Workpiece transfer apparatus

A workpiece transfer apparatus includes a stationary base, an elevation base, first and second arms, a workpiece-holding hand, and a driving mechanism for the hand. The first arm is supported on the elevation base so as to be rotatable about a first vertical axis. The second arm is supported on the distal end of the first arm such that the second arm is rotatable about a second vertical axis. The hand is supported on the distal end of the second arm so as to be rotatable about a third vertical axis. A motor is arranged in the first arm, whereas a transmission is arranged to extend in a region from the interior of the first arm through the interior of the second arm.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a workpiece transfer apparatus for transferring workpieces in the form of a thin plate. Specifically, the invention relates to a workpiece transfer apparatus for transferring e.g. wafers in the process of manufacturing semiconductor devices.

2. Description of the Related Art

In the manufacture of semiconductor devices, a robot for transferring workpieces such as wafers is used (see JP-A-2003-188231, for example). Such a workpiece transfer apparatus transfers workpieces between a load port storing wafers and a process chamber.

FIG. 7shows an example of workpiece transfer system including a conventional workpiece transfer apparatus. The workpiece transfer system90illustrated in the figure includes two load ports91, a transfer chamber92, a process chamber93and a workpiece transfer apparatus94. The workpiece transfer apparatus94comprises a horizontal articulated robot having the structure described below, and is arranged in the transfer chamber92. On one side of the transfer chamber92, the two load ports91are arranged side by side adjacent to the transfer chamber92. Each of the load ports91accommodates a cassette for holding a plurality of workpieces W. On a side of the transfer chamber92opposite from the load ports91, the process chamber93is arranged adjacent to the transfer chamber92. In the process chamber93, treatment such as heating, working, or testing is performed with respect to the workpieces W.

FIG. 8is a side view showing a schematic structure of the workpiece transfer apparatus94. The workpiece transfer apparatus94includes a hollow stationary base941having a vertically extending center axis, an elevation base942, a lower arm943, an upper arm944and a hand945. The elevation base942is supported by the stationary base941and vertically movable by the operation of an elevation mechanism, not shown. The lower arm943is supported at its base end on the elevation base942and is rotatable around the vertical axis O1by the operation of a lower arm driving mechanism, not shown. The upper arm944is supported at its base end on the distal end of the lower arm943and is rotatable around the vertical axis O2by the operation of an upper arm driving mechanism, not shown.

The hand945is supported at its base end on the distal end of the upper arm944and is rotatable around the vertical axis O3by the operation of a hand driving mechanism946. The hand driving mechanism946includes a hand driving motor947supported by the elevation base942and a transmission mechanism948for transmitting rotational output of the motor947to the hand945. The transmission mechanism948is provided with a speed reducer949. The speed reducer949is arranged directly under the base end of the hand945, and the base end of the hand945is connected to the output shaft of the speed reducer949. With this arrangement, when the motor947is driven, the hand945rotates about the vertical axis O3.

In the workpiece transfer apparatus94having the above-described structure, workpieces W are transferred between each of the load ports91and the process chamber93by appropriately controlling the operation of the lower arm driving mechanism, the upper arm driving mechanism and the hand driving mechanism946.

In recent years, the size of the workpieces W, which are the object to be transferred by the workpiece transfer apparatus94, tends to increase. For instance, in the field of semiconductor device manufacture, wafers having a diameter of 450 mm and a relatively large thickness are expected to be used instead of the wafers having a diameter of 300 mm. Such an increase in diameter and thickness of the workpieces W leads to an increase in the transfer stroke of the workpieces W in horizontal and vertical directions.

