SMPTE RP 55-1997 8-mm Type S Sprocket Design《8 mm S型输片齿轮设计》.pdf

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1、STD.SMPTE RP 55-ENGL L777 8357403 0002880 777 SMPTE RECOMMENDED PRACTICE RP 55-1997 Revision of RP 55-1993 8-mm Type S Sprocket Design I Scope This practice provides the dimensions and specifica- tions for the design and maximum pitch of sprockets used with 8-mm type S motion-picture raw stock or pr

2、ocessed film. 2 Dimensions and specifications 2.1 The teeth shall be equally spaced at an index angle of 3601N degrees where N is the number of teeth. A suitable tolerance for the index angle is f 1 minute of arc for sprockets having 12 to 24 teeth and k 30 seconds of arc for sprockets having 25 to

3、84 teeth. 2.2 The root diameter is computed from the equation - P D= NX IT-T where P Is the sprocket pitch, N is the numberofteeth, and T is the film thickness. The different root diameters in tables 1A and I B were derived using a value for T of 0.006 in (O. 15 mm). If optimum working conditions ar

4、e desired with different thickness film materials, tables IA and 1 B should be recomputed. 2.3 The minimum value of RI has been chosen as O. 156 in (3.96 mm). 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

5、is determined by film stiffness, set, and tension as well as by the shape and location of rollers or guides. Page 1 of 7 pages For the specified tooth shape, the film has been allowed to slip back over the root circle a distance of 0.0018 in (0.046 mm), measured at the pitch line (film thickness ass

6、umed to be 0.006 in or 0.15 mm) by the time the contact point between film and tooth has reached the maximum assumed working height of 0.026 in (0.66 mm) (measured radially from the root circle). This analysis applies to the feed sprocket for which the sprocket pitch is generally greater than the fi

7、lm pitch and the film must slip in the direction opposite to the direction of motion. The direction of the friction force between the film and the root surface is such as to assist the feed or the driving action. Of the total 0.001 8-in (0.046-mm) accommodation provided at each tooth for film slippa

8、ge, approximately 0.0005 in (0.013 mm) is allocated to the combined tolerance of perforation pitch and sprocket tooth pitch (shorter- than-average perforation pitch combined with longer- than-average tooth pitch). An additional 0.0003 in (0.008 mm) is allocated for and corresponds approxi- mately to

9、 the distortion resulting from 2 oz (56.7 grams) of contact loading. The remaining 0.0010 in (0.025 mm) corresponds to 0.6% of film shrinkage. It should be noted that a combination of 4 oz (113.4 grams) of load and approximately 0.4% shrinkage with pitch tolerances is about equivalent. By this pro-

10、cedure, the values of XT are determined. 2.4 The minimum value of R2 has been com- puted for the same XT and the same accommo- dation of 0.0018 in (0.046 mm) assuming a parabolic schedule (displacement function pro- portional to the square of time) of reduction versus time (reference 2). These value

11、s of R2 are set forth in tables IA and IB. For exit film paths Copyright O 1997 by the SOCIETY OF MOTION PICTURE AND TELEVISION ENGINEERS 595 W Hartsdale Ave , White Plains. NY 10607 (914) 761-1100 Approved September 18,1997 STD-SMPTE RP 55-ENGL 3977 IPI 8357403 0002883 BO3 D RP 55-1 997 correspondi

12、ng to larger values of RI and R2, including a straight tangent path, the accommo- dation of 0.0018 in (0.046 mm) for film slippage takes place in less than 0.026 in (0.66 mm) of the working height (or more accommodation results at the same height). The accommodation takes place more slowly for the e

13、xit path defined by minimum values of R2; therefore, these are recommended where maximum uniformity of motion is desired. 2.5 The desired tooth shape can be generated by a hob corresponding to the basic rack speci- fied by KH and BH as tabulated (see table 2 and figure 4). If the first hob covers th

14、e range of N from 12 to 24, inclusively, and the second hob the range of N from 25 to 84, inclusively, no deviations in tooth shape greater than 0.00020 in (0.0051 mm) will occur. 2.6 The tooth width at the base, dimension W, allows ample material for rounding off the tip while preserving the 0.026

15、in (0.66 mm) or more of working height. The value 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 in the arc of con- tact, C (

16、figure l), then the wrap length may be as high as 9V4 pitch lengths without producing interference at the entering teeth of a drive sprocket if the film shrinkage does not exceed 0.8%. 2.7 The lateral profile has been derived on the assumption that the film is channel-guided at or near the sprocket.

