Abstract:
A robot arm mechanism includes a handling member for supporting and handling an object, a robot arm made up of at least four arm links, and a robot arm driving mechanism for driving the robot arm to assume its contracted and extended position. The robot arm comprises first and second arm links and a link retaining mechanism pivotably retaining the first and second arm links. The link retaining mechanism comprises first and second joint cross linkages similar in shape and each having two arms crossed to each other. The first joint cross linkage is integrally connected with one of the first and second arm links of the robot arm. The second joint cross linkage is integrally connected with the other one of the first and second arm links of the robot arm. This leads to the advantage of providing a robot arm mechanism exempt from driven gears, belts and pulleys forming part of a synchronous motion mechanism necessitated by conventional robot arm mechanisms to ensure that no dust is produced and fallen in a vacuum working chamber of highly pure air.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a robot arm mechanism having arms contracted and extended, and more particularly to a robot arm mechanism incorporating an arm driving mechanism for driving the arms to assume its contracted and extended positions. 
     2. Description of the Related Art 
     The robot arm mechanism of this type is used in the process of producing semiconductors in which the robot arm mechanism is operated to have arms contracted and extended to handle works, i.e., objects to be treated. These objects include for example such as wafers and other precision parts that are to be transferred and then unloaded onto a work table by the robot arm mechanism. 
     A conventional robot arm mechanism of this kind is disclosed in, for example, Japanese patent laying-open publication Tokkaihei 7-227777 and comprises a handling member for holding and releasing objects, and robot arms for operating and moving the hand. The robot arms are constituted by a plurality of parallel links having joint portions on which are provided synchronous gears for maintaining the links in their parallel attitudes. The synchronous gears are rotated to have the hand maintained in its predetermined direction by moving the hand forwardly and rearwardly while the parallel links are operated. Another conventional robot arm mechanism of this kind is disclosed in Japanese patent laying-open publication Tokkaihei 9-272084 and comprises robot arms constituted by a plurality of parallel links to form a parallelogram linkage contractable and extensible, and a synchronous motion mechanism including gears, belts and pulleys operatively mounted on the links. The synchronous motion mechanism is operated to have gears, belts and pulleys driven so that the parallelogram linkage can be contracted and extended. 
     It is another object of the present invention to provide a robot arm mechanism which is exempt from such driven gears, belts and pulleys of the synchronous motion mechanism necessitated by the conventional robot arm mechanisms to ensure that no dust is produced and fallen in the vacuum working chamber of highly pure air. 
     SUMMARY OF THE INVENTION 
     According to the first aspect of the present invention there is provided a robot arm mechanism comprising: a handling member for supporting and handling an object; a robot arm connected to the handling member, the robot arm comprising a first arm link having first and second end portion, a second arm link having first and second end portion, and a link retaining mechanism having a center line, the link retaining mechanism pivotably retaining the first and second arm links respectively at the first end portions of the first and second arm links and keeping parallel a first line and a second line, the first line being a line passing through the first and second end portions of the first arm link and the second line being a line symmetrical with respect to the center line with the line passing through the first and second end portions of the second arm link, the link retaining mechanism comprising a first joint cross linkage including a first short link having first and second end portions, a first long link having first and second end portions and longer than the first short link of the first joint cross linkage of the link retaining mechanism, the first short and long links of the first joint cross linkage of the link retaining mechanism pivotably connected with each other at the second end portion of the first short link of the first joint cross linkage of the link retaining mechanism and the first end portion of the first long link of the first joint cross linkage of the link retaining mechanism, a second short link having first and second end portions and substantially equal in length to the first short link of the first joint cross linkage of the link retaining mechanism, the first long link of the first joint cross linkage of the link retaining mechanism and the second short link of the first joint cross linkage of the link retaining mechanism pivotably connected with each other at the second end portion of the first long link of the first joint cross linkage of the link retaining mechanism and the first end portion of the second short link of the first joint cross linkage of the link retaining mechanism, and a second long link having first and second end portions and substantially equal in length to the first long link of the first joint cross linkage of the link retaining mechanism, the second short and long links of the first joint cross linkage of the link retaining mechanism pivotably connected with each other at the second end portion of the second short link of the first joint cross linkage of the link retaining mechanism and the first end portion of the second long link of the first joint cross linkage of the link retaining mechanism, the second long link of the first joint cross linkage of the link retaining mechanism and the first short link of the first joint cross linkage of the link retaining mechanism pivotably connected with each other at the second end portion of the second long link of the first joint cross linkage of the link retaining mechanism and the first end portion of the first short link of the first joint cross linkage of the link retaining mechanism under the state that the second long link of the first joint cross linkage of the link retaining mechanism is crossed with the first long link of the first joint cross linkage of the link retaining mechanism, and a second joint cross linkage including a first short link having first and second end portions, a first long link having first and second end portions and longer than the first short link of the second joint cross linkage of the link retaining mechanism, the first short and long links of the second joint cross linkage of the link retaining mechanism pivotably connected with each other at the second end portion of the first short link of the second joint cross linkage of the link retaining mechanism and the first end portion of the first long link of the second joint cross linkage of the link retaining mechanism, a second short link having first and second end portions and substantially equal in length to the first short link of the second joint cross linkage of the link retaining mechanism, the first long link of the second joint cross linkage of the link retaining mechanism and the second short link of the second joint cross linkage of the link retaining mechanism pivotably connected with each other at the second end portion of the first long link of the second joint cross linkage of the link retaining mechanism and the first end portion of the second short link of the second joint cross linkage of the link retaining mechanism, and a second long link having first and second end portions and substantially equal in length to the first long link of the second joint cross linkage of the link retaining mechanism, the second short and long links of the second joint cross linkage of the link retaining mechanism pivotably connected with each other at the second end portion of the second short link of the second joint cross linkage of the link retaining mechanism and the first end portion of the second long link of the second joint cross linkage of the link retaining mechanism, the second long link of the second joint cross linkage of the link retaining mechanism and the first short link of the second joint cross linkage of the link retaining mechanism pivotably connected with each other at the second end portion of the second long link of the second joint cross linkage of the link retaining mechanism and the first end portion of the first short link of the second joint cross linkage of the link retaining mechanism under the state that the second long link of the second joint cross linkage of the link retaining mechanism is crossed with the first long link of the second joint cross linkage of the link retaining mechanism, the length ratio of each of the first and second short links of the first joint cross linkage of the link retaining mechanism to each of the first and second long links of the first joint cross linkage of the link retaining mechanism substantially equal to the length ratio of each of the first and second short links of the second joint cross linkage of the link retaining mechanism to each of the first and second long links of the second joint cross linkage of the link retaining mechanism, the first short link of the first joint cross linkage of the link retaining mechanism integrally formed with and in parallel relationship with the first long link of the second joint cross linkage of the link retaining mechanism under the state that the second end portion of the first short link of the first joint cross linkage of the link retaining mechanism is connected with the first end portion of the first long link of the second joint cross linkage of the link retaining mechanism, the first long link of the first joint cross linkage of the link retaining mechanism integrally formed with and in parallel relationship with the first short link of the second joint cross linkage of the link retaining mechanism under the state that the first end portion of the first long link of the first joint cross linkage of the link retaining mechanism is connected with the second end portion of the first short link of the second joint cross linkage of the link retaining mechanism, the first end portion of any one of the first and second arm links integrally formed with the second short link of the first joint cross linkage of the link retaining mechanism, the first end portion of the other one of the first and second arm links integrally formed with the second long link of the second joint cross linkage of the link retaining mechanism; and a robot arm driving mechanism for driving the robot arm. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects, features and advantages of the present invention will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is an enlarged fragmentary skeleton view of the robot arm mechanism shown in FIG. 2 to be used for explaining the principle of the robot arm mechanism according to the present invention; 
     FIG. 2 is a skeleton view of one condition of the first preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 2 a  and FIG. 2 b  are schematic illustrations used to explain the operation of the robot arm mechanism of FIG.  2 . 
     FIG. 3 is a skeleton view of another condition of the first preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 4 is a cross-sectional view taken on the lines F 1 —F 1  in FIG. 2; 
     FIG. 5 is a skeleton view of one condition of the second preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 6 is a skeleton view of another condition of the second preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 7 is a skeleton view of the third preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 8 is a cross-sectional view taken on the lines F 2 —F 2  in FIG. 7; 
     FIG. 9 is a skeleton view of one condition of the fourth preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 10 is a skeleton view of another condition of the fourth preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 11 is a cross-sectional view taken on the lines F 3 —F 3  in FIG. 9; 
     FIG. 12 is a skeleton view of one condition of the fifth preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 13 is a skeleton view of another condition of the fifth preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 14 is a skeleton view of one condition of the sixth preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 15 is a skeleton view of another condition of the sixth preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 16 is a skeleton view of the seventh preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 17 is a skeleton view of the eighth preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 18 is an enlarged fragmentary skeleton view of the robot arm mechanism shown in FIGS. 19,  24 , and  25  to be used for explaining the principle of the robot arm mechanism according to the present invention; 
     FIG. 19 is a skeleton view of the ninth preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 20 is an enlarged fragmentary skeleton view of the robot arm mechanism shown in FIGS. 21,  22 , and  23  to be used for explaining the principle of the robot arm mechanism according to the present invention; 
     FIG. 21 is a skeleton view of the tenth preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 22 is a skeleton view of the eleventh preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 23 is a skeleton view of the twelfth preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 24 is a skeleton view of the thirteenth preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 25 is a skeleton view of the fourteenth preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 26 is an enlarged fragmentary skeleton view of the robot arm mechanism shown in FIG. 27 to be used for explaining the principle of the robot arm mechanism according to the present invention; 
     FIG. 27 is a skeleton view of the fifteenth preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 28 is an enlarged fragmentary skeleton view of the robot arm mechanism shown in FIG. 29 to be used for explaining the principle of the robot arm mechanism according to the present invention; 
     FIG. 29 is a skeleton view of the sixteenth preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 30 is an enlarged fragmentary skeleton view of the robot arm mechanism shown in FIG. 31 to be used for explaining the principle of the robot arm mechanism according to the present invention; 
     FIG. 31 is a skeleton view of one condition of the seventeenth preferred embodiment of the robot arm mechanism according to the present invention; 
     FIG. 32 is a skeleton view of another condition of the seventeenth preferred embodiment of the robot arm mechanism according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Throughout the following detailed description, similar reference characters and numbers refer to similar elements in all figures of the drawings. 
     Referring to FIGS. 1 to  4  of the drawings, there is shown a first preferred embodiment of the robot arm mechanism according to the present invention. The robot arm mechanism  101  is shown in FIGS. 1 to  4  as comprising a handling member  125  for supporting and handling an object. 
     The handling member  125  should be configured to be available for handling, i.e., holding and releasing a wafer and other materials to be used for producing semiconductors. In this embodiment particularly shown in FIG. 2, the handling member  125  is formed with a recess  125   a  which is designed suitably to receive and release such materials. The configuration of the handling member  125  depends upon the sizes and shapes of the materials to be handled by the handling member  125  according to the present invention. 
     The robot arm mechanism  101  further comprises a robot arm  810  connected to the handling member  125 . The robot arm  810  comprises a first arm link  811  having first and second end portion, a second arm link  812  having first and second end portion, and a link retaining mechanism  200  having a center line  201 . 
     The link retaining mechanism  200  pivotably retains the first and second arm links  811  and  812  respectively at the first end portions of the first and second arm links  811  and  812  and keeps parallel a first line and a second line, the first line being a line passing through the first and second end portions of the first arm link  811  and the second line being a line symmetrical with respect to the center line  201  with the line passing through the first and second end portions of the second arm link  812 . In fact the first and second arm links  811  and  812  are in symmetrical relationship with each other with respect to the center line  201 . The above-described parallel relationship is illustrated in FIGS. 2 a  and  2   b . FIG. 2 a  illustrates the specific relationship shown in FIG. 2 wherein the first line L 1  passing through the first and second end portions of the link  811  is maintained colinear with the line L 2 , which is symmetrical with respect to the center line  201  with the line passing through the first and second end portions of the second arm link  812 . FIG. 2 b  illustrates the parallel relationship wherein the first line L 1  passing through the first and second end portions of the link  811  is maintained parallel, but not colinear, with the second line L 2  which is symmetrical with respect to the center line  201  with the line passing through the first and second end portions of the second arm link  812 . 
