Abstract:
A transfer mechanism for transferring optical glass material to be molded into optical glass elements such as lenses or the like, one after another from a container holding a large number of work pieces of the optical glass material onto a molding surface of a lower mold member of a mold assembly unit located at a work loading/unloading station of a glass molding line. The transfer mechanism employs a tubular positioning member which is located in such a way as to circumvent a suction nozzle and adapted to hold the outer periphery of optical glass material for accurate positioning. The positioning member is supported on a lift means together with the suction nozzle, but independently movable vertically over a predetermined stroke length relative to the lift member to assume a work loading position and a work unloading position, uncovering a suction pad at the lower end of the suction nozzle into an exposed state and permitting same to pick up a molded optical element which is increased in diameter as compared with the size of a work piece before press-molding.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Art 
     This invention relates generally to fabrication by press-molding of precision optical glass elements such as optical glass lenses or the like, and more particularly to a transfer mechanism for transferring work pieces of optical glass material each having curved surfaces on the opposite sides, accurately from a work container like a pallet to a predetermined position on a mold assembly unit to be used in press-molding. 
     2. Prior Art 
     For fabrication of precision optical glass elements like lenses, for example, press-molding processes are increasingly resorted to more than ever. Generally, an optical glass press-molding apparatus has a construction as shown in FIG.  12 . In that figure, indicated at  1  is a mold assembly unit, at  2   a  is an upper pressing member, and at  2   b  a lower pressing member. In this case, upper and lower pressing members  2   a  and  2   b  constitute a press means. The mold assembly unit  1  is largely composed of an upper mold member  3 , a lower mold member  4  and a girdler shell  5 . Normally, the lower mold member  4  is fixedly assembled into the girdler shell  5 , while the upper mold member  3  is movable toward and away from the lower mold member  4  under the guidance of the girdler shell  5 . 
     In a preparatory stage prior to press-molding, the upper mold member is  3  is once separated from the lower mold member  4 , and, after setting optical glass material  6  on a glass shaping surface  4   a  of the lower mold  4 , the upper mold member  3  is closed again on the lower mold  4 . Nextly, the mold assembly  1  as a whole is heated by the use of heating means  7  to soften the glass material  6 , and at the same time the upper and lower molds  3  and  4  are pressed toward each other by the upper and lower pressing members  2   a  and  2   b.  As a consequence, the optical glass material  6  in the mold  1  is pressed to shape to produce an optical glass element  6  which have predetermined surface characteristics copied from glass molding surfaces  3   a  and  4   a  of the upper and lower mold members  3  and  4 . 
     In order to carry out the lens molding operation automatically, for instance, a lens molding apparatus basically of the above-described construction can be incorporated into an automatic lens molding line in the manner as shown schematically in FIG.  13 . In that figure, indicated at  10  is a molding chamber which is equipped with a heating system  7  along with upper and lower pressing members  2   a  and  2   b.  Indicated at  11  is an entrance/exit way or station through which a mold assembly unit  1  with optical glass material  6  is loaded into the molding chamber  10  or to which a mold assembly unit  1  with a molded glass product is delivered from the molding chamber  10  after press-molding therein. Indicated at  12  is an upper mold assembling/dissembling station, at  13  a work loading/unloading station. At the work loading/unloading station, optical glass material  6  is placed on a lower mold member  4 , or an optical lens element which has been fabricated by press-molding is ejected from a lower mold. Accordingly, at the upper mold assembling/dissembling station  12 , an upper mold member  3  is removed from a mold assembly unit  1  on the way to the loading/unloading station  13 . Conversely, an upper mold member is set on a mold assembly unit  1  which arrives from the loading/unloading station  13 . The mold assembly unit  1  is supported on a suitable transfer jig and thereby transferred horizontally to and from the above-mentioned stations. 
