WO1998050920A1

WO1998050920A1 - Optical element for belt-driven tape cartridge

Info

Publication number: WO1998050920A1
Application number: PCT/US1997/016719
Authority: WO
Inventors: Robert L. Derhaag; James A. Eggebeen; Brian J. Austin; Kenneth W. Smallwood, Jr.
Original assignee: Gigatek Memory Systems
Priority date: 1997-05-05
Filing date: 1997-09-19
Publication date: 1998-11-12

Abstract

A belt-driven tape cartridge having an optical element with at least two reflecting surfaces, and which is preferably an acrylic prism. The two reflecting surfaces are each disposed at predetermined angles that are substantially larger than a critical angle for the prism, wherein the critical angle is a property characteristic of the prism and determines the angle above which light is reflected instead of passed through. The inclusion of two reflecting surfaces and the choice of materials for the prism allows a substantially large range of angles for which the critical angle requirements is met.

Description

OPTICAL ELEMENT FOR BELT-DRIVEN TAPE CARTRIDGE

BACKGROUND OF THE INVENTION

1 . Field of the Invention

The present invention relates generally to magnetic tape data storage media for computer systems and, more specifically, to a new optical element useful in a belt-driven tape cartridge for cooperating with tape positioning indicators including a transmitter and receptor in a tape drive.

2. Description of the Related Art

The belt-driven tape cartridge described in U.S. Patent No. 3,692,255, issued to von Behren, is used in conjunction with a tape drive unit to store and retrieve data in a computer system. The cartridge includes a base plate and a housing. Two spools are rotatably mounted in the housing on pins perpendicular to the base plate. Like the spools of other tape recording systems, the spools of the von Behren cartridge comprise a cylindrical hub with two flanges having diameters greater than that of the hub. The tape is wound around the hub between the flanges. The hubs are aligned on an axis parallel to the front wall of the housing in which the tape drive and tape read/write openings are located. The tape is driven between the hubs by means of a flexible elastic drive belt that extends around a drive roller at the front of the housing and contacts the tape on the two hubs before extending around a pair of corner rollers. The drive belt moves in response to rotation of the drive roller. When the front of the cartridge is inserted through the drive door, a capstan in the drive engages the drive roller and a read/write head in the drive engages the tape. In operation, the drive roller rotates in response to rotation of the capstan, and the tape moves past the head in response to rotation of the drive roller. To sense the position of the tape in the cartridge, prior art von Behren- type cartridges typically use an optical element including a guide and reflector wherein the reflector may be a mirror or a prism or reflector. The optical element guides a light path from a transmitter in the drive and back to a receptor in another location in the drive. Whether or not the light is returned depends on the presence or absence of holes at predetermined positions in the tape. The presence/absence of light at the receptor indicates the presence/absence of holes and because the holes are positioned at relative locations, tape positioning may be determined.

Typical optical elements for von Behren-type tape cartridges include a clear wall that passes the light from the transmitter to the reflective surface. In such an arrangement, a second window, orthogonal to the first, passes the reflected light to the sensor. U.S. Patent 5,522,562 discloses such an arrangement. That patent discloses an optical configuration in which the light strikes a reflective surface at a prescribed angle and passes to the tape surface, where it is either blocked or allowed to pass through, depending on presence/absence of tape holes. The prescribed angle is edicted by the orthogonal relationship of the transmitter relative to the receptor. Since the light must be reflected with respect to the location of the transmitter, a typical prior art arrangement is to dispose the reflecting surface at a 45 degree angle relative to a plane perpendicular to the light path.

The above-described reflecting surface may be a mirror or part of a prism. Mirrors are economically disadvantageous due to the cost of coating a reflective surface onto a substrate of the optical element. Prisms are sometimes used to avoid the coating requirement. However, in a prism arrangement, the light may pass through the prism without being reflected. Thus, it is very important to adhere to strict geometrical constraints to avoid this which may lead to increased manufacturing costs. Additionally, the combined requirements that ( 1 ) the reflecting surface for the prism obey optical physics principles that determine whether light is reflected or passed, and (2) that light be reflected so that it reaches a receptor in the drive edicts tight manufacturing tolerances. In other words, only a small variance from a prescribed norm is tolerated, and any prisms having reflecting surfaces outside of this range may be rejected causing waste. Worse, if such flawed prisms are used the tape positioning system will not function correctly. U.S. Patent 4,848,698 to Newell et. al discloses an optical element that is a prism for discerning position-indicating markers on tape. The prism is folded with the fold being a reflective surface. Various shapes of the optical element are shown, but in each case the reflecting surface must be held to tight tolerances, possibly leading to the problems discussed above. What is needed is an optical element for a von Behren-type belt-driven data cartridge that is made of low cost components, is inexpensive to assemble, and has a wide tolerance for the reflection angle of the reflecting surface in order to reduce waste and/or operational errors.