     The link retaining mechanism  200  comprises a first joint cross linkage  210  which includes a first short link  211  having first and second end portions. 
     The first joint cross linkage  210  further includes a first long link  212  having first and second end portions and longer than the first short link  211 . The first short and long links  211  and  212  are pivotably connected with each other at the second end portion of the first short link  211  and the first end portion of the first long link  212 . 
     The first joint cross linkage  210  further includes a second short link  213  having first and second end portions and substantially equal in length to the first short link  211 . The first long link  212  and the second short link  213  are pivotably connected with each other at the second end portion of the first long link  212  and the first end portion of the second short link  213 . 
     The first joint cross linkage  210  further includes a second long  214  link having first and second end portions and substantially equal in length to the first long link  212 . The second short and long links  213  and  214  are pivotably connected with each other at the second end portion of the second short link  213  and the first end portion of the second long link  214 . 
     The second long link  214  and the first short link  211  are pivotably connected with each other at the second end portion of the second long link  214  and the first end portion of the first short link  211  under the state that the second long link  214  is crossed with the first long link  212 . 
     The robot arm  810  comprises a second joint cross linkage  220  which includes a first short link  221  having first and second end portions. The first long link  212  and the first short link  221  are substantially equal in length to each other. 
     The second joint cross linkage  220  further includes a first long link  222  having first and second end portions and longer than the first short link  221 . The first short and long links  221  and  222  are pivotably connected with each other at the second end portion of the first short link  221  and the first end portion of the first long link  222 . 
     The second joint cross linkage  220  further includes a second short link  223  having first and second end portions and substantially equal in length to the first short link  221 . The first long link  222  and the second short link  223  are pivotably connected with each other at the second end portion of the first long link  222  and the first end portion of the second short link  223 . 
     The second joint cross linkage  220  further includes a second long link  224  having first and second end portions and substantially equal in length to the first long link  222 . The second short and long links  223  and  224  are pivotably connected with each other at the second end portion of the second short link  223  and the first end portion of the second long link  224 . 
     The second long link  224  and the first short link  221  are pivotably connected with each other at the second end portion of the second long link  224  and the first end portion of the first short link  221  under the state that the second long link  224  is crossed with the first long link  222 . 
     The length ratio of each of the first and second short links  211  and  213  to each of the first and second long links  212  and  214  is substantially equal to the length ratio of each of the first and second short links  221  and  223  to each of the first and second long links  222  and  224 . 
     The first short link  211  is integrally formed with and in coaxial relationship with the first long link  222  under the state that the second end portion of the first short link  211  is connected with the first end portion of the first long link  222 . The first long link  212  is integrally formed with and in coaxial relationship with the first short link  221  under the state that the first end portion of the first long link  212  is connected with the second end portion of the first short link  221 . 
     The first end portion of the second arm link  812  is integrally formed with the second short link  213 . The first end portion of the first arm link  811  is integrally formed with the second long link  224 . The center line  201  passes through the first and second end portions of the first long link  212 . The first end portions of the first and second arm links  811  and  812  are positioned on the center line  201 . 
     The robot arm  810  further comprises a third arm link  813  having first and second end portions. The handling member  125  has first and second portions. The third arm link  813  and the handling member  125  are pivotably connected with each other at the second end portion of the third arm link  813  and the first portion of the handling member  125 . 
     The robot arm  810  further comprises a fourth arm link  814  having first and second end portions. The fourth arm link  814  and the handling member  125  are pivotably connected with each other at the second end portion of the fourth arm link  814  and the second portion of the handling member  125 . The first and second arm links  811  and  812  are substantially equal in length to each other. The third and fourth arm links  813  and  814  are substantially equal in length to each other. 
     The robot arm  810  further comprises a first joint mechanism  140  retaining the first and third arm links  811  and  813  respectively at the second end portion of the first arm link  811  and the first end portion of the third arm link  813  under the state that the first arm link  811  is pivotable around the second end portion of the first arm link  811  with respect to the third arm link  813 . The second end portion of the first arm link  811  and the first end portion of the third arm link  813  are connected with each other. 
     The first joint mechanism  140  comprises a first link  141  having first and second end portions and substantially equal in length to the first arm link  811 . The first link  141  is integrally formed with and in coaxial relationship with the first arm link  811  under the state that the first end portion of the first link  141  is connected with the first end portion of the first arm link  811 . 
     The first joint mechanism  140  further comprises a second link  142  having first and second end portions. The first and second links  141  and  142  are pivotably connected with each other at the second end portion of the first link  141  and the first end portion of the second link  142 . The second link  142  is pivotably connected with the first end portion of the third arm link  813 . 
     The first joint mechanism  140  further comprises a third link  143  having first and second end portions and substantially equal in length to the first link  141 . The second and third links  142  and  143  are pivotably connected with each other at the second end portion of the second link  142  and the first end portion of the third link  143 . 
     The first joint mechanism  140  further comprises a fourth link  144  having first and second end portions and substantially equal in length to the second link  142 . The third and fourth links  143  and  144  are pivotably connected with each other at the second end portion of the third link  143  and the first end portion of the fourth link  144 . The fourth and first links  144  and  141  are pivotably connected with each other at the second end portion of the fourth link  144  and the first end portion of the first link  141  under the state that the first link  141  is in parallel relationship with the third link  143  and that the second link  142  is in parallel relationship with the fourth link  144 . The second end portion of the fourth link  144  is integrally connected with the first long link  212 . 
     The robot arm  810  further comprises a second joint mechanism  132  retaining the second and fourth arm links  812  and  814  respectively at the second end portion of the second arm link  812  and the first end portion of the fourth arm link  814  under the state that the second arm link  812  is pivotable around the second end portion of the second arm link  812  with respect to the fourth arm link  814 . The second end portion of the second arm link  812  and the first end portion of the fourth arm link  814  are connected with each other. 
     The robot arm  810  further comprises a stabilizing mechanism  160  which includes a first link  161  having first and second end portions and substantially equal in length to the third arm link  813 . The first link  161  is integrally formed with and in coaxial relationship with the third arm link  813  under the state that the first end portion of the first link  161  is connected with the first end portion of the third arm link  813 . 
     The stabilizing mechanism  160  further includes a second link  162  having first and second end portions. The first and second links  161  and  162  are pivotably connected with each other at the second end portion of the first link  161  and the first end portion of the second link  162 . The second link  162  is integrally formed with the handling member  125 . 
     The stabilizing mechanism  160  further includes a third link  163  having first and second end portions and substantially equal in length to the first link  161 . The second and third links  162  and  163  are pivotably connected with each other at the second end portion of the second link  162  and the first end portion of the third link  163 . 
     The stabilizing mechanism  160  further includes a fourth link  164  having first and second end portions and substantially equal in length to the second link  162 . The third and fourth links  163  and  164  are pivotably connected with each other at the second end portion of the third link  163  and the first end portion of the fourth link  164 . The fourth and first links  164  and  161  are pivotably connected with each other at the second end portion of the fourth link  164  and the first end portion of the first link  161  under the state that the first link  161  is in parallel relationship with the third link  163  and that the second link  162  is in parallel relationship with the fourth link  164 . The second end portion of the fourth link  164  is integrally connected with the second link  142 . 
     The robot arm mechanism  101  further comprises a robot arm driving mechanism  120  for driving the robot arm  810 . 
     The arm driving mechanism  120  comprises a first driving shaft  121  rotatable around a rotation axis  123 . 
     The arm driving mechanism  120  further comprises a second driving shaft  122  in the form of a hollow shape to rotatably receive therein the first driving shaft  121  and rotatable around the rotation axis  123 . 
     The second driving shaft  122  is integrally connected with the first long link  212  and rotates the first long link  212  around the rotation axis  123 . The first driving shaft  121  is integrally connected with the first arm link  811  and rotates the first arm link  811  around the first end portion of the first arm link  811 . 
     When the second driving shaft  122  rotates the first long link  212  around the rotation axis  123 , the center line  201  is rotated around the rotation axis  123 . This results in the rotation of the robot arm mechanism  101  around the rotation axis  123 . 
     When the first arm link  811  is rotated by the first driving shaft  121  with respect to the first long link  212 , the fact that the first and second arm links  811  and  812  are respectively and integrally formed with the second long link  224  and the second short link  213  results in the rotation of the second arm link  812  with respect to the first long link  212  and the first arm link  811 . This results in the contracted or extended condition of the robot arm mechanism  101 . 
     While there have been described in the above about the fact that the second driving shaft  122  is integrally connected with the first long link  212  and that the first driving shaft  121  is integrally connected with the first arm link  81  , the first driving shaft  121  may be integrally connected with the second arm link  812  instead of the first arm link  811 , according to the present invention. 
     In this case that the first driving shaft  121  is integrally connected with the second arm link  812  instead of the first arm link  811 , the operation of the robot arm mechanism  101  is similar to the robot arm mechanism  101  in the case that the first driving shaft  121  is integrally connected with the first arm link  811 . 
     While there have been described in the above about the fact that the second driving shaft  122  is integrally connected with the first long link  212  and that the first driving shaft  121  is integrally connected with the first arm link  811 , the second driving shaft  122  may be integrally connected with the second arm link  812  instead of the first long link  212 , according to the present invention. 
     In this case that the first long link  212  is replaced by the second arm link  812 , the second long link  224  is rotated around the rotation axis  123  when the first arm link  811  is rotated by the first driving shaft  121 , resulting from the fact that the first arm link  811  is integrally formed with the second long link  224 . When the second arm link  812  is rotated by the second driving shaft  122 , the fact that the second arm link  812  is integrally formed with the second short link  213  results in the rotation of the second short link  213  around the rotation axis  123 . The rotation of the second long link  224  and the rotation of the second short link  213  can result in the rotation of the first long link  212  around the rotation axis  123 . This results in the rotation of the center line  201 . The rotation of the center line  201  around the rotation axis  123  results in the rotation of the robot arm mechanism  101  around the rotation axis  123 . 
     When the first arm link  811  rotated by the first driving shaft  121  rotates with respect to the second arm link  812  rotated by the second driving shaft  122 , the robot arm mechanism  101  can be contracted and extended. 
     According to the present invention, the first and second driving shafts  121  and  122  may be replaced by each other about the connection with the first arm link  811 , the second arm link  812 , or the first long link  212 . 
     According to the present invention, the fact that the fourth link  144  is integrally connected with the first long link  212  results in the fact that the fourth link  144  is at all times at a same angle to the center line  201 . This results in the fact that the second link  142  in parallel relation with the fourth link  144  is at all times at a same angle to the center line  201 . This results in the fact that the fourth link  164  integrally connected with the second link  142  is at all times at a same angle to the center line  201 . This results in the fact that the second link  162  in parallel relationship with the fourth link  164  is at all times at a same angle to the center line  201 . This results in the fact that the handling member  125  integrally formed with the second link  162  is at all times at a same angle to the center line  201 . 
     Referring to FIGS. 5 and 6 of the drawings, there is shown a second preferred embodiment of the robot arm mechanism according to the present invention. The robot arm mechanism  102  is shown in FIGS. 5 and 6 as comprising a handling member  125  for supporting and handling an object. 
     The robot arm mechanism  102  further comprises a robot arm  820  connected to the handling member  125 . The robot arm  820  comprises a first arm link  821  having first and second end portion, a second arm link  822  having first and second end portion, and a link retaining mechanism  200 . 
     The link retaining mechanism  200  pivotably retains the first and second arm links  821  and  822  respectively at the first end portions of the first and second arm links  821  and  822  and keeps parallel a first line and a second line, the first line being a line passing through the first and second end portions of the first arm link  821  and the second line being a line symmetrical with respect to the center line  201  with the line passing through the first and second end portions of the second arm link  822 . The first end portion of the first arm link  821  is integrally formed with the second short link  213 . The first end portion of the second arm link  822  is integrally formed with the second long link  224 . The first end portions of the first and second arm links  821  and  822  are positioned on the center line  201 . In fact the first and second arm links  821  and  822  are in symmetrical relationship with each other with respect to the center line  201 . 
     The robot arm  820  further comprises a third arm link  823  having first and second end portions. The third arm link  823  and the handling member  125  are pivotably connected with each other at the second end portion of the third arm link  823  and the first portion of the handling member  125 . 
