Abstract:
A translation system comprising: a linear support having first and second opposite ends; a carriage slid ably mounted on said support for movement in reciprocal linear directions between said first and second ends of said support; a rotary drive rotatable in opposite rotary directions located at one end of said support; a rotatable member mounted at the other end of said support; and a multiple cable assembly attached to said carriage and extending around said rotary drive and said rotatable member moving said carriage in said reciprocal linear directions as a function of rotation of said rotary drive in said opposite rotary directions.

Description:
FIELD OF THE INVENTION 
     This invention relates in general to internal drum scanner assemblies and laser imaging systems incorporating such scanner assemblies. In particular, the present invention relates to a translation system for moving a laser or optical scanning system relative to media being scanned. 
     BACKGROUND OF THE INVENTION 
     Laser imaging systems are commonly used to produce photographic images from digital image data generated by magnetic resonance (MR), computed tomography (CT) or other types of medical image scanners. Systems of this type typically include a continuous tone laser imager for exposing the image on photosensitive film, a film processor for developing the film, and an image management subsystem for coordinating the operation of the laser imager and the film processor. 
     The digital image data is a sequence of digital image values representative of the scanned image. Image processing electronics within the image management subsystem processes the image data values to generate a sequence of digital laser drive values (i.e., exposure values), which are input to a laser scanner. The laser scanner is responsive to the digital laser drive values for scanning across the photosensitive film in a raster pattern for exposing the image on the film. 
     The continuous-tone images used in the medical imaging field have very stringent image-quality requirements. A laser imager printing onto transparency film exposes an image in a raster format, the line spacing of which must be controlled to better than one micrometer. In addition, the image must be uniformly exposed such that the observer cannot notice any artifacts. In the case of medical imaging, the observers are professional image analysts (e.g., radiologists). 
     Film exposure systems are used to provide exposure of the image on photosensitive film. Known film exposure systems include a linear translation system and a laser or optical scanning system. The laser scanning system includes a laser scanner with unique optical configurations (i.e., lenses and mirrors) for exposure of the image onto the film. The linear translation system provides for movement of the laser scanning system in a direction perpendicular to the scanning direction, such that a fall image may be scanned on a piece of photosensitive film. 
     In an internal drum type laser scanner assembly, a piece of film is positioned onto a film platen, wherein the film platen has a partial cylindrical or partial drum shape. The photosensitive film is positioned against the film platen. The laser or optical scanning system is positioned at the center of curvature of the photosensitive film for scanning a scan line across the photosensitive film surface. A linear translation system moves the laser or optical scanning system lengthwise along a longitudinal axis as defined by the center of curvature of the film to expose an entire image onto the film. 
     Traditional linear translation systems include three main components, a stationary member, a moving member (e.g., a carriage), and a drive mechanism. In a linear translation system where rigidity, positional accuracy, and high load carrying capacity are required, lead screw mechanisms are preferred as the drive mechanism. Belts and cable systems are used in systems characterized by flexibility, light loads, and low costs, such as plotters and ink jet printers. 
     Known linear translation systems are usually designed for positional repeatability. Although such systems work well for positional repeatability type scanning operations, such linear translation systems were not designed to minimize velocity variation which is critical for imaging continuous tone photosensitive film. In continuous laser scanning applications, velocity variations cause the scan lines to be unevenly spaced and result in a variety of image artifacts on the photosensitive film. 
     U.S. Pat. No. 6,064,416, issued May 16, 2000, inventors Esch et al., discloses an optics translation module with a single drive cable. The optics translation module uniformly places laser scan lines to form complete images. The translation direction is perpendicular to the scan line direction. 
     The optics translation module, controls image quality in the cross scan direction. Speed variation will be reflected in images as bands or streaks of non-uniform densities on film. Unstable motion during the translation of the optics module causes inaccurate placement of pixels, resulting in a variety of image artifacts. 