     First of all, a work loading pallet in the form of a container which is arranged to hold a large number of pieces of the optical glass material  6  is located at the loading/unloading station  13  along with a work unloading pallet or a jig which is arranged to hold pieces of molded lens product thereon. Besides, for automatic loading and unloading operations, a robot with a suction arm is provided at the work loading/unloading station to transfer pieces of optical glass material  6  onto the loading pallet and to pick up a molded lens product  8  from a mold assembly unit  1 . This is the main reason why an upper mold member is put on or off at the upper mold assembling/dissembling station. An upper mold member  3  is picked up and retained on a holder member at the upper mold assembling/dissembling station  12 , and a lower mold assembly consisting of a lower mold member  4  and a girdler shell  5  is sent to the loading/unloading station  13  with a molding surface  4   a  faced upward in an open state. As soon as optical glass material  6  is placed in the lower mold  4 , the lower mold assembly is transferred to the upper mold assembling/dissembling station to receive an upper mold member  3  into the girdler shell  5 . Then, the mold assembly unit  1  is sent into the molding chamber  10  through the entrance/exit way  11 , and, while being softened under heating by the heating mechanism  7 , the optical glass material  6  is pressed to shape by the press means. 
     Upon finishing the press-molding of a lens element within the molding chamber  10 , the mold assembly unit  1  is transferred to the entrance/exit way  11  and then to the upper mold assembling/dissembling station  12  to remove the upper mold member  3  off the lower mold  4  and out of the girdler shell  5 . The lower mold assembly, with a molded lens element  8  on the opened molding surface  4   a  of the lower mold  4 , is further transferred to the work loading/unloading station where the molded optical lens product on the lower mold  4  is ejected therefrom and replaced by fresh optical glass material  6 . These operations are repeated to mold optical lens elements automatically and continuously. 
     In this connection, the shape of optical glass material is determined in relation with the shape of optical lens elements of the end product. For example, in the case of an optical lens product with a large radius of curvature, the optical glass material can be spherical or nearly spherical in shape. However, in the case of an optical lens product with a small radius of curvature, individual work pieces of optical glass material should be of a somewhat flattened shape having curved surfaces of a predetermined radius of curvature instead of surfaces of spherical shape. At the time of press-forming optical glass material having such flattened curved surfaces, a center O 1  of curvature on a front side  6   a  of glass material  6  as well as a center of curvature O 2  on a rear side  6   b  of the glass material should be positioned exactly on an axis A which connects the centers of curvature O 3  and O 4  of molding surfaces  3   a  and  4   a  of the upper and lower molds  3  and  4  as shown in FIG.  14 . If the centers of curvature O 1  and O 2  on the front and rear sides of the optical glass material is deviated from the axis A, pressure is non-uniformly applied to the glass material in the pressing stage to produce a lens element which is distorted in optical characteristics. 
     In the work loading stage, the optical glass material  6  is picked up from a pallet by a robot with a suction gripper means or the like and set on the shaping surface  4   a  of the lower mold  4 . At the time when the optical glass material  6  is released from the suction gripper, compressed air is usually blasted on the glass material in order to transfer same onto the lower mold  4  positively or in a forced way. Therefore, positional deviations may occur to the optical glass material  6  when it is transferred in this manner, more particularly, when it is picked up and also when it is set on the lower mold  4 . Especially, since the lower mold  4  is circumvented by the girdler shell  5 , the pressure of compressed air which is used to blow the optical glass material off the suction gripper means can find no way to escape and acts on the optical glass material directly and repeatedly to cause positional deviations to the latter, shifting the centers of curvatures O 1  and O 2  on the front and rear surfaces of the optical glass material  6  away from the axis A. 
     SUMMARY OF THE INVENTION 
     In view of the above-described situations, it is an object of the present invention to provide a transfer mechanism which is capable of transferring work pieces of optical glass material from a container such as a pallet or the like onto a mold unit in such an accurate and reliable manner as to preclude positional deviations. 
     It is another object of the present invention to provide a transfer mechanism of the sort as mentioned above, which can transfer work pieces of optical glass material having curved surface on the opposite sides thereof accurately in an aligned or centered position on a mold unit, so that substantially uniform pressure is applied to the glass material as a whole in a press-molding stage. 
     It is still another object of the present invention to provide a transfer mechanism of the sort as mentioned above, which can be incorporated into an optical glass press-molding line for automation of glass molding operation or for improvement of product yield. 
