1、I. I I 1. MIL-HDBK-231A 59 9999970 0069781 7 II - MILITARY HANDBOOK ENCODERS - SHAFT ANGLE TO DIGITAL INCH-POUND EZJ MIL-WDBK-231A SUPERSEDING MIL-HDBK-231(AS) 1 JULY 1970 30 September 1991 - AMSC N/A FSC 5990 DSTRIBUTION!,STATEMENT A. Approved for public release; distribution ia unlimited. Provided
2、 by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-HDBK-231A 59 W 9999970 00b82 9 Wi MIL-HDBK-23lA FOREWORD 1. This military handbook is approved for use by all Departments and Agencies of the Department of Defense and supersedes MIL-HDBK-231(AS) dated 1 Ju
3、ly 1970. 1, 2. Beneficial .comments (recommendations, additions, deletions) and any . : pertinent data which may be of use in improving this do.cument should be 1 addressed to: Commanding Officer, Naval Air Engineering Center, Engineering Specificatipns and Standards Department, Code 53, Lakehurst,
4、NJ 08733-5100, by using the self-addressed. Standardization Document Improvement Proposal (DD Form 1426) appearing at the end of this document or by letter. 3. This handbook provides basic and fundamental information- on .encoder techniques, terminology, operation, and number systems. It will provid
5、e valuable information and guidance to personnel conc:erned with the preparation of specifications and the procurement of encoders. The handbook is not intended to be ref-erenced in purchase specifications except for informational purpose,s , nor shall. it supersede. any: specification requirements.
6、 4. An encoder is a device for sensing the rotatdon or position of a shaft and providing a means. for indicating that posjltion. A rudimentary application of the basic encoder Goncept, which is still widely used today in the maintenance of automobile engines, employs a simple index mark on the. flyw
7、heel and a fixed reference mark adjacent to the flywheel. Rotation of the flywheel results in movement of the index mark relative to the reference mark and is a function of engine op.eration and main shaft position. The, reference mark and the index mark are placed so that alignment.of the two. - -
8、indicates that a selected piston is sitting at top dead center. Another common example of the encoder principle is the familiar automobile speedometer and odometer. This device senses the rotation-af the drive shaft of the vehicle, thereby providing the operator with an indication of . shaft -speed
9、in analog.form calibrated in miles per hour (speedometer needle), as well as a digital count of shaft revolutions-calibrated in - linear miles to an accuracy of 0.1 mile (odometer). In general, any variable which can be. represented as a function of the-rotation of a shaft (pressure, speed, flow rat
10、e, positioning, distance,-time, and sio.on) can be . sensed using an encoder and a representative indication or signal can be .-. . provided for a broad variety of uses including control, operation, maintenance, and sequencing. i. . .E 5. The dramatic advancement in weapon systems during World War I
11、I .- emphasized the need for rapid and accurate transmi.ssion of shaft position - data to remote devices. Fire control systems were developed for automatlc, high-speed gun laying which required a means for transmitting radar posi- tional data to a remote gun position to aim and fire the weapon. The
12、. . . primary solution was, of necessity, an analog approach .using.synchro devices - Although adequate for the applications of that time, the analog technique has inherent inaccuracies due to deviations from linear input-output characteristics. However, development in this area led to the subsequen
13、t development of fast, accurate, and compact digital shaft encoders. ii ! ? Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-HDBK-231A CONTENTS PARAGRAPH 1.0 SCOPE 1.1 Scope . 1.2 Applicability . 1.3 Purpose 2.0 REFERENCED DOCUMENTS b . * . b p 2.
14、1 . Government documents . 2.1.2 Specifications. standards. and handbooks . 2.2 Non-Government publications 2.3 Order of precedence 3.0 DEFINITIONS . o e e 4.0 GENERAL REQUIREMENTS m b o o s e o o 4.1 Need for computer control . 4.2 Survey of encoder8 - general . . PAGE 1 . 1 3 1 3 9 9 9 5.0 . DETAI
15、LED REQUIREMENTS. . . . . . 9 5.1 Encoder description 9 5.2.1 Contact encoder 10 5.2.2 Non-contact encoder 10 Functional systems of encoder 11 5.3 5.3.1 input function 11 5.3.2 Detection function 13 5.3.3 Logic processing function 17 . Encoder classification . 10 . 9 52 . 5.3.4 Output function 20 5.
