Abstract:
A snap-on lens carrier for optical pointing devices has retaining legs which structurally affix the lens to the IC to automatically align and register the lens with the aperture plate of the optical sensor. The lens carrier has a body portion which includes the lens and retaining legs arranged on the ends of the body portion. The retaining legs may take various forms, but in general are perpendicular to the body portion with a retaining detent formed at each of their free ends. The retaining legs are configured so that their length between a bearing area on the body portion and the detent corresponds to the thickness of an optical sensor IC. The retaining legs of the lens carrier are resiliently biased to enable the carrier to snap-on to the IC, and thus attached, the IC and lens function as an integral unit when assembled with the remaining components of the pointing device. By attaching the IC and lens in this manner the optical sensor and the lens are in fixed relation to one another and repeatedly precise registration of parts is ensured. In an optical trackball environment, the snap-on lens carrier is employed with a ball cup having an integrally molded transparent tracking window to be aligned with the lens and sensor. The ball cup supports a ball of the trackball device and prevents contamination of the optical components within the device housing.

Description:
TECHNICAL FIELD 
     This invention relates generally to a tracking lens carrier for an optical sensor carried on an integrated chip (IC) and an assembly integrating the lens carrier into an optical trackball device. More particularly, the invention provides a tracking lens carrier which snaps onto the IC such that the aperture plate of the IC bears against the carrier and the lens registers and aligns with the optical sensor. In a trackball environment the lens carrier is also aligned with the tracking aperture of a ball cup. 
     BACKGROUND OF THE INVENTION 
     Integrated chips with optical sensors are typically used for solid state computer input devices which rely on optical tracking to calculate relative displacement values to be communicated to an output converter. These input devices include optical pointing devices such as computer mice and trackballs. An IC with a reflective optical sensor is commercially available from Hewlett-Packard under the designation HDNS-2000, and is typically mounted on a printed circuit board (PCB). which is assembled with a lens plate. The assembly is mounted on a base plate of a housing for the computer input device. The base plate has an aperture operatively registered with and aligned with the magnified light from an LED for the optical sensor. Conventional assemblies of these components have relied on simple registration tabs and mating in the base plate, lens plate and IC mounted PCB to ensure that the aperture plate of the optical sensor, lens and aperture are operatively aligned. 
     With multiple components which must be assembled and registered together, any misalignment or registration error in such a conventional assembly is compounded and results in an unreliable or even inoperable pointing device. This can be a particular problem during manufacture since these components of pointing devices are most often assembled by hand. 
     Due to the multiplicity of parts which must be registered and assembled together these conventional assemblies are inefficient to manufacture and suffer from reliability flaws. With currently employed parts and techniques, there is no reliable way of ensuring repeatable and precise registration of the lens and base plate aperture with the aperture plate of the IC optical sensor. 
     In both optical mouse and trackball type devices, the lens must be aligned with a tracking aperture through which light is supplied to enable the optical sensor to “read” a pattern on a tracking surface. The tracking surface is a flat surface for an optical mouse or a ball for an optical trackball. In conventional optical input devices, the tracking aperture is a through-hole which provides an avenue for contaminants such as dust or other particles to enter the device housing. 
     In optical trackball devices the ball itself presents the tracking surface that is “read” by the optical sensor. For typical optical trackballs, the ball is placed in a socket on the top of the housing or along a side of the housing for manipulation by a user&#39;s finger or thumb. A drawback of the conventional optical trackball devices is that the optics or the lens and the electronics including the sensor are extremely sensitive to dust, dirt, liquid spills and other contaminants. With the ball socket located at the top or on the side of the housing makes the device components more susceptible to contaminants since contaminants can fall down easily into the socket and accumulate on the sensor. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the problems of the prior art by providing a lens carrier with retaining legs which structurally affix the lens to the IC in such a manner as to automatically align and register the lens with the aperture plate of the optical sensor. The retaining legs of the lens carrier are resilient to enable the carrier to snap-on to the IC, and thus attached, the IC and lens function as an integral unit when assembled with the remaining components of the pointing device. By attaching the IC and lens in this manner the optical sensor and the lens are in fixed relation to one another and repeatedly precise registration of parts is ensured. 