SUMMARY OF THE INVENTION

To overcome the limitations of the prior art discussed above, and in view of other limitations which will become apparent upon reading the detailed description below, this invention provides a new optical element for use in a belt-driven tape cartridge. The optical element includes at least two reflecting surfaces in order to widen the range of tolerated variances in the geometric configuration of each reflective surface in the optical element.

The optical element includes a light entry surface disposed substantially perpendicular to the initial transmitted light path, a first reflective surface disposed at a first predetermined angle relative to the light entry surface, and a second reflective surface disposed at a second predetermined surface relative to the second reflective surface, such that a light beam entering the light entry surface, and reflecting off the first and second reflective surfaces is passed in a path substantially perpendicular to the initial transmitted light path and toward a tape surface and receptor in a tape drive.

In a preferred embodiment the optical element is a prism composed substantially of acrylic. A preferred method of making the optical element employs conventional injection molding techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference is now made to the following detailed description of the embodiments illustrated in the accompanying drawings in which identical numbers in various views represent the same or similar elements, and wherein: Fig. 1 is a plan view of a belt-driven tape cartridge including the optical element of the present invention and showing cooperative portions of a prior art drive useful with the cartridge;

Fig. 2 is a plan view of a cover that is part of the belt-driven tape cartridge of Fig. 1 and showing the optical element of Fig.1 coupled thereto; Fig. 3 is a schematic showing an exemplary arrangement of positioning and other information indicating marks sensitive to light passed through the optical element of Figs. 1 and 2;

Fig. 4 is a perspective view of the optical element of Figs. 1 and 2; Fig. 5 is a plan (bottom) view of the optical element of Figs. 1 , 2, and

4;

Fig. 6 is a simplified sectional view taken along lines 5-5 and including a simplified operational schematic illustrating geometric relationships of portions of the optical element of Figs. 4 and 5 with light passed from the drive's transmitter; and

Fig. 7 is an alternative embodiment of the optical element of the invention in relation to the drive's transmitter.

DESCRIPTION OF PREFERRED EMBODIMENTS The following is a detailed description of the preferred embodiments, wherein reference is made to the accompanying drawings in which is shown specific embodiments for practicing this invention. Nevertheless, other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. Fig. 1 shows a von Behren type cartridge 1 1 for reading and writing of recording tape 1 8 by tape head 24 that is part of the drive 40. Data cartridge 1 1 comprises a metal base plate 1 0, a transparent plastic cover 1 2, and a pair of tape spools 14. Together base plate 1 0 and cover 1 2 form cartridge housing 1 3. Spools 1 4 are rotatably supported on the base plate 1 0 by cylindrical spindles 1 6 that are fixed perpendicularly into the base plate. A magnetic recording tape 1 8 is wound around spools 1 4 at opposite ends and extends between spools 1 4 along a predetermined path around various fitted tape guides 20. The path extends across a tape head opening 22 in the front wall of the cartridge to provide access for a tape head 24. A belt driving roller 26 is mounted adjacent a drive opening 28 in the front wall of the cartridge. A drive belt 30 extends around belt driving roller 26 and around belt guide rollers 32, which are rotatably mounted on base plate 1 0.

