DE2811807A1 - Digital coder for angular position of shaft - employs vernier principle and has photoelectric devices to provide accurate measurement - Google Patents

Abstract

The shaft encoder contains a disc (1) fixed to a shaft (2) running in bearings (3). Light from the annular sources (51, 52) impinges on the ring of detectors(41) through two concentric rings of slots (11, 12) in the disc. The outer (Vernier) ring has equidistantly-spaced slots whereas the inner (Key bit) ring has not. Signals from the photodetectors (41) and clock (7) are processed in logic circuits (9) to give the angular position of the shaft. The high redundancy of linear coding provides both good resolution and some self-correction and fault diagnosis if a sensor fails.

Description

Digital absolute angular encoder based on the vernier principle. The invention relates to a digital-absolute angle encoder for electrical-digital measurement the analog mechanical angular position of a rotatable shaft without a stop Full circle range from 0 ° to 3600 is provided.

Digital absolute angle encoders are becoming electrical ones in process engineering Measurement of mechanical movements especially used when electrical-digital Output data are required.

It is known that digital absolute angle encoder each from one rotatable code disk and a fixed arrangement of scanning sensors are. The code disk has a geometric pattern; this pattern is in a any physical material property for which the Scanning sensors are sensitive, usually electrical conductivity with contact brush scanning, optical transparency with photoelectric scanning or magnetization strength with magnetic scanning. The scanning sensors are in the simplest case, the requires very little effort in terms of scanning sensors and signal evaluation, in one exactly aligned radial line arranged, the individual scanning sensors each generate one bit of information of the Meadatenousganges, and those on the code disk a circular track pattern with a sectoral division that differs from track to track is assigned according to a non-redundant or less redundant binary code, mostly the gray code, often also the natural binary code or a BCD rode.

It is known that as an alternative to the less redundant binary codes Linear codes are also used: The code disk has a special pattern just a simple single mark. There is a number N of sensors for scanning present in a simple, even, equidistant, concentric circle arrangement, so that there is always one, but a maximum of two scanning sensors in the vicinity of the individual marking report on the code disk. This is done by a "1-out-of-N" decoding circuit the identification of the current position of the input shaft sought with the Angular resolution 3600 / N. This linear code is highly redundant with regard to the Utilization of the scanning sensors by using the N scanning sensors in the linear code only (log2 N) bits supply measurement information, whereas the same number N of sensors in binary code results in a maximum of N bit measurement information. For this, the linear code has compared to the linear code the advantage of not allowing angular synchronization between several scanning tracks require.

The well-known digital absolute angle encoders have a number of Disadvantages: 1, Binary-coded angle encoders require very high manufacturing accuracy, especially in the alignment of the scanning sensors and the execution of the delicate Pattern of the code disk. If a scanning sensor fails, the overall function is of the angle encoder disturbed without the possibility of diagnosis and correction; redundant Multiple arrangement of the scanning elements is not necessary for reasons of space and accuracy easily possible.

2. Linear-coded angle encoders achieve high angular resolutions only with very large numbers of scanning sensors, in the event of failure one The scanning sensor is the overall function of the angle encoder without the possibility of diagnosis and correction disturbed. A redundant multiple arrangement of the scanning elements enlarges the anyway very high expenditure on scanning sensors.

The invention is based on the object of a digital absolute To create angle encoder on the basis of the linear code, which is given Number N of scanning sensors exploits the high redundancy of the linear code in order to achieve Failure of a scanning sensor to allow error diagnosis and correction and at the same time to achieve a higher measurement resolution.

According to the invention, this object is achieved in that in the angle encoder a fixed, uniform, equidistant, closed ring arrangement of N similar Scanning elements at an angular distance of 36D0 / N on one concentric with the input shaft There is a circular track of a rotatable code disk with a special pattern faces; this special pattern is the superposition of two sub-patterns: 1. a non-rotationally symmetrical group of individual markings that are angularly spaced 36D0 / N of the scanning sensors, but not regularly and only over a sector section of the full circle are arranged; this in the following in clear analogy as Partial pattern labeled key bit pattern is used for the rough measurement of the angular position.

2 a rotationally symmetrical, equidistant ring arrangement of (N + 1) similar individual markings at angular distance 36D0 / (N + 1); this In the following, in a clear analogy, the partial pattern is referred to as the "vernier pattern" serves for the fine measurement of the angular position.