     The robot arm  820  further comprises a fourth arm link  824  having first and second end portions. The fourth arm link  824  and the handling member  125  are pivotably connected with each other at the second end portion of the fourth arm link  824  and the second portion of the handling member  125 . The first and second arm links  821  and  822  are substantially equal in length to each other. The third and fourth arm links  823  and  824  are substantially equal in length to each other. 
     The robot arm  820  further comprises a first joint mechanism  140  retaining the first and third arm links  821  and  823  respectively at the second end portion of the first arm link  821  and the first end portion of the third arm link  823  under the state that the first arm link  821  is pivotable around the second end portion of the first arm link  821  with respect to the third arm link  823 . The second end portion of the first arm link  821  and the first end portion of the third arm link  823  are connected with each other. The first link  141  of the first joint mechanism  140  is substantially equal in length to the first arm link  821 . The first link  141  is integrally formed with and in coaxial relationship with the first arm link  821  under the state that the first end portion of the first link  141  is connected with the first end portion of the first arm link  821 . The second link  142  of the first joint mechanism  140  is pivotably connected with the first end portion of the third arm link  823 . The second end portion of the fourth link  144  of the first joint mechanism  140  is integrally connected with the first long link  212 . 
     The robot arm  820  further comprises a second joint mechanism  132  retaining the second and fourth arm links  822  and  824  respectively at the second end portion of the second arm link  822  and the first end portion of the fourth arm link  824  under the state that the second arm link  822  is pivotable around the second end portion of the second arm link  822  with respect to the fourth arm link  824 . The second end portion of the second arm link  822  and the first end portion of the fourth arm link  824  are connected with each other. 
     The robot arm  820  further comprises a stabilizing mechanism  170  similar to the stabilizing mechanism  160  in the first preferred embodiment of the robot arm mechanism according to the present invention. The stabilizing mechanism  170  includes first, second, third, and fourth links  171 ,  172 ,  173 , and  174  which are respectively similar to first, second, third, and fourth links  161 ,  162 ,  163 , and  164  in the first preferred embodiment of the robot arm mechanism according to the present invention. The stabilizing mechanism  170  and the stabilizing mechanism  160  in the first preferred embodiment are different from each other in the fact that the fourth link  174  has a set angle with respect to the second link  142  to prevent the state that the first and third links  171  and  173  are positioned on a straight line while the robot arm driving mechanism  120  drives the robot arm  820 . 
     The first link  171  is substantially equal in length to the third arm link  823 . The first link  171  is integrally formed with and in coaxial relationship with the third arm link  823  under the state that the first end portion of the first link  171  is connected with the first end portion of the third arm link  823 . The second link  172  is integrally formed with the handling member  125 . The second end portion of the fourth link  174  is integrally connected with the second link  142 . 
     The robot arm mechanism  102  further comprises a robot arm driving mechanism  120  for driving the robot arm  820 . The second driving shaft  122  of the arm driving mechanism  120  is integrally connected with the first long link  212  and rotates the first long link  212  around the rotation axis  123 . The first driving shaft  121  of the arm driving mechanism  120  is integrally connected with the first arm link  821  and rotates the first arm link  821  around the first end portion of the first arm link  821 . 
     While there have been described in the above about the fact that the second driving shaft  122  is integrally connected with the first long link  212  and that the first driving shaft  121  is integrally connected with the first arm link  821 , the first driving shaft  121  may be integrally connected with the second arm link  822  instead of the first arm link  821 , according to the present invention. 
     While there have been described in the above about the fact that the second driving shaft  122  is integrally connected with the first long link  212  and that the first driving shaft  121  is integrally connected with the first arm link  821 , the second driving shaft  122  may be integrally connected with the second arm link  822  instead of the first long link  212 , according to the present invention. 
     According to the present invention, the first and second driving shafts  121  and  122  may be replaced by each other about the connection with the first arm link  821 , the second arm link  822 , or the first long link  212 . 
     The operation of the robot arm mechanism  102  in the second preferred embodiment is similar to the operation of the robot arm mechanism  101  in the first preferred embodiment according to the present invention except for the fact that the stabilizing mechanism  170  prevents the state that the first and third links  171  and  173  are positioned on a straight line while the robot arm driving mechanism  120  drives the robot arm  820 . 
     Referring to FIGS. 7 and 8 of the drawings, there is shown a third preferred embodiment of the robot arm mechanism according to the present invention. The robot arm mechanism  103  is shown in FIGS. 7 and 8 as comprising a handling member  125  for supporting and handling an object. 
     The robot arm mechanism  103  further comprises a robot arm  830  connected to the handling member  125 . The robot arm  830  comprises a first arm link  831  having first and second end portion, a second arm link  832  having first and second end portion, and a link retaining mechanism  300  having a center line  301 . 
     The link retaining mechanism  300  comprises first and second joint cross linkages  310  and  320  are respectively similar to the first and second joint cross linkages  210  and  220  in the first preferred embodiment of the robot arm mechanism according to the present invention. The first joint cross linkage  310  includes first short and long links  311  and  312  and second short and long links  313  and  314  which are respectively similar to first short and long links  211  and  212  and second short and long links  213  and  214  in the first preferred embodiment of the robot arm mechanism according to the present invention. The second joint cross linkage  320  includes first short and long links  321  and  322  and second short and long links  323  and  324  which are respectively similar to first short and long links  221  and  222  and second short and long links  223  and  224  in the first preferred embodiment of the robot arm mechanism according to the present invention. 
     The link retaining mechanism  300  similar to the link retaining mechanism  200  in the first preferred embodiment of the robot arm mechanism according to the present invention, except for the fact that the first long link  312  and the first short link  321  are differ in length from each other and the first short link  311  and the first long link  322  are substantially equal in length to each other. 
     The link retaining mechanism  300  pivotably retains the first and second arm links  831  and  832  respectively at the first end portions of the first and second arm links  831  and  832  and keeps parallel a first line and a second line, the first line being a line passing through the first and second end portions of the first arm link  831  and the second line a line symmetrical with respect to the center line  301  with the line passing through the first and second end portions of the second arm link  832 . 
     The first end portion of the second arm link  832  is integrally formed with the second short link  313 . The first end portion of the first arm link  831  is integrally formed with the second long link  324 . The center line  301  passes through the first and second end portions of the first long link  312 . The first end portions of the first and second arm links  831  and  832  are positioned on the center line  301 . 
     The robot arm  830  further comprises a third arm link  833  having first and second end portions. The third arm link  833  and the handling member  125  are pivotably connected with each other at the second end portion of the third arm link  833  and the first portion of the handling member  125 . 
     The robot arm  830  further comprises a fourth arm link  834  having first and second end portions. The fourth arm link  834  and the handling member  125  are pivotably connected with each other at the second end portion of the fourth arm link  834  and the second portion of the handling member  125 . The first and second arm links  831  and  832  are substantially equal in length to each other. The third and fourth arm links  833  and  834  are substantially equal in length to each other. 
     The robot arm  830  further comprises a first joint mechanism  140  retaining the first and third arm links  831  and  833  respectively at the second end portion of the first arm link  831  and the first end portion of the third arm link  833  under the state that the first arm link  831  is pivotable around the second end portion of the first arm link  831  with respect to the third arm link  833 . The first link  141  of the first joint mechanism  140  is substantially equal in length to the first arm link  831 . The first link  141  is integrally formed with and in coaxial relationship with the first arm link  831  under the state that the first end portion of the first link  141  is connected with the first end portion of the first arm link  831 . The second link  142  of the first joint mechanism  140  is pivotably connected with the first end portion of the third arm link  833 . The second end portion of the fourth link  144  of the first joint mechanism  140  is integrally connected with the first long link  212 . 
     The robot arm  830  further comprises a second joint mechanism  150  similar to the first joint mechanism  140  and retaining the second and fourth arm links  832  and  834  respectively at the second end portion of the second arm link  832  and the first end portion of the fourth arm link  834  under the state that the second arm link  832  is pivotable around the second end portion of the second arm link  832  with respect to the fourth arm link  834 . The second joint mechanism  150  comprises the first, second, third, and fourth links  151 ,  152 ,  153 , and  154  which are respectively similar to the first, second, third, and fourth links  141 ,  142 ,  143 , and  144 . The first link  151  of the second joint mechanism  150  is substantially equal in length to the second arm link  832 . The first link  151  is integrally formed with and in coaxial relationship with the second arm link  832  under the state that the first end portion of the first link  151  is connected with the first end portion of the second arm link  832 . The second link  152  of the second joint mechanism  150  is pivotably connected with the first end portion of the fourth arm link  834 . The second end portion of the fourth link  154  of the second joint mechanism  150  is integrally connected with the first long link  212 . 
     The fourth links  144  and  154  are substantially equal in length to each other. The fourth links  144  and  154  are integrally formed with and in coaxial relationship with each other under the state that the first end portion of the fourth link  144  is connected with the first end portion of the fourth link  154 . 
     The robot arm  830  further comprises a stabilizing mechanism  160 . The first link  161  of the stabilizing mechanism  160  is substantially equal in length to the third arm link  833 . The first link  161  is integrally formed with and in coaxial relationship with the third arm link  833  under the state that the first end portion of the first link  161  is connected with the first end portion of the third arm link  833 . The second link  162  of the stabilizing mechanism  160  is integrally formed with the handling member  125 . The second end portion of the fourth link  164  of the stabilizing mechanism  160  is integrally connected with the second link  142 . 
     The robot arm mechanism  103  further comprises a robot arm driving mechanism  120  for driving the robot arm  830 . 
     The second driving shaft  122  of the robot arm driving mechanism  120  is integrally connected with the first long link  312  and rotates the first long link  312  around the rotation axis  123 . The first driving shaft  121  of the robot arm driving mechanism  120  is integrally connected with the third link  143  of the first joint mechanism  140  and rotates the first arm link  831  around the first end portion of the first arm link  831  through the first joint mechanism  140 . 
     While there have been described in the above about the fact that the second driving shaft  122  is integrally connected with the first long link  312  and that the first driving shaft  121  is integrally connected with the third link  143 , the first driving shaft  121  may be integrally connected with the second arm link  832  instead of the third link  143 , according to the present invention. 
     While there have been described in the above about the fact that the second driving shaft  122  is integrally connected with the first long link  312  and that the first driving shaft  121  is integrally connected with the third link  143 , the second driving shaft  122  may be integrally connected with the second arm link  832  instead of the first long link  312 , according to the present invention. 
     According to the present invention, the first and second driving shafts  121  and  122  may be replaced by each other about the connection with the third link  143 , the second arm link  832 , or the first long link  312 . 
     The operation of the robot arm mechanism  103  in the third preferred embodiment is similar to the operation of the robot arm mechanism  101  in the first preferred embodiment except for the fact that the first and second joint mechanisms  140  and  150  firmly retains the first and second arm links  831  and  832  respectively, according to the present invention. 
     Referring to FIGS. 9 to  11  of the drawings, there is shown a fourth preferred embodiment of the robot arm mechanism according to the present invention. The robot arm mechanism  104  is shown in FIGS. 9 to  11  as comprising a handling member  125  for supporting and handling an object, a robot arm  840 , and a robot arm driving mechanism  120  for driving the robot arm  840 . The robot arm  840  comprises a driving assist parallelogram linkage  190 . 
     The robot arm  840  further comprises first, second, third, and fourth arm links  841 ,  842 ,  843 , and  844  which are similar to the first, second, third, and fourth arm links  831 ,  832 ,  833 , and  834  in the third preferred embodiment of the robot arm mechanism according to the present invention. 
     The robot arm mechanism  104  is substantially similar to the robot arm mechanism  103  in the third preferred embodiment of the robot arm mechanism according to the present invention, except for the driving assist parallelogram linkage  190  of the robot arm  840  and the position of the robot arm driving mechanism  120 . 
     The driving assist parallelogram linkage  190  includes a first link  191  having first and second end portions and substantially equal in length to the distance between the rotation axis  123  and the second end portion of the second arm link  842 . The first link  191  is integrally formed with and in parallel relationship with the first long link  312 . 
     The driving assist parallelogram linkage  190  further includes a second link  192  having first and second end portions. The first and second links  191  and  192  are pivotably connected with each other at the second end portion of the first link  191  and the first end portion of the second link  192 . The second link  192  is integrally formed with and in parallel relationship with the second arm link  842 . 