17、 This guiding may be provided by fixed guides, by the flanges of an adjacent roller at the entering 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 lateral dimension L

18、of the tooth can be increased somewhat. If the sprocket teeth are to perform the function of side guiding, then their lateral width, L, may be increased to 0.0355 in + O in - 0.0005 in (0.902 mm + O mm - 0.013 mm) with special consideration given to tooth align- ment, smoothness of the sides. and ro

19、unding or tapering 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, nominally 0.005 in (0.13 mm). 2

20、.8 In order for the film guides to function prop- erly, the sprocket eccentricity as mounted in operation shall not exceed 0.0010 in (0.025 mm) and the lateral weave or wobble measured at the root circle shall not exceed k 0.0010 in (0.025 mm). Less eccentricity may be required for a special applica

21、tion such as a sound printer sprocket. 2.9 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 4, XT is the distance measured perpendicular to the radial line inter- secting the root of the tooth

22、from a point on the tooth which is 0.026 in (0.66 mm) above the root circle. Page 2 of 7 pages STD-SMPTE RP 55-ENGL 1997 D 8357401 O002882 74T W RP 55-1 997 Figure 1 - Sprocketlfilm relationship 0.318 tO.001 -0 0.028 0.001 (0.71 fO.03) 4 0.259 tO.002-7 1 (6.58 t0.05) 0.024 REF: (0.61 REF) W II 0.005

23、 f0.00 2, R4= (0.13 20.05) 0.006 MAX. MAX. OPTIONAL Figure 2 - Sprocket drum profile 0.017MIN. (0.043 MIN.) (0.61 f 0.03) w= 0.028 +0.002 -0 (0.71 i0.05 -O) R MAX. 3-(0.08) H = 0.028 t 0.004 - (0.71 t0.05 - (0.18) Figure 3 -Sprocket drum side profile Dimensions in inches; millimeters in parentheses.

24、 Page 3 of 7 pages STD.SMPTE RP 55-ENGL 1797 8357401 Il002883 b8b W RP 55-1 997 Table 1A - Sprocket dimensions, inch specifications 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 Root diameter, D DD DC 0.6307 0.6838 0.7369 0.7899 0.8430 0.896

25、1 0.9491 1.0022 1.0552 1.1083 1.1614 1.2144 1.2675 1.3736 1.4797 1.5859 1.6920 1.7981 1.9042 2.0104 2.1 165 2.2226 2.3287 2.4349 2.5410 2.6471 2.7532 2.8594 2.9655 3.1 777 3.3900 3.6022 3.8145 4.0267 4.2390 0.6288 0.6817 0.7346 0.7875 0.8404 0.8934 0.9463 ,9992 .O52 1 ,1050 ,1579 ,2108 .2637 ,3695 1

26、.4753 1.6869 1.7927 1.8985 2.0043 2.1 101 2.2159 2.3217 2.4275 2.5333 2.6392 2.7450 2.8508 2.9566 3.1682 3.3798 3.5914 3.8030 4.0146 4.2262 I ,581 I DH 0.6258 0.6784 0.731 1 0.7837 0.8364 0.8890 0.941 7 0.9943 1.0470 1.0996 1 .I 523 1.2049 1.2576 1.3629 1.4682 1.5735 1.6788 1.7840 1.8893 1.9946 2.09

27、99 2.2052 2.3105 2.4158 2.521 I 2.6264 2.731 7 2.8370 2.9423 3.1529 3.3635 3.5741 3.7847 3.9953 4.2059 - K B 0.0598 0.0620 0.0640 0.0659 0.0678 0.0696 0.0714 0.0731 0.0747 0.0764 0.0780 0.0795 0.081 1 0.0840 0.0869 0.0897 0.0924 0.0951 0.0977 0.1003 O. 1028 O. 1053 0.1077 0.1101 0.1124 0.1148 0.1171