     The snap-on lens carrier has a body portion which includes the lens and retaining legs arranged on the ends of the body portion. The retaining legs may take various forms, but in general are perpendicular to the body portion with a retaining detent formed at each of their free ends. The retaining legs are configured so that their length between a bearing area on the body portion and the detent corresponds to the thickness of an optical sensor IC. When the snap-on lens carrier is assembled to the IC, in a cradle-like manner, the body portion of the carrier bears against a flat side of the IC so that the IC aperture plate is aligned and registered with the lens with each retaining leg extending along an end of the IC and affixed thereto by the detents bearing against the opposite side of the IC. 
     In order to take maximum advantage of the inventive lens carrier in a pointing device assembly, the PCB is configured to receive the optical sensor IC and includes sufficient openings for the retaining legs of the lens carrier to protrude through the PCB and attach to the IC. Once the IC is mounted to one side of the PCB, the lens carrier is positioned from the opposite side of the PCB with its retaining legs extending through assembly openings to snap onto the IC and provide automatic alignment and registration of the lens with the optical sensor. By affixing the IC to the lens carrier in this manner, several registration and alignment issues during the assembly process are nullified, and precision and repeatability are enhanced. 
     The snap-on lens carrier is adapted to be used in both optical mouse and optical trackball environments. Another aspect of the assembly for trackball devices is the provision of a ball cup to line the socket. The ball cup completely supports the ball and surrounds the portion of the ball received therein. The cup includes a tracking aperture having an integral window pane to keep out contaminants and provide higher electrostatic discharge protection to the components. The cup also includes alignment guides for attaching a PCB having an optical sensor IC and snap-on lens carrier mounted thereon. The snap-on lens carrier ensures that the optical components are automatically aligned with the tracking window of the ball cup. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of the components of a conventional optical sensor IC and aperture plate assembly for an optical mouse environment. 
     FIG. 2 is an exploded view of the snap-on lens carrier in accordance with the present invention, shown with exemplary components of the optical sensor IC assembly in an optical mouse environment. 
     FIG. 2A is a perspective view of the snap-on lens carrier affixed to an optical sensor IC. 
     FIG. 3 is a perspective view of the snap-on lens carrier. 
     FIG. 4 is a side elevational view of the snap-on lens carrier of FIG.  3 . 
     FIG. 5 is a plan view of the snap-on lens carrier of FIG.  3 . 
     FIG. 6 is a bottom plan view of the snap-lens carrier of FIG.  3 . 
     FIG. 7 is an end elevational view of one end the snap-on lens carrier of FIG.  3 . 
     FIG. 8 is an end elevational view of the other end of the snap-on lens carrier of FIG.  3 . 
     FIG. 9 is cross-sectional view taken along line  9 — 9  of FIG.  7 . 
     FIG. 10 is a cross-sectional view taken along line  10 — 10  of FIG.  5 . 
     FIG. 11 is a cross-sectional view taken along line  11 — 11  of FIG.  5 . 
     FIG. 12 is an exploded view of the snap-on lens carrier assembly similar to FIG. 2 but shown with a paned tracking aperture. 
     FIG. 13 is an exploded view of the snap-on lens carrier assembly in accordance with the present invention, shown with exemplary components of the optical sensor IC assembly in an optical trackball environment including a ball cup and ball. 
     FIG. 14 is an elevational view of the ball cup assembly and snap-on lens carrier of FIG. 13, shown assembled together. 
     FIG. 15 is a plan view of the ball cup viewed from the concave side. 
