Abstract:
A method and apparatus for attaching a mirror to a housing with a spring clip such that the spring clip applies a substantially constant force to the mirror when a fastener for attaching the spring clip to a mounting structure of the housing has an axis defining an angle with a surface of the mounting structure that is within a predetermined range of angles. An arched contact surface with an aperture for receiving the fastener is provided on the spring clip such that the fastener contacts the contact surface tangentially.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and apparatus for retaining a mirror to a housing with a spring clip. 
     BACKGROUND OF THE INVENTION 
     Optical systems used in color laser printers may be characterized as having three sub-systems or assemblies, namely, a laser diode/pre-scan optical assembly, a scanning assembly, and a post scan assembly. Conventionally, four laser diodes generate separate laser beams corresponding, for example, to the colors yellow, cyan, magenta and black. In the pre-scan optical assembly, the individual beams are collimated and directed onto a rotating polygonal mirror in the scanning assembly. The facets of the rotating mirror sweep the individual beams across the surfaces of a plurality of mirrors and through lenses within the post scan assembly. The beams then scan along surfaces of four photoconductive drums within the printer. The mirrors in the post scan assembly are mounted to surfaces on the printhead housing via two spring clips positioned near opposite ends of the mirrors. 
     It is desirable to provide spring clips for applying a uniform mirror retaining force. It is further desirable to use a single spring clip to retain two or more mirrors in the post scan assembly, wherein the two or more mirrors are mounted at different angles. 
     SUMMARY OF THE INVENTION 
     In accordance with a first aspect of the present invention, a spring clip is provided for retaining a mirror to a first mounting structure of a housing when a fastener for fastening the spring clip to a second mounting structure of the housing has an axis defining an angle with a surface of the second mounting structure that is within a predetermined range of angles. The spring clip may comprise: a first section to apply a retaining force against the mirror and an arcuate second section coupled to the first section including an aperture for receiving the fastener. The fastener is capable of contacting the arcuate second section at a location such that the retaining force applied by the first section upon the mirror remains substantially constant when the angle defined by the axis of the fastener and the second mounting structure is within the predetermined range. 
     The arcuate second section may further comprise an arched contact surface positioned such that the fastener contacts the arched contact surface tangentially. 
     The second mounting structure may comprise an arcuate ridge and the arcuate second section may be shaped to receive the arcuate ridge of the second mounting structure so that rotation of the spring clip about the fastener is prevented when the fastener is rotated. 
     The first section may comprise a protrusion adapted to contact a center section of the mirror. 
     The protrusion may comprise a second arcuate ridge. 
     The spring clip may comprise a substantially planar third section coupled to the second section on a side of the second section opposite a side coupled to the first section. The fastener may not contact the third section when the angle defined by the axis of the fastener and the second mounting surface is within the predetermined range. 
     The first section may comprise a first part and a second part extending at an angle to the first part. 
     In accordance with a second aspect of the present invention, a printhead for a laser printer is provided. The printhead may comprise: a mirror, a spring clip, a housing having a first mounting structure to receive the mirror and a second mounting structure to receive the spring clip, and a fastener to couple the spring clip to the second mounting structure such that the spring clip retains the mirror to the first mounting structure. The spring clip may apply a substantially constant retaining force to the mirror when an angle defined by the axis of the fastener and the second mounting structure is within a predetermined range. 
     The spring clip may comprise a first section to apply a retaining force against the mirror and an arcuate second section coupled to the first section including an aperture for receiving the fastener. The fastener may contact the arcuate second section at a location such that the retaining force applied by the first section against the mirror remains substantially constant when the angle defined by the axis of the fastener and the second mounting structure is within the predetermined range. 
