DE1265206B - Magnetic encoder with a rotatable magnetized code disk - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

H03k

German class: 21 al -36/20

Number: 1265 206

File number: G 45607 VIII a / 21 al

Filing date: December 30, 1965

Open date: April 4, 1968

The invention relates to a magnetic encoder, which consists of a perpendicular to its surface magnetized rotatable code disk with several tracks of different importance, the each comprise a plurality of segments with alternating high and low magnetic flux, as well as read heads assigned to the tracks for determining the different magnetic flux strengths consists.

Magnetic encoders for determining the angular position of a shaft are superior to conventional encoders working with brushes because of the properties that result from the fact that there is no contact between the code disk carrying the data and the scanning element. These properties provide a coding device with a long service life, which is only limited by the service life of the bearings used in it. In addition, these properties have the advantage of a significantly higher signal-to-noise ratio. Magnetic encoders in which the data carrier has areas that exhibit changes in magnetic properties are extremely advantageous. A read head with a highly permeable core generates a change in inductance in a winding depending on and controlled by the different magnetic properties of the respective data carrier area. So far, coding devices of this type have generated a read signal which, as a function of the change in inductance in the winding of the core, has represented an evaluable output signal. The disadvantage of this is the low resolution of the signal generated in this way, ie the binary 1 generated by areas with low inductance is difficult to distinguish from a binary 0 generated by areas with high inductance. The cause of this poor resolution is the magnetic stray lines that penetrate the reading heads when they are opposite areas of low magnetization, ie when only a few or no magnetic lines are to appear. To solve this problem, the distance between the reading head and the data carrier has been made as small as possible in order to prevent magnetic stray lines from penetrating the reading heads. However, by keeping the distance between the reading head and the code disk small, new problems arose. One of them is that due to these tight tolerances, shocks and vibrations of the coding device cause "collisions" between the two parts during operation, which leads to damage and thus to repair or replacement costs. In any case, costs arise magnetic encoder with a rotatable
magnetized code disk

Applicant:

General Precision,

Inc., Glendale, Calif. (V. St. A.)

Representative:

Dipl.-Ing. H. v. Schumann, legal and

Patent attorney,

8000 Munich 22, Widenmayerstr. 5

Named as inventor:
Edward Lloyd Packard,
Glendale, Calif. (V. St. A.)

Claimed priority:

V. St. v. America February 1, 1965 (429 350)

and the reliability of the encoder is decreased. An added disadvantage of the normally required distance between read head and data carrier is that the amount of work and so that the total manufacturing costs increase to these tolerances in the setting when assembling to be observed.

According to the invention, these disadvantages in a magnetic coding device are described at the outset Art avoided by a flux leakage element shielding the magnetic flux from the reading heads.

This makes it possible to make the ratio between a read 0 and a 1 large without that a particularly small distance between the reading head and the code disk would be required. Particularly A simple and advantageous embodiment is one in which the code tracks consist of raised and lowered Segments exist. In a further advantageous embodiment of the invention, the reading heads consist of a saturable iron core with two possible states of remanence, one when scanning one Segment with high magnetic flux, the other when scanning a segment with low magnetic flux occurs. The reading of the respective remanence state is advantageously carried out in that the iron cores are provided with windings, the inductance of which varies with the state of the iron core changes.

809 537/508

Further details of the invention emerge from the exemplary embodiment described below with reference to the drawings, in which

F i g. 1 is a section through a magnetic encoder according to the invention,

F i g. 2 shows one of the many reading heads used according to the invention,

F i g. Figure 3 is a partial view of an enlarged section showing the improvements of the invention and in particular the magnetic flux density can be seen in the event that a read head is over an area with low magnetic resistance, i.e. above a raised segment of the data carrier,

F i g. 4 shows a representation similar to FIG. 3, but with the read head over an area with high magnetic resistance, d. H. stands over a recessed segment of the information carrier,

F i g. 5 shows a section through the magnetic data carrier along the line 5-5 in FIG. 1 is and the have the same magnetic properties as track 30 for the lowest binary digit, i.e. the raised ones Segments have greater magnetic flux density than the recessed ones. The innermost trace corresponds to that top binary digit. This coding apparatus uses a standard pattern, the tracks in this embodiment are offset in order to get a better distance between the reading heads However, this is only a preferred embodiment, and of course others can also Code pattern can be selected.

A cover plate 36 is fastened to the upper part of the housing 12 with bolts 38 and consists of a magnetizable material. To determine the magnetic flux density of the segments 32 or 34 is a A plurality of read heads 40 are used, each of which, as shown in FIG. 2, consists of a magnetic core 41, which is annular in this embodiment. A winding 42 is in series on both legs of the

different tracks with different places- 20 toroidal core 41 applied. Preferably there is the

value, the hatched segments of each track having a different magnetic flux density than that are not hatched and are raised compared to these, F i g. 6 is a section along line 6-6 of FIG. 1 Core 41 made of saturable magnetic material, which is capable of two states of remanence.

The special distribution of the reading heads 40 corresponds to the standard arrangement for V-scanning and

and shows a cover plate on which the reading heads 25 is shown in FIG. 6 in a top view of the cover plate 36

are mounted and the return path for the from the in F i g. 5 outgoing magnetic disk shown Forms flow lines,

F i g. 7 is a section along line 7-7 of FIG. 1 and shows a back yoke plate as the second The return path is used for the magnetic lines of force that should not enforce a read head, and

F i g. 8 is the block diagram for a typical read circuit used with the subject invention.