     FIG. 16 is a cross-sectional view of the ball cup taken along line  16 — 16  in FIG.  15 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A conventional tracking lens and optical sensor assembly in an optical mouse environment is illustrated in FIG. 1 in which a light source such as an LED is operatively assembled with an optical sensor IC  10  and PCB  12  shown aligned with a lens plate  14  and base plate  16 . The LED is typically coupled to the IC by a clip or other means. The aperture plate of IC  10  is oriented downward in FIG. 1 so that the optical sensor will be registered with lens  18  of lens plate  14  once the IC is mounted to the PCB. The. registration mechanism between lens  18  and the optical sensor comprises a rectangular walled opening  20  with at least opposing walls received in assembly opening  22  of the PCB. Registration of lens plate  14  to base plate  16  is achieved by projecting registration column  24  through walled opening  20 . The simple registration guides such as walled opening  20 , assembly opening  22  of the PCB and column  24  of the base plate are arranged so that the optical sensor aligns with lens  18  and tracking aperture  26  of base plate  16 . The PCB is registered with base plate  16  by alignment posts  28  on the base plate being received in alignment apertures  30  of the PCB. None of the critical components are affixed relative to another, and the dimensional tolerances necessitated by conventional assembly using these registration guides results in some “play” between the components. These simple geometric registration constraints prevent precise and repeatable alignment of the critical components such as the sensor, lens and tracking aperture. 
     The snap-on lens carrier of the present invention eliminates the geometric registration guides of the prior art and all of the problems associated with dimensional tolerances between the sensor and the lens. FIG. 2 illustrates the lens carrier employed in an optical mouse environment. FIG. 2 is an exploded assembly view of a lens carrier  32  shown aligned with IC  34  as they would be assembled on a PCB  36  through assembly opening  38 . Also illustrated is a base plate  40  with alignment posts  42  arranged to be received in alignment apertures  44  of the PCB. Base plate  40  has a tracking aperture  46 . 
     Reference is made to FIG. 2A for a detailed perspective view of lens carrier  32  assembled to IC  34 , again in an optical mouse environment, and to FIGS. 3-11 for detailed views of lens carrier  32 . For the sake of convenient explanation, when directional descriptions are used this in specification, they are made with reference to the orientation of the components as shown in FIG. 2 which is for a typical optical mouse. However, the actual orientation of the components may vary depending on the type of pointing device, or in various stages of assembly and manufacture. 
     Lens carrier  32  has a carrier body portion  48  including a lens  50  formed within in a well  52  with an annular bearing surface  54 . Bearing surface  54  may be a variety of shapes, and is generally parallel to the main plane of body  48 . At opposing ends of body  48  are generally perpendicularly extending retaining legs  56  and  58  having sloped cam surfaces  60  and  62  at their free ends forming retaining detents  64  and  66 . Retaining legs  56  and  58  generally appear to be perpendicular to body  48 , but are actually angled slightly less than 90° from body  48 . Carrier  32  is preferably molded from a material such as thermoset resin so that legs  56  and  58  can flex slightly outward relative to one another and snap back into their resting positions. Alternative materials which can be made to resiliently bias retaining legs inward toward each other may be employed for carrier  32 . 
     Body portion  48  of carrier  32  also comprises further bearing surfaces in the manner of two bearing posts  68  which are spaced laterally from annular bearing surface  54 . Bearing posts  68  and bearing surface  54  provide bearing surfaces in the same plane which is parallel to the main plane of body  48 . As best seen in FIGS. 2A and 4, the distance between these bearing surfaces and the detents  64  and  66  corresponds to the thickness of an optical sensor IC so that one side of the IC bears against surfaces  54  and  68  and detents  64  and  66  bear against the opposite side of the IC. The optical sensor is not shown in FIG. 2A because in that orientation, the sensor is on the underside of IC  34 , however, the broken line rectangle on the top of IC  34  corresponds to the location of the sensor on the opposite side. Carrier  32  is precision designed to ensure that lens  50  is aligned with the optical sensor on IC  34  when the carrier is assembled to the IC. 
     Another feature of carrier  32  is an LED rest  70  formed on body  48 . As seen in FIG. 3, rest  70  is disposed on the underside of carrier  32 , and has a smooth curved surface for guiding an LED into a predetermined position relative to lens  50  and the tracking aperture of the base plate. As best seen in FIG.  7  and in the cross-sectional view FIG. 9, rest  70  is angled sufficiently to aim LED into an optimal position relative to lens  50  for the sensor. Carrier  32 , and in particular retaining leg  58 , are structurally engineered to facilitate positioning of the LED into the assembly. Retaining leg  58  includes two parallel upstanding portions  72  connected by a bridging member  74  which has the integrally formed detent  66  on its inward side. Upstanding portions  72  are extended away from body  48  by a pair of struts  76  which are parallel to the body. Employing struts  76  creates sufficient space to insert an LED through an LED guide opening  78  formed between upstanding portions  72  and bridging member  74  of retaining leg  58 . In this manner, carrier  32  structurally supports an LED and ensures proper positioning and registration of the LED as well as the lens and IC. 