     The driving assist parallelogram linkage  190  further includes a third link  193  having first and second end portions and substantially equal in length to the first link  191 . The second and third links  192  and  193  are pivotably connected with each other at the second end portion of the second link  192  and the first end portion of the third link  193 . 
     The driving assist parallelogram linkage  190  further includes a fourth link  194  having first and second end portions and substantially equal in length to the second link  192 . The third and fourth links  193  and  194  are pivotably connected with each other at the second end portion of the third link  193  and the first end portion of the fourth link  194 . The fourth and first links  194  and  191  are pivotably connected with each other at the second end portion of the fourth link  194  and the first end portion of the first link  191  under the state that the first link  191  is in parallel relationship with the third link  193  and that the second link  192  is in parallel relationship with the fourth link  194 . 
     The second driving shaft  122  is integrally connected with the fourth link  194  at the second end portion of the fourth link  194  and rotates the second arm link  842  around the first end portion of the second arm link  842  through the driving assist parallelogram linkage  190 . The first driving shaft  121  is integrally connected with the first long link  312  and rotates the first long link  312  around the rotation axis  123 . 
     According to the present invention, the first and second driving shafts  121  and  122  may be replaced by each other about the connection with the first long link  312  or the fourth link  194 . 
     The operation of the robot arm mechanism  104  in the fourth preferred embodiment is similar to the operation of the robot arm mechanism  103  in the third preferred embodiment except for the fact that the position of the arm driving mechanism  120  in the fourth preferred embodiment is different from the position of the arm driving mechanism  120  in the third preferred embodiment, according to the present invention. 
     Referring to FIGS. 12 and 13 of the drawings, there is shown a fifth preferred embodiment of the robot arm mechanism according to the present invention. The robot arm mechanism  105  is shown in FIGS. 12 and 13 as comprising a handling member  125  for supporting and handling an object, a robot arm  850 , and a robot arm driving mechanism  120  for driving the robot arm  850 . The robot arm  850  comprises a link retaining mechanism  350 . 
     The robot arm  850  further comprises first, second, third, and fourth arm links  851 ,  852 ,  853 , and  854  which are similar to the first, second, third, and fourth arm links  841 ,  842 ,  843 , and  844  in the fourth preferred embodiment of the robot arm mechanism according to the present invention. 
     The robot arm mechanism  105  is substantially similar to the robot arm mechanism  104  in the fourth preferred embodiment of the robot arm mechanism according to the present invention. 
     The link retaining mechanism  350  comprises first and second joint cross linkages  360  and  370  which are respectively similar to the first and second joint cross linkages  310  and  320  in the fourth preferred embodiment of the robot arm mechanism according to the present invention. The first joint cross linkage  360  includes first short and long links  361  and  362  and second short and long links  363  and  364  which are respectively similar to first short and long links  311  and  312  and second short and long links  313  and  314  in the fourth preferred embodiment of the robot arm mechanism according to the present invention. The second joint cross linkage  370  includes first short and long links  371  and  372  and second short and long links  373  and  374  which are respectively similar to first short and long links  321  and  322  and second short and long links  323  and  324  in the fourth preferred embodiment of the robot arm mechanism according to the present invention. 
     The link retaining mechanism  350  similar to the link retaining mechanism  300  in the fourth preferred embodiment of the robot arm mechanism according to the present invention, except for the fact that the first short link  361  and the first long link  372  are not substantially equal in length to each other. 
     The retaining mechanism  300  pivotably retains the first and second arm links  831  and  832  respectively at the first end portions of the first and second arm links  831  and  832  and keeps parallel a first line and second line, the first line beign a line passing through the first and second end portions of the first arm link  831  and the second line a line symmetrical with respect to the center line  301  with the line passing through the first and second end portions of the second arm link  832 . 
     The first end portion of the first arm link  851  is integrally formed with the second short link  363 . The first end portion of the second arm link  852  is integrally formed with the second long link  374 . The center line  351  passes through the first and second end portions of the first long link  362 . The first end portions of the first and second arm links  851  and  852  are positioned on the center line  351 . 
     The second driving shaft  122  is integrally connected with the fourth link  194  at the second end portion of the fourth link  194  and rotates the second arm link  852  around the first end portion of the second arm link  852  through the driving assist parallelogram linkage  190 . The first driving shaft  121  is integrally connected with the first long link  362  and rotates the first long link  362  around the rotation axis  123 . 
     According to the present invention, the fourth link  194  and the first long link  362  may be replaced by each other about the connection with the first or second driving shafts  121  or  122 . 
     The operation of the robot arm mechanism  105  in the fifth preferred embodiment is similar to the operation of the robot arm mechanism  104  in the fourth preferred embodiment, according to the present invention. 
     Referring to FIGS. 14 and 15 of the drawings, there is shown a sixth preferred embodiment of the robot arm mechanism according to the present invention. The robot arm mechanism  106  is shown in FIGS. 14 and 15 as comprising a handling member  125  for supporting and handling an object, a robot arm  860 , and a robot arm driving mechanism  120  for driving the robot arm  860 . The robot arm mechanism  106  is substantially similar to the robot arm mechanism  105  in the fifth preferred embodiment of the robot arm mechanism according to the present invention. The robot arm  860  comprises first, second, third, and fourth arm links  861 ,  862 ,  863 , and  864 . 
     The stabilizing mechanism  160  in the fifth preferred embodiment of the robot arm mechanism according to the present invention is replaced by the stabilizing mechanism  170  in the present preferred embodiment. 
     The link retaining mechanism  350  in the fifth preferred embodiment of the robot arm mechanism according to the present invention is replaced by the link retaining mechanism  200  and an additional link retaining mechanism  250  in the present preferred embodiment. 
     The additional link retaining mechanism  250  comprises first and second joint cross linkages  260  and  270  are respectively similar to the first and second joint cross linkages  210  and  220 . The first joint cross linkage  260  includes first short and long links  261  and  262  and second short and long links  263  and  264  which are respectively similar to first short and long links  211  and,  212  and second short and long links  213  and  214 . The second joint cross linkage  270  includes first short and long links  271  and  272  and second short and long links  273  and  274  which are respectively similar to first short and long links  221  and  222  and second short and long links  223  and  224 . 
     The second driving shaft  122  is integrally connected with the fourth link  194  at the second end portion of the fourth link  194  and rotates the second arm link  862  around the first end portion of the second arm link  862  through the driving assist parallelogram linkage  190 . The first driving shaft  121  is integrally connected with the first link  191  and rotates the first long link  212  around the rotation axis  123  through the first link  191 . 
     According to the present invention, the fourth link  194  and the first link  191  may be replaced by each other about the connection with the first or second driving shafts  121  or  122 . 
     The operation of the robot arm mechanism  106  in the sixth preferred embodiment is similar to the operation of the robot arm mechanism in the above-mentioned preferred embodiment, according to the present invention. 
     Referring to FIG. 16 of the drawings, there is shown a seventh preferred embodiment of the robot arm mechanism according to the present invention. The robot arm mechanism  107  is shown in FIG. 16 as comprising a handling member  125  for supporting and handling an object, a robot arm  870 , and a robot arm driving mechanism  120  for driving the robot arm  870 . The robot arm mechanism  107  further comprises an additional handling member  126  for supporting and handling an object. 
     The robot arm  870  comprises first, second, third, and fourth arm links  871 ,  872 ,  873 , and  874  which are similar to the first, second, third, and fourth arm links  861 ,  862 ,  863 , and  864  in the sixth preferred embodiment of the robot arm mechanism according to the present invention. 
     The robot arm  870  further comprises a fifth arm link  875  having first and second end portions. The additional handling member  126  has first and second portions. The fifth arm link  875  and the additional handling member  126  are pivotably connected with each other at the second end portion of the fifth arm link  875  and the first portion of the additional handling member  126 . The fifth arm link  875  is pivotably retained by the first joint mechanism  140  at the first end portion of the fifth arm link  875 . 
     The robot arm  870  further comprises a sixth arm link  876  having first and second end portions. The sixth arm link  876  and the additional handling member  126  are pivotably connected with each other at the second end portion of the sixth arm link  876  and the second portion of the additional handling member  126 . The fifth and sixth arm links  875  and  876  are substantially equal in length to each other. The sixth arm link  876  is pivotably retained by the second joint mechanism  150  at the first end portion of the sixth arm link  876 . 
     The robot arm  870  further comprises an additional stabilizing mechanism  180  similar to the stabilizing mechanism  170 . 
     The robot arm mechanism  107  is similar to the robot arm mechanism  106  in the sixth preferred embodiment of the robot arm mechanism according to the present invention, except for the additional the additional handling member  126 , fifth arm link  875 , sixth arm link  876 , and the additional stabilizing mechanism  180 . 
     The second driving shaft  122  is integrally connected with the fourth link  194  at the second end portion of the fourth link  194  and rotates the second arm link  872  around the first end portion of the second arm link  872  through the driving assist parallelogram linkage  190  (See FIG.  14 ). 
     The first driving shaft  121  is integrally connected with the first link  191  and rotates the first long link  212  around the rotation axis  123  through the first link  191  (See FIG.  14 ). 
     According to the present invention, the fourth link  194  and the first link  191  may be replaced by each other about the connection with the first or second driving shafts  121  or  122 . 
     The operation of the robot arm mechanism  107  in the seventh preferred embodiment is similar to the operation of the robot arm mechanism  106  in the sixth preferred embodiment except for the following operation of the robot arm mechanism  107  in the seventh preferred embodiment. 
     The another handling member  126  approaches the rotation axis  123  when the handling member  125  leave from the rotation axis  123 , resulting from the fact that the robot arm mechanism  107  comprises the handling member  125  and the additional handling member  126 . By the same reason, the handling member  125  approaches the rotation axis  123  when the another handling member  126  leave from the rotation axis  123 . 
     Referring to FIG. 17 of the drawings, there is shown a eighth preferred embodiment of the robot arm mechanism according to the present invention. The robot arm mechanism  108  is shown in FIG. 17 as comprising a handling member  125  for supporting and handling an object, a robot arm  880 , and a robot arm driving mechanism  120  for driving the robot arm  880 . 
     The robot arm  880  comprises first, second, third, and fourth arm links  881 ,  882 ,  883 , and  884  which are similar to the first, second, third, and fourth arm links  821 ,  822 ,  823 , and  824  in the second preferred embodiment of the robot arm mechanism according to the present invention. 
     The robot arm  880  further comprises the second joint mechanism  132 . The robot arm  880  further comprises the first joint mechanism  131  which is similar to the second joint mechanism  132  and retains the first and third arm links  881  and  883 . 
     The robot arm  880  further comprises a fifth arm link  885  having first and second end portion, a sixth arm link  886  having first and second end portion, and an additional link retaining mechanism  250  having an additional center line  251 . The additional link retaining mechanism  250  pivotably retains the fifth and sixth arm links  885  and  886  respectively at the first end portions of the fifth and sixth arm links  885  and  886  and keeps parallel a first line and a second line, the first line being a line passing through the first and second end portions of the fifth arm link  885  and the second line being a line symmetrical with respect to the additional center line  251  with the line passing through the first and second end portions of the sixth arm link  886 . In fact the fifth and sixth arm links  885  and  886  are in symmetrical relationship with each other with respect to the center line  251 . 
     The first end portion of the sixth arm link  886  is integrally connected with the second short link  263 . The first end portion of the fifth arm link  885  is integrally connected with the second long link  274 . 
     The additional center line  251  passes through the first and second end portions of the first long link  262 . The first end portions of the fifth and sixth arm links  885  and  886  are positioned on the additional center line  251 . 
     The second end portion of the first arm link  881  and the first end portion of the third arm link  883  are connected with each other. 
     The second end portion of the second arm link  882  and the first end portion of the foruth arm link  884  are connected with each other. 
     The first long link  212  is integrally formed with and in parallel relationship with the first long link  262  under the state that the first end portion of the first long link  212  is connected with the first end portion of the first long link  262 . 
     The robot arm  880  further comprises a first stabilizing parallelogram linkage  230  comprising a first link  231  having first and second end portions and substantially equal in length to the first arm link  881 . The first link  231  is integrally formed with and in coaxial relationship with the first arm link  881  under the state that the first end portion of the first link  231  is connected with the first end portion of the first arm link  881 . 
