RU2748388C1 - Absolute encoder with a vernier scale - Google Patents

Abstract

FIELD: measuring equipment.SUBSTANCE: invention relates to the field of measuring equipment and relates to an encoder. The encoder contains a raster with a sequence of adjacent sections of size h, called coding steps and containing Gray codes available for reading by readers, a block of readers with numbers 0, …1, …, n-1, having a fixed position relative to other reading devices and logical device. The readers are spaced from the zero device by the length xi=h(mi+i/n) where m0= 0, and for i=1, …, n-1, all miare integers. The logical device simultaneously receives the read Gray codes gifrom each i-th reader, determines the numbers of the corresponding coding steps pifrom them, and as a result of enumerating the numbers of the readers from 0 to n-1, determines the last number t for which the relation pt=р0+mtis effective, and forms the result as h(p0+t/n).EFFECT: improved measurement accuracy.1 cl

Description

FIELD OF TECHNOLOGY

The invention relates to a measuring technique for measuring quantities using an absolute encoder and is intended to increase the measurement accuracy.

LEVEL OF TECHNOLOGY

Absolute encoders are now widely used in science and technology. The device described in the invention relates to measuring instruments. This invention is associated with an encoder and involves an increase in accuracy compared to traditional encoders using a principle proposed as early as the 16th century by Pedro Nunes (Nonius in Latin). This principle is realized, for example, with a vernier scale in a vernier caliper.

DISCLOSURE OF THE INVENTION

1) The offered absolute encoder, like any encoder, contains a linear or circular raster. Unlike a traditional encoder, the proposed encoder contains not one readout device, but a whole block of readout devices, each of which has a fixed position relative to other readout devices.

2) The raster consists of a sequence of adjacent sections of the same size h, which will be further referred to as coding steps, which contain records of a binary code unique for each coding step, available for reading by reading devices. The raster and the block of reading devices can move relative to each other. If the reader reads the code from any part of the same coding step, then the result is the same. If the reader is located near the boundary of adjacent coding steps, then the read code can be a mixture of codes of both coding steps. In order for the result to be equal to either the code of one coding step or a neighboring one, for coding successive coding steps it was proposed to use the Gray code back in the last century, each value of which contains the same number of bits, and the consecutive values differ by exactly one bit. This property ensures that if the reader is located near the boundary of adjacent coding steps, the code is read either from the previous coding step or the next one. Thus, if the coding steps are renumbered with the index i = 0, 1, 2, ... then the Gray codes g ₀ , g ₁ , g ₂ , ... recorded in them will have the indicated property. The number of bits in the used Gray code is determined by the number of coding steps required for the encoder, and the Gray codes of different coding steps are unique. There is a one-to-one correspondence between the coding step number and the code it contains.

If you use only one reader with number 0, then for the code g _i read by it, the corresponding measured value will be equal to the product hi.

If the raster is rectilinear, then it can be a rectilinear movement of some point, and if the raster is round, then it will be a movement of the point along a circle.

The resulting precision in this case will be equal to the encoding step size h.

3) To increase the accuracy by n times, it is proposed to use a block of n reading devices located relative to each other in a certain way.

Let's renumber the readers with the index k = 0, 1,…, n-1. Let x _k be the distance from the zero reading device to the kth one. Let's arrange the reading devices so that

where m _k are integer values. Let the readers with numbers k = 0, ..., n-1 simultaneously read the codes of the coding steps g _k corresponding to the numbers in the order of the coding steps p _k on the raster. We will call the boundaries of each coding step left (adjacent coding step is the previous one) and right (adjacent coding step is next). If the zero reader is displaced relative to the left boundary of the coding step number p ₀ by some rh, where h is the size of each coding step, and r has a value greater than or equal to 0 and less than 1, for example,

where t can range from 0 to n-1. Then the values of the numbers of coding steps for k≤t will be obtained by the formula

and for k> t we get

This follows from the determination of the position of the reading devices given by the relation (1), the value of the value r given by the relation (2).

Let the readers transmit the received coding step codes to the logical device and, after converting them into coding step numbers, the following actions are performed. For each k = 0, ..., n-1, the value of the coding step number is compared with formulas (3) and (4). The last k for which relation (3) is satisfied is taken as t. The refined value measured by the zero reading device is assumed to be

In this case, the measurement error will be no more than h / n.

In the ideal case, when the total length of all coding steps is sufficient to obtain a value from each reader, and the readers are infinitely thin, there are no restrictions on the value of n (the number of readers and the factor of increasing the encoder accuracy). In real conditions, even assuming a sufficient total length of coding steps and compliance with the absolute equality of the sizes of coding steps, there is a limitation associated with the length of the section from which the reader reads the code from the raster. In real conditions, it is not infinitely small. The value of n cannot be greater than the ratio of the length of the coding step to this parameter (this ratio is equal to the number of adjacent positions of the reader at one coding step, in which the read sections of the coding step are adjacent to each other, but do not overlap).

4) What is stated in the previous paragraphs means that the encoder proposed in this invention contains one more component, a logical device that simultaneously receives Gray codes g _i from all reading devices, determines the numbers of the corresponding coding steps p _i for them and checks them sequentially for i = 0 , 1,…, n-1 fulfillment of relation (3). If the last index, for which relation (3) is satisfied, is equal to t, then a more accurate value of the measured value is given by relation (5).

All the above ratios are valid both for a rectilinear raster, in which all the mentioned lengths are determined along a rectilinear raster, and for a circular raster, if the lengths are measured along a circular raster (the lengths of the corresponding arcs).

Claims (5)

An encoder containing a straight line or round raster with a sequence of adjacent sections of size h (measured along the raster), hereinafter called coding steps, containing Gray codes readable by readers, a block of readers with numbers 0, ... 1, ..., n- 1, having a fixed position relative to other reading devices, as well as a logical device that forms, according to the readings of the reading devices, a measured value of increased accuracy, estimated by the value of h / n, characterized in that the reading devices are spaced from the zero device by the length x _i = h (m _i + i / n), where m ₀ = 0, and when i = 1, ..., n-1, all m _i are integers; the indicated distances are counted along a rectilinear or circular raster; if p _i are numbers in the order of the coding steps on the raster, the codes of which g _{i are} read from the raster by readers with numbers i = 0, 1, ..., n-1, then the value h (p ₀ + t / n), where t is the last number i when iterating over i from 0 to n-1, for which the relation p _i = p ₀ + m _i is satisfied; the logical device simultaneously from each i-th reader receives the read Gray codes g _i , determines the numbers of the corresponding coding steps p _{i from them} and, as a result of enumerating the numbers of the reading devices from 0 to n-1, determines the last number t for which the relation p _t = p ₀ + m _t , and forms the result in the form h (p ₀ + t / n).