The sets of individual markings belonging to the two partial patterns cause distinguishable signals in the scanning sensors, in such a way that a any scanning sensor from the set of N sensors by means of a signal discrimination process emits one of the following four possible discrete messages: 1. no individual marking present 2. only a single marking of the ~ "key bit pattern" present 3. only a single marking of the "Nonius pattern" is present 4. both a single marking of the 11 key bit pattern "as well as a single marking of the" Nonius pattern "is present The entirety of the 11 key mustache pattern 11 of the code disk in the ring arrangement discrete messages evoked by the N scanning sensors are repeated with each Revolution of the input shaft, d # h. is periodic with 3600. All of these N messages is clearly the position of the input shaft, with an angular resolution of 36n0 / N, assigned By logical decoding, from the totality of the N discrete messages the current coarse angular position, namely one of N possible equidistant positions to be identified in the full circle The entirety of the the '8Nonius pattern'2 of the code disk in the ring line of the N scanning sensors N discrete messages are repeated after each rotation of the input shaft about the Angle 360 ° / (N + 1), since the undulating hover pattern from the Superposition (interference) of the equidistant, even circular division of N scanning sensors and the equidistant regular circular division of (N + 1) individual markings of the Vernier pattern runs through a full circle within the angle of rotation interval 36D0 / (N + 1). The totality of these N discrete messages is thus clearly the position of the Input shaft within the interval 360 ° / (N + 1) with the angular resolution 3600 / N '(N + 1) assigned. Logical decoding enables the total of the N discrete messages the current fine angular position, namely one of N positions, # identified will.

This process of increasing accuracy through a fine measurement is the same as with the vernier reading of the length scale of a common one Workshop measuring tool, such as a caliper.

The totality of the coarse and fine measurement of the angular position provides thus an angular resolution of 3600 / N2.

According to the further invention, the "key bit pattern" is on the Code disk as an irregular sequence of individual marks and gaps (i.e. positions without individual markings) with an angular distance of 3600 / N designed redundantly in such a way that that the decoding of the current position of the input shaft from the N sensor messages of individual brands of the key bit pattern remains unambiguous even if one or several sensor messages are erroneous, for example due to a failure of individual sensors, but in these cases an additional one in the decoding Output signal is generated, which indicates the occurrence of at least one sensor error indicates. The measurement of the rough position of the input shaft is made possible by this redundancy measure self-correcting and self-diagnosing errors.

According to the further invention, instead of the number (N + 1) of equidistant Individual markings of the "Nonius pattern" on the code disk a number (N + A) of such markings are present, where A is a positive or negative number unequal IAI <N is zero. Such an arrangement also provides a fine measurement the angular position of the input shaft, albeit with a lower resolution than in Case of the number (N + 1) individual markings.

The advantages achieved by the invention are that by the additional vernier reading with the help of the vernier pattern the measurement resolution of the linear encoded angle encoder with a given number of scanning sensors the measurement resolution of simple linear-coded angle encoders is significantly increased: in particular, the information content of the measured angle value is increased from (log2 N) to 2s (log2N) doubled. Furthermore, the invention uses the high redundancy of the linear code, an automatic sensor error correction and sensor error diagnosis in the rough angle measurement to execute. In addition, the failure of individual scanning sensors also leads to the Fine; measurement only to a small disturbance, the maximum of one measured value falsification about some fine resolution steps; the applied vernier measuring principle is thus fault-tolerant against isolated sensor errors, provided that the amount or the smallest Bits of the measurement data word are disregarded, depending on whether one or more Sensor errors should be tolerated.

The geometric misplacement of one or more scanning sensors within the angular equidistant ring arrangement of the N scanning sensors has a maximum has the same falsifying effect as a single failure of the measured value, so that the Measurement accuracy of the angle kodisrers on the degree of regularity of the whole Ring arrangement from scanning sensors, but not from the local positional accuracy of the individual Sensing element depends; in this property there is a significant advantage over binary coded angle encoders; this property has the consequence that the angle encoder can be manufactured with large manufacturing tolerances or that sensor components with an inexactly known local sensitivity distribution may be used.

An embodiment of the invention is shown in the drawing and is described in more detail below.

Figure 1 shows a possible arrangement of the components of the digital absolute Angle encoder based on the vernier principle with N = 64 photoelectric scanning sensors and optical code disk as well as time-division multiplex signal discrimination of the sensor messages of individual markings of the key bit pattern and the "vernier pattern" for the maximum Angular measurement resolution of 3600/4096 (= 360 ° / 1212).

FIG. 2 shows the optical pattern of the code disk for the in FIG 1 shown arrangement.

FIG. 3 shows a linear scaling of the "key bit pattern" of FIG Code disk from Figure 2.

The optical code disk 1 is firmly connected to the input shaft 2. The input shaft 2 is freely rotatably mounted in the bearing 3 fixed to the housing. The code disk 1 is made of transparent material and has an optical blackening pattern, that consists of two partial patterns arranged in concentric tracks, the "key bit pattern" 11 and the "Nonius pattern" 12.