     In accordance with the present invention, for achieving the above-stated objectives, there is provided a transfer mechanism for transferring optical glass material to be molded into an optical element, from a container holding a large number of work pieces of the optical glass material, each having a curved surface contour on upper and lower sides thereof, onto a molding surface of a lower mold member of a mold unit located at a work loading station of a glass molding line, the transfer mechanism comprising: a suction nozzle having a suction pad at a lower distal end thereof for gripping an upper surface of the optical glass material; a lift means adapted to move the suction nozzle member up and down in the vertical direction; a tubular positioning member located in such a way as to circumvent the nozzle member and adapted to hold outer periphery of the optical glass material in position; a support member adapted to support the positioning member vertically movably over a predetermined stroke length relative to the lift means; a stroke delimiting means adapted to limit a downward stroke of the positioning member such that a lower end of the positioning member is located at a position at least beneath the suction nozzle when lowered to a lowermost position. 
     The above-mentioned lift means may be arranged as a robot which is capable of moving in horizontal and vertical directions. Preferably, the positioning member is constituted by a simple cylindrical tube having an inside diameter substantially corresponding to outside diameter of the optical glass material, and an outside diameter smaller than inside diameter of work receptacle pockets provided on the container. Since there is little difference between the outside diameter of the optical glass material and the inside diameter of the positioning member, it is preferable for the positioning member to be provided with a tapered guide surface at and around lower inner edges for urging the optical glass material to get into the positioning member in a guided fashion. In a more particular form of the invention, the support means is constituted by a liftable support member which is securely fixed to an upper end of the positioning member, and a pair of guide rods which are fixedly connected to the liftable support plate and vertically movable over a predetermined stroke length relative to the lift means. Further, as for a more particular example of the stroke delimiting means, it can be constituted by stoppers which are provided on the guide rods, and arranged to be brought into and out of abutting engagement with the lift means to determine a lowermost position of said support means. In this case, the lowermost position of the support means is limited by abutting engagement of the stoppers with the lift means. Further, a biasing means may be interposed between the support means and the lift means thereby to urge the support means toward the lowermost position. Preferably, a push-up means is provided between the guide rods and the lift means thereby to push up the lower end of the positioning member to a position above a work gripping surface of the suction nozzle and to hold the suction nozzle in an open state whenever necessary. 
    
    
     The above and other objects, features and advantages of the present invention will become apparent from the following particular description, taken in conjunction with the accompanying drawings which show by way of example a preferred embodiment of the invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a schematic illustration of a work loading/unloading station employing an optical glass transfer mechanism embodying the present invention; 
     FIG. 2 is a schematic front view of a work handling means; 
     FIG. 3 is a schematic sectional view taken through a suction nozzle and a positioning member on the verge of picking up a piece of optical glass material from a work loading pallet; 
     FIG. 4 is a schematic sectional view taken through the suction nozzle and positioning member in an operational phase in which a piece of optical glass material is set in position within a recessed nesting pocket of the loading pallet; 
     FIG. 5 is a schematic sectional view taken through the suction nozzle and positioning member in an operational phase in which a piece of optical glass material is being sucked by the suction nozzle; 
     FIG. 6 is a schematic sectional view taken through the suction nozzle and positioning member in an operational phase in which a piece of optical glass material is picked up from the loading pallet; 
     FIG. 7 is a schematic sectional view taken through the suction nozzle and positioning member in an operational phase in which the optical glass material is transferred onto a mold; 
     FIG. 8 is a schematic sectional view taken through the suction nozzle and positioning member in an operational phase in which the optical glass material is set in position in the mold; 
     FIG. 9 is a schematic sectional view taken through the suction nozzle and positioning member in an operational phase in which the suction nozzle is disengaged from the optical glass material; 
     FIG. 10 is a schematic sectional view taken through the suction nozzle and positioning member which are separated away from the mold; 
     FIG. 11 is a schematic sectional view taken through the suction nozzle and positioning member to show their positional relations at the time of a work unloading operation by a handling means; 
     FIG. 12 is a schematic sectional view of a prior art lens molding apparatus; 
     FIG. 13 is a schematic illustration of an automatic lens molding apparatus; and 
     FIG. 14 is a schematic illustration showing positional relations of optical glass material with upper and lower mold members of a mold assembly unit. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereafter, the present invention is described more particularly by way of its preferred embodiment with reference to the accompanying drawings. In the following description of a preferred embodiment, the present invention is described in relation with molding of an optical glass lens. However, it is to be understood that the invention can be similarly applied to optical glass products other than lenses, and that the invention is not restricted to a molding machine of a particular construction as shown below. 
