Abstract:
A lens blocking device is disclosed that includes a frame, a light source mounted on the frame, a carriage having a first end and a second end mounted on the frame for sliding movement between first and second positions, a first mirror mounted on the carriage first end and a lens block holder mounted on the carriage second end and shiftable between third and fourth positions with respect to the carriage, a stage disposed between the light source and the carriage, and including an opening, for supporting an object, an at least partially translucent screen generating a display image operably connected to the support frame, at least one second mirror arranged to reflect an image of an object on the stage from the first mirror, when the carriage is in the first position, onto the screen, and an actuator operably connected to the carriage. The actuator shifts the carriage between the first position and the second position and shifts the block holder between the third position and the fourth position, and the display image on the screen is superimposed over an image of the object on the stage when the carriage is in the second position.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS AND CLAIM TO PRIORITY 
   The present application is a division of application Ser. No. 10/238,898, filed Sep. 11, 2002, now U.S. Pat. No. 6,869,333 which is related to an application entitled “A System and Method for Aligning Reference Marks on A Lens Blank Using Adjustable Alignment Marks”, Ser. No. 10/238,894, filed Sep. 11, 2002, entitled A System and Method for Aligning Reference Marks on a Lens Blank, the disclosures of which are hereby incorporated by reference, and to which priority is claimed under 35 U.S.C. §120. 

   FIELD OF THE INVENTION 
   The present invention is directed toward a device and method facilitating the alignment of a lens blank with a lens block, and, more specifically, toward a device and method facilitating the alignment of a lens blank with a lens block through use of a display screen that displays alignment markings and a projector that projects an image of a lens blank against the display screen so that, by aligning the image of the lens blank with the alignment markings on the display, the lens blank can be properly positioned for blocking and thereafter blocked. 
   BACKGROUND OF THE INVENTION 
   An ophthalmic lens blank requires certain processing before it can be fitted into a frame. Specifically, after a lens blank has been formed with the optical properties desired, it must be edged to a size and shape appropriate for a given frame to ensure a good fit with the frame. However, the optical properties of lens blanks are not uniform over their surfaces. The variation in optical properties depends in part on the type of lens blank, e.g. single vision, multi-focal, so-called progressive designs, and a variety of other factors. It is therefore important that a lens blank be properly positioned before it is edged to its final shape to ensure that necessary areas of the finished lens will be aligned with a user&#39;s eye when the lens is mounted in a frame. Even small errors in alignment can significantly degrade the quality of a lens and degrade the quality of a patient&#39;s corrected vision. 
   Before a lens can be edged, it is generally attached to a mount or a “block” in a process often referred to as “blocking.” Once the lens has been blocked, the block carrying the lens is placed in a chuck in an edging machine so as to hold the lens in a predetermined orientation with respect to the edging machine. Various devices are known in the prior art for blocking lenses. Most such devices require a user to have a certain degree of skill in order to properly align reference markings on the lens blank with alignment markings on a lens blocker and to hold the blank in position while a lens block is attached to the blank. Prior art lens blocking devices are shown, for example, in U.S. Pat. No. 5,505,654 to Wood, U.S. Pat. No. 5,721,644 to Murray, U.S. Pat. No. 5,720,647 to Gottschald and U.S. Pat. No. 6,056,633 to Sesena, the disclosures of which are hereby incorporated by reference. 
   In one of these prior art devices, shown in U.S. Pat. No. 5,505,654 to Wood, a lens blank  14  is supported over a display screen  5 , which may be an LCD, on which various data concerning the lens are displayed. A diffusing surface  37 , comprising frosted Mylar film, is mounted over the display screen. A light source  34  shining down on the lens from above forms a shadow of the lens blank on the diffusing surface, and this shadow, superimposed on the data from display screen  5 , is reflected off a series of mirrors and projected through a front viewing port  30 . However, the quality of the LCD image may be diminished after being reflected several times, and the arrangement of mirrors presents a user with a virtual image of the lens blank—an image that appears to be as far away from the user&#39;s eyes as the entire optical path length from the diffusing surface to the user&#39;s eyes. Moreover, the mirrors invert the image of the lens. This means that when a user moves the lens blank to the left in order to align it with reference markings, the reflected image of the lens blank will move to the right. Movement of the lens blank toward and away from the user will also be reversed. While operators with experience can learn to work with such a system, it can be difficult for novices or infrequent users to use. 