Concentric around the input shaft 1 on the housing 31 attached is the scanning sensor carrier 4, which is an equidistant, uniform, concentric Ring line of N similar photoelectric scanning sensors 41 at an angular distance 3600 / N, two of which are visible in section in the drawing. This N Scanning sensors 41 supply N independent discrete sensor signals over signal lines 42, two of which are shown in the drawing. The signals of the photoelectric Scanning sensors are caused by two concentric linear ring light sources 51 and 52, which are fed from the power source 6 and from the clock 7 by means of of the switch 8 can be switched in alternation so that only one light source, 51 or 52, emits light and thus the scanning sensor line 41 through the conical inclined incidence of light reports a light distribution that alternates through intensity modulation is caused by the partial pattern 11 or the partial pattern 12. The measured value decoder logic circuit 9, consisting of AND, OR and NOT gates and logical storage elements, sets the signals arriving via the sensor signal lines 42 together with the clock signal 71 in the measurement output signal 10 to, which is clearly the angular position of the input shaft indicates.

The blackening pattern of the code disk 1 shown in FIG. 2 consists from the irregular concentric pattern 11 ("key bit pattern") that on the inner track for scanning by N = 64 sensors from individual markings in the Angular spacing grid consists of 3600/64, and the regular concentric Pattern 12 (11Nonius pattern'1), which is arranged on the outer track and (N + 1) = 65 carries equidistant individual markings.

The linear rolling of the partial pattern 11 ("key bit pattern") shown in FIG. the code disk is according to the invention an arrangement of 4 individual markings and 6 gaps (= missing individual markings) over 10 adjacent angular interval steps at a distance of 3600/64 in the following order (M = single marking, L = gap) M-L-M-L-L-M-L-L-L-M and (N-10) = 54 further gaps to fill the full circle; these are not shown in the drawing, but only the essential part of the partial pattern 11 is shown. This partial pattern 11 is redundant in such a way that when it occurs of a single error (false signal instead of gap or zero signal instead of of signal) in error-correcting effect in the decoding logic circuit error-free signal pattern can be completely reconstructed from the disturbed residual pattern is.

With regard to the functional principle of the invention, it does not matter in which physical material property the partial pattern to be scanned in the Code disks are embossed, according to which sensor technology they are scanned, whether the code disk is designed in a modified geometric shape, for example as a cylindrical drum is and in what way the signal discrimination in distinguishing the two Partial pattern takes place, for example through amplitude discrimination (pulse height discrimination), geometric discrimination, time or frequency discrimination.

Claims (4)

Patent claims 1. Digital absolute angle encoder based on the vernier principle, characterized in that it is firmly connected to one of the rotatable input shafts Code disk is embossed with a special pattern, which is angularly equidistant regular closed ring arrangement of a number of N scanning sensors at an angular distance 3600 / N is scanned, whereby the special pattern of the code disk consists of two partial patterns is constructed from an irregular one extending over a sector of the circle of people Pattern of individual markings and gaps (= missing individual markings) in the angular distance 360 ° / N ("key bit pattern") and one evenly extended over the full circle Regular patterns of (N + 1) individual markings spaced apart at equidistant angles 360Q / (N + 1) ("Vernier Pattern"); the scanning sensors report the presence a kind of individual markings regardless of the presence of individual markings the other type abpdOhO the scanning sensors perform a signal discrimination between the individual markings of the "key bit pattern" and the individual markings of the "Vernier pattern" through, so that by means of a decoder logic circuit a digital Coarse-fine measurement of the angular position of the input shaft of the angle encoder Type of vernier reading of a scale can be done. 2. angle encoder according to claim 1, characterized in that the irregular partial patterns of individual markings ("key bit pattern" 2) through use a number of individual markings is designed redundantly in such a way that at the If one or more scanning sensor errors occur, an error-free reconstruction of the undisturbed pattern is possible (error correction) and also the output of a Error message occurs (error diagnosis). 3, angle encoder according to claims 1 and 2, characterized in that that instead of the number (N + 1) of regular equidistant individual markings on the code disk ("Nonius pattern") a number (N + A) of such individual markings may be present, where A is positive or negative, other than zero can be an integer of the amount | A | <N N. 4. angle encoder according to claims 1 to 3, characterized in that that the signal discrimination of the discrete sensor signals between the different Individual markings (of the key bit pattern and the "Noniusmusterstl") with photoelectric Scanning an optical code disk in time division multiplex is carried out by the Code disk two concentric tracks with the thus geometrically separated from each other Bears partial patterns that alternate between separate and conically inclined incidence of light Light sources are alternately illuminated. 5, angle encoder according to claims 1 to 4, characterized in that that an arrangement of 4 individual marks and 6 gaps (= missing individual marks) over 10 contiguous angular interval steps with a distance of 3600 / N in the following Sequence (M = single marking, L = gap) M-L-M- L-L-I1-L-L-L-I9 as well as (N-10) others Gaps to fill in the Full circle as code disk pattern for the position coarse measurement ("key bit pattern") is available against a any single sensor fault is fault tolerant,