28、 0.1 194 0.1216 0.1260 0.1303 0.1346 O. 1388 O. 1428 O. 1469 a4 4.451 2 4.4379 4.4165 O. 1509 N = Number of teeth. 0.0018 0.0022 0.0026 0.0030 0.0034 0.0041 0.0045 0.0049 0.0052 0.0056 0.0059 0.0062 0.0069 0.0075 0.0081 0.0087 0.0094 0.0099 0.0105 0.01 11 0.01 17 0.0122 0.0128 0.0133 0.0138 0.0144 0

29、.0149 0.0154 0.0165 0.0175 0.0185 0.0194 0.0204 0.0214 0.0038 R2 XT 0.4954 0.5267 0.5583 0.5900 0.6220 0.6540 0.6862 0.7185 0.7509 0.7835 0.8161 0.8488 0.8815 0.9474 .O1 36 .O802 .I471 ,2143 .28 19 ,3499 1.41 83 1.4870 1.5561 1.6256 1.6954 1.7656 1.8362 1.9072 1.9786 2.1226 2.2682 2.41 54 2.5644 2.7

30、1 50 2.8673 O. 00968 0.00947 0.00930 0.00914 0.00901 0.00888 0.00878 0.00868 0.00859 0.00851 0.00843 0.00837 0.00830 0.0081 9 0.00810 0.00801 0.00794 0.00787 0.00782 1 0.00776 0.00772 0.00767 0.00763 0.00760 0.00756 0.00753 0.00751 0.00748 0.00746 0.00741 0.00737 0.00734 0.00731 0.00728 0.00726 0.00

31、723 - . 0.0223 3.0214 DD = Root diameter, D + 0.001 - O of drive sprocket of 0.1667 pitch. DC = Root diameter, D + 0.001 - O of combination sprocket of 0.1662 pitch. DH = Root diameter, D + O - 0.001 of holdback sprocket of 0.1654 pitch. Film thickness = 0.006. For other thickness: root diameter = N

32、 times pitch/x -thickness K B = Radial distance of arc center inside root circle, + 0.0005 - O. R2 = Minimum radius of film path concave to sprocket. XT = Circular arc radius for tooth shape, + O - 0.002. = Offset of tooth at working height. Page 4 of 7 pages STD-SMPTE RP 55-ENGL 1797 83574011 00028

33、84 512 RP 55-1 997 Table 1 B - Sprocket dimensions, millimeter specifications N 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 DD 16.021- 17.369 18.717 20.064 21.412 22.760 24.108 25.455 26.803 28.151 29.499 30.847 32.194 34.890 37.586 40.281

34、 42.977 45.672 48.368 51 .O63 53.759 56.455 59.150 61.846 64.541 67.237 69.932 72.628 75.324 80.715 86.106 91.497 96.888 102.279 107.670 84 113.061 Root diameter, D N = Number of teeth. DC 15.972 17.316 18.660 20.004 21.347 22.691 24.035 25.379 26.722 28.066 29.410 30.754 32.097 34.785 37.472 40.160

35、 42.847 45.535 48.222 50.910 53.597 56.285 58.972 61.660 64.347 67.035 69.722 72.410 75.097 80.472 85.847 91.222 96.597 101.972 107.347 112.722 . DH 15.895 17.232 18.569 19.907 21.244 22.581 23.919 25.256 26.593 27.930 29.268 30.605 31.942 34.617 37.291 39.966 42.640 45.31 5 47.989 50.664 53.339 56.

36、013 58.688 61.362 64.037 66.71 1 69.386 72.060 74.735 80.084 85.433 90.782 96.131 1 01.480 106.829 112.179 3.832 K 1.520 1.574 1.625 1.674 1.721 1.768 1.812 1.856 1.898 I .940 1.980 2.020 2.059 2.134 2.208 2.279 2.348 2.416 2.482 2.547 2.61 1 2.674 2.735 2.796 2.856 2.915 2.974 3.032 3.088 3.201 3.3

37、10 3.41 9 3.525 3.628 3.732 B 0.046 0.056 0.067 0.077 O. 086 0.096 0.105 0.1 14 O. 123 O. 132 0.141 0.150 0.158 0.175 0.191 0.207 0.222 0.238 0.252 0.267 0.282 0.296 0.310 0.324 0.338 0.352 0.365 0.379 0.392 0.418 0.444 0.469 0.494 0.518 0.543 0.566 R2 XT 12.583 0.2458 13.378 14.180 14.987 15.798 16