   Lens blockers are often operated by staff who are not trained in the inner workings of the device. Thus, if the blocker malfunctions, it is generally necessary to contact a technician. Even changing the lamp in a typical lens blocker may be beyond the skill of the average operator. Thus, for example, if the lamp in the blocker burns out, the blocker will not be usable until a technician arrives to correct the problem. If this occurs when a technician is not readily available, the blocker may be out of service for hours. 
   It is therefore desirable to provide a lens alignment system for a lens blocker that 1) presents a non-inverted image of a lens blank to a user, 2) that includes a directly viewable display screen rather than screen that is only viewable in reflection 3) that presents a viewer with a real image of a lens blank and lens support rather than a virtual image and 4) that includes a mechanism for replacing a burned out lamp that is easy to operate and that does not require access to the interior of the blocker. 
   SUMMARY OF THE INVENTION 
   These difficulties and others are addressed by the present invention, which, in a first aspect, comprises an alignment device having a light source, a first mirror and a stage, disposed between the light source and the first mirror, for supporting an object such that an image of an object supported on the stage is reflected by the first mirror. A screen is also provided on which a processor generates images. A second mirror is arranged to receive the image reflected from the first mirror and project the image of an object on the stage onto the screen. In this manner, the generated image on the screen is combined with the image of the object on the stage that is projected onto the screen. 
   In another aspect, the invention comprises a lens blocking device having a frame, a light source mounted on the frame, and a carriage having a first end and a second end mounted on the frame for sliding movement between first and second positions. A first mirror is mounted on the carriage first end and a lens block holder is mounted on the carriage second end. The block holder is shiftable between third and fourth positions with respect to the carriage. A stage for supporting an object is located between the light source and the carriage, which stage includes an opening. An at least partially translucent screen generating a display image is operably connected to the support frame. At least one second mirror is arranged to reflect an image of an object on the stage from the first mirror, when the carriage is in the first position, onto the screen. An actuator is operably connected to the carriage, the actuator shifting the carriage between the first position and the second position, and shifting the block holder between the third position and the fourth position, so that the display image on the screen is superimposed over the image of the object on the stage when the carriage is in the first position. 
   Another aspect of the invention comprises an image alignment device including a liquid crystal display having a first region and a second region and a first side and a second side. A backlight is mounted over the first region of the second side. A processor is operably connected to the liquid crystal display for generating an image on the liquid crystal display, while a projector projects an image against the second region of the second side so that the generated image on the liquid crystal display second portion is superimposed over the projected image when the display screen is viewed from the first side. 
   A further aspect of the invention comprises a lens alignment device with a stage for supporting a lens blank and an at least partially translucent screen having a first side and a second side. An image generator generates an image on the screen and a projector projects an image of an object on the stage against the second side of the screen, so that, when the screen is viewed from the first side, the generated image is superimposed over the projected image. 
   The invention also comprises a method of blocking a lens blank that involves providing an at least partially translucent screen having a first side and a second side and placing a lens blank on a stage near the screen. Alignment markings are generated on the screen while a non-inverted image of a lens blank supported on the stage is projected against the second side of the screen. The lens blank having alignment markings is moved with respect to the stage until the image of the lens and its alignment markings projected on the screen is aligned with the generated alignment markings on the screen. A lens block bearing an adhesive is provided at a predetermined location adjacent the stage and moved from the predetermined location into contact with the lens blank to adhere the lens block to the lens blank. 