     In this design, a translation carriage with kinematic support on a pair of cylindrical rails is used. The carriage, with precision mounting surfaces, serves as an interface between the optics module and the optics translation module. Kinematic support is achieved by a pair of V-shaped bearing surfaces and a flat sliding surface built into the carriage. When the carriage slides on the rails during translation, there is little friction on the carriage in the translation direction, while its position is rigidly determined in the other directions. 
     Weight of the carriage and the attached optics module is necessary for maintaining contact between the carriage and the rails. If the carriage is lifted from the rails, the kinematic support will not function properly. The position of the carriage will then be undetermined. 
     The optics module is attached to the translation carriage with position reference at an edge formed by two perpendicular planes. This ensures easy mounting of the optics module to the translation module. 
     The support points of the carriage need to enclose the center of gravity of the optics module and carriage assembly. 
     A cable drive mechanism is used for driving the translation carriage. For a carriage that relies on kinematic mounting, the drive mechanism should exert as little force as possible in the directions perpendicular to the translation direction. The cable drive mechanism satisfies this requirement. Cable drive is also suitable in this application because of the low load and low mass nature of the carriage and optics module. 
     The cable is driven by a pair of pulleys, one of which is the drive pulley and the other an idler. The pulleys have 90-degree V-grooves for holding the cable at its desired location. 
     The drive pulley for the cable is attached to the coaxial with a circular flywheel. The flywheel is driven by a stepping motor through friction drive. On the shaft of the stepping motor, a polyurethane tire is mounted for driving the flywheel through friction. 
     In order to maintain desired speed uniformity, to better than 0.25% error for motor once-around, the tire needs to be ground on the motor after it is mounted on the motor shaft. 
     A nylon coated steel cable is used. The cable needs to be strong (i.e., high Young&#39;s modulus) so that the spring constant of the cable in the longitudinal direction is high. For durability of the cable, it needs to be flexible enough to be used with the pulleys. 
     For long term performance stability of the mechanism, a cable tensioner is necessary. In this design, the cable tensioner is a compression spring. 
     Mass of the optics module and the carriage, along with the spring constants of the cable and cable tensioner spring, determine the resonant frequency of the translation module. Since it is desirable to increase the resonant frequency, reduced total mass that is attached to the cable is a design consideration. 
     There is a need for a translation system which overcomes the problems and satisfies the needs discussed before. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a translation system which satisfies the needs and overcomes the problems of known systems. 
     According to a feature of the present invention, there is provided a translation system comprising: a linear support having first and second opposite ends; a carriage slid ably mounted on said support for movement in reciprocal linear directions between said first and second ends of said support; a rotary drive rotatable in opposite rotary directions located at one end of said support; a rotatable member mounted at the other end of said support; and a multiple cable assembly attached to said carriage and extending around said rotary drive and said rotatable member moving said carriage in said reciprocal linear directions as a function of rotation of said rotary drive in said opposite rotary directions. 
     ADVANTAGEOUS EFFECT OF THE INVENTION 
     The invention has the following advantages. 
     1. Higher rigidity over single drive cable systems. 
     2. Ease in tracking over metal belt system, ease of alignment, assembly and adjustment over lead screw systems. 
     3. Overall system cost can be substantially lower that those for a lead screw or a linear motor system with equivalent performance. 
     4. The spring stiffness of the drive system is increased approximately by a factor equal to the number of cables used. Independently driven and tensioned cables are easy to align, assemble and adjust. 
     5. Multiple cable driven system significantly reduces system sensitivity to external noise disturbance, when compared with a single cable drive system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic elevational view of a laser imaging apparatus including the present invention. 
     FIG. 2 is a perspective view of an exemplary film exposure assembly incorporating the present invention. 
     FIG. 3 is an end view of the film exposure assembly shown in FIG.  2 . 
     FIG. 4 is a perspective view of an embodiment of the present invention. 
     FIG. 5 is a detailed perspective views of the embodiment of FIG.  4 . 
     FIG. 6 is a cut-out view of the detailed perspective view of the embodiment of FIG.  4 . 