     Referring first to FIG. 1, there is shown the general arrangement of a work loading/unloading station  20 . As shown particularly in that figure, provided at the work loading/unloading station  20  are a work loading pallet or tray which holds a number of pieces of optical glass material  21  to be formed into optical lenses on a molding press which will be described hereinlater, and a work unloading pallet  24  which serves to hold molded lens products  23 . Indicated at  25  are a number of mold assembly units (four mold assembly units are shown in FIG. 1) which are placed on a transfer plate  26  for transfer to and from the work loading/unloading station  20  where pieces of optical glass material  21  are picked up from the loading pallet  22  and set on the respective mold units  25  after picking up and putting molded lens products  23  on the unloading pallet  24 . At this time, each mold unit  25  consists of a lower mold member  25   a  and a girdler shell  25   b  since an upper mold member is removed therefrom before arrival at the loading/unloading station  20 . 
     In order to carry out the above-mentioned loading and unloading operations, an optical glass transfer mechanism  30  is provided at the loading/unloading station  20 . The optical glass transfer mechanism  30  includes a handling means  31  which is movable along two perpendicularly intersecting axes in a horizontal plane, that is, in X- and Y-directions, and also movable along a vertical axis Z within a limited stroke. For this purpose, the optical glass transfer mechanism  30  is provided with a tipple axis robot as its drive means. In one particular form of the 3-axis robot, it includes an X-axis guide  32  which is fixedly located in a predetermined position, a Y-axis arm  33  which is supported on the X-axis guide  32  movably for movements in the direction of X-axis, and a Z-axis block  34  which is connected to the Y-axis arm  33  movably for movements in the direction of Y-axis. Provided on the Z-axis block  34  is a Z-axis guide thereby to guide a lift portion  35  up and down in the direction of Z-axis. The handling means  31  is connected to the just-mentioned lift member  35 . It follows that the handling means  31  is movable in the directions of the three axes X, Y and Z. As drive means for moving the Y-axis arm  33 , Z-axis block  34  and lift member  35  in the directions of X-, Y- and Z-axes, respectively, there may be employed, for example, ball screw feeders or similar drive means which are capable of precise positioning of these members. Since the drive means of this sort are well known in the art, they are omitted in the drawings. 
     Shown in FIG. 2 is a construction of the handling means  31 . In this figure, indicated at  40  is a main body block which is fixedly connected to the lift member  35 . Fixedly attached to the main body block  40  is a suction nozzle  41  which is extended straight in the downward direction from the lower side of the main body block  40 . The suction nozzle  41  is constituted by a tubular main body  41   a  of a predetermined length, and a nozzle head  41   b  which is fixedly fitted in a fore end portion of the tubular main body  41   a  and internally provided with an axial suction passage. Detachably attached to the nozzle head  41   b  is a suction pad  42  which is formed of resilient material such as rubber or the like. Thus, as the suction pad  42  is resiliently abutted against a work piece of optical glass material  21 , it can pick up and hold the latter without damaging its surfaces. 