   Another aspect of the invention is a lens blocking device having a frame, a light source mounted within the frame, and a carriage having a first end and a second end mounted for sliding movement between first and second positions with respect to the frame. A first mirror is mounted on the carriage first end and a lens block holder is mounted on the carriage second end so that it is shiftable between third and fourth positions with respect to the carriage. A transparent stage having an opening is mounted between the light source and the carriage, and an LCD having a first region and a second region and a first side and a second side is mounted on the frame. A backlight overlies the LCD first region on the second side and a processor generates alignment markings on the LCD second region and alphanumeric characters on the screen first region. At least one second mirror is mounted on the frame and arranged to reflect an image of an object on the stage reflected from the first mirror, when the carriage is in the second position, onto the second side of the second portion of the LCD. Optics are also provided between the first mirror and the at least one second mirror for inverting an image reflected from the first mirror. An actuator is operably connected to the carriage for selectively shifting the carriage between the first and second positions and the lens block holder between the third and fourth positions. In this manner, the generated alignment markings on the screen second region overlie the image of the lens blank reflected on the second side of the screen when the carriage is in the first position. 
   Another aspect of the invention comprises a method of positioning a lens blank for blocking that involves providing a screen having a first side and a second side adjacent to a stage and placing a lens blank on the stage. The lens blank has a first surface facing the stage with reference markings on the first surface. Alignment markings are generated on the screen so that they are viewable from the first side of the screen, and a non-inverted image of the reference markings on the first side of the lens blank are projected onto the second side of the screen. The lens blank is moved with respect to the stage while directly viewing the real image of the lens blank and the generated alignment markings until the image of the reference markings on the lens blank projected on the screen are aligned with the generated alignment markings on the screen. 
   Another aspect of the invention comprises a method of positioning a lens blank for blocking that involves providing a screen having a first side and a second side and a stage. A lens blank is placed on the stage, and alignment markings are generated on the screen so that they are viewable from the first side of the screen. An enlarged image of the lens blank is projected onto the second side of the screen, and the lens blank is moved with respect to the stage while viewing the enlarged image of the lens blank and the generated alignment markings until selected portions of the enlarged image of the lens blank projected on the screen are aligned with the generated alignment markings on the screen. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood after a reading of the following detailed description of the invention in connection with the following drawings. 
       FIG. 1  is a front elevational view of an alignment device according to the present invention. 
       FIG. 2  is a perspective view of the alignment device of the  FIG. 1  with the keyboard removed and the carriage positioned in the alignment position. 
       FIG. 3  is a perspective view of the alignment device of  FIG. 1  with the keyboard removed and the carriage positioned in the blocking position with the block holder raised. 
       FIG. 4  is a schematic view of the optical system of the alignment device of  FIG. 1 . 
       FIG. 5  is a left side elevational view of the alignment device of  FIG. 1 . 
       FIG. 6  is a rear elevational view of the alignment device of  FIG. 1  with a rear portion of the device frame removed to show the interior of the device. 
       FIG. 7  is a detail perspective view of the interior of the lamp assembly housing and lamp assembly door shown in circle VII of  FIG. 2 . 
       FIG. 8  is a side elevational view of the lamp assembly and lamp assembly door of  FIG. 7 . 
       FIG. 9  is a rear elevational view of the display screen of the alignment device. 
       FIG. 10  is a front elevational view of the display screen of  FIG. 9 . 
       FIG. 11  is a sectional view taken along line  11 — 11  in  FIG. 10 . 
       FIG. 12  is a front perspective view of the carriage assembly with the carriage in the viewing position 
       FIG. 13  is a rear perspective view of the carriage assembly of  FIG. 12  with the mirror removed. 
       FIG. 14  is a front perspective of the carriage assembly with the carriage in the blocking position and the blocking chuck raised. 