     The preferred order of assembly of the components is best understood with reference to FIG.  2 . PCB  36  is provided with an appropriate assembly opening  38  and IC  34  is mounted onto the PCB in the usual manner. Once the IC is mounted, lens carrier  32  is brought from the underside of the IC so that retaining legs  56  and  58  project through assembly opening  38 . As carrier  32  and the IC are assembled together, cam surfaces  60  and  62  bear against the end walls of the IC and guide legs  56  and  58  apart from one another. Once the underside of the IC comes to a rest on bearing surfaces  54  and  68 , legs  56  and  58  resiliently snap back into their resting position, a little less than 90° from the plane of body  48 . At this point detents  64  and  66  engage the top side of the IC as best seen in FIG. 2A to affix the carrier to the IC. It will be apparent to one of skill in the art that by affixing the carrier and IC together in this manner, all potential registration problems between the IC and the lens are eliminated. Since carrier  32  is structurally affixed to the IC itself, any imprecision in the formation of assembly opening  38  in the PCB does not affect the alignment of the lens and sensor. The critical alignment of lens  50  to the IC sensor is achieved in this one assembly step and is not affected by further assembly. 
     Once the IC mounted PCB and carrier  32  are assembled together, the PCB is assembled to base plate  40  so that the lens and sensor are aligned with tracking aperture  46 . While the LED is shown in FIG. 2 adjacent to carrier  32  for ease of understanding, in the assembly of the components, the LED is actually inserted through LED guide opening  78  from the top side of the PCB. As seen in FIG. 2A, once the carrier and IC are assembled, it will be apparent that the LED guide opening will be provided on the top side of the PCB. The LED is inserted through guide opening  78  and bears against LED rest  70  on the underside of carrier  32 . Rest  70  has a tapered end surface near lens  50  which facilitates positioning of the LED relative to the lens and tracking aperture  46 . Normally tracking aperture  46  is relatively large so that there is clearance around the sensor and lens and LED, and no registration problems are caused by misalignment of the tracking aperture. 
     FIG. 12 is identical to FIG. 2 but illustrates another aspect of the invention, an integral window pane  47  covering tracking aperture  46 . Window pane  47  is integrally molded with base plate  40  to keep out contaminants and provide a higher level of electrostatic discharge protection. The thickness of window pane  47  is limited by the minimum thickness that can be injection molded, i.e., the minimum filling thickness in a tool. As is currently contemplated, window pane  47  is approximately 1 mm thick, transparent and flush with the bottom surface of the base plate. It is possible to make pane  47  with some tint or color as long as light can be provided to the tracking surface by the LED. 
     FIGS. 13-16 illustrate another aspect of the invention, the use of a ball cup for the component assembly in an optical trackball environment. Components already identified in the preceding description are referred to with the same reference numerals. FIG. 13 is an exploded perspective view of components of an optical trackball device employing snap-on lens carrier  32 . When assembled, ball  80  is supported and partially surrounded by a ball cup  82  which is received in a socket of a trackball housing (not shown). Ball cup  82  is transparent and includes various structural elements integrally molded along its circumferential opening and on its convex side. A circumferential lip  84  extends around the circumference of the opening and includes any number of assembly tabs  86 . A number of alignment guides  88  are provided for aligning and assembling PCB  36  to the ball cup. PCB  36  has mounted on it an optical sensor equipped IC  34  assembled to snap-on lens carrier  32 . The snap-on lens carrier, IC  34  and PCB  36  are assembled for the trackball environment identically to their assembly for an optical mouse environment described herein. 