     FIG. 7 is a diagrammatic view of the embodiment of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is an elevational diagram illustrating an exemplary embodiment of a laser imaging system  30  suitable for use in the medical imaging industry including optical scanning assembly translation system in accordance with the present invention. The imaging system  30  includes a film supply mechanism  32 , a film exposure assembly  34 , a film processing station  36 , a film receiving area  38 , and a film transport system  40 . The film supply mechanism  32 , film exposure assembly  34 , film processing station  36 , and film transport system  40  are all located within an imaging system housing  42 . 
     Photosensitive film is stored within the film supply mechanism  32 . The film transport system  40  allows the photosensitive film to be moved between the film exposure assembly  34 , film processing station  36 , and the film receiving area  38 . The film transport system  40  may include a roller system (not shown) to aid in transporting the film along a film transport path, indicated by dashed line  44 . The direction of film transport along film transport path  44  is indicated by arrows  46 . In particular, the film supply mechanism  32  includes a mechanism for feeding a piece of film along film transport path  44  into the film exposure assembly  34  for exposing the desired image on the photosensitive film using a laser or optical scanner assembly. After exposure of the desired image on the photosensitive film, the photosensitive film is moved along the film transport path  44  to the film processing station  36 . The film processing station  36  develops the image on the photosensitive film. After film development, the photosensitive film is transported to the film receiving area  38 . 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     FIG. 2 shows a top perspective view of the film exposure assembly  34  including a mechanism for positioning a photosensitive film into a scanned position in accordance with the present invention. The film exposure assembly  34  has an internal-drum type configuration. The film exposure assembly  34  includes a laser or optical scanner assembly  50  mechanically coupled to a linear translation system  52 , mounted within drum frame  54  for exposure of the film. The drum frame  54  includes a curved film platen  55 , which can be defined as the internal drum surface. The center of curvature of the curved film platen  55 , which is coincident with the drum longitudinal axis  56  is indicated by a dashed line. During a scanning process, the optics translation system  52  operates to move the optical scanner assembly  50  along the longitudinal axis  56  (in a direction generally perpendicular to the scanning direction), indicated by directional arrow  58 , and after scanning, returns the optical scanner assembly  50  to a start position, along the longitudinal axis  56 , indicated by directional arrow  60 . 
     Drum frame  54  is constructed of metal, and includes a first end  62 , a second end  64 , a first side  66 , a second side  68 , a bottom  70 , and a top  72 . Film platen  55  is positioned within the drum frame  54 . Film platen  55  provides a cylindrical or partially cylindrically-shaped scanning surface. 
     The linear translation system  52  extends along the top  72  for positioning the optical scanner assembly  50  along the center of curvature (of a piece of film in scanning position on the film platen), indicated as longitudinal axis  56 . In particular, the linear translation system  52  is positioned between the first end  62  and the second end  64 . 
     Referring to FIG. 3, an end elevational view of the film exposure assembly  34  is shown, having a portion of the drum frame  54  removed for clarity. Laser or optical scanner assembly  50  is shown mechanically coupled to the linear translation system  52 , positioned along the center of curvature. 
     A piece of photosensitive film  76  is shown positioned on the film platen  55 . During exposure of the photosensitive film  76 , the photosensitive film  76  is held against the film platen  55  in a scanning position. In a scanning position the photosensitive film  76  assumes the shape of the curved film platen  55 , which has a cylindrical, partial cylindrical, or drum shape. The photosensitive film  76  is positioned in a scanning position (i.e., aligned and centered) using the film positioning mechanism as described in U.S. Pat. No. 5,956,071. 
     In the scanning position, the photosensitive film  76  is aligned (skew removed), centered and held against the film platen  55 . The optical scanner assembly  50  scans a laser beam representative of an image to be exposed on the film, across the film scanning surface in an image-wise pattern. In particular, the scanning laser beam (indicated at  78 ) emanates radially from the center of curvature of the film platen  55  and film  76 , which is coincident with longitudinal axis  56 . The optical scanner assembly  50  scans the laser beam containing image data representative of the image to be exposed in raster lines by rotating about the longitudinal axis  56  of the cylinder drum (indicated by directional arrow  80 ). As the optical scanner assembly  50  scans the image and raster lines in an image-wise pattern across the photosensitive film  76  located on the internal drum surface  55 , the linear translation system  52  moves the optical scanner assembly  50  along longitudinal axis  56  to expose a full image on the photosensitive film. The linear translation system  52  moves the optical scanner assembly  50  along the longitudinal axis  56  in a direction which is generally perpendicular to the scanning direction of laser beam  78 . Since the linear translation system  52  moves the optical scanner assembly  50  during each scan line, the resulting scan lines may not be perpendicular, but are “generally” perpendicular to the direction of movement of the linear translation system. 