       FIG. 15  is a rear perspective view of the carriage assembly of  FIG. 14  with the blocking chuck raised. 
       FIG. 16  is a rear perspective view of the carriage assembly of  FIG. 14  with the blocking chuck in a lowered position. 
       FIGS. 17   a–b  are a flow chart showing the operation of the alignment device of the foregoing figures. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, wherein the showings are for purposes of illustrating a preferred embodiment of the invention only, and not for purposes of limiting same,  FIGS. 1 ,  2 ,  5  and  6  show a lens blank alignment and blocking device  10  according to the present invention that includes a frame  12  having a front portion  14  and a rear portion  16 . The frame  12  further comprises a base  18 , a rear wall  20  extending from rear portion  16 , and a screen support  22  extending from base  18  approximately midway between frame front portion  14  and frame rear portion  16  in the same direction as rear wall  20 , which direction will be referred to as “up” with reference to these figures. To frame  12  are mounted, proceeding generally from the front portion  14  of frame  12  toward rear portion  16 , a motor support  24  supporting a motor  26 , a carriage assembly  28 , and a generally C-shaped optics housing  30  that extends from screen support  22  along base  18  to rear wall  20 , upwardly along rear wall  20  and back toward the front portion  14  of frame  12  ending at a screen  32  mounted on screen support  22 . The optics housing  30  includes a lamp housing door  34  in a sidewall thereof. A stage  36  is supported adjacent to frame  22  by an outer housing of lens blank alignment and blocking device  10  (not shown). Stage  36  is transparent and, as shown in  FIG. 3 , includes a central opening  38  surrounded by three pegs  40  for supporting a workpiece, such as lens blank  42  shown in  FIG. 2 , over central opening  38 . 
   Lens blank alignment and blocking device  10  projects an image of a workpiece supported on pegs  40  onto screen  32  using a projection system  34 , as best shown in  FIG. 4 , that includes cooperating lenses and mirrors, many of which are positioned inside optics housing  30 . The relative positions of the mirrors and lens are shown schematically in  FIG. 4 . The projection system  34  includes a lamp  44 , preferably a halogen lamp having a faceted reflector, such as typically used in movie projection and the like, directed at a first mirror  46  mounted above stage  36  and angled with respect to lamp  44  and stage  36 , such that light rays  48  from lamp  44  are directed downwardly on stage  36  and any workpiece supported thereon. A Fresnel lens  50  is mounted between first mirror  46  and stage  36  to collimate the light shining onto the stage  36 . A second mirror  52  is mounted beneath stage  36 , and, because stage  36  is transparent, an image  42 ′ of lens blank  42  is projected onto the second mirror  52 . Second mirror  52  is angled to direct image  42 ′ toward the rear portion  16  of the lens alignment and blocking device  10  and toward a third mirror  54 , the image  42 ′ passing through several condenser lenses  56  between the second mirror  52  and the third mirror  54  and upwardly along rear wall  20  through an image conditioning assembly  58  that includes various lens. These lenses include first, second and third achromats  60  for correcting chromatic aberrations that could degrade the image  42 ′. The remaining lenses  62  further condition image  42 ′ by magnifying the image  42 ′ approximately 1.3 times and inverting the image for reasons explained hereafter. After leaving the image conditioning assembly  58 , the image  42 ′ is reflected off a fourth mirror  64  angled to project the image  42 ′ onto screen  32 . 
   Lens  42  includes reference markings  43 , best shown in  FIG. 1 . The reference markings are on the front or convex side  41  of lens  42 , the side that faces stage  36  and second mirror  52  on carriage assembly  28 . Therefore, it is an image of this front side  41  that is projected toward screen  32  by the projection system  34 . Certain prior art alignment devices required reference markings to be viewed through a lens, and therefore, fact that the images of the reference markings had been refracted had to be taken into account when aligning the reference markings on the lens with fixed reference markings. This problem is avoided in the present invention by viewing the reference markings from the side of the lens blank on which they exist rather than through the lens blank. 