In order that the transfer efficiency of the workpieces W does not decrease even when the transfer stroke in horizontal and vertical directions is increased, the transfer speed needs to be increased. However, with the conventional workpiece transfer apparatus94having the above-described structure, the hand driving motor947is arranged in the elevation base942so that the power transmission path from the motor947to the hand945is relatively long. This provides limitation on the increase in the workpiece transfer speed. As another means to increase the transfer speed, increasing the size of the motor947or the speed reducer949may be considered. With the above-described conventional structure, an increase in size of the motor947or the speed reducer949results in an increase in height of the work transfer apparatus94, whereby the height of the hand945increases. Such an increase in height of the hand945is not desirable, because the lowest position where workpieces can be transferred in the load ports91cannot be changed in most cases due to various limitations. Thus, with the above-described conventional structure, it is difficult to achieve transfer of relatively large workpieces W at high speed by increasing the size of the motor947or the speed reducer949.

A double-hand workpiece transfer apparatus including two hands arranged in the vertical direction is also known as an apparatus for realizing more efficient workpiece transfer. Such a double-hand workpiece transfer apparatus needs to include two motors and two transmission mechanisms. With the above-described conventional structure, however, the provision of two motors and two transmission mechanisms increases the height of the workpiece transfer apparatus94and hence increase the height of the hand945, so that it is difficult to adapt such an apparatus for relatively large workpieces W.

SUMMARY OF THE INVENTION

The present invention has been proposed under the circumstances described above. It is therefore an object of the present invention to provide a workpiece transfer apparatus suitable for transferring workpieces at high speed, without increasing the height of the apparatus.

According to a first aspect of the present invention, there is provided a workpiece transfer apparatus comprising a stationary base, an elevation base vertically movably supported by the stationary base, a first arm and a second arm each of which includes a base end and a distal end, a hand for holding a workpiece, and a hand driving mechanism for driving the hand for rotation. The base end of the first arm is supported on the elevation base such that the first arm is rotatable about a first vertical axis. The base end of the second arm is supported on the distal end of the first arm such that the second arm is rotatable about a second vertical axis. The hand is supported on the distal end of the second arm such that the hand is rotatable about a third vertical axis. The hand driving mechanism includes a motor and a transmission mechanism for transmitting rotational output of the motor to the hand. The motor is arranged in the first arm, whereas the transmission mechanism is arranged to extend in a region from an interior of the first arm through an interior of the second arm.

According to a second aspect of the present invention, the transmission mechanism comprises a speed reducer for reducing rotation speed of the output shaft of the motor, an intermediate transmission shaft including a first end and a second end and arranged rotatably about the second vertical axis, an operation shaft including a first end and a second end and arranged rotatably about the third vertical axis, a first through a fourth pulleys, and a first and a second endless belts. The first pulley is attached to the output shaft of the speed reducer. The second pulley is attached to the first end of the intermediate transmission shaft. The first endless belt is wound around the first pulley and the second pulley. The third pulley is attached to the second end of the intermediate transmission shaft. The fourth pulley is attached to the first end of the operation shaft. The second endless belt is wound around the third pulley and the fourth pulley. The second end of the operation shaft is connected to the hand.

According to a third aspect of the present invention, in the workpiece transfer apparatus, the first arm includes a projecting portion projecting downward, and part of the transmission mechanism is arranged in the projecting portion.

According to a fourth aspect of the present invention, the workpiece transfer apparatus further comprises a wiring extending from the stationary base to the hand via the first and the second arms, and a slip ring arranged at a portion of the wiring.

According to a fifth aspect of the present invention, the workpiece transfer apparatus further comprising an additional hand for holding a workpiece, and an additional hand driving mechanism for driving the additional hand for rotation. The additional hand is supported on the distal end of the second arm such that the additional hand is rotatable about the third vertical axis. The additional hand driving mechanism includes an additional motor and an additional transmission mechanism for transmitting rotational output of the additional motor to the additional hand. The additional motor is arranged in the first arm, whereas the additional transmission mechanism is arranged to extend in a region from an interior of the first arm through an interior of the second arm.