     In one exemplary embodiment, the film exposure area on the internal drum surface is 17 inches by 14 inches, suitable for exposure of a 17 inch by 14 inch piece of photosensitive film. In the exemplary embodiment disclosed herein, the film is exposed in a vertical direction. In particular, since the film is fed into the exposure module in the 14 inch direction and subsequently scanned in the 17 inch direction, the scanned raster lines appear in the vertical direction. The laser beam is scanned 180° (or greater than 180°) across the internal drum surface, for exposure of 17 inches across the photosensitive film. The linear translation system moves the optical scanner assembly along the longitudinal axis located at the center of curvature of the internal drum surface for a distance of 14 inches, for full exposure of a desired image/images on the photosensitive film. 
     The photosensitive film can be a photosensitive film which is sensitive to laser beam light. The film can be a light sensitive photothermographic film having a polymer or paper base coated with an emulsion of dry silver or other heat sensitive material. 
     Referring to FIGS. 4 and 5; a perspective view of one exemplary embodiment of a linear translation system for use in a laser imaging system in accordance with the present invention is shown, removed from the drum frame  54 . The linear translation system  52  is uniquely designed to minimize velocity variation, allowing continuous scanning or continuous step scanning of an image during a laser scanning process. 
     The linear translation system  52  includes a base member  104 , a carriage mechanism  106 , and a rotary to linear motion mechanism or drive mechanism  108 . The base member  104  is mechanically coupled to and held stationary relative to the drum frame, The carriage mechanism  106  is carried by the base member  104 . The carriage mechanism  106  is coupled to (and carries) the optical scanner assembly or laser imaging assembly. The rotary to linear motion mechanism  108  converts rotary motion to linear motion for moving the carriage mechanism  106  along the base member  104  during the scanning process. 
     Base member  104  includes a pair of longitudinally extending guide rails, indicated as first guide rail  110 , and second guide rail  112 , which are positioned parallel to each other. In one exemplary embodiment, the guide rails  110 ,  112  are polished stainless steel guide rails. Further, the guide rails may include a lubricating coating thereon. In one preferred embodiment, the guide rails  110 ,  112  are coated with polytetrafluoroethylene (PTFE) (commercially available under the tradename TEFLON). Base member  104  further includes a first base bracket  114  and second base bracket  116 . First guide rail  110  and second guide rail  112  extend longitudinally between first base bracket  114  and second base bracket  116 . In particular, first guide rail  110  includes a first end  118  and a second end  120  and second guide rail  112  includes a first end  122  and a second end  124 . The first guide rail  110 , first end  118  is fixedly coupled to first base bracket  114  (e.g., by tapping and screwing into the first base bracket indicated at  126 ), and second end  120  is fixedly coupled to the second base bracket  116  in a similar manner. Similarly, the second guide rail  112 , first end  122 , is fixedly coupled to the first base bracket  114  (indicated at  128 ) and the second end  124  is fixedly coupled to the second base bracket  116  (indicated at  130 ). 
     First support pin  86  and second support pin  88  extend from first base bracket  114 , and third support pin  90  and fourth support pin  92  extend from second base bracket  116 . Further, first base bracket  114  includes recessed portion  130  which holds a portion of drive mechanism  108 . 
     Second base bracket  116  is generally L-shaped, having a first leg  132 , and second leg  134 . The first guide rail  110  and the second guide rail  112  are fixedly coupled to the first leg  132 . First leg  132  and second leg  134  are utilized as a support bracket for supporting and coupling other components of the rotary to linear motion mechanism  108 , which will be described in detail later herein. 
     The carriage mechanism  106  is carried by the base member  104 . In particular, the carriage mechanism  106  is coupled to the guide rails. Carriage mechanism  106  is slid ably coupled to first guide rail  110 , indicated at  136 , and to second guide rail  112 , indicated at  138 . Carriage mechanism  106  is slid ably coupled to first guide rail  110  and second guide rail  112  at three locations using a unique kinematic design. Carriage mechanism  106  may also include a first retaining bracket  140  to maintain the carriage mechanism  106  on the guide rail  110 . 
