1、SMPTE RP*73 92 m 8357403 0000544 309 m SMPTE RECOMMENDED PRACTICE 8-mm Type R (Regular 8) Sprocket Design RP 73-1 992 Revision of RP 73-1977 1 Scope This practice provide dimensions and specifications for the design of sprockets used with 8-mm type R (regular 8) motion-picture raw stock or processed
2、 film. 2 Dimensions and specifications 2.1 The teeth shall be equally spaced at an index angle of 360/N0 where N is the number of teeth. A suitable tolerance for the index angle is I 1 minute of arc for sprockets having 8 to 24 teeth and I 30 seconds for arc for sprockets having 25 to 84 teeth. 2.2
3、The root diameter is computed from the equation: P D= NX jj -T where N is the num-er of teeth, P is the sprocke pitch, and T is the film thickness. The different root diameters in tables I a and 1 b were derived using a value for T of 0.15 mm (0.006 in). If optimum working conditions are desired wit
4、h film materials of different thicknesses, the root diameter values in tables 1 a and 1 b should be recomputed. 2.3 Figure 1 shows that either the entering or leaving film path may fall within the limits speci- fied by radii Ri and R2. If the film path is convex with respect to the sprocket surface
5、(curvature away from the sprocket surface), a minimum value of 3.962 mm (0.1560 in) for RI is recom- mended. This is an arbitrary choice, but seems appropriate for 8-mm equipment. The shape of the film path as the film leaves the root of the sprocket is determined by film stiffness, curl, Page 1 of
6、8 pages set, and tension as well as by the shape and location of rollers or guides. For the specified tooth shape, the film will be allowed to back-slip over the root circle a maximum distance of 0.046 mm (0.0018 in) for each tooth, measured at the pitch line (film thickness assumed to be 0.15 mm 0.
7、006 in), by the time the contact point between film and tooth has reached the assumed maximum work- ing height of 0.66 mm (0.026 in), measured radially from the root circle. Figure 1 - Sprocket 2.4 The drive sprocket is most sensitive to tooth shape because the tooth action may take place over the e
8、ntire working height and is, therefore, used to derive the desired shape. For the usual drive sprocket, the pitch is greater than the film pitch which causes the film to slip backward in relation fo the sprocket travel. The direction of the friction force between the film and the root surface is suc
9、h as to assist the feed or driving action. Copyright Q 1992 by the SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 595 W. Hartsdale Ave., White Plains, NY 10607 (91 4) 761 -1 1 O0 Approved November 6,1992 _ - SMPTE RP*73 92 = 83571101 00005115 2115 W RP 73-1992 Table la - Sprocket dimensions in m
10、illimeters - - N RDD RDC 14.363 12 13 14 15 16 17 18 19 20 21 22 23 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 60 64 68 72 76 80 14.401 15.614 16.827 I 8.039 19.252 20.465 21.678 22.890 24.103 25.31 6 26.529 27.741 28.954 31.380 33.805 36.231 38.656 41 .O82 43.507 45.933 48.358 50.784 53.209
11、 55.635 58.601 60.486 62.91 2 65.337 67.763 72.61 4 77.465 82.31 6 87.167 92.01 8 96.869 15.573 16.782 17.992 19.201 20.41 1 21.620 22.830 24.040 25.249 26.459 27.668 28.878 31 -297 33.71 6 36.135 38.554 40.974 43.393 45.81 2 48.231 50.650 53.069 55.489 57.908 60.327 62.746 65.165 67.584 72.423 77.2
12、61 82.099 86.938 91.776 96.61 4 RDH K B R2 XT 1.457 0.034 1 1.837 0.2534 14.287 15.490 16.693 17.896 19.099 20.303 21.506 22.709 23.91 2 25.115 26.31 9 27.522 28.725 31.131 33.538 35.944 38.351 40.757 43.164 45.570 47.976 50.383 52.789 55.196 57.602 60.009 62.41 5 64.82 1 67.228 72.041 76.854 81.666