     In accordance with a third aspect of the present invention, a method of retaining a mirror to a housing with a spring clip is provided. The method may comprise: defining the housing to comprise a first mounting structure to receive the mirror and a second mounting structure to receive the spring clip; defining the spring clip to comprise a first section to apply a retaining force against the mirror and an arcuate second section coupled to the first section including an aperture for receiving a fastener; passing the fastener though the aperture in the spring clip second section; and engaging the fastener with the housing second mounting structure to attach the spring clip to the second mounting structure. The fastener may contact the arcuate second section at a location such that the retaining force applied by the first section upon the mirror remains substantially constant when an angle defined by the axis of the fastener and the second mounting structure is within a predetermined range. 
     Defining a spring clip may further comprise providing an arched contact surface positioned such that the fastener contacts the arched contact surface tangentially. 
     The second mounting structure may comprise an arcuate ridge and the arcuate second section may be shaped to receive the arcuate ridge of the second mounting structure such that rotation of the spring clip about the fastener is prevented when the fastener is rotated. 
     Defining a spring clip may further comprise providing a substantially planar third section coupled to the second section on a side of the second section opposite to a side coupled to the first section. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description of the preferred embodiments of the present invention can best be understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals, and in which: 
         FIG. 1  is a plan view of a printhead for use in a color laser printer showing a scanning assembly and a post scan assembly taken from the post scan side; 
         FIG. 2  is a perspective view of a part of the printhead housing showing mirrors, mounting structures, spring clips and fasteners; 
         FIG. 3  is a diagrammatic view of a first mirror, spring clip and fastener of  FIG. 2  showing the mirror in a first position in the printhead housing; and 
         FIG. 4  is a diagrammatic view of a second mirror, spring clip and fastener of  FIG. 2  showing the mirror in a second position in the printhead housing. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration, and not by way of limitation, specific preferred embodiments in which the invention may be practiced. It is understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention. 
     Referring now to  FIG. 1 , a printhead, indicated generally by reference numeral  10 , for use in a color laser printer, is shown. The printhead includes a housing  30  containing first, second, third and fourth laser diode/pre-scan assemblies (not shown), a scanning assembly  12 , and a post scan assembly  13 , see  FIG. 1 . In the illustrated embodiment of the present invention, first, second, third and fourth laser diodes (not shown) forming part of the first, second, third and fourth laser diode/pre-scan assemblies generate separate laser beams (not shown) corresponding, for example, to the colors yellow, cyan, magenta, and black. The individual laser beams are collimated in first, second, third and fourth pre-scan assemblies forming part of the laser diode/pre-scan assemblies and directed onto facets  14  of a rotating polygonal mirror  16  defining the scanning assembly  12 . As the mirror  16  rotates, it causes the laser beams to move along the surfaces of first, second, third, fourth, fifth and sixth stationary linear mirrors  18 ,  20 ,  22 ,  24 ,  26  and  28  and pass through a plurality of F-theta lenses  29 A and  29 B. In the illustrated embodiment, each beam passes through only one of the F-theta lens  29 A and  29 B. The mirrors  18 ,  20 ,  22 ,  24 ,  26  and  28  and the F-theta lenses  29 A and  29 B define the post scan assembly  13 . The beams subsequently exit the printhead housing  30  through corresponding first, second, third and fourth slots or windows (not shown) and scan along first, second, third and fourth photoconductive drums (not shown) within the laser printer. 
     In the illustrated embodiment, the first, second, third, fourth, fifth and sixth mirrors  18 ,  20 ,  22 ,  24 ,  26  and  28  are retained against respective mounting structures on the printhead housing  30  using spring clips. 
     For simplicity and clarity, discussion herein will refer specifically to the first and second mirrors  18  and  20  retained by first and second spring clips  32  and  32 A and third and fourth spring clips  34  and  34 A, respectively, see  FIGS. 1 and 2  where spring clips  32 A and  34 A are shown in  FIG. 1  only. It is understood that the concepts and principles of the present invention apply equally well to the spring clips used to retain each of the other mirrors  22 ,  24 ,  26  and  28 . 