According to a sixth aspect of the present invention, the workpiece transfer apparatus according to the second aspect further comprises an additional hand for holding a workpiece, and an additional hand driving mechanism for driving the additional hand for rotation. The additional hand is supported on the distal end of the second arm such that the additional hand is rotatable about the third vertical axis. The additional hand driving mechanism includes an additional motor and an additional transmission mechanism for transmitting rotational output of the additional motor to the additional hand. The additional motor is arranged in the first arm, whereas the additional transmission mechanism is arranged to extend in a region from an interior of the first arm through an interior of the second arm.

According to a seventh aspect of the present invention, in the workpiece transfer apparatus according to the sixth aspect, the additional transmission mechanism comprises an additional speed reducer for reducing rotation speed of an output shaft of the additional motor, an additional intermediate transmission shaft including a first end and a second end and arranged rotatably about the second vertical axis, an additional operation shaft including a first end and a second end and arranged rotatably about the third vertical axis, a first through a fourth additional pulleys, and a first and a second additional endless belts. The first additional pulley is attached to the output shaft of the additional speed reducer. The second additional pulley is attached to the first end of the additional intermediate transmission shaft. The first additional endless belt is wound around the first additional pulley and the second additional pulley. The third additional pulley is attached to the second end of the additional intermediate transmission shaft. The fourth additional pulley is attached to the first end of the additional operation shaft. The second additional endless belt is wound around the third additional pulley and the fourth additional pulley. The second end of the additional operation shaft is connected to the additional hand.

According to an eighth aspect of the present invention, in the workpiece transfer apparatus according to the fifth aspect, the first arm includes a projecting portion projecting downward, and part of the transmission mechanism and part of the additional transmission mechanism are arranged in the projecting portion.

According to a ninth aspect of the present invention, the workpiece transfer apparatus according to the fifth aspect further comprises a wiring extending from the stationary base to the hand and the additional hand via the first and the second arms, and a slip ring arranged at a portion of the wiring.

In the workpiece transfer apparatus according to the present invention, the motor for driving the hand and part of the transmission mechanism are arranged in the internal space of the first arm. With this arrangement, the height of the transmission mechanism within the distal end of the second arm is suppressed, and the total height of the stationary base and the elevation base is also suppressed. Further, since the transmission mechanism is arranged to extend in a region from an interior of the first arm through an interior of the second arm, the power transmission path from the motor to the hand is relatively short. This structure is suitable for workpiece transfer at high speed and with high accuracy. Moreover, since the speed reducer, which is one of the elements constituting the transmission mechanism, is arranged in the first arm, the rotation element operates stably. Thus, the workpiece transfer apparatus according to the present invention is capable of transferring even a relatively large workpiece at high speed and with high accuracy.

Other features and advantages of the present invention will become more apparent from detailed description given below with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-6show a workpiece transfer apparatus according to an embodiment of the present invention. The workpiece transfer apparatus10of this embodiment is designed to transfer workpieces W in the form of a thin plate such as a wafer, and includes a stationary base1, an elevation base2, elongated lower arm3and upper arm4, two hands5A and5B for holding a workpiece W, and a hand driving mechanisms6A,6B for driving the hands for rotation.

As shown inFIG. 2, the stationary base1is structured as a hollow housing which is substantially rectangular in cross section and includes a bottom11and a side wall12.

The elevation base2is supported by the stationary base1movably in the vertical direction. A pair of vertically extending guide rails13are provided in the stationary base1. The elevation base2is provided with a slider21. The slider21is supported on the guide rails13slidably in the vertical direction. A screw shaft14is rotatably supported in the stationary base1. The elevation base2is further provided with a nut22threadingly engaging with the screw shaft14. An elevation motor15is provided at a lower portion in the stationary base1. A pulley16is attached to the output shaft of the elevation motor15, whereas a pulley17is attached to the screw shaft14. An endless belt18is wound around the pulleys16and17. With this arrangement, when the elevation motor15is driven, the screw shat14rotates, and the elevation base2moves vertically in accordance with the rotation. In this way, the elevation mechanism for moving the elevation base2vertically relative to the stationary base1is provided.