   With reference to  FIGS. 9–11 , screen  32  comprises a liquid crystal display (LCD)  66  mounted to front frame  68  connected to screen support  22 . A backlight  70  covers a first region  72  of the LCD  66  and the amount of illumination provided by the backlight is controllable via keyboard  83  and processor  82 . Second portion  74  of the LCD  66  does not include a backlight and is partially translucent. The LCD  66  comprises a polarizing layer  76  and a layer  78  of liquid crystal material sandwiched between front and rear planar supports  80 ,  81 . Rear surface  79  of planar support  81  includes a translucent film  87  on which projected image  42 ′ appears when the image is projected on screen  32 . The liquid crystal material lies essentially in a first plane, and the rear surface of screen  32  is formed by the translucent film  87 . The distance separating the translucent film  87  and the liquid crystal layer  78  is less than 1 mm and, preferably, less than about 0.5 mm, to minimize parallax between images produced in the liquid crystal layer  78  and images projected on the translucent film  87  on planar support  81 . The ideal separation would be 0 mm or as close thereto as possible given the physical dimensions of the LCD. 
   The LCD  66  is connected to a processor  82  having a memory  85 , as best shown in  FIG. 5 , in a well known manner and serves as a display for displaying images produced by processor  82  and characters input using keyboard  83  as best shown in  FIG. 1 . The first backlit region  72  displays alphanumeric data and graphics  84  within defined fields, while the second region  74  displays fiducial marks, such as crosshairs or other alignment images  86  as best shown in  FIG. 10 . The image  42 ′ of the lens blank  42  is projected against the rear surface  79  of rear planar support  81 , and, because the second region  74  of the LCD is translucent or at least partially translucent, the image  42 ′ projected onto the translucent film  87  on rear surface  79  of the rear planar support  81  is visible from the front or frame side of the LCD  66 . Images  40 ′ of the pegs  40  are also visible. The projection system  34  enlarges the image  42 ′ making it easier to accurately align image  42 ′ with the alignment images  86 . The alignment images  86  are seen combined with the projected image  42 ′ on the screen  32 . The lens blank  42  on pegs  40  can be moved as necessary to align projected images  43 ′ of alignment markings  43  on lens  42  with alignment images  86  on the screen. Because the image conditioning assembly  58  inverts image  42 ′, the image  42 ′ that is projected against rear surface  79  of screen  32  moves in the same direction as the lens  42 , i.e., when lens  42  is moved to the left, the image  42 ′ also moves to the left, as viewed in  FIG. 10 , and when lens  42  is moved away from a user (toward the rear  16  of the lens alignment and blocking device  10 ), the image  42 ′ on screen  32  will move upwardly, in a direction away from backlit first region  72  of LCD  66 . This makes the lens alignment and blocking device  10  easier to use than prior art devices in which images of lens blanks often appeared to move in the opposite direction from the direction in which the lens blank was moved. Moreover, rear planar support  81  is only about one half of one millimeter thick. Thus, image  42 ′ exists in the plane of the rear surface  79  of planar support  81  which is less than about 1 mm and preferably about 0.5 millimeters from the plane of the image generated by the liquid crystal material in liquid crystal layer  78 . This close alignment of the planes of the alignment images  86  and the projected image  42 ′ substantially eliminates the problem of parallax for a person viewing screen  32  from an angle. This, in turn, allows for more accurate alignment of a lens blank  42  with a lens block  148  and the production of higher quality lenses. 
     FIGS. 12–16  show carriage assembly  28 . With reference to  FIGS. 13 ,  15  and  16 , carriage assembly  28  comprises a carriage  100  having a horizontal platform  102  and a vertical frame  104  extending upwardly from the horizontal platform  102 . A linear slide  106  is mounted on base  18  rearwardly from motor support  24 , and a groove  108  in the underside of horizontal platform  102  receives linear slide  106 . Linear slide  106  and groove  108  are configured such that carriage  100  slides freely in a single linear direction between first and second positions with respect to base  18 . Horizontal platform  102  further includes a mirror support notch  110  for supporting and retaining the lower edge of second mirror  52 , and a pin  112  to which a spring is attached as described herein. 