     Referring now to  FIGS. 1 and 2 , the printhead housing  30  of the illustrated embodiment has a first side  36  having an edge  36 A, a second side  38  having an edge  38 A, a third side  40  having an edge  40 A and a fourth side  42  having an edge  42 A. The edges  36 A,  38 A,  40 A and  42 A define a printhead mounting surface plane, see  FIG. 1 . 
     The first mirror  18  comprises first and second side surfaces  18 A and  18 B, front and rear surfaces  18 C and  18 D and first and second ends  18 E and  18 F, see  FIGS. 1-3 . The second mirror  20  comprises first and second side surfaces  20 A and  20 B, front and rear surfaces  20 C and  20 D and first and second ends  20 E and  20 F, see  FIGS. 1 ,  2  and  4 . The printhead housing  30  further comprises first and second mirror mounting structures  44  and  45  for mounting the first mirror  18  and third and fourth mirror mounting structures  46  and  47  for mounting the second mirror  20 , see  FIG. 1 . The first mirror mounting structure  44  is located near the first end  18 E of the first mirror  18 , the second mirror mounting structure  45  is located near the second end  18 F of the first mirror  18 , the third mirror mounting structure  46  is located near the first end  20 E of the second mirror  20  and the fourth mirror mounting structure  47  is located near the second end  20 F of the second mirror  20 , see  FIG. 1 . 
     The first mirror mounting structure  44  comprises a base portion  44 A and first, second and third mounting features  50 A,  50 B and  50 C, which extend out from the base portion  44 A, see  FIGS. 2 and 3 . The first mounting feature  50 A engages the second side surface  18 B of the mirror  18 . The second mounting feature  50 B engages a lower portion of the rear surface  18 D of the first mirror  18  near the second side surface  18 B. An end of a screw  150 C extends out from the third mounting feature  50 C and engages the rear surface  18 D of the first mirror  18  near its first side surface  18 A, see  FIG. 3 . The first and second mounting features  50 A and  50 B and the screw  150 C extending out of the third mounting feature  50 C locate the first mirror  18  within the printhead housing  30  such that the first mirror front surface  18 C is located at a desired angle θ 5  relative to the edge  36 A of the printhead housing first side  36  and the printhead mounting surface plane, see  FIG. 2 . The screw  150 C extending through the third mounting feature  50 C may be rotated during manufacturing to adjust the angular position of the first mirror  18  relative to the first and second mirror mounting structures  44  and  45  such that a corresponding laser beam moving along the mirror  18  strikes a corresponding PC drum at a desired location. It is noted that the third mounting feature  50 C may not include a screw extending through it but may contact the first mirror rear surface  18 D directly. 
     The second mirror mounting structure  45  is similar to the first mirror mounting structure and comprises first, second and third mounting features (not shown) extending from a base portion (not shown). The first and second mounting features are sized and shaped in a similar manner to the first and second mounting features  50 A and  50 B of the first mirror mounting structure  44 . The third mounting feature of the second mirror mounting structure  45  may differ from the third mounting feature  50 C of the first mirror mounting structure  44  as the third mounting feature of the second mirror mounting structure  45  may not include a screw extending through it and may contact the first mirror rear surface  18 D directly. 
     The third mirror mounting structure  46  comprises a base portion  45 A and first, second and third mounting features  51 A,  51 B and  51 C, which extend out from the base portion  45 A, see  FIGS. 2 and 4 . The first mounting feature  51 A engages the second side surface  20 B of the second mirror  20 . The second mounting feature  51 B engages a lower portion of the rear surface  20 D of the second mirror  20  near the second side surface  20 B. An end of a screw  151 C extends out from the third mounting feature  51 C and engages the rear surface  20 D of the second mirror  20  near its first side surface  20 A, see  FIG. 3 . The first and second mounting features  51 A and  51 B and the screw extending out of the third mounting feature  51 C locate the second mirror  20  within the printhead housing  30  such that the second mirror front surface  20 C is located at a desired angle θ 5A  relative to the edge  36 A of the printhead housing first side  36  and the printhead mounting surface plane, see  FIG. 2 . The screw extending through the third mounting feature  51 C may be rotated during manufacturing to adjust the angular position of the second mirror  20  relative to the third and fourth mirror mounting structures  46  and  47  such that a corresponding laser beam moving along the mirror  20  strikes a corresponding PC drum at a desired location. It is noted that the third mounting feature  51 C may not include a screw extending through it. 