     The first stabilizing parallelogram linkage  230  further comprises a second link  232  having first and second end portions and substantially equal in length to the fifth arm link  885 . The first and second links  231  and  232  are pivotably connected with each other at the second end portion of the first link  231  and the first end portion of the second link  232 . The second link  232  is integrally formed with and in parallel relationship with the third arm link  883  under the state that the first end portion of the second link  232  is connected with the first end portion of the third arm link  883 . 
     The first stabilizing parallelogram linkage  230  further comprises a third link  233  having first and second end portions and substantially equal in length to the first link  231 . The second and third links  232  and  233  are pivotably connected with each other at the second end portion of the second link  232  and the first end portion of the third link  233 . 
     The first stabilizing parallelogram linkage  230  further comprises a fourth link  234  having first and second end portions and substantially equal in length to the second link  232 . The third and fourth links  233  and  234  are pivotably connected with each other at the second end portion of the third link  233  and the first end portion of the fourth link  234 . The fourth and first links  234  and  231  are pivotably connected with each other at the second end portion of the fourth link  234  and the first end portion of the first link  231  under the state that the first link  231  is in parallel relationship with the third link  233  and that the second link  232  is in parallel relationship with the fourth link  234 . The fourth link  234  is integrally formed with and in coaxial relationship with the fifth arm link  885  under the state that the second end portion of the fourth link  234  is connected with the first end portion of the fifth arm link  885 . 
     The robot arm  880  further comprises a second stabilizing parallelogram linkage  240  which is similar to the first stabilizing parallelogram linkage  230 . 
     The second stabilizing parallelogram linkage  240  comprises first, second, third, and fourth links  241 ,  242 ,  243 , and  244  which are respectively similar to the first, second, third, and fourth links  231 ,  232 ,  233 , and  234 . 
     The first link  241  is substantially equal in length to the second arm link  882 . The first link  241  is integrally formed with and in coaxial relationship with the second arm link  882  under the state that the first end portion of the first link  241  is connected with the first end portion of the second arm link  882 . 
     The second stabilizing parallelogram linkage  240  further comprises a second link  242  having first and second end portions and substantially equal in length to the sixth arm link  886 . The second link  242  is integrally formed with and in parallel relationship with the fourth arm link  884  under the state that the first end portion of the second link  242  is connected with the first end portion of the fourth arm link  884 . 
     The third link  243  is substantially equal in length to the first link  241 . The fourth link  244  is substantially equal in length to the second link  242 . The fourth link  244  is integrally formed with and in coaxial relationship with the sixth arm link  886  under the state that the second end portion of the fourth link  244  is connected with the first end portion of the sixth arm link  886 . 
     The second driving shaft  122  is integrally connected with the first arm link  881  at the first end portion of the first arm link  881  and rotates the first arm link  881  around the rotation axis  123 . The first driving shaft  121  is integrally connected with the second arm link  882  at the first end portion of the second arm link  882  and rotates the second arm link  882  around the rotation axis  123 . 
     According to the present invention, the first and second arm links  881  and  882  may be replaced by each other about the connection with the first or second driving shafts  121  or  122 . 
     The operation of the robot arm mechanism  108  in the eighth preferred embodiment is similar to the operation of the robot arm mechanism  101  in the first preferred embodiment except for the following operation of the robot arm mechanism  108 , according to the present invention. 
     According to the present invention, the fact that the fifth and sixth arm links  885  and  886  are retained by the additional link retaining member  250  results in the fact that the fifth and sixth arm links  885  and  886  are in symmetrical relationship with each other with respect to the center line  201 . The first stabilizing parallelogram linkage  230  makes the third and fifth arm links  883  and  885  in parallel relationship with each other. The second stabilizing parallelogram linkage  240  makes the fourth and sixth arm links  884  and  886  in parallel relationship with each other. The third and fourth arm links  883  and  884  are in symmetrical relationship with each other with respect to the center line  201 , resulting from the fact that the third and fourth arm links  883  and  884  are respectively in parallel relationship with the fifth and sixth arm links  885  and  886 . The handling member  125  moves parallel to the center line  201 , by the reason that the third and fourth arm links  883  and  884  are in symmetrical relationship with each other with respect to the center line  201 . 
     Referring to FIGS. 18 and 19 of the drawings, there is shown a ninth preferred embodiment of the robot arm mechanism according to the present invention. The robot arm mechanism  109  is shown in FIGS. 18 and 19 as comprising a handling member  127  for supporting and handling an object. 
     The robot arm mechanism  109  further comprises a robot arm  890  connected to the handling member  127 . The robot arm  890  comprises a first arm link  891  having first and second end portion, a second arm link  892  having first and second end portion, and a link retaining mechanism  400  having a center line  401 . 
     The link retaining mechanism  400  pivotably retains the first and second arm links  891  and  892  respectively at the first end portions of the first and second arm links  891  and  892  and keeps parallel a first line and a second line, the first line being a line passing through the first and second end portions of the first arm link  891  and the second line being a line symmetrical with respect to the center line  401  with the line passing through the first and second end portions of the second arm link  892 . In fact the first and second arm links  891  and  892  are in symmetrical relationship with each other with respect to the center line  401 . 
     The link retaining mechanism  400  comprises a first joint cross linkage  410  which includes a first short link  411  having first and second end portions. 
     The first joint cross linkage  410  further includes a first long link  412  having first and second end portions and longer than the first short link  411 . The first short and long links  411  and  412  are pivotably connected with each other at the second end portion of the first short link  411  and the first end portion of the first long link  412 . 
     The first joint cross linkage  410  further includes a second short link  413  having first and second end portions and substantially equal in length to the first short link  411 . The first long link  412  and the second short link  413  are pivotably connected with each other at the second end portion of the first long link  412  and the first end portion of the second short link  413 . 
     The first joint cross linkage  410  further includes a second long  414  link having first and second end portions and substantially equal in length to the first long link  412 . The second short and long links  413  and  414  are pivotably connected with each other at the second end portion of the second short link  413  and the first end portion of the second long link  414 . 
     The second long link  414  and the first short link  411  are pivotably connected with each other at the second end portion of the second long link  414  and the first end portion of the first short link  411  under the state that the second long link  414  is crossed with the first long link  412 . 
     The link retaining mechanism  400  comprises a second joint cross linkage  420  which includes a first short link  421  having first and second end portions. 
     The second joint cross linkage  420  further includes a first long link  422  having first and second end portions and longer than the first short link  421 . The first short and long links  421  and  422  are pivotably connected with each other at the second end portion of the first short link  421  and the first end portion of the first long link  422 . 
     The second joint cross linkage  420  further includes a second short link  423  having first and second end portions and substantially equal in length to the first short link  421 . The first long link  422  and the second short link  423  are pivotably connected with each other at the second end portion of the first long link  422  and the first end portion of the second short link  423 . 
     The second joint cross linkage  420  further includes a second long link  424  having first and second end portions and substantially equal in length to the first long link  422 . The second short and long links  423  and  424  are pivotably connected with each other at the second end portion of the second short link  423  and the first end portion of the second long link  424 . 
     The second long link  424  and the first short link  421  are pivotably connected with each other at the second end portion of the second long link  424  and the first end portion of the first short link  421  under the state that the second long link  424  is crossed with the first long link  422 . 
     The length ratio of each of the first and second short links  411  and  413  to each of the first and second long links  412  and  414  is substantially equal to the length ratio of each of the first and second short links  421  and  423  to each of the first and second long links  422  and  424 . 
     The first short link  411  is integrally formed with and in coaxial relationship with the first long link  422  under the state that the second end portion of the first short link  411  is connected with the first end portion of the first long link  422 . The first long link  412  is integrally formed with and in coaxial relationship with the first short link  421  under the state that the first end portion of the first long link  412  is connected with the second end portion of the first short link  421 . 
     The first end portion of the first arm link  891  is integrally formed with the second short link  413 . The first end portion of the second arm link  892  is integrally formed with the second long link  424 . 
     The center line  401  is substantially equally spaced apart from the second end portion of the first long link  412  and the first end portion of the first short link  421  and in perpendicular relationship with the first long link  412 . The first end portions of the first and second arm links  891  and  892  are positioned on the line passing through the first and second end portions of the first long link  412 . 
     The robot arm  890  further comprises a third arm link  893  having first and second end portions. 
     The robot arm  890  further comprises a fourth arm link  894  having first and second end portions. The first and second arm links  891  and  892  are substantially equal in length to each other. The third and fourth arm links  893  and  894  are substantially equal in length to each other. 
     The robot arm  890  further comprises a first joint mechanism  131  retaining the first and third arm links  891  and  893  respectively at the second end portion of the first arm link  891  and the first end portion of the third arm link  893  under the state that the first arm link  891  is pivotable around the second end portion of the first arm link  891  with respect to the third arm link  893 . The first and third arm links  811  and  813  are pivotably connected with each other at the second end portion of the first arm link  811  and the first end portion of the third arm link  813 . 
     The robot arm  890  further comprises a second joint mechanism  132  retaining the second and fourth arm links  892  and  894  respectively at the second end portion of the second arm link  892  and the first end portion of the fourth arm link  894  under the state that the second arm link  892  is pivotable around the second end portion of the second arm link  892  with respect to the fourth arm link  894 . The second and fourth arm links  812  and  814  are pivotably connected with each other at the second end portion of the second arm link  812  and the first end portion of the fourth arm link  814 . 
     The handling member  127  is integrally connected with the first long link  412 . 
     The robot arm mechanism  109  further comprises a robot arm driving mechanism  120  for driving the robot arm  890 . 
     The arm driving mechanism  120  comprises a first driving shaft  121  rotatable around a rotation axis  123 , and a second driving shaft  122  in the form of a hollow shape to rotatably receive therein the first driving shaft  121  and rotatable around the rotation axis  123 . The first driving shaft  121  is integrally connected with the second end portion of the third arm link  893  and rotating the third arm link  893  around the rotation axis  123 . The second driving shaft  122  is integrally connected with the second end portion of the fourth arm link  894  and rotating the fourth arm link  894  around the rotation axis  123 . 
     According to the present invention, the center line  401  passes through the rotation axis  123  at all times, by the reason that the link retaining mechanism  400  retains the first and second arm links  891  and  892  under the state that the first and second arm links  891  and  892  are in symmetrical relationship with each other with respect to the center line  401 , that the first and second arm links  891  and  892  are equal in length to each other, and that the third and fourth arm links  893  and  894  are equal in length to each other. By the reason that the center line  401  passes through the rotation axis  123  at all times, The handling member  127  approaches and leaves from the rotation axis  123  with keeping a direction with respect to the rotation axis  123  fixed. 
     According to the present invention, the rotation of the third arm link  893  and the rotation of the fourth arm link  894  can result in the rotation of the center line  401  around the rotation axis  123 . The robot arm mechanism  109  is rotated around the rotation axis  123  by the reason that the center line  401  is rotated around the rotation axis  123 . 
     According to the present invention, the third and fourth arm links  893  and  894  may be replaced by each other about the connection with the first or second driving shafts  121  or  122 . 
     Referring to FIGS. 20 to  21  of the drawings, there is shown a tenth preferred embodiment of the robot arm mechanism according to the present invention. The robot arm mechanism  110  is shown in FIGS. 20 to  21  as comprising a handling member  125  for supporting and handling an object. 
     The construction of the robot arm mechanism  110  in the present preferred embodiment is similar to the construction of the robot arm mechanism  109  in the ninth preferred embodiment except for the following construction of the robot arm mechanism  110  in the present preferred embodiment. 
     The robot arm mechanism  110  further comprises a robot arm  900  connected to the handling member  125 . The robot arm  900  comprises a first arm link  901  having first and second end portion, a second arm link  902  having first and second end portion, and a link retaining mechanism  500  having a center line  501 . 
     The link retaining mechanism  500  pivotably retains the first and second arm links  901  and  902  respectively at the first end portions of the first and second arm links  901  and  902  and keeps parallel a first line and a second line, the first line being a line passing through the first and second end portions of the first arm link  901  and the second line being a line symmetrical with respect to the center line  501  with the line passing through the first and second end portions of the second arm link  902 . In fact the first and second arm links  901  and  902  are in symmetrical relationship with each other with respect to the center line  501 . 
     The link retaining mechanism  500  comprises a first joint cross linkage  510  which includes a first short link  511  having first and second end portions. 
