hole  66  at its center. 
   A screw is also formed on a piston rod  71  of an air cylinder  70  so as to correspond to the threaded fixing hole  66 . During assembling, the piston rod  71  of the air cylinder  70  passes through the fixing hole  66  of the hollow plate and the through hole  64  of the bracket, and is then fixed by a nut  70  screwed to the threaded portion. 
   The air cylinder  70  is a double-acting cylinder. As shown in  FIG. 6 , the air cylinder  70  includes a first port  72  and a second port  74  provided at both ends for introducing the compressed air from a pneumatic source  90 . Thus, the inside of the air cylinder  70  may is balanced to have a static pressure by using the compressed air supplied to the second port  74  and the first port  72 . 
   The air cylinder  70  has a piston  73  for sliding along its inner wall. The piston  73  is connected to a piston rod  71 . In addition, the pressing force of the grinding tool  64  exerted to the workpiece on the table  27  may change during the polishing process. At this time, the changed pressing force is transmitted to the fixing bracket  52  through the rotary shaft  63 , the connection portion  61  and the connection rod  57 . Therefore, the fixing bracket  52  moves forward and backward, and the piston rod  71  connected to the fixing bracket  52  also moves forward and backward, thereby moving the position of the piston  73  and changing the pressure in the air cylinder  70 . 
   Here, the pressure change in the air cylinder  70  may be detected and controlled using a pressure adjustment unit to be described later with reference to FIG.  6 . Therefore, it becomes possible to always keep a constant pressing force of the grinding tool  64  against the workpiece on the table  27 . 
   On the other hand, as shown in  FIG. 4 , a spindle head  62  and the air cylinder  70  are fixed to a plate  78 , which is fixed to an LM guide  79 . This LM guide  79  is mounted to be slidable along a guide rail  81  fixed to the base  48 . Thus, as described later in detail, if the piston rod  71  moves forward or backward by the operation of the pressure adjustment unit, the LM guide  79  of the plate  78  in which the air cylinder  70  and the spindle head  62  are mounted slides on the guide rail  81  of the base  48 , thereby keeping the pressing force of the grinding tool  64  against the workpiece on the table  27  regularly. 
   The air cylinder  70  is provided with the pressure adjustment unit as shown in FIG.  6 . The conduit connected to the first port  72  of the air cylinder  70  is connected to an electro-pneumatic regulator  80 , while the conduit connected to the second port  74  is subsequently connected to a pressure sensor  82  for detecting pressure and to a first solenoid valve  84  for controlling the direction of the compressed air. 
   The conduit getting out of the first solenoid valve  84  is diverged into two conduits. One of them is connected to the electro-pneumatic regulator  80 , and the other is connected to a precise regulator  86 . 
   The conduits for providing compressed air to the precise regulator  86  and the electro-pneumatic regulator  80  are connected to an air unit (FRL)  88 , which is an assembly of an air filter, a regulator and a lubricator. Between the air unit  88  and the pneumatic source  90 , a second solenoid valve  92  is connected. 
   The pressure sensor  82  detects pressure in the conduit and transmits the detected value to a control unit (not shown) in the control box  31 . The control unit compares the value transmitted from the pressure sensor  82  with a set value and then sends a control signal to the electro-pneumatic regulator  80  and the first solenoid valve  84  to control the air pressure supplied to the air cylinder  70 . 
   Here, the precise regulator  86  preferably employs a regulator capable of adjusting the pressure into 3 stages, thereby controlling the air pressure more accurately than general regulators. 
   In the preferred embodiment of the present invention, the electro-pneumatic regulator  80  and the precise regulator  86 , which are used as a pressure adjustment unit, the pressure sensor  82  and the air unit  88  are well known to those skilled in the art, and not described here in detail. 
   Now, the operation of the polishing machine according to the preferred embodiment of the present invention constructed as above is described. 