     The fourth mirror mounting structure  47  is similar to the third mirror mounting structure and comprises first, second and third mounting features extending from a base portion. The first and second mounting features are sized and shaped in a similar manner to the first and second mounting features  51 A and  51 B of the third mirror mounting structure  46 . The third mounting feature of the fourth mirror mounting structure  47  may differ from the third mounting feature  51 C of the third mirror mounting structure  46  as the third mounting feature of the fourth mirror mounting structure  47  may not include a screw extending through it. 
     Referring again to  FIGS. 1 and 2 , the printhead housing  30  may be made from a material such as a glass filled plastic, one of which is sold under the product designation NORYL 5246, from General Electric Plastics, and may be formed by processes such as die casting or injection molding. As is well known to those skilled in the art, it is customary to use multiple part molds that can be separated to remove finished parts from the mold once the parts have solidified. Commonly, two-part molds are used in order to minimize tooling costs. Such two-part molds may be separated in a single direction only. 
     The printhead housing  30  in the illustrated embodiment may be formed in a two-part mold of this type having a mold separation direction, commonly called a mold pull direction, perpendicular to the printhead mounting surface plane previously defined. As is also well known to those skilled in the die casting and injection molding arts, structures made by these processes may have features such as protrusions and voids defined by the mold extending only in a direction parallel to the mold pull direction. 
     Referring now to  FIGS. 2 and 3 , the first mirror front surface  18 C is a reflecting surface against which a first laser beam (not shown) is directed. The first mirror rear surface  18 D defines a first mounting surface, which, as noted above, is positioned against the second mounting feature  50 B and the screw  150 C extending out of the third mounting feature  50 C, while the first mirror second side surface  18 B defines a second mounting surface, which, as noted above, is positioned against the first mounting feature  50 A. The first spring clip  32  is configured to apply a retaining force in a direction F 1  substantially perpendicular to the front surface  18 C of the first mirror  18  in order to retain the first mirror  18  in place on the first and second mounting features  50 A- 50 B and the screw  150 C, see  FIGS. 2 and 3 . In a similar manner, the second spring clip  32 A is configured to apply a retaining force to the front surface  18 C of the first mirror  18  in order to retain the first mirror  18  in place on the first, second and third mounting features of the second mirror mounting structure  45 . 
     Referring now to  FIGS. 2 and 4 , the second mirror front surface  20 C is a reflecting surface against which a second laser beam (not shown) is directed. The second mirror rear surface  20 D defines a first mounting surface, which, as noted above, is positioned against the second mounting feature  51 B and the screw  151 C of the third mounting feature  51 C, while the second mirror second side surface  20 B defines a second mounting surface, which, as noted above, is positioned against the first mounting feature  51 A. The third spring clip  34  is configured to apply a retaining force in direction F 1 A substantially perpendicular to the front surface  20 C of the second mirror  20  in order to retain the second mirror  20  in place on the first and second mounting features  51 A- 51 B and the screw  151 C. In a similar manner, the fourth spring clip  34 A is configured to apply a retaining force to the front surface  20 C of the second mirror  20  in order to retain the second mirror  20  in place on the first, second and third mounting features of the fourth mirror mounting structure  47 . 