     The first joint cross linkage  510  further includes a first long link  512  having first and second end portions and longer than the first short link  511 . The first short and long links  511  and  512  are pivotably connected with each other at the second end portion of the first short link  511  and the first end portion of the first long link  512 . 
     The first joint cross linkage  510  further includes a second short link  513  having first and second end portions and substantially equal in length to the first short link  511 . The first long link  512  and the second short link  513  are pivotably connected with each other at the second end portion of the first long link  512  and the first end portion of the second short link  513 . 
     The first joint cross linkage  510  further includes a second long  514  link having first and second end portions and substantially equal in length to the first long link  512 . The second short and long links  513  and  514  are pivotably connected with each other at the second end portion of the second short link  513  and the first end portion of the second long link  514 . 
     The second long link  514  and the first short link  511  are pivotably connected with each other at the second end portion of the second long link  514  and the first end portion of the first short link  511  under the state that the second long link  514  is crossed with the first long link  512 . 
     The link retaining mechanism  500  comprises a second joint cross linkage  520  which includes a first short link  521  having first and second end portions. 
     The second joint cross linkage  520  further includes a first long link  522  having first and second end portions and longer than the first short link  521 . The first short and long links  521  and  522  are pivotably connected with each other at the second end portion of the first short link  521  and the first end portion of the first long link  522 . 
     The second joint cross linkage  520  further includes a second short link  523  having first and second end portions and substantially equal in length to the first short link  521 . The first long link  522  and the second short link  523  are pivotably connected with each other at the second end portion of the first long link  522  and the first end portion of the second short link  523 . 
     The second joint cross linkage  520  further includes a second long link  524  having first and second end portions and substantially equal in length to the first long link  522 . The second short and long links  523  and  524  are pivotably connected with each other at the second end portion of the second short link  523  and the first end portion of the second long link  524 . 
     The second long link  524  and the first short link  521  are pivotably connected with each other at the second end portion of the second long link  524  and the first end portion of the first short link  521  under the state that the second long link  524  is crossed with the first long link  522 . 
     The length ratio of each of the first and second short links  511  and  513  to each of the first and second long links  512  and  514  is substantially equal to the length ratio of each of the first and second short links  521  and  523  to each of the first and second long links  522  and  524 . 
     The first short link  511  is integrally formed with and in axial alignment with the first long link  522  under the state that the second end portion of the first short link  511  is connected with the first end portion of the first long link  522 . The first long link  512  is integrally formed with and in axial alignment with the first short link  521  under the state that the first end portion of the first long link  512  is connected with the second end portion of the first short link  521 . 
     The first end portion of the first arm link  901  is integrally formed with the second short link  513 . The first end portion of the second arm link  902  is integrally formed with the second long link  524 . The center line  501  is substantially equally spaced apart from the second end portion of the first long link  512  and the first end portion of the first short link  521  and in perpendicular relationship with the first long link  512 . The first end portions of the first and second arm links  901  and  902  are positioned on the line passing through the first and second end portions of the first long link  512 . In prevent preferred embodiment the first and second arm links  901  and  902  are respectively integrally formed with and in coaxial relationship with the second short link  513  and the second long link  524 . 
     The robot arm further comprises third and fourth arm links  903  and  904  which are similar to the third and fourth arm links  893  and  894  in the ninth preferred embodiment of the robot arm mechanism according to the present invention. 
     The first driving shaft  121  is integrally connected with the second end portion of the fourth arm link  904  and rotating the fourth arm link  904  around the rotation axis  123 . The second driving shaft  122  is integrally connected with the second end portion of the third arm link  903  and rotating the third arm link  903  around the rotation axis  123 . 
     According to the present invention, the third and fourth arm links  903  and  904  may be replaced by each other about the connection with the first or second driving shafts  121  or  122 . 
     According to the present invention, the operation of the robot arm mechanism  110  in the tenth preferred embodiment is substantially similar to the operation of the robot arm mechanism  109  in the ninth preferred embodiment. 
     Referring to FIGS. 20 and 22 of the drawings, there is shown a eleventh preferred embodiment of the robot arm mechanism according to the present invention. The robot arm mechanism  111  is shown in FIGS. 20 and 22 as comprising a handling member  125  for supporting and handling an object and a robot arm  910 . 
     The robot arm  910  comprises first, second, third, and fourth arm link  911 ,  912 ,  913 , and  914  which are similar to the first, second, third, and fourth arm link  901 ,.  902 ,  903 , and  904  in the tenth preferred embodiment of the robot arm mechanism according to the present invention. 
     The robot arm  910  further comprises a fifth arm link  915  having first and second end portions. The robot arm  910  further comprises a sixth arm link  916  having first and second end portions. The fifth and sixth arm link  915  and  916  substantially equal in length to each other. 
     The robot arm  910  further comprises a first stabilizing mechanism  610  including a first link  611  having first and second end portions. The first link  611  is integrally formed with and in coaxial relationship with the first arm link  911  under the state that the second end portion of the first link  611  is connected with the second end portion of the first arm link  911 . 
     The first stabilizing mechanism  610  includes a second link  612  having first and second end portions. The first and second links  611  and  612  are pivotably connected with each other at the second end portion of the first link  611  and the first end portion of the second link  612 . The second link  612  is integrally formed with and in axial alignment with the third arm link  913  under the state that the first end portion of the second link  612  is connected with the second end portion of the third arm link  913 . 
     The first stabilizing mechanism  610  includes a third link  613  having first and second end portions and substantially equal in length to the first link  611 . The second and third links  612  and  613  are pivotably connected with each other at the second end portion of the second link  612  and the first end portion of the third link  613 . The third link  613  is integrally formed with and in parallel relationship with the fifth arm link  915  under the state that the first end portion of the third link  613  is connected with the second end portion of the fifth arm link  915 . 
     The first stabilizing mechanism  610  includes a fourth link  614  having first and second end portions and substantially equal in length to the second link  612 . The third and fourth links  613  and  614  are pivotably connected with each other at the second end portion of the third link  613  and the first end portion of the fourth link  614 . The fourth and first links  614  and  611  are pivotably connected with each other at the second end portion of the fourth link  614  and the first end portion of the first link  611  under the state that the first link  611  is in parallel relationship with the third link  613  and that the second link  612  is in parallel relationship with the fourth link  614 . 
     The robot arm  910  further comprises a second stabilizing mechanism  620  which is similar to the first stabilizing mechanism  610 . The first link  621  is integrally formed with and in coaxial relationship with the second arm link  912  under the state that the second end portion of the first link  621  is connected with the second end portion of the second arm link  912 . The second link  622  is integrally formed with and in axial alignment with the fourth arm link  914  under the state that the first end portion of the second link  622  is connected with the second end portion of the fourth arm link  914 . The third link  623  is integrally formed with and in parallel relationship with the sixth arm link  916  under the state that the first end portion of the third link  623  is connected with the second end portion of the sixth arm link  916 . 
     The handling member  125  has first and second portions. The fifth arm link  915  and the handling member  125  are pivotably connected with each other at the first end portion of the fifth arm link  915  and the first portion of the handling member  125 . The sixth arm link  916  and the handling member  125  are pivotably connected with each other at the first end portion of the sixth arm link  916  and the second portion of the handling member  125 . 
     The first driving shaft  121  is integrally connected with the second end portion of the third arm link  913  and rotating the third arm link  913  around the rotation axis  123 . The second driving shaft  122  is integrally connected with the second end portion of the fourth arm link  914  and rotating the fourth arm link  914  around the rotation axis  123 . 
     According to the present invention, the third and fourth arm links  913  and  914  may be replaced by each other about the connection with the first or second driving shafts  121  or  122 . 
     According to the present invention, the operation of the robot arm mechanism  111  in the eleventh preferred embodiment is similar to the operation of the robot arm mechanism  110  in the tenth preferred embodiment. 
     Referring to FIGS. 20 and 23 of the drawings, there is shown a twelfth preferred embodiment of the robot arm mechanism according to the present invention. The robot arm mechanism  111  is shown in FIGS. 20 and 23 as comprising a handling member  125  for supporting and handling an object and a robot arm  920 . 
     The robot arm  920  comprises first, second, third, and fourth arm link  921 ,  922 ,  923 , and  924  which are similar to the first, second, third, and fourth arm link  901 ,  902 ,  903 , and  904  in the tenth preferred embodiment of the robot arm mechanism according to the present invention. 
     The robot arm  920  further comprises a fifth arm link  925  having first and second end portions. The robot arm  920  further comprises a sixth arm link  926  having first and second end portions. The fifth and sixth arm link  925  and  926  substantially equal in length to each other. 
     The robot arm  920  further comprises a first stabilizing mechanism  630  including a first link  631  having first and second end portions. The first link  631  is integrally formed with and in axial alignment with the first arm link  921  under the state that the second end portion of the first link  631  is connected with the second end portion of the first arm link  921 . 
     The first stabilizing mechanism  630  includes a second link  632  having first and second end portions. The first and second links  631  and  632  are pivotably connected with each other at the second end portion of the first link  631  and the first end portion of the second link  632 . The second link  632  is integrally formed with and in axial alignment with the third arm link  923  under the state that the first end portion of the second link  632  is connected with the second end portion of the third arm link  923 . 
     The first stabilizing mechanism  630  includes a third link  633  having first and second end portions and substantially equal in length to the first link  631 . The second and third links  632  and  633  are pivotably connected with each other at the second end portion of the second link  632  and the first end portion of the third link  633 . The third link  633  is integrally formed with and in parallel relationship with the fifth arm link  925  under the state that the first end portion of the third link  633  is connected with the second end portion of the fifth arm link  925 . 
     The first stabilizing mechanism  630  includes a fourth link  634  having first and second end portions and substantially equal in length to the second link  632 . The third and fourth links  633  and  634  are pivotably connected with each other at the second end portion of the third link  633  and the first end portion of the fourth link  634 . The fourth and first links  634  and  631  are pivotably connected with each other at the second end portion of the fourth link  634  and the first end portion of the first link  631  under the state that the first link  631  is in parallel relationship with the third link  633  and that the second link  632  is in parallel relationship with the fourth link  634 . 
     The robot arm  920  further comprises a second stabilizing mechanism  640  which is similar to the first stabilizing mechanism  630 . The first link  641  is integrally formed with and in axial alignment with the second arm link  922  under the state that the second end portion of the first link  641  is connected with the second end portion of the second arm link  922 . The second link  642  is integrally formed with and in axial alignment with the fourth arm link  924  under the state that the first end portion of the second link  642  is connected with the second end portion of the fourth arm link  924 . The third link  643  is integrally formed with and in parallel relationship with the sixth arm link  926  under the state that the first end portion of the third link  643  is connected with the second end portion of the sixth arm link  926 . 
     The handling member  125  has first and second portions. The fifth arm link  925  and the handling member  125  are pivotably connected with each other at the first end portion of the fifth arm link  925  and the first portion of the handling member  125 . The sixth arm link  926  and the handling member  125  are pivotably connected with each other at the first end portion of the sixth arm link  926  and the second portion of the handling member  125 . 
     The first driving shaft  121  is integrally connected with the second end portion of the third arm link  923  and rotating the third arm link  923  around the rotation axis  123 . The second driving shaft  122  is integrally connected with the second end portion of the fourth arm link  924  and rotating the fourth arm link  924  around the rotation axis  123 . 
     According to the present invention, the third and fourth arm links  923  and  924  may be replaced by each other about the connection with the first or second driving shafts  121  or  122 . 
     According to the present invention, the operation of the robot arm mechanism  112  in the twelfth preferred embodiment is similar to the operation of the robot arm mechanism  110  in the tenth preferred embodiment. 
     Referring to FIGS. 18 and 24 of the drawings, there is shown a thirteenth preferred embodiment of the robot arm mechanism according to the present invention. The robot arm mechanism  113  is shown in FIGS. 18 and 24 as comprising a handling member  127  and a robot arm  930 . 
     The construction of the robot arm mechanism  113  in the present preferred embodiment is similar to the construction of the robot arm mechanism  109  in the ninth preferred embodiment except for the following construction of the robot arm mechanism  113  in the present preferred embodiment. 
     The robot arm  930  comprises first, second, third, and fourth arm links  931 ,  932 ,  933 , and  934  which are similar to the first, second, third, and fourth arm links  891 ,  892 ,  893 , and  894  in the ninth preferred embodiment of the robot arm mechanism according to the present invention (See FIG.  19 ). 