Referring to Figs. 1 and 2, optical element 42 is shown in a preferred coupled relationship to plastic cover 1 2, in which cooperative elements 45 accept spindles 1 6. The element is provided with mounting apertures 76 that slide over and are dimensioned to engage guide post 80 which are part of cover 1 2. Such a relationship is preferred; however, it will be appreciated by those skilled in the art that the optical element could be part of the base or part of the drive without deviating from the superior scope of the invention. In a preferred embodiment, light transmitted from transmitter 38 which is part of drive 40, enters light entry surface 43 and is transmitted toward tape 1 8 after being reflected through exit surface 46. Light transmitted from transmitter 38 passes through an aperture or window 36 which is part of base plate 1 0 before reaching element 42. A light sensor 48 receives the light passed through optical element 42 and passes it onto communication electronics (not shown) in a well-known manner to determine the position of tape 1 8 as it travels in direction 50 relative to the tape cartridge. It should be understood that the arrangement of the transmitter and receptor is a feature of drives that cooperate with the invented optical element and a cartridge having the same. Therefore, the transmitter may pass through the tape surface first and then to the optical element, which is disposed proximate a receptor instead of the preferred relationship described above. Such an arrangement is discussed in more detail below, with reference to Fig. 7. Tape data cartridges which include an optical element and an optical window for passing optical signals that identify the end and bottom of tape are well known in the art and are standardized in terms of dimension and orientation of components according to American National Standard Institute (ANSI) standards and standards provided by Quarter Inch Cartridge (QIC) Drive Standards, Inc. of Santa Barbara, California. The optical signals generally are passed through apertures in the tape which is then used in light sensor 48 to determine the position of tape. Nevertheless, the optical element of the preset invention is novel and provides advantages over prior art optical elements as discussed below. Figure 3 is a schematic showing an exemplary arrangement of positioning and other information of marks on tape 1 4 in accordance with the above-referenced Q.I.C. standard. Generally, direction of the tape is shown in direction 50 which corresponds to direction 50 shown in Figure 50. The tape includes apertures that serve as beginning of tape markers 54, 56 which correspond to the physical beginning of tape 52, and cartridge I. D. holes 58 and 60. Apertures for end of tape markers 66, 68, and 70 are preceded by an early warning aperture 64, and are each disposed generally in the vicinity approximate the physical end of tape 72.

Figs. 4 and 5 show a perspective view of the optical element 42 discussed above with reference to Figs. 1 and 2, and a plan (bottom) view of the optical element, respectively. The element includes the light entry surface 43 (Fig. 5) and the exit surface 46. Sides 82 and 84 are generally spaced apart by structural member 80 disposed between the two sidewalls. The side portions 82 and 84 include apertures 76 for mounting to guideposts 80 which are part of plastic cover 1 2. The element further includes walls 1 00 and 1 02 which are sloped at predetermined angles for reflecting and guiding the transmitted light to light sensor 48 in the drive. It is the inventor's critical recognition of applicable principles of optical physics and selection of materials for this invention which have enabled a low-cost, easy to manufacture part with wide tolerance for varying geometry of walls 1 00 and 1 02. While not wishing to be limited to any particular theory or operation, the inventor believes that the relationship of a light beam transmitted from transmitter 38 with a particular optical medium, which is preferably acrylic, and the selection of particular angles of inclination enable the advantages of this invention. Preferably, the light emitted from transmitter 38 should be selected to be in the infra-red wavelength of about 940 plus or minus 50 nanometers. Nonetheless, the optical element will work with a wide range of bandwidth in the spectrum from white light (visible light) to infra-red light. A good choice for the transmitter is a well-known infra-red light emitting diode (L.E.D.) . The index of refraction for acrylic at about 940 nanometers is recognized to be approximately 1 .48. The acrylic optical medium is dispersed in a medium of surrounding air in the cartridge itself, and air is known to have an index of refraction of 1 .00.

The inventor has recognized that an optical effect called "total internal reflection" can occur when light attempts to move from a medium having a given index or refraction to one having a lower index or refraction. The inventor has critically taken advantage of this relationship by recognizing that at some particular angle of incidence, θ_c, called the "critical angle," the refractive light ray will move parallel to the boundary, and for angles of incidence greater than θ_c, the beam is entirely reflected at the boundary. In other words, the ray is reflected at the boundary as though it had struck a perfectly reflecting surface. Thus, the surface in the prism behaves like a mirror. However, such a surface in a prism does not need a coating or other reflecting add-on to achieve a mirroring effect, which saves cost. Additionally, as will be described in more detail with reference to Fig. 6, the particular geometry chosen for the two sloping walls 1 00 and 1 02 enables, in operation, an effective angle of reflection that is substantially greater (in a preferred embodiment, 50% greater) than the critical angle. Thus, even if manufacturing tolerances vary as much as 1 0° or 1 5 ° the light will be reflected and passed to sensor 48 without the disadvantage of using mirrors or requiring tight tolerance angles providing further economic advantage. The above described principles are now described in more detail below with reference to Fig. 6.