     Carriage mechanism  106  includes carriage  152 , and cable system  154 . Carriage  152  includes a first termination bracket  156  and a second termination bracket  158 . Multi-cable system  154  includes four cables  160 A- 160 D cable terminators  162 A- 162 D,  164 A- 164 D and cable tensioners  166 A- 166 D, as depicted in cut-out view in FIG.  6 . In one exemplary embodiment, cables  160 A- 160 D are a stranded steel cable. Each cable  160 A- 160 D respectively has a first end  168 A- 168 D which passes through first cable termination bracket  156  and terminates at cable terminator  162 A- 162 D and has a second end  170 A- 170 D which passes through second termination bracket  158  and terminates at cable terminator  164 A- 164 D. Further, each cable tensioner  166 A- 166 D (e.g., a spring mechanism) is positioned between first cable terminator  162 A- 162 D and first termination bracket  156  to aid in maintaining independent tension in each cable  160 A- 160 D. Cable tension adjustments are made by turning screw pairs  172 A- 172 D, which push the springs through tensioning plates  174 A- 174 D. Cables  160 A- 160 D loop around grooved rotary member  210 . 
     By using multiple drive cables, the optics translation system achieves a higher level of rigidity. For the drive system, the effective spring constant in the longitudinal direction is multiplied by the number of drive cables. Consequently, the translation system has a higher resonance frequency in the longitudinal direction, which is the main source of vibration noise for laser scanning applications. In addition, the increase in system stiffness also reduces susceptibility of the system to external disturbance to the optics translation system. Such disturbance may be introduced by impact or vibration due to components internal to the imaging system, or due to external motion from the environment. 
     The main reason for a separate tensioning mechanism for each drive cable is to eliminate the effects of drive cable length variation. By adjusting tension of each drive cable separately, all drive cables can be adjusted to have the same desired level of tension. With precise control of cable lengths, independent tensioning plates can be combined with a slid ably adjusted termination bracket  156 . 
     Referring to FIG. 7 (and also FIG. 4) an end elevational view illustrating the rotary to linear motion mechanism  108  (hereinafter referred to as drive mechanism  108 ) is shown. Drive mechanism  108  transforms rotary motion into the linear motion required by movement of the carriage system on the guide rails. Drive mechanism  108  includes a motor mechanism  193 , the flywheel mechanism  194 , and a capstan  195 . Motor mechanism  193  includes motor  196 , motor mount  197 , compression mechanism  198 , and extension mechanism  200 . Flywheel mechanism  194  includes flywheel  202  and cable drive pulley  204 . 
     Motor  196  includes a rotating shaft which extends through the second base bracket  116 , second leg  134 . Capstan mechanism  195  is coupled to the motor shaft. Compression mechanism  198  is coupled between motor  196  and motor mount  197 . Extension mechanism  200  is coupled between motor mount  197  and second leg  134 . Flywheel  202  includes a shaft  206  extending therefrom which is fixedly coupled to second leg  134 , indicated at bracket extension  207 . Drive pulley  204  extends from a bottom surface of flywheel  202  and may be an integral part of flywheel  202 . 
     Motor  196  is pivotally mounted with respect to second base bracket  116 , second leg  134 . The flywheel  202  is driven by motor  196  through the capstan  195 . Capstan  195 , mounted on the stepping motor shaft has a polyurethane cover which contacts the edge of the flywheel  202 . The outside diameter of the capstan  195  is concentric to the motor  196 . In particular, after the capstan mechanism  195  is mounted to the motor  196  shaft, the polyurethane cover is finish ground to remove any eccentricities due to the motor shaft and to minimize the runout of the capstan. The motor  196  and capstan mechanism  195  are then attached to the pivotal motor mount. The pivotal motor mount  197  is held down on the bracket second leg  134  through the compression mechanism  198  to minimize motor wobble. Further, nip pressure is created between the capstan mechanism  195  and the flywheel  202  by the extension mechanism  200 . 
     The capstan mechanism  195  provides a gear reduction allowing the use of a higher speed motor and can include an aluminum core with a polyurethane coating. The polyurethane coating provides a compliant coating which grips the flywheel  202  as the motor  196  drives the flywheel  202  through the capstan  195 . 
     Flywheel  202  adds inertia to the system to dampen out any artifacts that may be caused by the stepping motor  196 . In one exemplary embodiment, flywheel  202  is made of a precision machined brass. 
     Drive pulley  204  is integrated with flywheel  202  and positioned along the flywheel axis of rotation. Drive pulley  204 , in turn, has a shaft  208  extending therefrom which is fixedly coupled to second base bracket  116  indicated at bracket extension  209 . Drive pulley  204  has V-grooves for retaining cables  160 A- 160 D. Referring also to FIG. 4, an idler pulley  210  is positioned at the opposite end of the linear translation system  52 , coupled to first base bracket  114 . 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 PARTS LIST 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 30 
                 laser imaging system 
               