16、3.5 Summary of interrelation of functions 22 5.3.6 Conclusion - functional systems 23 . . . 5.4 Encoder types - 23 5.4.1 Encoder techniques 23 5.4.2 Encoders 24 5.4.3 Contact encoders 25 5.4.4 Magnetic encoders . 27 31 5.4.5 Capacitive encoders 5.4.6 Optical encoder 34 5.4.7 Special devices 39 5.4.8
17、 Comparisons and summaries - encoders 41 5.5 Construction of encoders -44 5.5.1 Size. shape and performance 44 5.5.2 Structural design and housing 45 5.5.4 Mountings and physical interfaces . 51 . . 5.5.3 Weight of encoders 50 5.5.5 EnvironmentaL determinants 51 ii Provided by IHSNot for ResaleNo re
18、production or networking permitted without license from IHS-,-,-. MIL-HDBK-23LA 59 = 9999970 0069784 2 I! PARAGRAPH 5.5.6 5.6 5.6.2 5.6.3 5.6.4 5.7 5.7.1 5.7.2 5.7.3 5.7.4 5.7.5 5.8 5.8.1 5,8.2 5s8.3 5.9 5,g.l 5.9e2 5.9.3 5,9.4 5.9.5 5.9.6 5.9.7 5.9.9 5.9.10 5.9.11 5,9.12 5.10 5.10.1 5.19.2 5.11 5.6
19、1 5.9.8 . 5.10,3 5s11.1 5,11.2 MIL-HDBK-231A CONTENTS Comparative evaluation of size and structure . . . . Systems technology Input mechanics Detection mechanics Logic mechanics Output mechanics . Testing and evaluation Test requirements and criteria Quality assurance methods . Mechanical inspection
20、 Electrical tests . Typical test sequence. Research and development . Performance problem areas . Research - current programs Encoder of the future . Number systems and codes . Number systems Coding techniques . Binary decimal system . Nonweighted binary codes . Cyclic decimal code Combination codes
21、 . Gray coded Excess-3 BCD Two-out-of-five-codes . Special purpose codes . Code selection criteria Encoder logic . Applications. tradeoffs. and error Noncyclic codes - nonreflected codes . Applications . Tradeoffs . Accuracy factors. encoder error. and minimization . Selection of an encoder Encoder
22、characteristics - general . Selection of encoders for military use PAGE 53 54 54 59 67 77 81 81 82 83 84 86 92 94 97 99 99 92 105 107 108 111 113 114 116 117 118 119 119 125 125 130 144 -136 144 147 iv Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
23、4 MIL-HDBK-23LA 59 9999970 0069785 4 li I . II . III . . IV . V . VI . VI11 . IX . .X . XI . xy1 . XII1 . XIV . XV . hysteresis loop and readout voltage . . Capcitve encoder, cutaway view . . . . . . . . . . Capacitive encoer . . . . . . . , . . . . Inductive encoder symbolized by resolver windings.
24、 . . . Optical encoder operation. . . . . . . . . . . . . Typical optical encoder configuration. . , . . . . . . Optical sensing, functional diagram . . . . + . . . Incanescent bulb“ life, voltage curve. . . . . i . . . . Generalized response of variouslight sensitive materials Light spectrum:. . .