Referring now to Fig. 6, a simplified sectional view taken along lines 6-6 of Fig. 5 shows a simplified operational schematic of optical element 42 including light entry surface 43 reflecting wall 1 02, reflecting wall 1 00 and exit wall 46, in relationship to tape 1 8, light transmitter 38 and light sensor 48. The light beam transmitted from transmitter 38 is composed of several portions which are so denominated for convenience of explaining the operation of the element. Also for simplicity, only those beam portions which play a part in the optics of the tape positioning indicator mechanism are discussed. In other words, any incidental beams (not shown) that are emitted from the preferred L.E.D. can be ignored since they do not effect operation of the transmitter, receptor, or optical element. Accordingly, Portion 200 is the entry portion of the light beam that travels from the transmitter to the light entry surface interface. Light beam 202 represents the portion that travels between light entry surface 43 and the intersection with wall 1 02 at point 1 03. Portion 204 is the portion that travels from point 1 03 to the intersection point 21 8 with wall 1 02. Portion 206 travels between point 21 8 and exits surface 46, and portion 208 travels from the exit surface to tape 1 8. It may also travel to sensor 48, depending on whether holes are present in tape 1 8. The angle between wall 1 02 and beam 202 measured from the normal 21 0 must be greater than the critical angle θ_c which is determined by the choice of interface materials, i.e., acrylic and air to determine whether the light is reflected or simply passed through wall 102. Thus, angle θ₂ must be greater than θ_c for the chosen mediums. Of course, it is recognized that other mediums may be chosen and other principles of physics other than total internal reflectance may be relied upon in view of these teachings without limiting the scope of this invention. Wall 1 02 is sloped by angle α relative to light entry surface 43. In a preferred embodiment, α is selected to be 67 ° . In accordance with principles of Euclidian geometry, angle α determines angle θ₂ which is equal to . Thus, θ₂ in a preferred embodiment is also 67° .

The critical angle for the preferred interface medium acrylic with light at the above-referenced preferred wavelength, (about 940 nanometers) disposed in air is 42.5° . Since 67 ° is much greater than 42.5 °, even a variance of 5° to 1 0° will not render the optical element ineffective for its intended mission. Of course the angle between wall 1 00 and wall 1 02, must be selected so that the light beam 206 exits perpendicular to the path of light beam 200 in order to reach light sensor 48. Thus, in a preferred embodiment θ₃, which is the angle between wall 1 00 and the normal 21 6 is selected by ordinary geometric principles to be 68° to achieve this result. The selection of the particular angle of reflection θ₃ is of course dependent upon the choice of θ₂ which is equal to α. Thus, for the first time the inventor's selection of a plurality of reflecting surfaces and materials enables a high acceptable range of angles of reflection that can be internally reflected by optical element 42, such that beam 204 reflected from wall 1 02 at intersection point 1 03 reflects at an almost equal angle of reflection at point 21 8 and then leaves exit surface 46 perpendicular to the entry light path 200 and is either blocked or allowed to pass through tape 1 8, depending on the position of holes in tape 1 8. Thus, for the first time the inventor has provided an optical element having a light entry surface disposed substantially perpendicular to the transmitted light path from transmitter 38, and a first reflective surface 1 00 disposed at a first predetermined angle (α, θ₂) relative to the light entry surface, and a second reflective surface 1 02 disposed at a second predetermined angle (θ₂) relative to the second reflective surface, such that a light beam entering the light entry surface and reflecting off the first and second reflective surface is passed, substantially perpendicular to the transmitted light path 200 which is also parallel to the light entry surface and in a straight line toward the receptor in the drive. The inventor has provided this in a low-cost embodiment that is advantageous over mirrors and prior art prisms having only one reflective surface which are known to be relatively intolerant of wide variances of angles of reflection. Generally, prisms of the prior art having only one reflective surface must pass light perpendicular to the light beam leaving the transmitter because of the relationship of the transmitter to the sensor and therefore in the prior art an angle of inclination of 45° has been typically selected for prisms. This is unfortunate because the difference between 42.5 and 45 is only 2 Vι ° . Thus, without the teachings provided by this inventor for the first time in this specification one the low-cost simple to manufacture optical element having wide tolerance acceptance would not be available. Although only two reflective surfaces have been shown, one skilled in the art will recognize that the invention is applicable to any number of a plurality of reflective surfaces. Although straight angles have been shown, one skilled in the art will also recognize that this invention will cover those optical elements, and in particular prisms, using curved surfaces in accordance with the teachings of this invention.

Referring to Fig. 7, an alternative embodiment is shown in simplified schematic form. The optical element may be arranged in essentially complementary fashion to that described with reference to Fig. 6 above, to cooperate with transmitter 38 arranged proximate tape 1 8. Light enters through light entry surface 43a, if not blocked by tape 1 8. Once it enters it is reflected off a plurality of reflecting surfaces, not shown but arranged similar to those shown in Fig. 6, respectively arranged for the light entry and exit arrangement. Accordingly, light exits through surface 46a toward the receptor 48. Such arrangement is well within those skilled in the art, in view of the teachings of this invention.

A new optical element for use with a belt-driven tape cartridge has been shown. Modifications may occur to those skilled in the art in view of the teachings above. Therefore this invention is only to be limited by the claims appended below and their equivalents.