13、 86.479 91.292 96.105 1.510 1.560 1.608 1.655 1.700 1.744 1.787 1.828 1.869 1 .go9 1.947 1.986 2.060 2.132 2.202 2.270 2.336 2.401 2.464 2.526 2.588 2,648 2.707 2.766 2.823 2.880 2.936 2.991 3.1 O0 3.206 3.31 1 3.413 3.514 3.612 0.044 0.054 O. 064 O. 073 0.082 0.092 o. 1 O0 o. 1 o9 0.118 O. 126 O. 1
14、34 O. 142 O. 158 O. 174 0.190 0.204 0.21 9 0.234 0.248 0.262 0.276 0.290 0.303 0.31 6 0.330 0.343 0.356 0.368 0.394 0.41 8 0.443 0.467 0.490 0.51 3 12.576 13.31 7 14.065 14.81 6 15.573 16.328 17.097 1 7.853 18.625 19.387 20.160 20.941 22.497 24.065 25.634 27.224 28.81 4 30.41 3 32.032 33.652 35.285
15、36.929 38.582 40.263 41.928 43.61 7 45.307 47.01 9 50.461 53.962 57.51 7 61 .O89 64.739 68.430 0.2477 0.2428 0.2385 0.2347 0.2313 0.2283 0.2255 0.2231 0.2208 0.21 88 0.21 69 0.2151 0.2120 0.2093 0.2070 0.2049 0.2031 0.201 5 0.2000 O. 1987 O. 1975 O. 1964 O. 1954 O. 1944 O. 1935 O. 1928 0.1921 0.1914
16、 O. 1902 0.1891 0.1881 O. 1873 O. 1865 O. 1858 84 1 01.720 1 01.453 100.91 8 3.709 0.536 72.157 O. 1852 NOTES N: Number of teeth RDD: RDC: RDH: K: B: RP: XT: RI: Tooth working height: 0.660 Maximum pitch difference: 0.046 Film thickness: 0.1 52 Other thickness: root diameter = N*Ditch/n - thickness
17、Root diameter +0.03 -0.00 of drive sprocket of 3.81 O pitch Root diameter +0.03 -0.00 of combination sprocket of 3.800 pitch Root diameter +O.OO -0.03 of holdback sprocket of 3.780 pitch Circular arc radius for tooth shape, +O.OO -0.05 Radial distance of arc center inside root circle, +0.013 -0.000
18、Minimum radius of film path concave to sprocket Offset of tooth at working height Minimum film path radius convex to sprocket, 3.962 Page 2 of 8 pages - SMPTE RP*73 92 8357403 000054b 383 W RP 73-1 992 Table 1 b - Sprocket dimensions in inches N RDD RDC RDH K B R2 XT 12 13 14 15 16 17 18 19 20 21 22
19、 23 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 60 64 68 72 76 80 0.5670 0.61 47 0.6625 0.7102 0.7580 0.8057 0.8535 0.9012 0.9489 0.9967 1 .O444 1.0922 1.1399 1.2354 1.3309 1.4264 1.521 9 1.61 74 1.71 29 1.8084 1.9039 1.9994 2.0948 2.1904 2.2859 2.3813 2.4769 2.5723 2.6678 2.8588 3.0498 3.240
20、8 3.431 8 3.6228 3.81 37 0.5655 0.6131 0.6607 0.7083 0.7559 0.8036 0.8512 0.8988 0.9465 0.9941 1 .O41 7 1 .O893 1.1369 1.2322 1.3274 1.4226 1.51 79 1.61 31 1.7084 1.8036 1.8989 1.9941 2.0893 2.1846 2.2798 2.3751 2.4703 2.5656 2.6608 2.8513 3.041 8 3.2322 3.4228 3.61 32 3.8037 0.5625 0.6098 0.6572 0.
21、7046 0.751 9 0.7993 0.8467 0.8941 0.941 4 0.9888 1 .O362 1 .O835 1.1309 1.2256 1.3204 1.41 51 1.5099 1.6046 1.6994 1.7941 1.8888 1.9836 2.0783 2.1731 2.2678 2.3626 2.4573 2.5520 2.6468 2.8363 3.0257 3.21 52 3.4047 3.5942 3.7837 0.0574 0.0594 0.0614 0.0633 0.0652 0.0669 0.0687 0.0704 0.0720 0.0736 0.
22、0752 0.0767 0.0782 0.081 1 0.0839 0.0867 0.0894 0.0920 0.0945 0.0970 0.0994 0.1019 0.1043 0.1 066 0.1 089 0.1111 0.1 134 0.1 156 0.1178 o. 1220 O. 1 262 O. 1304 0.1344 0.1 383 0.1 422 0.0013 0.0017 0.0021 0.0025 0.0029 0.0032 0.0036 0.0039 0.0043 0.0046 0.0050 0.0053 0.0056 0.0062 0.0069 0.0075 0.00
23、80 0.0086 0.0092 0.0098 0.01 03 0.01 o9 0.01 14 0.01 19 0.01 24 0.01 30 0.01 35 0.01 40 0.01 45 0.01 55 0.01 65 0.01 74 0.0184 0.01 93 0.0202 0.4660 0.4951 0.5243 0.5537 0.5833 0.6131 0.6428 0.6731 0.7029 0.7333 0.7633 0.7937 0.8244 0.8857 0.9474 1.0092 1.071 8 1.1344 1.1974 1.261 1 1.3249 1.3892 1.