     It is desirable that each spring clip apply a substantially uniform retaining force against the surface of the mirror it contacts. It is further desirable that a single spring clip design suffice for use in retaining at least two mirrors positioned in the printhead housing  30  at different angles relative to the edges  36 A,  38 A,  40 A and  42 A and the printhead mounting surface plane. It is yet further desirable that protrusions forming part of and voids formed within the printhead housing  30  be oriented perpendicular to the printhead mounting surface plane previously defined so that the printhead housing  30  may be formed in the type of two-part mold previously discussed. Hence, longitudinal axes of the printhead housing protrusions and voids are generally parallel to the single separation or pull direction of the mold parts. 
     Referring now to  FIG. 3 , the first spring clip  32  comprises a first section  56  for applying the retaining force in the direction F 1 , noted above, and an arcuate-shaped second section  58 . The printhead housing  30  further comprises a first spring-clip mounting structure  144 , which is positioned adjacent to the first mirror mounting structure  44 , see  FIG. 2 . The first spring-clip mounting structure  144  comprises an arcuate-shaped mounting feature  66  and an adjacent substantially planar surface  67 , see  FIGS. 2 and 3 . The mounting feature  66  is received in the arcuate-shaped second section  58  of the first spring clip  32 . 
     In the illustrated embodiment, the first section  56  of the first spring clip  32  comprises a substantially planar first part  60  and a second part  62 , integral with the first part  60  and extending at an angle Θ 1  to the first part  60 . The angle Θ 1  may be approximately 135 degrees. The first section  56  further comprises an arcuate-shaped protrusion  64  extending in the direction F 1  and configured to contact a center portion of the front surface  18 C of the first mirror  18 . 
     The arcuate-shaped second section  58  of the first spring clip  32  includes an aperture  68 , see  FIG. 2 , for receiving a fastener  70 , a screw in the illustrated embodiment, to couple the spring clip  32  to the mounting feature  66  of the first spring clip mounting structure  144 , see  FIGS. 2 and 3 . The fastener  70  extends through the aperture  68  in the first spring clip second section  58  and further into a bore  72  in the mounting feature  66  of the first spring-clip mounting structure  144 , see  FIG. 2 . The bore  72  may be defined during forming of the printhead housing by a feature (not shown) on a two-part mold. As a result, an axis A 1  of the bore  72  is parallel to the pull direction of the mold, which is perpendicular to the printhead housing side edges  36 A,  38 A,  40 A and  42 A and the printhead mounting surface plane. 
     Referring again to  FIG. 3 , the spring clip  32  in the illustrated embodiment further comprises a substantially planar third section  74  integral with the second section  58 . The third section  74  is positioned adjacent to and substantially parallel with a plane P 1  defined by the substantially planar surface  67  of the first spring clip mounting structure  144 , see  FIGS. 2 and 3 . The third section  74  may be substantially planar with the first part  60  of the spring clip first section  56 . A fourth substantially planar section  76  of the first spring clip  32  is integral with and substantially perpendicular to the first section second part  62 . In other embodiments of the present invention, a fourth section may not be provided or, if provided, the fourth section  76  may not be planar and/or may extend at other angles relative to the first section  56 . 
     As noted above, the axis A 1  of the bore  72  in the mounting feature  66  of the first spring clip mounting structure  144  is perpendicular to the printhead housing side edge  36 A and the printhead mounting surface plane. Further in the illustrated embodiment, the axis A 1  of the bore  72  is positioned at an angle θ 2  of about 87 degrees relative to the plane P 1  defined by the surface  67  of the first spring clip mounting structure  144 , see  FIG. 2 . An angle θ 3  between the first mirror front surface  18 C and the plane P 1  of the surface  67  of the first spring clip mounting structure  144  is about 122.25 degrees. An angle θ 4  between the plane P 1  and a plane P 2  parallel with the edge  36 A of the printhead housing first side  36  is about 3 degrees. The angle θ 5 , noted above, between the first mirror front surface  18 C and the edge  36 A of the printhead housing first side  36  is about 50 degrees. 