   For the movement of the tool head unit  46  in the X-, Y- and Z-axis directions, a worker operates the operation switches and the operation buttons installed in the control unit  29 . Then, the control unit of the control box  31  outputs control signals to the first to third carrying units  36 ,  40  and  42  on the basis of the input signal. 
   By use of the signal from the control unit, the servo motor  386  of the first carrying unit  36  starts to move. Then, the ball screw  364  rotates and the carrying block  38  moves in the X-axis direction along the guide rail  362 . Therefore, the tool head unit  46  moves in the X-axis direction. 
   On the other hand, if a control signal for Y-axis directional movement of the tool head unit  46  is transmitted to the driving source mounted in the second carrying unit  40 , the second carrying unit  40  moves in a direction (Y-axis direction) perpendicular to the first carrying unit  36 , thereby moving the tool head unit  46  in the Y-axis direction. 
   In addition, if a control signal for Z-axis directional movement of the tool head unit  46  is transmitted to the driving source mounted in the third carrying unit  42 , the third housing  426  of the third carrying unit  40  moves vertically, thereby moving the tool head unit  46  in the Z-axis direction. 
   On the other hand, if a tilting signal of the tool head unit  46  is input, the control unit outputs a control signal to the tilting servo motor  43  included in the tilting unit  44  shown in FIG.  5 . If the tilting servo motor  43  rotates the driving axis  45 , the driven axis  47  fixed to the base  48  also rotates together, thereby rotating the tool head unit  46  at a certain angle. Therefore, it is made possible to tilt the grinding tool  64  against the workpiece on the table  27 . 
   Afterwards, if a worker pushes an operation switch for rotation of the grinding tool  64 , the control unit in the control box  31  outputs a control signal to the tool-rotating servo motor  50  shown in FIG.  4 . If the servo motor  50  rotates the driving pulley  54  according to the electric connection of the servo motor  50 , the rotation of the driving pulley  54  is transmitted to the driven pulley  56  through the belt  58 , and the rotation of the driven pulley  56  is transmitted to the rectangular spindle  60  through the connection rod  57 , thereby rotating the rectangular spindle  60 . 
   The rotation of the rectangular spindle  60  is also transmitted to the tool-fixing rotary shaft  63  coupled to the connection portion  61  as shown in  FIG. 5 , thereby rotating the grinding tool  64  mounted to the lower end of the tool-fixing rotary shaft  63 . Therefore, the grinding tool  64  may execute the polishing process to the workpiece on the table  27 . 
   At this time, in case of adjusting the rotation speed of the grinding tool  64 , the rotation speed of the grinding tool  64  is controlled more simply and accurately by adjusting the rotation speed of the tool-rotating servo motor  50 . 
   In addition, in the pressure adjustment unit using the air cylinder  70 , as shown in  FIG. 6 , the compressed air generated by the pneumatic source  90  is supplied to the air unit  88  through the second solenoid valve  92 . The air flowed in the air unit  88  becomes static and is kept constant. 
   The compressed air having a certain pressure passing from the air unit  88  is respectively supplied to the precise regulator  86  and the electro-pneumatic regulator  80 , respectively. At this time, the compressed air supplied to the 3-stage type precise regulator  86  is adjusted more precisely in three stages, and then supplied to the second port  74  of the air cylinder  70  through the first solenoid valve  84 . In addition, the compressed air supplied from the air unit  88  to the electro-pneumatic regulator  80  is supplied to the first port  72  of the air cylinder  70  in a regular pressure. 
   Therefore, the inside of the air cylinder  70  is balanced to have a static pressure by the compressed air supplied to the second port  74  and the first port  72 . At this time, if the piston rod  71  in the air cylinder moves forward or backward according to the procedure of the polishing process, the piston  73  connected to the piston rod  71  slides along the inner wall of the air cylinder  70 , thereby changing the air pressure in the air cylinder  70 . 