     A pair of guide rods  43  are passed through the main body block  40  of the handling means  31 , and a liftable support plate  44  is securely connected to the lower ends of the guide rods  43 . The suction nozzle  41  is loosely received in an aperture  45  which is bored in the liftable support plate  44 , and extended to a predetermined position beneath the liftable support plate  44 . Securely fixed to the lower side of the liftable support plate  44  is a positioning member  46  in the form of a cylindrical tube which is located in such a way as to circumvent the outer periphery of the suction nozzle  41  to function as a positioning member for holding the outer periphery of the optical glass material  21  accurately in position. Accordingly, the outside diameter of the suction nozzle  41  is smaller than that of the optical glass material  21 , while the inside diameter of the positioning member  46  is larger than the outside diameter of the optical glass material  21 . In order to place the outer periphery of the optical glass material  21  in position as precisely as possible, the positioning member  46  should preferably be dimensioned such that, when it is located around the optical glass material, its inner peripheral surface substantially comes into contact with the outer periphery of the optical glass material  21  without forming a gap space therearound. Instead of circumventing the entire outer periphery of the optical glass material  21 , the positioning member may be arranged to position the optical glass material by engaging the outer periphery of the glass material  21  at three different points thereof. Further, the positioning member  46  is provided with a tapered guide portion  46   a  around inner edges of its lower end. By this tapered guide portion  46   a,  the optical glass material  21  is positively urged into engagement with the positioning member  46  despite the little difference in diameter between the positioning member  46  and the optical glass material  21  and even in a case where the optical glass material  21  on the loading pallet  22  happens to be in a somewhat deviated position relative to the positioning member  46 . 
     The guide rods  43  which are passed through the main body block  40  are each provided with a stopper  47  on the upper side of the main body block  40 . Springs  48  are charged between the liftable support plate  44  and the main body block  40 , urging the liftable support plate  44  in the downward direction until the stoppers  47  on the guide rods  43  are abutted against the upper side of the main body block  40 , holding the liftable support plate  44  into its lowermost position. The lowermost position of the liftable support plate  44  is determined relative to the position of the suction nozzle  41  such that, when the optical glass material  21  is sucked onto the suction nozzle  41 , the positioning member  46  which is fixed to the liftable support plate  46  is located in a position where the outer periphery of the optical glass material  21  is surrounded by the positioning member  46 , preferably completely received in a lower end portion of the positioning member  46 . 
     The paired guide rod  43  are projected above the stoppers  47  by a predetermined length and are connected with each other by a connecting plate  49  at their upper ends. The connecting plate  49  is tied to a rod member  50   a  of an air cylinder  50  which is mounted on the main body block  40 . In this instance, the rod member  50   a  of the air cylinder  50  is extended out upon introducing an air pressure into an internal pressure chamber of the air cylinder  50  to push the support plate  44  upward (an actuated state). As soon as the pressure chamber is opened to the atmosphere, the cylinder  50  substantially loses its functions as an air cylinder (a de-actuated state). When in the de-actuated state, the liftable support plate  44  is pushed down to the lowermost position by the action of the spring  48 , holding the positioning member  46  stably in the lowered position. On the other hand, as soon as an air pressure is introduced into the air cylinder  50  to put same in the actuated state, extending out the rod  50   a,  the connecting plate  49  is lifted up along with the guide rods  43 . As a consequence, the liftable support plate  44  which is connected to the lower ends of the guide rods  43  is pushed up against the action of the springs  48 . This upward stroke of the liftable support plate  44  corresponds to the distance between the lower and upper positions which are indicated by solid and imaginary lines in FIG.  2 . While the liftable support plate  44  is lifted to an upper stroke end position, the positioning member  46  is moved upward relative to the suction nozzle  41 , uncovering the suction nozzle  42  in a completely exposed state. 
     Accordingly, when the air cylinder  50  is put in the de-actuated state, the transfer mechanism  30  functions as a loading transfer device to transfer the optical glass material  21  from a loading pallet  22  to a mold unit  25 . When the air cylinder  50  is put in the actuated state by supply of an air pressure, moving the liftable support plate  44  to the upper position and uncovering the circumference of the suction nozzle  41 , the transfer mechanism  30  functions as an unloading transfer device, picking up a molded lens product  23  of an increased diameter by the suction nozzle and transferring it to a work unloading pallet  24 . 
     The present embodiment of the transfer mechanism according to the present invention operates in the manner as described below with reference to FIGS. 3 through 11. 
     Firstly, for a work loading operation, the air cylinder  50  of the transfer mechanism  30  is put in the de-actuated state. In this state, the positioning member  46  which is attached to the liftable support plate  44  is held in the lowermost position by the action of the springs  48 , with the lower end of the positioning member  46  located at a lower level than the lower end of the suction nozzle  41  which is suspended from the main body block  40 . Then, as shown in FIG. 3, the Y-axis arm  33  and Z-axis block  34  are moved in suitable directions for positioning the suction nozzle  41  over the optical glass material  21  which is placed in a recessed nesting pocket  22   a  of a loading pallet  22 . 