     The printhead housing  30  further comprises a second spring-clip mounting structure  145 , which is positioned adjacent to the second mirror mounting structure  45 , see  FIG. 1 . The second spring-clip mounting structure  145  is configured in the same manner as the first spring-clip mounting structure  144  and comprises an arcuate-shaped mounting feature (not shown) and an adjacent substantially planar surface (not shown). The second spring clip  45  is identical to the first spring clip  44 . Further, the second spring clip  45  is mounted to the second spring-clip mounting structure  145  via a screw  171 , see  FIG. 1 , in the same manner that the first spring clip  44  is mounted to the first spring-clip mounting structure  144  via the screw  70 . 
     Referring now to  FIGS. 2 and 4 , the third spring clip  34  is identical to the first and second spring clips  32 ,  32 A previously discussed. The third spring clip  34  comprises a first section  56 A for applying a retaining force in a direction F 1 A substantially perpendicular to the front surface  20 C of the second mirror  20 , see  FIG. 4 . The third spring clip  34  further comprises an arcuate-shaped second section  58 A. The printhead housing  30  further comprises a third spring-clip mounting structure  146 , which is positioned adjacent to the third mirror mounting structure  46 , see  FIG. 2 . The third spring-clip mounting structure  146  comprises an arcuate shaped mounting feature  66 A and an adjacent substantially planar surface  67 A, see  FIGS. 2 and 4 . The mounting feature  66 A is received in the arcuate-shaped second section  58 A of the third spring clip  34 . 
     In the illustrated embodiment, the first section  56 A of the third spring clip  34  comprises a substantially planar first part  60 A and a second part  62 A, integral with first part  60 A and extending at an angle Θ 1A  to the first part  60 A. The angle Θ 1A  is identical to the angle Θ 1  of the spring clip  32 , see  FIGS. 3 and 4 . The first section  56 A further comprises an arcuate-shaped protrusion  64 A extending in the direction F 1A  and configured to contact a center portion of the front surface  20 C of the second mirror  20 . 
     The arcuate-shaped second section  58 A of the third spring clip  34  includes an aperture  68 A, see  FIG. 2 , for receiving a fastener  70 A, a screw in the illustrated embodiment, to couple the spring clip  34  to the mounting feature  66 A of the third spring-clip mounting structure  146 , see  FIGS. 2 and 4 . The fastener  70 A extends through the aperture  68 A and further into a bore  72 A in the mounting feature  66 A of the third spring-clip mounting structure  146 , see  FIG. 2 . The bore  72  may be defined during forming of the printhead housing by a feature (not shown) of a two-part mold as previously discussed. As a result, an axis of the bore A 1A  is preferably parallel to the pull direction of the mold, which is perpendicular to the printhead housing side edges  36 A,  38 A,  40 A and  42 A and the printhead mounting surface plane. 
     Referring again to  FIG. 4 , the spring clip  34  in the illustrated embodiment further comprises a substantially planar third section  74 A integral with the second section  58 A. The third section  74 A is positioned adjacent to and substantially parallel with a plane P 1A  defined by the substantially planar surface  67 A of the third spring-clip mounting structure  146 , see  FIGS. 2 and 4 . The third section  74 A may be substantially planar with the first part  60 A of the spring clip first section  56 A. A fourth substantially planar section  76 A is integral with and substantially perpendicular to the first section second part  62 A. In other embodiments of the present invention, a fourth section may not be provided or, if provided, the fourth section  76 A may not be planar and/or may extend at other angles relative to the first section  56 A. 