The elevation base2is provided with an elevation cover23substantially rectangular in cross section and loosely fitted to the outer surface of the side wall12of the stationary base1. The elevation cover23moves vertically along with the elevation base2and constantly covers an upper portion of the stationary base1. The height of the elevation cover23is set such that a lower portion of the elevation cover23covers part of the side wall12even when the elevation base2is raised to the uppermost position.

A speed reducer24is provided at an upper portion of the elevation cover23. The speed reducer24is one of the elements constituting a lower arm driving mechanism, which will be described later, and arranged to face the opening formed at an upper portion of the elevation cover23. In this embodiment, a unit type speed reducer incorporating e.g. a cross roller bearing is used as the speed reducer24. A speed reducer incorporating a cross roller bearing is used also as the speed reducers34,621aand621b, which will be described later.

As shown inFIG. 2, the lower arm3is substantially in the form of a hollow rectangular prism and supported at its base end31on the elevation base2such that its longitudinal direction corresponds to the horizontal direction. The lower arm3includes a projecting portion33projecting downward. The projecting portion33is provided toward the distal end of the lower arm3so as not to interfere with the elevation base2(elevation cover23) when the lower arm3rotates about the vertical axis O1. (That is, the projecting portion33is spaced from the elevation cover23in the horizontal direction.) The base end31of the lower arm3has an opening at its lower portion, and the portion of the lower arm3around the opening is connected to the output shaft of the speed reducer24. With this arrangement, the lower arm3is supported by the elevation base2via the speed reducer24rotatably about the vertical axis O1.

The elevation base2is provided with a lower arm driving motor25. An intermediate transmission shaft26for the lower arm is provided at a position deviated from the vertical axis O1. The intermediate transmission shaft26is rotatably supported by the elevation base2via a bearing261. A pulley251is attached to the output shaft of the motor25, whereas a pulley262is attached to the lower end of the intermediate transmission shaft26. An endless belt263is wound around the pulleys251and262. A pulley264is attached to the upper end of the intermediate transmission shaft26, whereas a pulley241is attached to the input shaft of the speed reducer24. An endless belt265is wound around the pulleys264and241. With this arrangement, when the lower arm driving motor25is driven, the lower arm3rotates about the vertical axis O1due to the linked operation of the pulley251, the endless belt263, the pulley262, the intermediate transmission shaft26, the pulley264, the endless belt265, the pulley241and the speed reducer24. In this way, the lower arm driving mechanism for rotating the lower arm3about the vertical axis O1is provided.

A speed reducer34is provided at an upper portion of the distal end32of the lower arm3. The speed reducer34is one of the elements constituting an upper arm driving mechanism, which will be described later, and arranged to face the opening formed at an upper portion of the distal end32of the lower arm3.

The upper arm4is substantially in the form of a hollow rectangular prism and supported on the lower arm3such that its longitudinal direction corresponds to the horizontal direction. The base end41of the upper arm4has an opening at its lower portion, and the portion of the upper arm4around the opening is connected to the output shaft of the speed reducer34. With this arrangement, the upper arm4is supported by the lower arm3via the speed reducer34rotatably about the vertical axis O2.

The elevation base2is further provided with an upper arm driving motor27. An intermediate transmission shaft28for the upper arm is provided to penetrate through the hollow portion of the speed reducer24. The intermediate transmission shaft28is connected to the lower portion of the base end31of the lower arm3via a bearing281and connected to the pulley241via a bearing282. With this arrangement, the intermediate transmission shaft28is rotatable about the vertical axis O2. A pulley271is attached to the output shaft of the motor27, whereas a pulley283is attached to the lower end of the intermediate transmission shaft28. An endless belt284is wound around the pulleys271and283. A pulley285is attached to the upper end of the intermediate transmission shaft28, whereas a pulley341is attached to the input shaft of the speed reducer34. An endless belt286is wound around the pulleys285and341. With this arrangement, when the upper arm driving motor27is driven, the upper arm4rotates about the vertical axis O2due to the linked operation of the pulley271, the endless belt284, the pulley283, the intermediate transmission shaft28, the pulley285, the endless belt286, the pulley341and the speed reducer34. In this way, the upper arm driving mechanism for rotating the upper arm4about the vertical axis O2is provided.