24、4539 1.5190 1.5852 1.6507 1.7172 1.7837 1.851 1 1.9867 2.1245 2.2644 2.4051 2.5488 2.6941 0.00998 0.00975 0.00956 0.00939 0.00924 0,0091 1 0.00899 0.00888 0.00878 0.00869 0.00861 0.00854 0.00847 0.00835 0.00824 0.00815 0.00807 0.00800 0.00793 0.00787 0.00782 0.00778 0.00773 0.00769 0.00765 0.00762 0
25、.00759 0.00756 0.00754 0.00749 0.00744 0.00741 0.00737 0.00734 0.00731 84 4.0047 3.9942 3.9731 0.1460 0.021 1 2.8408 0.00729 NOTES N: Number of teeth RDD: RDC: RDH: K: B: Re: XT: RI: Tooth working height: 0.0260 Maximum pitch difference: 0.0018 Film thickness: 0.0060 Other thickness: root diameter =
26、 N*pitch/sc - thickness Root diameter tO.001 -0.000 of drive sprocket of 0.1 500 pitch Root diameter tO.001 -0.000 of combination sprocket of 0.1496 pitch Root diameter tO.000 -0.001 of holdback sprocket of 0.1488 pitch Circular arc radius for tooth shape, tO.000 -0.002 Radial distance or arc center
27、 inside roof circle, t0.0005 -0.0000 Minimum radius of film path concave to sprocket Offset of tooth at working height Minimum film path radius convex to sprocket, 0.1560 Page 3 of 8 pages SMPTE RP*73 72 8357403 0000547 018 m RP 73-1 992 2.4.1 Of the total 0.046-mm (0.0018-in) accom- modation provid
28、ed at each tooth for film slip- page, approximately 0.013 mm (0.0005 in) is allocated to the combined tolerance of perfora- tion pitch and sprocket tooth pitch (shorter- than-average perforation pitch combined with longer-than-average tooth pitch). An additional 0.010 mm (0.0004 in) is allocated for
29、 distortion of the perforation edge under light load (less than 0.56 N 2 oz-force between the perforation edge and the tooth for acetate film of 0.15 mm 0.006 in thickness). The remaining 0.023 mm (0.0009 in) approximates 0.6% film shrinkage. It should be noted that another combination of greater lo
30、ad and lower shrinkage could fall within the same allowable maximum of 0.033 mm (0.0013 in). The user is cautioned against high loading because of possible destructive film fatigue and wear, film distortion away from the base circle, and malfunction. The selected values of Ri, working height and max
31、imum pitch difference, in turn, determine the values of XT which have been computed and tabulated. 2.4.2 For a concave film path with respect to the sprocket surface (curvature toward the sprocket radius center), the limiting radius, R2 has been computed for the same XT and the same accom- modation
32、of 0.046 mm (0.0018 in), assuming a parabolic schedule (displacement function pro- portionate to the square of time) of reduction versus time (see reference 1). These values of R2 are set forth in tables la and Ib. For those existing film paths from drive sprockets corre- sponding to larger values o
33、f Ri and R2, including a straight tangent path, the accommodation of 0.046 mm (0.0018 in) for film slippage takes place in less than 0.66 mm (0.026 in) of the working height (or more accommodation results at the same height). Conversely, the slowest accommodation corresponds to the exiting path defi
34、ned by the minimum values of RP. Therefore, the R2 value is recommended where maximum uniformity of motion is desired. 2.5 The pitch of the usual holdback sprocket should be equal to or less than the pitch of the film. The shortest film pitch is assumed to be 3.780 mm (0.1488 in) corresponding to 0.