   Vertical frame  104  includes an opening  114  having a sidewall  116  which includes an arcuate recess  118  in a central portion thereof. Vertical frame  104  also includes an angled top wall  113  against which second mirror  52  rests. A second linear slide  120  is mounted on vertical frame  104  in a groove  122  next to opening  114 . An L-shaped platform  124  is mounted on the second linear slide  120  for sliding movement in a direction normal to horizontal platform  102 . L-shaped platform  124  comprises a first leg  126  generally parallel to vertical frame  104  and a second leg  128  normal to first leg  126  and extending away from vertical frame  104  in the direction of rear  16  of base  18 . A spring mount  130  is attached to the first leg  126  of L-shaped platform  124 , and a torsion spring  132  is attached to the spring mount. Torsion spring  132  has a Z-shaped end portion, comprising, in the direction from spring mount  130  to the free end of torsion spring  132 , a first portion  134  parallel to first leg  126 , a second portion  136  normal to first portion  134  and extending though opening  114  spaced apart from sidewall  116  by a gap  140 , and a third portion  138  substantially parallel to first portion  134 . A stop  142  extends from the first leg  126  of the L-shaped platform  124  and engages second portion  136  of torsion spring  132  to hold torsion spring  132  under a preload. 
   A chuck  144  is mounted on second leg  128  of L-shaped platform  124  which has a standard lower portion with which it mates to a projection (not shown) on the second leg  128 , and an upper portion  146  adapted to mate to one or more standard industry lens blocks, such as block  148  shown in  FIG. 13 . Different chucks are used for different blocks. An adhesive pad  150  is mounted on block  148  in a well known manner so that, when the chuck  144  and block  148  are pressed against lens blank  42 , the adhesive pad  150  will stick to the lens blank  42 . The L-shaped platform  124  thus can slide linearly with respect to vertical frame  104  between a first lowered position  152 , shown in  FIGS. 12 and 13 , and a second raised position  154 , shown in  FIGS. 14 and 16 . 
   A crank arm  156  is attached to motor  26 , as best shown in  FIGS. 13 ,  15  and  16  and extends in a direction generally parallel to vertical frame  104  and is rotated in first and second directions, clockwise and counterclockwise, respectively, as viewed in  FIGS. 13 ,  15  and  16  by motor  26 . A crank pin  158  extends from crank arm  156  and into opening  114  where it engages sidewall  116 . 
   An eccentric stop  160 , as best seen in  FIGS. 13 and 15 , is mounted on platform  18  and includes a pin  162  supporting spring  164  extending between pin  162  and pin  112  on horizontal platform  102 . Spring  164  biases carriage  100  toward eccentric stop  160  and holds it against the eccentric stop  160  until crank arm  156  and motor  26  overcome the force of the spring and move the carriage  100  away from the eccentric stop  160 . Eccentric stop  160  is mounted eccentrically on base  18 , so that it can be rotated to adjust its distance from carriage  100  and hence the stopping position of carriage  100 . 
   Lens alignment and blocking device  10  is shown with carriage  100  in the alignment position in  FIGS. 2 and 13  and in the blocking position in  FIGS. 3 and 16 . The shifting of the carriage  100  between the blocking position and alignment position will be described with reference primarily to  FIGS. 13 ,  15  and  16 . 