               
                 32 
                 film supply mechanism 
               
               
                 34 
                 film exposure assembly 
               
               
                 36 
                 film processing station 
               
               
                 38 
                 film receiving area 
               
               
                 40 
                 film transport system 
               
               
                 42 
                 imaging system housing 
               
               
                 44,46 
                 film transport path 
               
               
                 50 
                 optical scanner assembly 
               
               
                 52 
                 linear translation system 
               
               
                 54 
                 drum frame 
               
               
                 55 
                 curved film platen 
               
               
                 56 
                 drum longitudinal axis 
               
               
                 58 
                 scanning direction 
               
               
                 60 
                 directional arrow 
               
               
                 62 
                 first end 
               
               
                 64 
                 second end 
               
               
                 66 
                 first side 
               
               
                 68 
                 second side 
               
               
                 70 
                 bottom 
               
               
                 72 
                 top 
               
               
                 76 
                 photosensitive film 
               
               
                 78 
                 scanning laser beam 
               
               
                 80 
                 directional arrow 
               
               
                 86 
                 first support pin 
               
               
                 88 
                 second support pin 
               
               
                 90 
                 third support pin 
               
               
                 92 
                 fourth support pin 
               
               
                 104 
                 base member 
               
               
                 106 
                 carriage mechanism 
               
               
                 108 
                 drive mechanism 
               
               
                 110 
                 first guide rail 
               
               
                 112 
                 second guide rail 
               
               
                 114 
                 first base bracket 
               
               
                 116 
                 second base bracket 
               
               
                 118 
                 first end for first guide rail 
               
               
                 120 
                 second end for second guide rail 
               
               
                 122 
                 first end for second guide rail 
               
               
                 124 
                 second end for second guide rail 
               
               
                 126 
                 First base 
               
               
                 128 
                 first end (122) fixedly coupled to first base bracket (114) 
               
               
                 130 
                 second end (124) fixedly coupled to second base bracket 
               
               
                   
                 (116) 
               
               
                 132 
                 first leg 
               
               
                 134 
                 second leg 
               
               
                 136 
                 carriage mechanism slidably coupled to first guide rail 
               
               
                   
                 (110) 
               
               
                 138 
                 carriage mechanism slidably coupled to second guide rail 
               
               
                   
                 (112) 
               
               
                 140 
                 first retaining bracket 
               
               
                 152 
                 carriage 
               
               
                 154 
                 multi-cable system 
               
               
                 156 
                 first termination bracket 
               
               
                 158 
                 second termination bracket 
               
               
                 160A-160D 
                 stranded steel cables 
               
               
                 162 
                 cable terminators 
               
               
                 164 
                 cable terminators 
               
               
                 166 
                 cable tensioners 
               
               
                 168 
                 first end 
               
               
                 170 
                 second end 
               
               
                 172A-172D 
                 screw pairs 
               
               
                 174A-174D 
                 tensioning plates 
               
               
                 193 
                 motor mechanism 
               
               
                 194 
                 flywheel mechanism 
               
               
                 195 
                 capstan mechanism 
               
               
                 196 
                 motor 
               
               
                 197 
                 motor mount 
               
               
                 198 
                 compression mechanism 
               
               
                 200 
                 extension mechanism 
               
               
                 202 
                 flywheel 
               
               
                 204 
                 drive pulley 
               
               
                 206 
                 shaft 
               
               
                 207 
                 bracket extension 
               
               
                 208 
                 shaft 
               
               
                 209 
                 bracket extension 
               
               
                 210 
                 idler pulley