The hand5A includes a base portion51ahaving a box-like shape, and a work holding portion52ahaving a bifurcated end. Similarly, the hand5B includes a base portion51bhaving a box-like shape, and a work holding portion52bhaving a bifurcated end. The hands5A and5B are supported by the upper arm4such that their center axes extend in the horizontal direction.

A sensor for detecting a workpiece W is provided at appropriate portions of the hands5A,5B (work holding portions52a,52b). For instance, the sensor may be a reflective type photo interrupter.

A cylindrical operation shaft53aextending vertically downward is provided at the base portion51aof the hand5A. As shown inFIG. 3, the operation shaft53ais fitted in an opening formed at an upper portion of the distal end42of the upper arm4. The operation shaft53ais rotatably supported by the upper arm4via a bearing421. With this arrangement, the hand5A is supported by the distal end42of the upper arm4rotatably about the vertical axis O3.

A cylindrical operation shaft53bextending vertically downward is provided at the base portion51bof the hand5B. As shown inFIG. 3, the operation shaft53bis arranged in the operation shaft53acoaxially with the operation shaft53a. The operation shaft53bis connected to the base portion51aof the hand5A via a bearing532and connected to the operation shaft53avia a bearing533. With this arrangement, similarly to the hand5A, the hand5B is supported by the distal end42of the upper arm4rotatably about the vertical axis O3.

As shown inFIG. 2, the hand driving mechanism6A includes a motor61afor driving the hand5A, and a transmission mechanism62afor transmitting rotational output of the motor61ato the hand5A. Similarly, the hand driving mechanism6B includes a motor61bfor driving the hand5B, and a transmission mechanism62bfor transmitting rotational output of the motor61bto the hand5B.

The motors61aand61bare arranged in the lower arm3, and the transmission mechanisms62aand62bare arranged to extend in a region from the interior of the lower arm3through the interior of the upper arm4.

More specifically, the transmission mechanism62aincludes a speed reducer621a(seeFIG. 4) for reducing the rotation speed of the output shaft of the motor61a, an intermediate transmission shaft622aand the operation shaft53adescribed above. Similarly, the transmission mechanism62bincludes a speed reducer621b(seeFIG. 4) for reducing the rotation speed of the output shaft of the motor61b, an intermediate transmission shaft622band the operation shaft53bdescribed above.

As shown inFIG. 4, the speed reducers621aand621bare arranged in the lower arm3and connected to the output shafts of the motors61aand61b, respectively. Pulleys623aand623bare attached to the output shafts of the speed reducers621aand621b, respectively.

As shown inFIG. 4, the intermediate transmission shafts622aand622bare arranged coaxially and extend through the hollow portion of the speed reducer34to be positioned in the distal end32of the lower arm3and in the base end41of the upper arm4. The intermediate transmission shaft622bis connected to a lower portion of the base end41of the upper arm4via a bearing631and connected to the pulley341via a bearing632. The intermediate transmission shaft622bis provided with a pulley624bat its lower end and a pulley625bat its upper end. The intermediate transmission shaft622ais connected to the pulley625bvia a bearing633and connected to the pulley624bvia a bearing634. The intermediate transmission shaft622ais provided with a pulley624aat its lower end and a pulley625aat its upper end. The intermediate transmission shafts622aand622bare rotatable about the vertical axis O2.

As shown inFIGS. 2 and 3, the operation shaft53ais provided with a pulley531aat its lower end. The operation shaft53bis provided with a pulley531bat its lower end.