35、8% shrinkage of long-pitch film (3.810 mm 0.1500 in). (This value is chosen rather than the 0.6% used for the tooth shape to avoid inadvertent interference at entering teeth.) The user may again exercise control by correct choice of the root diameter if a change is warranted. The fric- tion between
36、the film and the root surface, as well as against guides, assists in film holdback. The tooth shape for a holdback sprocket has little control over the pitch differential accommodation, as the load shifts rather abruptly from the disengaging restraining tooth to the root of the following tooth. The
37、tooth shape specified will ensure clearance at the entering position. If a holdback sprocket is to provide the best possible uniformity of motion, the design must be developed with care (see reference 1). 2.6 The pitch of combination sprockets, 3.800 mm (0.1496 in), should correspond to the pitch of
38、 film with 0.3% shrinkage. This value is closer to the feed sprocket pitch than to the holdback sprocket pitch to prevent the film from riding high on the teeth or being damaged by guides at the entering path when used for driving action with the sprocket pitch shorter than the film pitch. Entering
39、guides may be needed for good hold- back action when the sprocket pitch is longer than the film pitch. 2.7 The desired tooth shape can be generated by a hob corresponding to the basic rack speci- fied by KH and BH in table 2 and figure 4. If the first hob covers the range of N from 12 to 24 inclusiv
40、ely and the second hob 25 to 84 inclu- sively, no deviations from the ideal tooth shape greater than 0.005 mm (0.0002 in) will occur. 2.8 The tooth width at the base, dimension W, allows ample material for rounding off the tip while preserving the 0.66 mm (0.026 in) or more of working height. The va
41、lue chosen does not limit the angle of wrap on the sprocket as a wider tooth would. If the wrap length is defined as one-half the sum of the number of pitch lengths in the arc of engagement, E, and the number of pitch lengths is the arc of contact, C (figure I), then the wrap length may be as high a
42、s 13-1/2 pitch lengths without producing interference at the entering teeth of a drive sprocket if the film shrinkage does not exceed 0.8%. 2.9 The lateral profile (see figures 2a and 2b) has been derived on the assumption that the film is channel-guided at or near the sprocket. This guiding may be
43、provided by fixed guides, by the flanges of an adjacent roller at the entering Page 4 of 8 pages SMPTE RP*73 92 357403 000054 T54 8.05 +O05 -0 10.517 +0.002 -0- - 1% :=e I%- 290 to -0.03 10.114 tu -0.0211 (O.OS3 fO.OOli 1.24 0.03 I o 048 iO.00l) LOCATION OF FILM REFERENCE EDGE 0.10 20.03 I 0.004 *O.
44、Wi I NOTE - Dimensions in millimeters, inches in parentheses. Figure 2a - Lateral profile for single-width equipment position or, preferably, by flanges on the sprocket itself. When a fixed guide is needed at the perforated edge and the film urged against the guide by a spring or other means, the la
45、teral dimension, LI of the tooth can be increased somewhat. If the sprocket teeth are to perform the function of side guiding, then their lateral dimension, LI may be increased to 1.803 mm to mm -0.013 mm (0.071 O in +O in -0.0005 in) with special consideration given to tooth alignment, smoothness o
46、f the sides, and rounding or taper- ing at the tips. When the sprocket teeth have been increased in width to perform the function of lateral guiding, the R3 value for the radius of the corners of the sprocket tooth should be increased to comply with the radius of the perforation fillet, 0.25 mm t0.0
47、5 mm -O mm (0.010 in +0.002 in -O in). UP 73-1 992 14.73 +O -003 10.134 +0.002 -0 13.03 +0.13 -0 2.90 +O -0.33 10.114 to -0 O211 16.00 C0.03 -0 10630 +O.OOZ -01 P.36 10.03 10.093 20.001 I 1.24 20.03 1O.OkB tO.OOl LOCATION Of FILM REfERENCE EDGE *LAND OPTIONAL NOTE - Dimensions in millimeters, inche.
48、s in parentheses. Figure 2b - Lateral profile for double-width equipment 2.10 in order for the film guides to function prop- erly, the sprocket eccentricity as mounted in operation shall not exceed 0.025 mm (0.0010 in), and the lateral weave or wobble measured at the root circle shall not exceed t0.
49、025 mm (0.0010 in). Less eccentricity may be required for a special application such as a sound printer sprocket. 2.11 In some cases of large-scale layouts or critical comparisons, it may be more convenient to work with values of XT than with values of B. As shown in figure 3, XT is the distance mea- sured perpendicular to the radial line intersect- ing the root of the tooth from a point on the tooth which is 0.66 mm (0.026 in) above the root circle. Further information on sprocket design is con- tained in reference 2. Page 5 of 8 pages - SMPT