   In the alignment position of  FIGS. 2 and 13 , crank pin  158  engages arcuate recess  118  in sidewall  116  of opening  114  in the vertical frame  104  and holds carriage  100  in the alignment position. In this position, spring  164  is stretched, held under tension and prevented from pulling carriage  100  toward eccentric stop  160 . Second mirror  52  is supported in mirror support notch  110  and by the angled top wall  113  of carriage  100 . Second mirror  52  is shown in  FIG. 2  and, for clarity, shown in phantom in  FIG. 13 . In this alignment position, second mirror  52  is positioned beneath central opening  38  in stage  36 . 
   To shift carriage  100  into the blocking position of  FIGS. 3 and 16 , motor  26  is actuated, under the control of processor  82 , to turn crank arm  156  clockwise as viewed in  FIGS. 13 and 15  and move crank pin  158  toward base  18  and through gap  140  between sidewall  116  and second portion  136  of torsion spring  132 . As crank arm  156  rotates, crank pin  158  moves in the direction of eccentric stop  160 , and thus allows spring  164  to contract and pull carriage  100  along linear slide  106  toward eccentric stop  160 . Crank arm  156  continues to rotate until carriage  100  contacts eccentric stop  160 . At this point, crank pin  158  is still in contact with sidewall  116 , as shown in  FIG. 15 , and block  148  is positioned beneath central opening  38  of stage  36  beneath a lens blank  42 . As the crank arm  156  continues to rotate in a clockwise direction, it moves away from sidewall  116  and engages third portion  138  of torsion spring  132 . Continued rotation of the crank arm  156  exerts upward pressure on third portion  136  of torsion spring  132  and moves L-shaped platform  124  upwardly, as shown in  FIG. 16 , so that block  148  passes through central opening  38  in the stage  36  and against lens blank  42 . Lens blank  42  is thus secured by adhesive pad  150  to block  148 , and thus may be placed onto a suitable edger. These steps are reversed to lower chuck  144  and move the carriage  100  back to the alignment position. 
   Referring now to  FIGS. 7 and 8 , the steps required for replacing lamp  44  with a secondary lamp  166  will be described. As noted above, persons operating lens blocking devices may not be trained to service the blocking devices, and replacing a burned out lamp may require that the lens blocking device be opened and/or partially disassembled. Thus, if a technician is not available when a lens needs to be replaced, the machine may experience significant out-of-service time. The lens alignment and blocking device  10  allows an unskilled operator to quickly switch a burned out lamp  44  with a secondary lamp  166 , so that the use of the lens alignment and blocking device  10  can continue substantially uninterrupted. A technician can then replace the burned out bulb when convenient. 
   As best shown in  FIGS. 7 and 8 , door  34  is opened to reveal lamp housing  168  and the inner side  170  of door  34 . When door  34  is closed, lamp  44  is directed toward first mirror  46  as shown schematically in  FIG. 4 . Door  34  includes an opening  172  through which a shaft  174  extends, shaft  174  being connected to a support frame  176 . Shaft  174  is rotatably mounted in opening  172  so that support frame  176  can be rotated by turning shaft  174  when door  34  is closed. Shaft  174  also includes a socket  178  for receiving a screwdriver or hexagonal wrench (not shown) with which shaft  174  can be more easily rotated. Lamp  44  and secondary lamp  166  are mounted on support frame  176  for rotation therewith. Inner side  170  of door  34  includes an electrical contact plate  180 , as best shown in  FIG. 8 , connected to a power source. Lamps  44  and  160  also include electrical contact plates  182  and  184 , respectively. By rotating shaft  174 , one or the other of lamp electrical contact plates  182 ,  184  can be brought into electrical contact with inner door contact plate  180  to provide power to one of the lamps. All this can be done from the outside of lens alignment and blocking device  10  without opening door  34 . In this manner, a new lamp  166  can be substituted for a burned out lamp  44  in a matter of minutes without the aid of a skilled technician. 