WHAT IS CLAIMED IS:

Claims

1 . A data storage tape cartridge positionable in a drive having a tape positioning indicator mechanism including a light transmitter and receptor, the cartridge comprising: a cover having a front, back, top, and first and second sides; a base plate having a front and a back and a top surface, the base plate top surface having mounted to the cover to form a housing; a media access opening formed in the front of the housing; two hubs rotatably mounted in the housing; tape media wrapped around the two hubs in the housing to form two tape packs, the tape media being accessible from the outside of the housing through the media access opening; and an optical element having a light entry surface disposed proximate the light transmitter, and the light entry surface being at a predetermined angle to a transmitted entry beam that interfaces with the light entry surface, and the optical element further having a plurality of light reflective surfaces that are each disposed at respective predetermined angles relative to the light entry surface such that a light beam entering the light entry surface and reflecting off the plurality of reflecting surfaces exits the optical element in an exit path toward the receptor in the drive.

2. The cartridge of claim 1 , wherein the light beam exiting toward the receptor is substantially perpendicular to the transmitted entry beam path.

3. The cartridge of claim 1 , wherein the optical element is composed substantially of acrylic.

4. The cartridge of claim 1 , wherein the optical element includes a light exiting surface such that the light beam is passed from the plurality of reflective surfaces and then through the exiting surface toward the tape surface.

5. The cartridge of claim 1 , wherein the tape is positioned between the transmitter and the light entry surface.

6. The cartridge of claim 1 , wherein the optical element is a prism.

7. The cartridge of claim 6, wherein the optical element is composed substantially of acrylic.

8. The cartridge of claim 1 , wherein the first reflective surface is disposed at a first predetermined angle relative to the light entry surface, and a second reflective surface is disposed at a second predetermined angle relative to the first reflective surface, such that a light beam entering the light entry surface, and reflecting off the first and second reflective surfaces is passed in a path substantially perpendicular to the light beam path as it is transmitted from the transmitter toward the receptor in the drive.

9. The cartridge of claim 8, wherein the optical element has a critical angle above which light is reflected and the first predetermined angle is about 50% larger than the critical angle.

1 0. The cartridge of claim 9, wherein the second predetermined angle is about 50% greater than the critical angle.

1 1 . The cartridge of claim 8, wherein the first predetermined angle and the second predetermined angle are within 3 degrees of each other.

1 2. The cartridge of claim 1 , wherein the light entry surface is disposed substantially perpendicular to the transmitted entry beam.

1 3. The cartridge of claim 8, wherein the light entry surface is disposed substantially perpendicular to the transmitted entry beam.

1 4. An optical element that cooperates with a data storage tape cartridge that is positionable in a drive having a tape positioning indicator mechanism including a light transmitter and receptor, the optical element comprising: a light entry surface disposed proximate the light transmitter and also disposed at a predetermined angle to a transmitted entry beam that interfaces with the light entry surface; and a plurality of light reflective surfaces that are each disposed at respective predetermined angles relative to the light entry surface such that a light beam entering the light entry surface and reflecting off the plurality of reflecting surfaces exits the optical element in an exit path toward the receptor in the drive.

1 5. The optical element of claim 1 4, wherein the optical element includes a light exiting surface such that the light beam is passed from the second reflective surface and then through the exiting surface toward the tape surface.

1 6. The optical element of claim 1 5, wherein the optical element is a prism.

1 7. The optical element of claim 1 6, wherein the optical element is composed substantially of acrylic.

1 8. The optical element of claim 1 5, wherein the first reflective surface is disposed at a first predetermined angle relative to the light entry surface, and a second reflective surface is disposed at a second predetermined angle relative to the first reflective surface, such that a light beam entering the light entry surface, and reflecting off the first and second reflective surfaces is passed in a path toward the receptor in the drive and substantially perpendicular to the transmitted entry beam path.

1 9. The optical element of claim 1 8, wherein the optical element has a critical angle above which light is reflected and the first predetermined angle is about 50% larger than the critical angle.

20. The optical element of claim 1 9, wherein the second predetermined angle is about 50% greater than the critical angle.

21 . The optical element of claim 1 8, wherein the first predetermined angle and the second predetermined angle are within 3 degrees of each other.

22. The optical element of claim 1 9, wherein the light entry surface is disposed substantially perpendicular to the transmitted entry beam path.

23. The optical element of claim 1 8, wherein the light entry surface is disposed substantially perpendicular to the transmitted entry beam path.

24. The optical element of claim 1 4, wherein the light beam exiting toward the receptor is substantially perpendicular to the transmitted entry beam path.