As shown inFIG. 4, an endless belt626ais wound around the pulley623aattached to the output shaft of the speed reducer621aand the pulley624aprovided at the lower end of the intermediate transmission shaft622a. An endless belt626bis wound around the pulley623battached to the output shaft of the speed reducer621band the pulley624bprovided at the lower end of the intermediate transmission shaft622b. As shown inFIG. 2, an endless belt627ais wound around the pulley625aprovided at the upper end of the intermediate transmission shaft622aand the pulley531aprovided at the lower end of the operation shaft53a. An endless belt627bis wound around the pulley625bprovided at the upper end of the intermediate transmission shaft622band the pulley531bprovided at the lower end of the operation shaft53b. With this arrangement, when the motor61ais driven, the hand5A rotates about the vertical axis O3due to the linked operation of the speed reducer621a, the pulley623a, the endless belt626a, the pulley624a, the intermediate transmission shaft622a, the pulley625a, the endless belt627a, the pulley531aand the operation shaft53a. Similarly, when the motor61bis driven, the hand5B rotates about the vertical axis O3due to the linked operation of the speed reducer621b, the pulley623b, the endless belt626b, the pulley624b, the intermediate transmission shaft622b, the pulley625b, the endless belt627b, the pulley531band the operation shaft53b. In this way, the hand driving mechanisms6A and6B for rotating the hands5A and5B about the vertical axis O3are provided.

The workpiece transfer apparatus10having the above-described structure ensures that the lower arm driving mechanism, the upper arm driving mechanism, the hand driving mechanism6A and the hand driving mechanism6B are controlled independently. Thus, the lower arm3, the upper arm4and the hands5A,5B are rotated about the vertical axes O1, O2and O3within a predetermined range. By appropriately controlling the rotation of each of the lower arm3, the upper arm4, the hand5A and the hand5B, each of the hands5A and5B is moved to a desired position. Further, by driving the elevation motor15, the elevation base2is moved up and down, whereby the hands5A and5B is moved to a desired height within a predetermined range.

If necessary, the clearances between the stationary base1and the elevation cover23, between the elevation cover23and the lower arm3, between the lower arm3and the upper arm4, and between the upper arm4and the hands5A,5B may be closed with a sealing member. In this case, the inner space of the workpiece transfer apparatus10is hermetically sealed, so that undesired particles such as dust in the workpiece transfer apparatus10are prevented from diffusing to the surroundings.

The workpiece transfer apparatus10according to this embodiment includes a workpiece holding mechanism to hold a workpiece W on the hand5A,5B by utilizing vacuum suction.

The workpiece holding mechanism of this embodiment includes a vacuum pump provided in the stationary base1or the elevation base2, vacuum suction ports provided in the hands5A and5B, and a conduit for connecting the vacuum pump and the vacuum suction ports. The conduit needs to be arranged so as not to prevent rotation of the lower arm3, the upper arm4and the hands5A,5B. The conduit comprises pipe shafts extending along the vertical axes O1and O2, pipes provided in the arms3and4, an axial flow path extending along the vertical axis O3, and branch pipes provided in the hands5A,5B.

The end of the pipe shaft extending along the vertical axis O1, O2and the pipe in the arm3,4are connected to each other via an interconnection chamber provided in the arm3,4. The interconnection chamber and the end of the pipe shaft are hermetically connected rotatably relative to each other via e.g. an O-ring. Such a connection structure between the pipe shaft, the interconnection chamber and the pipe can be realized by a structure similar to that disclosed in JP-A-2003-188231 (SeeFIG. 7of this document), and detailed description and illustration of this structure is omitted.

FIG. 5shows a schematic structure of the conduit for the above-described workpiece suction provided in the upper arm4and the hands5A,5B. As shown in the figure, annular interconnection chambers534and535are provided in a lower portion and in a middle portion, respectively, of the operation shaft53bof the hand5B. The annular interconnection chamber534is connected to the pipe43in the upper arm4. The annular interconnection chambers534and535are connected to each other via an axial flow path536. A branch pipe538extending into the base portion51bof the hand5B is connected to the annular interconnection chamber535. A branch pipe537extending into the base portion51aof the hand5A is provided in the operation shaft53aof the hand5A at a position corresponding to the annular interconnection chamber535.