     The robot arm mechanism  113  further comprises an additional handling member  128 . The robot arm  930  further comprises a fifth arm link  935  having first and second end portion and a sixth arm link  936  having first and second end portion. The fifth and sixth arm links  935  and  936  are substantially equal in length to each other. 
     The robot arm  930  further comprises an additional link retaining mechanism  450  having an additional center line  451 . The additional link retaining mechanism  450  pivotably retainins the fifth and sixth arm links  935  and  936  respectively at the first end portions of the fifth and sixth arm links  935  and  936  and keeps parallel a first line and a second line, the first line being a line passing through the first and second end portions of the fifth arm link  935  and the second line being a line symmetrical with respect to the additional center line  451  with the line passing through the first and second end portions of the sixth arm link  936 . In fact the fifth and sixth arm links  935  and  936  are in symmetrical relationship with each other with respect to the additional center line  451 . 
     The first end portion of the sixth arm link  936  is integrally connected with the second short link  463 . The first end portion of the fifth arm link  935  is integrally connected with the second long link  474 . 
     The first end portions of the fifth and sixth arm links  935  and  936  are positioned on the line passing through the first and second end portions of the first long link  462 . 
     The distance between the second end portion of the first long link  412  and the first end portion of the first short link  421  is substantially equal to the distance between the second end portion of the first long link  462  and the first end portion of the first short link  471 . 
     The first joint mechanism  601  retains the third arm link  933  at the first end portion of the third arm link  933 . The first joint mechanism  601  retains the first and fifth arm links  931  and  935  respectively at the second end portions of the first and fifth arm links  931  and  935  under the state that the first and fifth arm links  931  and  935  are pivotable respectively around the second end portions of the first and fifth arm links  931  and  935  with respect to the third arm link  933 . 
     The second joint mechanism  602  retains the fourth arm link  934  at the first end portion of the fourth arm link  934 . The second joint mechanism  602  retains the second and sixth arm links  932  and  936  respectively at the second end portions of the second and sixth arm links  932  and  936  under the state that the second and sixth arm links  932  and  936  are pivotable respectively around the second end portions of the second and sixth arm links  932  and  936  with respect to the fourth arm link  934 . 
     The additional handling member  128  is integrally connected with the first long link  462 . 
     The first joint mechanism  601  is formed by a link and has first and second end portions. The third arm link  933  is integrally connected with the first joint mechanism  601  at the portion substantially equally spaced apart from the first and second end portions of the first joint mechanism  601  under the state that first joint mechanism  601  and the third arm link  933  are in perpendicular relationship with each other. The first arm link  931  and the first joint mechanism  601  is pivotably connected with each other at the second end portion of the first arm link  931  and the first end portion of the first joint mechanism  601 . The fifth arm link  935  and the first joint mechanism  601  is pivotably connected with each other at the second end portion of the fifth arm link  935  and the second end portion of the first joint mechanism  601 . The second joint mechanism  602  is formed by a link and has first and second end portions. The fourth arm link  934  is integrally connected with the second joint mechanism  602  at the portion substantially equally spaced apart from the first and second end portions of the second joint mechanism  602  under the state that second joint mechanism  602  and the fourth arm link  934  are in perpendicular relationship with each other. The second arm link  932  and the second joint mechanism  602  is pivotably connected with each other at the second end portion of the second arm link  932  and the first end portion of the second joint mechanism  602 . The sixth arm link  936  and the second joint mechanism  602  are pivotably connected with each other at the second end portion of the sixth arm link  936  and the second end portion of the second joint mechanism  602 . 
     The first driving shaft  121  is integrally connected with the second end portion of the third arm link  933  and rotating the third arm link  933  around the rotation axis  123 . The second driving shaft  122  is integrally connected with the second end portion of the fourth arm link  934  and rotating the fourth arm link  934  around the rotation axis  123 . 
     According to the present invention, the third and fourth arm links  933  and  934  may be replaced by each other about the connection with the first or second driving shafts  121  or  122 . 
     According to the present invention, the operation of the robot arm mechanism  113  in the thirteenth preferred embodiment is similar to the operation of the robot arm mechanism  109  in the ninth preferred embodiment except for the following operation of the robot arm mechanism  113  in the thirteenth preferred embodiment. 
     By the reason that the robot arm mechanism  113  comprises the handling member  127  and the additional handling member  128 , the handling member  127  leaves from the rotation axis  123  when the additional handling member  128  approaches the rotation axis  123 . Similarly, the additional handling member  128  leaves from the rotation axis  123  when the handling member  127  approaches the rotation axis  123 . 
     Referring to FIGS. 18 and 25 of the drawings, there is shown a fourteenth preferred embodiment of the robot arm mechanism according to the present invention. The robot arm mechanism  114  is shown in FIGS. 18 and 25 as comprising a handling member  127  and a robot arm  940 . 
     The construction of the robot arm mechanism  114  in the present preferred embodiment is similar to the construction of the robot arm mechanism  109  in the ninth preferred embodiment except for the following construction of the robot arm mechanism  114  in the present preferred embodiment. 
     The robot arm  940  comprises first, second, third, and fourth arm links  941 ,  942 ,  943 , and  944  which are similar to first, second, third, and fourth arm links  891 ,  892 ,  893 , and  894  in the ninth preferred embodiment of the robot arm mechanism according to the present invention (See FIG.  19 ). 
     The robot arm mechanism  114  further comprises an additional handling member  128 . The robot arm  940  further comprises a fifth arm link  945  having first and second end portion, a sixth arm link  946  having first and second end portion, a seventh arm link  947  having first and second end portion, and a eighth arm link  948  having first and second end portion. The fifth and sixth arm links  945  and  946  are substantially equal in length to each other. The seventh and eighth arm links  947  and  948  are substantially equal in length to each other. 
     The robot arm  940  further comprises a third joint mechanism  133  retaining the fifth and seventh arm links  945  and  947  respectively at the second end portion of the fifth arm link  945  and the first end portion of the seventh arm link  947  under the state that the fifth arm link  945  is pivotable around the second end portion of the fifth arm link  945  with respect to the seventh arm link  947 . The robot arm  940  further comprises a fourth joint mechanism  134  retaining the sixth and eighth arm links  946  and  948  respectively at the second end portion of the sixth arm link  946  and the first end portion of the eighth arm link  948  under the state that the sixth arm link  946  is pivotable around the second end portion of the sixth arm link  946  with respect to the eighth arm link  948 . 
     The robot arm  940  further comprises an additional link retaining mechanism  450  having an additional center line  451 . The additional link retaining mechanism  450  pivotably retains the fifth and sixth arm links  945  and  946  respectively at the first end portions of the fifth and sixth arm links  945  and  946  and keeps parallel a first line and a second line, the first line being a line passing through the first and second end portions of the fifth arm link  945  and the second line being a line symmetrical with respect to the additional center line  451  with the line passing through the first and second end portions of the sixth arm link  946 . In fact the fifth and sixth arm links  945  and  946  are in symmetrical relationship with each other with respect to the additional center line  451 . 
     The additional link retaining mechanism  450  are similar to the link retaining mechanism  400 . 
     The first end portion of the fifth arm link  945  is integrally connected with the second short link  463  (See FIG.  18 ). The first end portion of the sixth arm link  946  is integrally connected with the second long link  474  (See FIG.  18 ). The first end portions of the fifth and sixth arm links  945  and  946  are positioned on the line passing through the first and second end portions of the first long link  462 . 
     The distance between the second end portion of the first long link  412  and the first end portion of the first short link  421  is substantially equal to the distance between the second end portion of the first long link  462  and the first end portion of the first short link  471 . 
     The first driving shaft  121  is integrally connected with the second end portion of the third arm link  943  and rotating the third arm link  943  around the rotation axis  123 . The second driving shaft  122  is integrally connected with the second end portion of the fourth arm link  944  and rotating the fourth arm link  944  around the rotation axis  123 . 
     The first driving shaft  121  rotates the eighth arm link  948  around the second end portion of the eighth arm link  948 . The second driving shaft  122  rotates the seventh arm link  947  around the second end portion of the seventh arm link  947 . The second end portions of the eighth and seventh arm links  948  and  947  are positioned on the rotation axis  943 . 
     In prevent preferred embodiment the third and fourth arm links  943  and  944  are respectively in axial alignment with the eighth and seventh arm links  948  and  947 . 
     The additional handling member  128  is integrally connected with the first long link  462 . 
     According to the present invention, the third and fourth arm links  943  and  944  may be replaced by each other about the connection with the first or second driving shafts  121  or  122 . Similarly, the seventh and eighth arm links  947  and  948  may be replaced by each other about the connection with the first or second driving shafts  121  or  122 . 
     According to the present invention, the operation of the robot arm mechanism  114  in the fourteenth preferred embodiment is similar to the operation of the robot arm mechanism  109  in the ninth preferred embodiment except for the following operation of the robot arm mechanism  114 . 
     By the reason that the robot arm mechanism  114  comprises the handling member  127  and the additional handling member  128 , the handling member  127  leaves from the rotation axis  123  when the additional handling member  128  approaches the rotation axis  123 . Similarly, the additional handling member  128  leaves from the rotation axis  123  when the handling member  127  approaches the rotation axis  123 . 
     Referring to FIGS. 26 and 27 of the drawings, there is shown a fifteenth preferred embodiment of the robot arm mechanism according to the present invention. The robot arm mechanism  115  is shown in FIGS. 26 and 27 as comprising a handling member  125  and a robot arm  950 . 
     The robot arm  950  comprises first, second, third, and fourth arm links  951 ,  952 ,  953 , and  954  which are similar to first, second, third, and fourth arm links  901 ,  902 ,  903 , and  904  in the tenth preferred embodiment of the robot arm mechanism according to the present invention. 
     The robot arm mechanism  115  further comprises an additional handling member  126 . The robot arm  950  further comprises a third arm link  950  having first and second end portion and a fourth arm link  954  having first and second end portion. The first, second, third, and fourth arm links  951 ,  952 ,  953 , and  954  are substantially equal in length to each other. 
     The robot arm  950  further comprises a link retaining mechanism  400  having a center line  400 . 
     The robot arm  950  further comprises a fifth arm link  955  having first and second end portion and a sixth arm link  956  having first and second end portion. The robot arm  950  further comprises an additional link retaining mechanism  450  having an additional center line  451 . The additional link retaining mechanism  450  pivotably retains the third and fourth arm links  953  and  954  respectively at the first end portions of the third and fourth arm links  953  and  954  and keeps parallel a first line and a second line, the first line being a line passing through the first and second end portions of the third arm link  953  and the second line being a line symmetrical with respect to the additional center line  451  with the line passing through the first and second end portions of the fourth arm link  954 . In fact the third and fourth arm links  953  and  954  are in symmetrical relationship with each other with respect to the additional link retaining mechanism  450 . 
     The first end portion of the first arm link  951  is integrally connected with the second short link  413 . The first end portion of the second arm link  952  is integrally connected with the second long link  424 . The first end portion of the third arm link  953  is integrally connected with the second short link  463 . The first end portion of the fourth arm link  954  is integrally connected with the second long link  474 . 
     The distance between the second end portion of the first long link  412  and the first end portion of the first short link  421  is substantially equal to the distance between the second end portion of the first long link  462  and the first end portion of the first short link  471 . 
     The handling member  125  has a first and second portions. The additional handling member  126  has a first and second portions. The first arm link  951  and the handling member  125  are pivotably connected with each other at the second end portion of the first arm link  951  and the first portion of the handling member  125 . The third arm link  953  and the handling member  125  are pivotably connected with each other at the second end portion of the third arm link  953  and the second portion of the handling member  125 . The fourth arm link  954  and the additional handling member  126  are pivotably connected with each other at the second end portion of the fourth arm link  954  and the first portion of the additional handling member  126 . The second arm link  952  and the additional handling member  126  are pivotably connected with each other at the second end portion of the second arm link  952  and the second portion of the additional handling member  126 . The arm driving mechanism  120  comprises a first driving shaft  121  rotatable around a rotation axis  123 , and a second driving shaft  122  in the form of a hollow shape to rotatably receive therein the first driving shaft  121  and rotatable around the rotation axis  123 . The first driving shaft  121  rotates the fifth arm link  955  around the second end portion of the fifth arm link  955 . The second driving shaft  122  rotates the sixth arm link  956  around the second end portion of the sixth arm link  956 . The second end portions of the fifth and sixth arm links  955  and  956  are positioned on the rotation axis  123 . The fifth arm link  955  is pivotable around the second end portion of the fifth arm link  955 . The sixth arm link  956  is pivotable around the second end portion of the sixth arm link  956 . The first end portion of the fifth arm link  955  is pivotally connected with the first long link  412  under the state that the first end portion of the fifth arm link  955  is substantially equally spaced apart from the second end portion of the first long link  412  and the first end portion of the first short link  421 . The first end portion of the sixth arm link  956  is pivotally connected with the first long link  462  under the state that the first end portion of the sixth arm link  956  is substantially equally spaced apart from the second end portion of the first long link  462  and the first end portion of the first short link  471 . 