     As noted above, the axis A 1A  of the bore  72 A in the mounting feature  66 A of the third spring clip mounting structure  146  is perpendicular to the printhead housing side edge  36 A and the printhead mounting surface plane. In the illustrated embodiment, the axis A 1A  of the bore  72 A is positioned at an angle θ 2A  of about 97.25 degrees relative to the plane P 1A  defined by the surface  67 A of the third spring clip mounting structure  146 , see  FIG. 4 . An angle θ 3A  between the third mirror front surface  20 C and the plane P 1A  of the surface  67 A of the third spring clip mounting structure  146  is about 122.25 degrees and is identical to the angle θ 3  between the first mirror front surface  18 C and the plane P 1  of the surface  67  of the first spring clip mounting structure  144 . An angle θ 4A  between the plane P 1A  and a plane P 2A  parallel with the edge  36 A of the printhead housing first side  36  is about 7.25 degrees. The angle θ 5A , noted above, between the second mirror front surface  20 C and the edge  36 A of the printhead housing first side  36  is about 65 degrees. 
     The printhead housing  30  further comprises a fourth spring-clip mounting structure  147 , which is positioned adjacent to the fourth mirror mounting structure  47 , see  FIG. 1 . The fourth spring-clip mounting structure  147  is configured in the same manner as the third spring-clip mounting structure  146  and comprises an arcuate-shaped mounting feature (not shown) and an adjacent substantially planar surface (not shown). The fourth spring clip  47  is identical to the first, second and third spring clips  44 - 46 . Further, the fourth spring clip  47  is mounted to the fourth spring-clip mounting structure  147  via a screw  271 , see  FIG. 1 , in the same manner that the third spring clip  46  is mounted to the third spring-clip mounting structure  146  via the screw  70 A. 
     It is noted that the angle θ 5  between the first mirror front surface  18 C and the edge  36 A of the printhead housing first side  36  differs from the angle θ 5A  between the second mirror front surface  20 C and the edge  36 A of the printhead housing first side  36 . It is also noted that the angle θ 2  between the axis A 1  of the bore  72  in the mounting feature  66  of the first spring clip mounting structure  144  and the plane P 1  defined by the surface  67  of the first spring clip mounting structure  144  differs from the angle θ 2A  between the axis A 1A  of the bore  72 A in the mounting feature  66 A of the third spring clip mounting structure  146  and the surface  67 A of the third spring clip mounting structure  146 . As noted above, both the bore  72  and the bore  72 A have axes A 1  and A 1A  substantially perpendicular to the printhead housing side edge  36 A and the printhead mounting surface plane. Even though angles θ 5  and θ 5A  are not equal to one another, the first, second, third and fourth clips  32 ,  32 A,  34 ,  34 A, which, as noted above, are identical to one another, can be used interchangeably to secure the first and second mirrors  18  and  20  to the first, second, third and fourth mirror mounting structures  44 - 47 . 
     In order for the spring clip  32  to apply a retaining force against the front surface  18 C of the first mirror  18  that is substantially equal to the retaining force applied by the spring clip  34  against the front surface  20 C of the second mirror  20 , it is necessary that the angle Θ 1  of the spring clip  32  be made approximately equal to the angle Θ 1 A of the spring clip  34  and further, the length of the spring clip  32  from where its corresponding screw  70  contacts its corresponding arcuate-shaped second section  58  to where its corresponding arcuate-shaped protrusion  64  contacts the center portion of the front surface  18 C of its corresponding mirror  18  must be substantially equal to the length of the spring clip  34  from where its corresponding screw  70 A contacts its corresponding arcuate-shaped second section  58 A to where its corresponding arcuate-shaped protrusion  64 A contacts the center portion of the front surface  20 C of its corresponding mirror  20 , see  FIGS. 3 and 4 . This may be accomplished by defining the positions of the first, second and third mounting features  50 A- 50 C of the first mirror mounting structure  44  as well as the first, second and third mounting features of the second mirror mounting structure  45  relative to the edge  36 A of the printhead housing first side  36  such that the first mirror front side  18 C is positioned at a desired angle θ 5  relative to the edge  36 A of the printhead housing first side  36 . Thereafter, the surface  67  of the first spring clip mounting structure  144  as well as a corresponding surface of the second spring clip mounting structure  145  are defined such that when the spring clips  32 ,  32 A are mounted to the spring-clip mounting structures  144 ,  145 , the angle θ 3  between the first mirror front surface  18 C and the plane P 1  of the surface  67  of the first spring clip mounting structure  144  and a corresponding angle between the first mirror front surface  18 C and a plane (not shown) of a corresponding surface of the second spring clip mounting structure  145  equal a desired first value. The desired value for the angle θ 3  between the first mirror front surface  18 C and the plane P 1  of the surface  67  of the first spring clip mounting structure  144  and a corresponding angle between the first mirror front surface  18 C and a plane (not shown) of a corresponding surface of the second spring clip mounting structure  145  corresponds to the angle Θ 1  of the first spring clip  32  as well as a corresponding angle of the second spring clip  32 A equaling a second desired value. 