An O-ring54is interposed between the pipe43in the upper arm4and the annular interconnection chamber534. Thus, the pipe43and the annular interconnection chamber534are hermetically connected rotatably relative to each other. An O-ring55is interposed between the annular interconnection chamber535and the branch pipe537. Thus, the annular interconnection chamber535and the branch pipe537are hermetically connected rotatably relative to each other.

The branch pipe537of the hand5A is provided with an electromagnetic valve (not shown) for opening or closing the branch pipe537. The end of the branch pipe537is connected to a vacuum suction port (not shown) provided in e.g. the work holding portion52a. The branch pipe538of the hand5B is provided with an electromagnetic valve (not shown) for opening or closing the branch pipe538. The end of the branch pipe538is connected to a vacuum suction port (not shown) provided in e.g. the work holding portion52b.

With the workpiece holding mechanism including the above-described conduit, a workpiece W can be held by suction regardless of the rotational positional relationship among the lower arm3, the upper arm4and the hands5A,5B. Moreover, by appropriately switching each of the electromagnetic valves provided in the branch pipes537,538of the hands5A,5B, the two hands5A and5B are individually switched between a state in which the hand holds a workpiece W by suction and a state in which the hand does not hold a workpiece W by suction.

The workpiece transfer apparatus10according to the present invention includes a wiring for signal transmission relative to the sensor provided in the hands5A,5B and for power supply and signal transmission to the electromagnetic valves. The wiring extends from the stationary base1to the hands5A and5B via the elevation base2, the lower arm3and the upper arm4. The wiring may comprise a multicore such as a curl cord or a flat cable at portions between the stationary base1and the elevation base2, between the elevation base2and the lower arm3, and between the lower arm3and the upper arm4, in order to accommodate changes in positional relationship.

FIG. 6shows a schematic structure of the above-described wiring in the upper arm4and the hands5A,5B. As illustrated in the figure, the distal end42of the upper arm4includes a shaft portion44extending vertically upward from the bottom. The wiring includes an arm wiring portion45extending through axial portion44and a hand wiring portion56provided in the hands5A,5B.

A slip ring7is provided on the inner side of the operation shaft53bof the hand5B. The slip ring7is to provide electrical connection to a rotary member via an annular electric path and a brush, and the arm wiring portion45and the hand wiring portion56are connected to the annular electric path and the brush. With the slip ring7, electrical connection between the arm wiring portion45and the hand wiring portion56is properly maintained while allowing endless relative rotation between the upper arm4and the hand5B.

The hand wiring portion56includes a first wiring portion56afor the hand5A and a second wiring portion56bfor the hand5B which are branched at a branch point. The first and the second wiring portions56aand56bare connected to the sensors and the electromagnetic valves described above. The first wiring portion56afor the hand5A comprises e.g. a flat cable in order to accommodate changes in positional relationship between the hands5A and5B due to rotation. The first wiring portion56aneeds to have a sufficient length to allow for relative rotation of the hands5A and5B. Herein, when the first wiring portion56acomprises a flat cable, the first wiring portion56acan be wound to overlap in the thickness direction around a winder portion58provided in a case57arranged on the hand5A.

As noted above, the hand driving mechanisms6A,6B include motors61a,61band transmission mechanisms62a,62bfor transmitting rotational output of the motors61a,61bto the hands5A,5B. The motors61aand61bare arranged in the lower arm3, and the transmission mechanisms62aand62bare arranged to extend in a region from the interior of the lower arm3through the interior of the upper arm4. According to this structure, the motors61a,61bare arranged in the internal space of the lower arm3in a space-efficient manner. As compared with the conventional structure in which the motor is arranged in the stationary base1or the elevation base2, the height of the stationary base1or the elevation base2is suppressed, whereby the height of the workpiece transfer apparatus10is suppressed.