     In this instance, as shown particularly in FIG. 3, the nesting pockets  22   a  of the loading pallet  22  are arranged to have a diameter which is larger than the outside diameter of the optical glass material  21  and can receive a the positioning member  46  therein. Accordingly, the outer periphery of the glass material  21  is not restricted by peripheral wall portions of the nesting pocket  22   a.  Nevertheless, since the optical glass material  21  has a curved surface of a predetermined radius of curvature on the back side thereof, it can be stably retained in position within the nesting pocket  22   b  by engagement with edges of a positioning aperture  22   b  which is formed centrally of the nesting pocket  22   b.  Therefore, the optical glass material  21  can be retained in position on the loading pallet  22  almost free of positional deviations. 
     The handling means  31  as a whole is lowered upon lowering the lift member  35  which is mounted on the Z-axis block  34 . At this time, first of all, a fore end portion of the positioning member  46  which is located in a lowermost position on the handling means  31  is allowed to enter the nesting pocket  22   a  of the work loading pallet  22 . At this time, along the tapered guide surface which is provided at inner edges of the positioning member  46 , the optical glass material  21  smoothly received in a distal end portion of the positioning member  46 . Since there is little difference between the inside diameter of the positioning member  46  and the outside diameter of the optical glass material  21 , the latter is securely and intimately captured in the positioning member  46 . 
     The positioning member  46  is stopped as soon as it is abutted against the bottom wall of the recessed nesting pocket  22   a.  The positioning member  46  is fixedly connected with the liftable support plate  44  which in turn is fixedly connected with the guide rods  43 . However, the guide rods  43  are relatively movably passed through the main body block  40 . Therefore, after the positioning member  46  has come to a stop, the main body block  40  is allowed to move further in the downward direction. Accordingly, as the lift member  35  is moved downward over a predetermined stroke length from that position, the main body block  40  and the suction nozzle  41  which is suspended from the main body block  40  are further moved downward, compressing the springs  48  until abutted against the surface of the optical glass material  21  as shown in FIG. 5, while the liftable support member  44  remains standstill in the stopped position along with the positioning member  46 . 
     As soon as the optical glass material  21  is gripped by the suction nozzle  41 , the lift block  35  is moved upward. Upon the lift block  35  starting an upward movement, the main body block  40  is immediately moved upward, accompanied by the suction nozzle  41  which is connected with the main body block  40 . At this time, however, the liftable support plate  44  and the positioning member  46  remain in the lower stopped position until the stoppers  47  on the guide rods  43  come into abutting engagement with the upwardly moving main body block  40 . As a result, the optical glass material  21  which is gripped on the suction pad  42  of the suction nozzle  41  is retracted into a deeper position within the positioning member  46 . As soon as the stoppers  47  come into abutting engagement with the main body block  40 , the liftable support plate  44  and the positioning member  46  are moved along with the main body block  40 . As a result, as shown in FIG. 6, the optical glass material is gripped by the handling means  31  and carried away from the work loading pallet  22 . In so doing, the gripping force on the optical glass material  21  is produced by the suction nozzle  41 . The optical glass material  21  is retained in position by the positioning member  46  and, at the same time completely covered under the positioning member  46  in a securely protected state to prevent same from dropping in the course of transfer. 
     After moving the lift member  35  up to a predetermined position along the Z-axis block  34 , the Y-axis arm  33  is moved along the X-axis guide  32 , and then the Z-axis block  34  is moved along the Y-axis arm  33 . By these movements, the handling means  31  is located in a position over a mold unit  25  which is placed on the transfer plate  26 . At this time, the mold unit  25 , which has been stripped of an upper mold member, is in the form of a lower mold assembly which is open on the upper side and composed of a lower mold  25   a  and a girdler shell  25   b.  Accordingly, the lower mold unit  25  becomes accessible by the handling means after moving the positioning member  46  to a centered position exactly in alignment with the lower mold member  25   a  as shown in FIG. 7, followed by lowering of the lift member  35 . In that position, firstly the positioning member  46  is moved into the girdler shell  25   b  until it comes into abutting engagement with a molding surface of the lower mold member  25   a.  Namely, the abutting engagement with the lower mold member  25   b  stops the downward movement of the positioning member  46  and of the liftable support plate  44  which is fixedly connected with the positioning member  46 . In this state, however, the optical glass material  21  which is sucked on the suction pad  42  of the suction nozzle  41  is still kept out of engagement with the lower mold member  25   b.    