     Next, the positions of the first, second and third mounting features  51 A- 51 C of the third mirror mounting structure  46  as well as the first, second and third mounting features of the fourth mirror mounting structure  47  are defined relative to the edge  36 A of the printhead housing first side  36  such that the second mirror front side  20 C is positioned at a desired angle θ 5A  relative to the edge  36 A of the printhead housing first side  36 . Thereafter, the surface  67 A of the third spring clip mounting structure  146  as well as a corresponding surface of the fourth spring clip mounting structure  147  are defined such that when the spring clips  34 ,  34 A are mounted to the spring-clip mounting structures  146 ,  147 , the angle θ 3A  between the second mirror front surface  20 C and the plane P 1A  of the surface  67 A of the third spring clip mounting structure  146  and a corresponding angle between the second mirror front surface  20 C and a plane (not shown) of a corresponding surface of the fourth spring clip mounting structure  147  equal the angle θ 3  between the first mirror front surface  18 C and the plane P 1  of the surface  67  of the first spring clip mounting structure  144 . When the angle θ 3A  is equal to angle θ 3 , the angle Θ 1A  of the third spring clip  34  as well as a corresponding angle of the fourth spring clip  34 A will equal the angle Θ 1  of the first spring clip  32  as well as a corresponding angle of the second spring clip  32 A. 
     It is also noted that because the second sections of the first, second, third and fourth springs clips  32 ,  32 A,  34 ,  34 A have an arcuate shape, the screws that couple the spring clips  32 ,  32 A,  34 ,  34 A to the first, second, third and fourth spring clip mounting structures  144 ,  145 ,  146 ,  147  only contact the arcuate-shaped second sections of the spring clips  32 ,  32 A,  34 ,  34 A and not an adjacent first section first part of the spring clip or an adjacent third section of the spring clip. For example, no part of the head  170  of the screw  70  makes contact with first section first part  60  of the first spring clip  32  or an adjacent third section  74  of the first spring clip  32 , see  FIG. 3 . Also, no part of the head  170 A of the screw  70 A makes contact with first section first part  60 A of the second spring clip  34  or an adjacent third section  74 A of the third spring clip  34 , see  FIG. 4 . 
     While the screws  70  and  70 A make contact at slightly different angular locations on the arcuate-shaped second sections  58 ,  58 A of the first and third spring clips  32 ,  34 , the length of the spring clip  32  from where its corresponding screw  70  contacts its corresponding arcuate-shaped second section  58  to where its corresponding arcuate-shaped protrusion  64  contacts the center portion of the front surface  18 C of its corresponding mirror  18  remains substantially equal to the length of the spring clip  34  from where its corresponding screw  70 A contacts its corresponding arcuate-shaped second section  58 A to where its corresponding arcuate-shaped protrusion  64 A contacts the center portion of the front surface  20 C of its corresponding mirror  20 . 
     Hence, the first, second, third and fourth clips  32 ,  32 A,  34 ,  34 A are interchangeable and can be used to secure either the first mirror  18  or the second mirror  20  to the printhead housing  30  with substantially the same retaining force. 
     While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of the invention.