Since the motors61a,61band the transmission mechanisms62a,62bare arranged in the lower arm3or in the upper arm4, the power transmission path from the motors61a,61bto the hands5A,5B is shorter than that in the conventional structure in which the motor is arranged in the stationary base1or the elevation base2. Thus, the workpiece transfer apparatus10according to this embodiment is suitable for transferring workpieces at high speed.

According to the arrangement of the motors61a,61bin the lower arm3, driving control of the hands5A,5B is easier than in the conventional structure in which the hand driving motor is arranged in the stationary base1or the elevation base2. This is suitable for transferring workpieces at high speed and with high accuracy.

Moreover, since the speed reducers621a,621bare arranged adjacent to the motors61a,61bwithin the lower arm3in a space-efficient manner, the height of the hands5A,5B is suppressed as compared with the conventional structure in which the speed reducer for hand driving is arranged under the base end of the hand. This arrangement is also suitable for suppressing the height of the workpiece transfer apparatus10.

The speed reducers621a,621b, which have a relatively large weight, are arranged not toward the distal end (i.e., adjacent to the hands5A,5B) but toward the base end (i.e., in the lower arm3) of the rotation element (consisting of the lower arm3, the upper arm4and the hands5A,5B). This arrangement ensures that the rotation element rotates more stably as compared with the conventional structure in which the speed reducer is arranged adjacent to the hand, which allows workpiece transfer with high accuracy.

As noted above, the lower arm3includes a projecting portion33projecting downward, and part of the transmission mechanisms62a,62b(the speed reducers621a,621b, pulleys623a,623b, pulleys624a,624band endless belts626a,626bin this embodiment, as shown inFIG. 4) is arranged in the projection portion33. With this arrangement, the transmission mechanisms62a,62bare arranged in the lower arm3in a space-efficient manner while keeping the height of the lower arm3substantially low. This is suitable for suppressing the height of the workpiece transfer apparatus10.

The workpiece transfer apparatus10according to this embodiment is of a double-hand type with two hands5A and5B. According to the present invention, even a workpiece transfer apparatus of such a double-hand type can have a suppressed height by arranging the two motors and the two transmission mechanisms in the lower arm3or the upper arm4in a space-efficient manner.

According to this embodiment, the first wiring portion56afor the hand5A can be made of a flat cable and wound around the winder portion58. With this arrangement, the height of the case57for accommodating the winder portion58will be sufficient if it is approximately equal to the width of the flat cable, so that the height of the hand5B can be suppressed. Unlike this embodiment, when a curl cord is used as the first wiring portion56a, the height of the case for accommodating the wiring needs to be larger to secure the movement area of the curl cord. Moreover, when a hollow slip ring is used as the first wiring portion56a, the case for accommodating the slip ring needs to have a relatively large height because of the large outer dimension of the slip ring. Thus, the first wiring portion56acomprising a flat cable is suitable for suppressing the height of the hand5B, and hence, suitable for suppressing the height of the workpiece transfer apparatus10.

As noted above, the workpiece transfer apparatus10according to this embodiment includes a workpiece holding mechanism utilizing vacuum suction, and the on state and the off state for holding a workpiece W by suction can be switched individually with respect to each of the hands5A,5B by the electromagnetic valves provided in the branch pipes537,538. Since the electromagnetic valves are arranged close to the work holding portions52a,52bwhere the vacuum suction ports are provided, excellent responsiveness is obtained with respect to the on-off switching of workpiece suction holing. This is suitable for transferring workpieces at high speed.

While the embodiment of the present invention has been described above, the technical scope of the present invention is not limited to the above-described embodiment. The specific structure of each part of the workpiece transfer apparatus according to the present invention can be modified in many ways without departing from the spirit of the invention.

Although a double-hand workpiece transfer apparatus including two hands5A,5B is described above as an example, the present invention is applicable also to a workpiece transfer apparatus including only one hand.