25、. . . . . . . . . , . , . . . Spectral response, silicon photosensor and gallium arsenide diode, temperature constant. , . . . . . . . . vi 183 186 187 187. I_ ! 188 188 189 189 . 190 190 191 19 1 192 192 193 194 19 5 197 197 198 199 200 201 202 203 204 205 206 206 207 , 208 209 209 2 10 200, 211 Pr
26、ovided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-HDBK-231A CONTENTS FIGURE 27 28 29 30 31 32 33 34 35 * 36 . 38 37 . 39 40 41 42 43 44 45 46 47 48 50 51 52 53 “ 54 55 . 56 57 58 59 60 . 61 49 . 62 63 . . 64 65 66 67 Gallium arsenide . silicon photoc
27、ell detector assembly. output .variations ,wit.h temperature change . . (both components) i Energy coupled encoder . Navigational serv-en er.modules Brush and brysh assembly . Brush encoder, ctaway view . Typical size 08 and 1-1 shaft gle encoder Typical size 23 shaftangle encoder, . Typical size 31
28、 . Typical logic scheme for a multi-turn encoder. . Selected graphic logic symbols and functions . Typical latch circuit ; . i . Typical 13-biut function. Conversion of a shaft angle position into a digital signal is the purpose of all shaft encoders, This digikal signal ie the output of an encoder
29、system and can be developed to represent a host of input varablea including the speed, direction, and amount of shaft rotation and the absolute position of the input shaft. Encoder outputs must be developed in a form suited to the associated sensing or recording device. Since encoders are most commo
30、nly employed as a component part.of a larger system, the encoder configuration and design must integrate with and be subordinate to system requirements. This fact is Crue of each functional section of an encoder, but output signal processing is especially important since the output signal must inter
31、face directly with peripheral components and the overall system. Conditioning of the final signal output offers great potential flexibility in encoder development by enabling the designer to use the input; detection, and logic processing techniques best suited for such considerations as weight, spac
32、e, speed, resolution, and accuracy (that is, encoder performance). These techniques may then be integrated with output. techniques to put the signal in the form required for system interface. 5.3.4.1 Output devices. Encoder outputs are usually produced in the form of serial or parallel pulses repres
33、enting input shaft movement in some digital code, Even where there is no movement at the input, shaft position. can be derived in digital form using static voltage or current levels. It is rare to design an encoder without some system application in mind, and it- is the system requirement that deter
34、mines the amount and the type of output . processing. Generally, the major types of output processing can be categorized as amplification, storage, and shaping. 5.3.4.11 Amplification, The basic encoder systems shown on Figures 2r 3 voltage supplied by batteries. and 4 provide outputs to simple indi
35、cator lamps in the form of a DC .*.-, The output signal can be considered the 20 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-HDBK-23LA 59 E 9999970 00b9810 T MILr.HDBK-23 1A energizing vo1tage.if the indicator lamps are not part of the encode
36、r, or the output can be considered the visual light signal if the lamps are integral to the encoder. In either case, the output requires no special . conditioning since a DC voltage is adequate=to drive the indicator lamps and the lamp signals can convey the necessary inteL1igence to a human observe
37、r, But suppose the indicator lamps are at a remote-location, as might be the qase in-a-missile fire control system. The encoder might be used to detect tbe.posltion of a control valve located at a firing site; and the indicator lamps and the operator would probably be in a remote bunker or control r
38、oom, perhaps as far as a mile away The losses inherent in transmission lines of this length would render the DC output totally inadequate. would be to use an AC voltage source and an AC indicator lamp. possibility would be the use of some form of amplification to compensate for line loss. In any eve
39、nt, this situation demonstrates the basic output design task of amplification including such associated problems as impedance matching and level setting. In most modern, high performance systems, this function is performed using solid state electronic amplifiers to provide an output of the level req
40、uired to drive ancillary devices. One solution Another 5.3.4.1.2 Storaqe. In the cam switch encoder used as an example throughout this section, the storage function is pegformed by an operator using a stop watch to provide a time reference-and paper and pencil to store pulse information. Again, this
41、 function is- usually accomplished electronically in most systems. .in incremental encoders the array of identical output signals representing some discrete amount of input shaft movemqnt must be sensed (usually at a very high rate) and a count accumulated which is related to some precise time base.
42、 This stored count is the elemental data from which shaft speed, direction, position, and relative movement can be computed, and then presented in-a form readily comprehended by people (for example, decimal count) or applied to other circuits for further processing,and refinement. 5,3.4.1.3 Shapinq.
43、 Since the output of most encoders is applied to other-.electronig processing or computing equipment , it is usually necessary to shape the pulse output and condition it for further use. - The pulse shaping or pulse forming function of encoder output circuits typically includes such operations as fi
44、ltering, clipping, inverting, differentiating, and integrating. These processes, applied singly or in combination, serve to modify the encoder output and produce pulses of the shape, amplitude, polazity, duration, and spacing required by ancillary data agd-information systems, For example, a steady
45、DC voltage sequentially applied and interrupted by the action of switch-contacts pr0duces.a square wave whose polarity and amplitude are determined by the natura of the power Supply, The duration and spacing of the pulses will.4e a function of the timing of the. switch action. Digital techniques and
46、 digital equipment depend on a fair amount of regularity in the pulse signals for proper operation. . If the variables in a pulse signal are shapei duration, amplitude, frequency, and total number, it is most efficient to standardize as many of these variables agIpossible and allow only one of them to change as a function of the intelligence contained in the signal. Thus, the shaping circuits included in encoder systems serve to standardize those pulse characteristics that do 21 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