     As the lift member  35  is lowered further, the main body block  40  as well as the suction nozzle  41  which is connected with the main body block  40  is lowered, compressing the springs  48  and bringing the optical glass material  21  into abutting engagement with the molding surface of the lower mold member  25   a  as shown in FIG.  8 . As a result, the positioning member  46  is accurately centered relative to the mold unit  25 , and at the same time the optical glass material  21  which is retained in a just-fit state within the positioning member  46  is located accurately in a centered position relative to the mold unit  25 . 
     Nextly, the suction nozzle  41  is turned off to cancel its suction grip on the optical glass material  21 , and the lift block  35  is moved upward, leaving the optical glass material  21  on the mold unit  25 . At this time, in order to separate the suction pad  42  from the optical glass material in an assured manner, in addition to cancellation of the suction force of the suction nozzle  41 , compressed air is blasted against the optical glass material  21  thereby to separate the latter forcibly from the suction nozzle  41 . For this purpose, immediately after initiation of an upward movement of the handling means  31  on the lift member  35 , compressed air is suppled to the suction pad  42  for instantaneously short period of time. When the handling means  31  starts an upward movement, it is accompanied by the suction nozzle  41 , but the positioning member  46  is abutted against the lower mold member  25   a  for a certain time period until the state of FIG. 9 is reached. Therefore, if compressed air is spurted out from the suction pad  42  during this time period, there is little possibility of the optical glass material  21  being pushed to a deviated position by the air pressure. 
     Accordingly, as the handling means  31  is moved to an upper position, completely disengaged from the mold unit  25  as shown in FIG. 10, the optical glass material  21  is handed over from the suction pad  42  of the suction nozzle  41  to the lower mold member  25   a  of the mold unit  25  in an extremely assured manner. Besides, the optical glass material  21  is set in a centered position in alignment with the axis of the lower mold member  25   a.  After this, the mold unit  25  is fed forward from the work loading/unloading station  20 , and, in the same manner as shown in FIG. 13, sent into a molding chamber  25  through an entrance/exit way to the molding chamber  25 , after assembling an upper mold member at an upper mold assembling/dissembling station. Within the molding chamber  25 , the mold unit  25  is pressed under heated conditions to produce a molded optical lens  23 . In this press-molding process, pressure is applied uniformly to the optical glass material  21  which is accurately placed in a centered position within the mold unit  25 , to produce a molded lens product which is free of distortions in shape or in optical properties. 
     The molded lens product  23  which is obtained by press-molding is increased in diameter as compared with the optical glass material  21 , so that it cannot be sucked onto the suction pad  42  of the suction nozzle  41  which is in a retracted position within the positioning member  46 . This is the very reason why the rod member  50   a  of the air cylinder  50  is connected to the connector plate  49  at the upper ends of the guide rods  43 . Namely, upon turning the air cylinder  50  into an actuated state, its rod  50   a  is extended out to move the guide rods  43  in the upward direction. Whereupon, the liftable support plate  44  and the positioning member  46  are moved upward to uncover the suction pad  42 . Accordingly, now the molded lens product  23  can be picked up by the suction pad  42  as shown in FIG. 11, without being blocked by the positioning member  46 . 
     As described above, by way of the air cylinder  50 , the transfer mechanism  30  can be switched between a loading position for transferring optical glass material  21  from a work loading pallet  22  to a mold unit and an unloading position for transferring a molded lens product from a mold unit to a work unloading pallet  24 . Besides, in the work loading stage, the optical glass material can be loaded accurately in a centered position within a mold unit by means of the positioning member  46 , and, in the unloading stage, a molded lens product  23  of an increased diameter can be securely sucked onto the suction pad for transfer to an unloading pallet  24 .