     The robot arm  950  further comprises a stabilizing mechanism  650  which includes a first link  651  having first and second end portions and substantially equal in length to the first arm link  951 . The first link  651  is integrally formed with and in coaxial relationship with the first arm link  951  under the state that the first end portion of the first link  651  is connected with the first end portion of the first arm link  951 . 
     The stabilizing mechanism  650  further includes a second link  652  having first and second end portions. The first and second links  651  and  652  are pivotably connected with each other at the second end portion of the first link  651  and the first end portion of the second link  652 . The second link  652  is integrally connected with the handling member  125 . 
     The stabilizing mechanism  650  further includes a third link  653  having first and second end portions and substantially equal in length to the first link  651 . The second and third links  652  and  653  are pivotably connected with each other at the second end portion of the second link  652  and the first end portion of the third link  653 . 
     The stabilizing mechanism  650  further includes a fourth link  654  having first and second end portions and substantially equal in length to the second link  652 . The third and fourth links  653  and  654  are pivotably connected with each other at the second end portion of the third link  653  and the first end portion of the fourth link  654 . The fourth and first links  654  and  651  are pivotably connected with each other at the second end portion of the fourth link  654  and the first end portion of the first link  651  under the state that the first link  651  is in parallel relationship with the third link  653  and that the second link  652  is in parallel relationship with the fourth link  654 . The second end portion of the fourth link  654  integrally formed with the first long link  412  or the first short link  421 . 
     The robot arm  950  further comprises an additional stabilizing mechanism  660 . The additional stabilizing mechanism  660  is similar to the stabilizing mechanism  650  and includes a first link  661  having first and second end portions and substantially equal in length to the fourth arm link  954 . The first link  661  is integrally formed with and in coaxial relationship with the fourth arm link  954  under the state that the first end portion of the first link  661  is connected with the first end portion of the fourth arm link  954 . 
     The additional stabilizing mechanism  660  further includes a second link  662  having first and second end portions. The first and second links  661  and  662  are pivotably connected with each other at the second end portion of the first link  661  and the first end portion of the second link  662 . The second link  662  is integrally connected with the additional handling member  126 . 
     The additional stabilizing mechanism  660  further includes a third link  663  having first and second end portions and substantially equal in length to the first link  661 . The second and third links  662  and  663  are pivotably connected with each other at the second end portion of the second link  662  and the first end portion of the third link  663 . 
     The additional stabilizing mechanism  660  further includes a fourth link  664  having first and second end portions and substantially equal in length to the second link  662 . The third and fourth links  663  and  664  are pivotably connected with each other at the second end portion of the third link  663  and the first end portion of the fourth link  664 . The fourth and first links  664  and  661  are pivotably connected with each other at the second end portion of the fourth link  664  and the first end portion of the first link  661  under the state that the first link  661  is in parallel relationship with the third link  663  and that the second link  662  is in parallel relationship with the fourth link  664 . The second end portion of the fourth link  664  integrally formed with the first long link  462  or the first short link  471 . 
     The first driving shaft  121  is integrally connected with the second end portion of the sixth arm link  956  and rotating the sixth arm link  956  around the rotation axis  123 . The second driving shaft  122  is integrally connected with the second end portion of the fifth arm link  955  and rotating the fifth arm link  955  around the rotation axis  123 . 
     According to the present invention, the fifth and sixth arm links  955  and  956  may be replaced by each other about the connection with the first or second driving shafts  121  or  122 . 
     According to the present invention, the link retaining mechanism  400  retains the first and second arm links  951  and  952  under the state that the first and second arm links  951  and  952  are in symmetrical relationship with each other with respect to the center line  401 . The additional link retaining mechanism  450  retains the third and fourth arm links  953  and  954  under the state that the third and fourth arm links  953  and  954  are in symmetrical relationship with each other with respect to the center line  451 . By the reason that the first and third arm links  951  and  953  are respectively in symmetrical relationship with the second and fourth arm links  952  and  954 , the handling member  125  leaves from the rotation axis  123  when the additional handling member  126  approaches the rotation axis  123 . By the same reason, the additional handling member  126  leaves from the rotation axis  123  when the handling member  125  approaches the rotation axis  123 . 
     According to the present invention, the robot arm mechanism  115  can be rotated around the rotation axis  123  by the rotation of the fifth or sixth arm links  955  or  956  around the rotation axis  123 . 
     Referring to FIGS. 28 and 29 of the drawings, there is shown a sixteenth preferred embodiment of the robot arm mechanism according to the present invention. The robot arm mechanism  116  is shown in FIGS. 28 and 29 as comprising a robot arm  960 . 
     The construction of the robot arm mechanism  116  in the present preferred embodiment is similar to the construction of the robot arm mechanism  115  in the fifteenth preferred embodiment except for the link retaining mechanism  500  and the additional link retaining mechanism  550 . 
     The robot arm  960  comprises first, second, third, and fourth arm links  961 ,  962 ,  963 , and  964  which are similar to first, second, third, and fourth arm links  951 ,  952 ,  953 , and  954  in the fifth preferred embodiment of the robot arm mechanism according to the present invention. 
     The first driving shaft  121  is integrally connected with the second end portion of the fifth arm link  965  and rotating the fifth arm link  965  around the rotation axis  123 . The second driving shaft  122  is integrally connected with the second end portion of the sixth arm link  966  and rotating the sixth arm link  966  around the rotation axis  123 . 
     According to the present invention, the fifth and sixth arm links  965  and  966  may be replaced by each other about the connection with the first or second driving shafts  121  or  122 . 
     According to the present invention, the operation of the robot arm mechanism  116  in the sixteenth preferred embodiment is similar to the operation of the robot arm mechanism  115  in the fifth preferred embodiment. 
     Referring to FIGS. 30 to  32  of the drawings, there is shown a seventeenth preferred embodiment of the robot arm mechanism according to the present invention. The robot arm mechanism  117  is shown in FIGS. 30 to  32  as comprising a handling member  125  and a robot arm  970 . 
     The robot arm  970  comprises first and second arm links  971  and  972 . 
     The robot arm  970  further comprises a third arm link  973  having first and second end portions and substantially equal in length to the first arm link  971 . The second and third arm links  972  and  973  are pivotably connected with each other at the first end portion of the second arm link  972  and the first end portion of the third arm link  973 . 
     The robot arm  970  further comprises a fourth arm link  974  having first and second end portions and substantially equal in length to the second arm link  972 . The first and second arm links  971  and  972  are substantially equal in length to each other. The first and fourth arm links  971  and  974  are pivotably connected with each other at the first end portion of the first arm link  971  and the first end portion of the fourth arm link  974 . 
     The robot arm  970  further comprises a fifth arm link  975  having first and second end portions and substantially equal in length to the distance between the second end portion of the first long link  512  and the first end portion of the first short link  521 . The first and fifth arm links  971  and  975  are pivotably connected with each other at the second end portion of the first arm link  971  and the first end portion of the fifth arm link  975 . The third and fifth arm links  973  and  975  are pivotably connected with each other at the second end portion of the third arm link  973  and the second end portion of the fifth arm link  975  under the state that the first long link  512  and the fifth arm link  975  are in parallel relationship with each other and that the first arm link  971  and the third arm link  973  are in parallel relationship with each other. 
     The robot arm  970  further comprises a sixth arm link  976  having first and second end portions and substantially equal in length to the distance between the second end portion of the first long link  512  and the first end portion of the first short link  521 . The second and sixth arm links  972  and  976  are pivotably connected with each other at the second end portion of the second arm link  972  and the first end portion of the sixth arm link  976 . The fourth and sixth arm links  974  and  976  are pivotably connected with each other at the second end portion of the fourth arm link  974  and the second end portion of the sixth arm link  976  under the state that the first long link  512  and the sixth arm link  976  are in parallel relationship with each other and that the second arm link  972  and the fourth arm link  974  are in parallel relationship with each other, the handling member  125  and the sixth arm link  976  integrally formed with each other. 
     The arm driving mechanism  120  comprises a first driving shaft  121  rotatable around a rotation axis  123 , and a second driving shaft  122  in the form of a hollow shape to rotatably receive therein the first driving shaft  121  and rotatable around the rotation axis  123 . The rotation axis  123  is positioned on the line passing through the first and second end portions of the fifth arm link  975 . The robot arm  970  further comprises a driving assist parallelogram linkage  690  including a first link  691  having first and second end portions and substantially equal in length to the distance between the rotation axis  123  and the second end portion of the first arm link  971 . The first link  691  is integrally formed with and in coaxial relationship with the fifth arm link  975  under the state that the second end portion of the first link  691  is connected with the first end portion of the fifth arm link  975 . 
     The driving assist parallelogram linkage  690  further includes a second link  692  having first and second end portions. The first and second links  691  and  692  are pivotably connected with each other at the second end portion of the first link  691  and the first end portion of the second link  692 . The second link  692  is integrally formed with and in parallel relationship with the first arm link  971  under the state that the first end portion of the second link  692  is connected with the second end portion of the first arm link  971 . 
     The driving assist parallelogram linkage  690  further includes a third link  693  having first and second end portions and substantially equal in length to the first link  691 . The second and third links  692  and  693  are pivotably connected with each other at the second end portion of the second link  692  and the first end portion of the third link  693 . 
     The driving assist parallelogram linkage  690  further includes a fourth link  694  having first and second end portions and substantially equal in length to the second link  692 . The third and fourth links  693  and  694  are pivotably connected with each other at the second end portion of the third link  693  and the first end portion of the fourth link  694 . The fourth and first links  694  and  691  are pivotably connected with each other at the second end portion of the fourth link  694  and the first end portion of the first link  691  under the state that the first link  691  is in parallel relationship with the third link  693  and that the second link  692  is in parallel relationship with the fourth link  694 . 
     The arm driving mechanism  120  comprises a first driving shaft  121  rotatable around a rotation axis  123 , and a second driving shaft  122  in the form of a hollow shape to rotatably receive therein the first driving shaft  121  and rotatable around the rotation axis  123 . 
     The second driving shaft  122  is integrally connected with the fourth link  694  at the second end portion of the fourth link  694  and rotating the fourth link  694  around the rotation axis  123 . The first driving shaft  121  is integrally connected with the fifth arm link  975  and rotating the fifth arm link  975  around the rotation axis  123 . 
     According to the present invention, while the second driving shaft  122  rotates the first arm link  971  through the driving assist parallelogram linkage  690 , the second driving shaft  122  may be directly and integrally connected with the first or third arm links  971  or  973  at the second end portions of the first or third arm links  971  or  973  without the driving assist parallelogram linkage  690 . 
     According to the present invention, the link retaining mechanism  500  retains the first and second arm links  971  and  972  under the state that the first and second arm links  971  and  972  are in symmetrical relationship with each other with respect to the center line  501 . By the reason that the first arm link  971  is in symmetrical relationship with the second arm link  972 , the fifth and sixth arm links  975  and  976  are positioned on a common line. By the reason that the fifth and sixth arm links  975  and  976  are positioned on the common line, the handling member  125  approaches and leaves from the rotation axis  123  with keeping a direction with respect to the rotation axis  123  fixed. 
     According to the present invention, the robot arm mechanism  117  can be rotated around the rotation axis  123  by the rotation of the first and second driving shafts  121  and  122  around the rotation axis  123 . 
     According to the present invention, the fifth arm link  975  and the fourth link  694  may be replaced by each other about the connection with the first or second driving shafts  121  or  122 .