   At this time, since the pressure sensor  82  is installed in the conduit between the first solenoid valve  84  and the second port  74  of the air cylinder  70 , a signal regarding the air pressure change on the conduit detected by the pressure sensor  82  is directly transmitted to the control unit of the control box  31 . 
   The control unit compares the input signal transmitted from the pressure sensor  82  with a set value, and then outputs a control signal to the electro-pneumatic regulator  80  when the detected pressure is different from the set value. Therefore, the electro-pneumatic regulator  80  controls the pressure supplied to the air cylinder  70  through the second port  74  so as to always keep the pressure of the air cylinder  70  regularly. 
   In an exemplified explanation, if the air pressure having a value of 1 is supplied to the first port  72  and the second port  74 , the piston  73  of the air cylinder  70  moves backward to reduce the inner space of the air cylinder  70  connected to the second air port  74 , thereby relatively increasing the air pressure. 
   For example, the air pressure increases to 1.3, the pressure sensor  82  detects it and sends a signal to the electro-pneumatic regulator  80 , and the air pressure established in the electro-pneumatic regulator  80  is supplied to the second port  74 , thereby moving the piston  73  of the air cylinder  70  into its initial position. 
   At this time, the compressed air supplied to the second port  74  has a value of 1.6 greater than the increased pressure, i.e., 1.3. If the pressure of the second port  74  decreases, a lower pressure is supplied to the second port  74 , thereby moving the piston  73  to its initial position. 
   The air cylinder  70  equipped with the above-mentioned pressure adjustment unit works together with the grinding tool  64  fixed to one side of the fixing bracket  52  since the piston rod  71  having a screw portion is fixed to the fixing bracket  52  by means of the nut  70 , as shown in  FIGS. 3 and 4 . 
   During the polishing process, the grinding tool  64  is pressed into the workpiece by about 10 mm. If the grinding tool  64  is pressed more than a set value or less than a set value due to the shape of the workpiece, the rectangular spindle  60  fixed to and working together with the grinding tool  64  slides in the connection rod  57 . 
   The tool-fixing rotary shaft  63  coupled to the grinding tool  64  is fixed in the spindle head  62 , and the air cylinder  70  also works together and moves along the LM guide  79 , being mounted to the plate  78 . 
   The operation of the air cylinder  70  activates the pressure adjustment unit according to the preferred embodiment of the present invention, thereby moving the piston rod  71  forward or backward. 
   Accordingly, the plate  78  to which the air cylinder  70  and the spindle head  62  are mounted slides along the LM guide  79 , so the grinding tool  64  polishes the workpiece fixed to the table  27  at a constant pressure. 
   The polishing machine according to the preferred embodiment of the present invention constructed as above can prevent any member from being overloaded since the first carrying unit  36  and the second carrying unit  40  are coupled in a shape of not a cantilever but a simple beam. In addition, the polishing machine gives more precise circumstances in the polishing process since vibration and noise are decreased. 
   In addition, though the grinding tool  64  is conventionally rotated using the compressed air, the present invention adopts the tool-rotating servo motor  50 , thereby enabling more accurate control of the rotation number. 
   Moreover, by using the rectangular spindle  60  which is capable of receiving a rotational force while being capable of sliding in the connection rod  57 , the polishing machine of the present invention gives a power transmission structure having increased free degrees, while receiving the rotational force more easily. 
   In addition, since the pressure adjustment unit is provided so that the grinding tool  64  may be contacted to the workpiece with a constant pressure, the polishing process may be accomplished more regularly. 
   INDUSTRIAL APPLICABILITY 
   As described above, by using the polishing machine of the present invention, it is possible to give a system which operates with more stable coupling structure between orthogonal carrying units, thereby ensuring a more precise polishing process. 
   In addition, since the grinding tool is driven using a motor, the rotation number of the grinding tool can be adjusted depending on working conditions, thereby improving the work efficiency. 
   Moreover, since the pressure adjustment unit is provided so that the grinding tool can be contacted to the workpiece at a constant pressure, the work reliability is more improved.