   The use of lens alignment and blocking device  10  will now be described with reference to the flow chart of  FIGS. 17   a  and  17   b . When lens alignment and blocking device  10  is turned on, a self-test is conducted at step  200  to determine whether firmware in the device is valid. If the firmware is valid, the operator may optionally change configuration parameters at step  202 , perform calibrations or diagnostics at step  204 , or view or manage blocking jobs in local storage at step  206 . Each of the stored jobs includes numerical data concerning a lens to be blocked and data for generating alignment images  86  for the particular lens, as best shown in  FIG. 10 . At step  208 , the carriage  100  is shifted into blocking position  154 , shown in  FIG. 3 , with the upper end  146  of chuck  144  extending though central opening  38  in stage  36  so that a block  148  can be attached to the chuck  144  on L-shaped platform  124 . Next, at step  210 , a job number is entered, either using keyboard  83  or a barcode reader (not shown), and at step  212 , memory  85  is queried to determine whether a job associated with that job number is stored in memory. If the job is in local storage, processor  82  causes relevant data  84  for that job to be displayed on screen  32  in position  72  in step  214  in appropriately designated fields. If the job is not in local storage, it is determined at step  216  whether a host device (not shown) is connected to lens alignment and blocking device  10 . If a host device is connected, a download of information is requested from the host at step  218 . If the download is successful, data are displayed on screen  32 . If the download is unsuccessful, or if there is no host device connected to the lens alignment and blocking device, then a job screen is displayed for data entry at step  220  and relevant data is manually entered via keyboard  83 . 
   The job data will often include data relating to the prescription of a patient&#39;s left eye and a patient&#39;s right eye, and at step  222 , a selection of either right eye or left eye is made (since only one lens blank can be blocked at a time), and at step  224  the job data is either entered or, optionally, edited. At step  226 , block  148  is attached to chuck  146 , and motor  26 , which is operably connected to processor  82 , is actuated via a key switch, preferably a foot-operated switch (not shown), to shift carriage  100  from the blocking position  154  to the viewing position  152  shown in  FIG. 2 . A lens blank  42  is then manually placed on pegs  40  at step  228 . An image  42 ′ of lens blank  42  will be visible on screen  32  in position  72  as the image is reflected off second mirror  52 , passed through the lens of C-shaped optics housing  30 , reflected off third mirror  54  and onto the rear surface of second region  74  of screen  32 .  FIG. 10  shows the projected image  42 ′ of lens blank  42  on screen  32 . Images  40 ′ of pegs  40  are also visible, as are images  43 ′ of reference markings  43  on the lens blank. Alignment images  86  generated by screen  32  can be seen combined with the projected image of reference markings  43 ′. At step  230 , the operator moves the lens blank  42  until the images  43 ′ of the reference markings  43  are aligned with the alignment images  86  on the screen  32 . As noted above, because the image  42 ′ of the lens blank is projected on a plane (the translucent film  87  on the rear surface  79  of screen  32 ) that is preferably less than about 0.5 millimeters from the alignment markings, which exist in the plane of liquid crystal layer  78  in screen  32 , parallax is substantially eliminated. The alignment of alignment images  86  with the images  43 ′ of reference markings  43  will be accurate even if screen  32  is viewed from an angle. Once the images  43 ′ of the reference markings  43  are aligned with the alignment images  86  on screen  32 , the operator, at step  232  engages motor  26 , again using a key switch or foot operated switch (not shown) to move carriage  100  from the viewing position  152  to the blocking position  154 . Crank arm  156  lifts L-shaped platform  124  as described above until adhesive pad  150  engages lens blank  42 , and, at step  234 , the lens block  148  with lens blank  42  adhered thereto is removed from the chuck  144  on lens alignment and blocking device  10 . The process is repeated if additional lenses are to be blocked. 
   The subject invention has been described herein in terms of a preferred embodiment, it being understood that numerous modifications and additions to this embodiment will become apparent to those skilled in the art after a reading of the foregoing description. It is intended that all such modifications and additions comprise a part of this invention to the extent that they come within the scope of the several claims appended hereto.