     Located proximate alignment guides  88  on ball cup  82  is an integrally molded tracking window  90 . Tracking window  90 , similar to tracking window  47  described above, is of the minimum thickness allowed by an injection molding process which is currently contemplated to be approximately 1 mm. Tracking window  90 , instead of a through-hole or a hole which is covered by a separate element, ensures that dust and other contaminants are kept out of the trackball housing. The integral tracking window also eliminates the possibility of adhesive failure or shifting of separate coverings. Integral tracking window  90  also provides an added measure of electrostatic discharge protection to the device. FIG. 15, viewing the ball cup from its concave side, i.e. into the hollow of the cup, illustrates the positions of the structural components molded to the convex side of the cup such as alignment guides  88  and LED support  92  relative to tracking window  90 . Closer to the lip of the ball cup, a larger through-hole  94  is provided to allow for easier removal of the ball. Through-hole  94  does not have an optical function. FIG. 16 describes pictorially integrally molded tracking window  90  along the surface of ball cup  82 . 
     Proximate window  90  is an LED support  92  which, in conjunction with LED rest  70  (not shown in FIG. 13) on the underside of lens carrier  32 , guides the LED into the correct position to illuminate the tracking surface on the ball. An LED retainer  96  is shown with LED in FIG. 13, and similar to the optical mouse environment, the LED is inserted through LED guide opening  78  and bears against LED rest  70  as seen in FIG.  14 . The tapered end surface of the lens carrier LED rest  70  facilitates positioning of the LED relative to the lens and tracking window  90  with the help of LED support  92  which has a U-shaped notch to receive a rounded surface of an LED or LED housing. 
     The LED illuminates the tracking surface of the ball, and in the trackball environment, the optimization of the optics takes more factors into account than in an mouse environment in which the tracking surface and tracking window are flat. First, tracking window  90  introduces a parallel plate to the IC and lens which shifts the focal length and bends the light from the LED. In addition, a clear overcoat on the ball surface also bends the light before it hits the target tracking surface. The size of the tracking window and positioning of the LED are determined with sufficient tolerances to ensure that the reading zone of the optical sensor and lens falls within an area that is illuminated by the LED. In one embodiment, the LED illuminates a 5 mm by 5 mm area of the ball, and the reading zone of the optical sensor and lens a 2 mm by 2 mm area that occurs within the illumination zone. 
     Another consideration in the trackball environment is to ensure that to the sensor, the tracking window is completely transparent. The currently contemplated way to achieve this is to tint the ball cup with a color having the same wavelength as the LED so that the tracking window does not interfere or hinder what the sensor is able to “read” on the tracking surface. In a particular embodiment, the ball cup is tinted a shade of red which corresponds in wavelength to the LED employed in the device. 
     Although the lens carrier has been illustrated with retaining legs in opposing relationship, a single retaining leg or multiple retaining legs in different configurations are also contemplated to be within the scope of the invention. Alternatively, other retaining structures which enable snap-on engagement of the lens carrier to the IC are also contemplated to be within the purview of the present invention. 
     Snap-on lens carrier  32  eliminates multiple registration problems of the prior art by affixing the structural relationship between the IC sensor and lens  50 . The dimensions of the IC and position of the sensor being known, precision engineering of the carrier enables automatic, repeatable alignment of the sensor and lens. Employing the carrier makes production more efficient and enhances reliability of the devices. 
     In an optical trackball environment a ball cup having an integrally molded tracking window is employed with the snap-on lens carrier. The optical sensor and PCB on which it is mounted are assembled to the ball cup so that the lens is automatically aligned with the tracking window and arranged in an optimal position for the sensor to “read” the tracking surface of the ball. The ball cup with integral tracking window can, however, be used with other types of optical sensor lenses, and provides a barrier for contaminants and extra electrostatic discharge protection. 
     Thus has been described a snap-on lens carrier for an optical sensor equipped IC for automatic and precise registration of the lens and sensor which is not affected by other assembly steps. In an optical trackball device, the same snap-on lens carrier has been described for use in conjunction with a ball cup having an integrally molded tracking window. The foregoing explanation includes many variations and embodiments, and the invention is not intended to be limited to the specific details disclosed herein, but only by the claims appended hereto.