38、.612 17.430 18.251 19.074 19.900 20.728 21.559 22.391 24.064 25.745 27.436 29.135 30.844 32.562 34.288 36.025 37.770 39.525 41.289 43.063 44.847 46.641 48.444 50.258 53.91 5 57.613 61.352 65.135 68.961 72.830 76.744 DD = Root diameter, D + 0.025 - O of drive sprocket of 4.234 pitch. DC = Root diamet

39、er, D + 0.025 - O of combination sprocket of 4.221 pitch. DH = Root diameter, D + O - 0.025 of holdback sprocket of 4.201 pitch. Film thickness = 0.1 52. For other thickness: root diameter = N times pitchln: - thickness. K = Circular arc radius for tooth shape, + O - 0.051. B = Radial distance of ar

40、c center inside root circle, + 0.01 3 - O. R2 = Minimum radius of film path concave to sprocket. XT = Offset of tooth at working height. . 0.2406 0.2361 0.2322 0.2288 0.2257 0.2229 0.2204 0.2181 0.2161 0.2142 0.21 25 0.2109 0.2081 0.2056 0.2035 0.201 7 0.2000 0.1985 0.1972 0.1960 o. 1949 0.1939 O. 1

41、930 0.1921 0.1914 0.1906 o. 1900 O. 1894 0.1882 0.1873 0.1864 0.1856 0.1849 0.1843 0.1837 Page 5 of 7 pages STD-SMPTE RP 55-ENGL 3797 8357403 0002885 459 RP 55-1997 I ,CUTTING DEPTH d Figure 4 - Basic rack Table 2 - Basic racks for hobs to make sprockets Distance of center + 0.0002 - O inch I l Pitc

42、h of rack, PH Shape radius, KH below root, BH + O - 0.001 inch I 0.0001 inch Offset at 0.026-inch Range of (I 0.0025 mm) (+ O - 0.025 mm) (+ 0.005 - O mm) (0.66-mm) height, XTH teeth Inches Millimeters Inches Millimeters Inches Millimeters Inches Millimeters 12-24 0.1651 4.194 0.0799 2.029 0.0067 0.

43、170 0.00671 0.1704 25-84 0.1662 4.221 O. 1327 3.371 0.0200 0.508 0.00671 O. 1704 Annex A (informative) Additional data A.l It is intended that the pitch of feed sprockets shall always be equal to or greater than the pitch of the film. The longest film pitch was assumed to be 0.1667 in (4.234 mm), co

44、rresponding to zero shrinkage with no allowance for plus tolerance during perforating. The pitch of unprocessed film under some conditions of high humidity may be longer. On the other hand, processed film perforated with the maximum plus tolerance at low humidity conditions may be shorter by 0.2% or

45、 0.3%. Another condition which gives rise to an effectively longer film pitch is the film distortion at the perforation resulting from higher-than-normal force at the contact point of the driving tooth. A classical example is the proven benefit to film life if the root diameter of the 16-tooth inter

46、mittent sprocket for 35-mm projectors is increased from 0.9464 in (24.039 mm corresponding to unshrunk film) to 0.950 in (24.13 mm). Presumably, the improvement can be explained in part by a better tooth action if the sprocket pitch is equal to or greater than the effective pitch between the loaded

47、perforation and the following perforation which must engage freely. If he desires, the designer may exercise control of the pitch by proper selection of the root diameter. The same hobs are usable for the new diameter. The friction between the film and the root surface of the normal feed sprocket as

48、sists in the driving action; however, friction between the film and guide members which control edge position and film path should be minimized. An excep- tion to these pitch considerations is the radial-tooth design concept (see reference 1). A.2 It is intended that the pitch of holdback sprockets

49、shall be equal to or less than the pitch of the film. The shortest film pitch is assumed to be 0.1654 in (4.201 mm), corresponding to 0.8% shrinkage of long pitch film (0.1667 in, 4.234 mm). (This value is chosen rather than the 0.6% used for the tooth shape to avoid inadvertent interference at entering teeth.) The user can again ex- ercise control by correct choice of the root diameter if he believes that a change is warranted. The friction between the film and the root surface assists in holding back and, in addition, the friction against guides also assis