In the drawings there is shown a single embodiment of the invention, and the same or corresponding ones Parts are denoted by the same reference numerals in the various figures. F i g. 1 shows a Shaft 10 made of stainless magnetizable steel.

shown. The track 30 for the lowest binary digit operates with one in the corresponding slot 44 arranged reading head 40 together. The cores 41 of the read heads 40 are preferably in the Cover plate 36 provided slots 44 cemented. On both sides of the slot 44 is through the cover plate 36 a hole 46 drilled. Both holes 46 are provided with insulating sleeves 48. The feeders 50 of the windings 42 are, as shown in FIG. 1 can be seen, inserted through the holes 46 and via a Control panel 52 is connected to a sensing circuit explained below.

As shown in FIG. 7, a return plate 54 can be seen by means of bolts 58 on a ring 56 (FIG. 1)

This shaft takes analog values in the form of angle-40 attached. The return plate 54 and the ring 56 Positions and is made of aluminum as is the cover plate 36 essentially

Assembled housing 12 provided, which can consist of two halves for better accessibility. The two Halves are held together by bolts 14. For frictionless storage of the shaft 10 in the Housing 12, bearings 16 can be used. On the shaft 10 within the housing 12 is a disk-shaped data carrier 18, which consists of an aluminum support surface 20 with a sleeve 22. The wing 20 is firmly connected to the shaft 10 and rotates with her. Firmly attached to it is a code disk 24 made of highly magnetized barium ferrite, of which FIG. Figure 5 shows a top view.

The code disk 24 comprises several data tracks of varying importance in binary encryption. The outermost track 30 corresponds to lowest binary digit and comprises a large number of individual segments with different magnetic Properties. Each hatched segment 32 is opposite the one next to it (not hatched) Segment 34 is raised and has a magnetic flux of higher density than the recessed Segments 34 when the disc 24 is magnetized so that one pole (north or south pole) in the in F i g. 5, the other is close to the wing 20. To be put to the target center the individual tracks each represent the next higher binary digits, with the individual segments of each track borrowed from magnetizable material. To hold the cover plate 36 against the housing, the ring 56 one shoulder up. As a clearance between the sleeve 22 and the return plate 54, a distance 61 is provided, so that there is no friction between these two parts when the shaft 10 rotates. Of the Distance also serves, as will be explained below, for the formation of the total resistance for the magnetic path. A plurality of slots 62 are provided in the return plate so that the cores 41 of the reading heads 40 can pass through them and face the data carrier 18 directly. In this preferred embodiment, the underside of the cores 41 closes with the lower surface of the End plate 54 just off. A clearance 63 is free between the plate 54 and the magnetic cores 41 to add further factors to the total magnetic resistance, as will be explained below to have.

Way of working

Before the in F i g. 8 is entered, an explanation of the mode of operation is intended this coding device are given. F i g. 3 shows a magnetic core 41 above a raised one Segment 32 of high magnetic flux density. The magnetic lines of force are shown in this illustration as

Claims (1)

5 6 dashed lines 64 drawn Normally, the special read head takes the remanence state, one interrogates the magnetic lines of force as from the north pole of its core 41. When a magnetic core 41 runs to the south pole of a permanent magnet. If the magnetic flux density has a high magnetic flux density or because of this special embodiment which is saturated with the magnetic lines of force 64, the surface of the code disk 5 adjacent to the cores 41 leads to the inductance of the winding 42 in a suppression 24 of the north pole, which is in the vicinity of the carrier plate 20 of the signal from generator 65. If there is little or no surface the south pole. If, therefore, no lines of force 64 pass the core 41, the read head 40 with its magnetic core over a winding 42 has little or no protruding segment 32, the magnetism decreases and the signal from the generator 65 is increased Lines of force 64 see the path not suppressed with the slightest io. Via a resistor 66 of at-resistance, which in this case flows through the raised 680 ohms, for example, a current flows to the leading segments 32 and the core 41. The and to the trailing side of each reading head 40 a magnetic flux thus penetrates the core and causes up to 40 g. With the resistors 66 and the read that this assumes a high remanence state heads 40 each have a diode 61 coupled around which, and possibly even, is saturated. This has to rectify a 15 signals for the following circuit, higher inductance of the winding 42 result. The read head 40 α works with the track 30 of the code magnetic lines of force 64 continue to run disk 24 together, thus corresponds to the lowest point through the cover plate 36, the shaft 10 and back and generates a binary signal of 2 °. The signal to the south pole of the magnetic code disk 24. For 2 ° is also an AND gate 68 and a pattern of closed magnetic flux is created via an inverter 72 to another AND gate lines. All of the other tracks are fed to the code disk 24 70. The signal for the next higher point outgoing lines of force 64 lead into the inference shows the remanence state of the leading reading plate 54 through the shaft 10 and back to the magnet head 40 b and the trailing reading head 40 b ' tized code disk 24. Since the carrier plate 20 and on . The reading head 40 b is connected to the AND gate 68, the sleeve 22 made of aluminum and the same 25 connected, which in the event that both signals have a large low permeability such as air, they remain, ie that both reading heads are practical over segments without any effect on the magnetic force ringer magnetic flux density or recessed segments 34 lines 64. is opened and a signal is sent to the OR In Fig. 4 shows another position in which gate 74 emits, which in turn generates a binary signal 2 ¹ from the core 41 of a read head 40 to a recessed 30. On the other hand, the signal from the read head 40 a segment 34 is opposite. Again, the low, that is, that this read head a segment of magnetic lines of force the path of the least high magnetic flux density (a raised segment) resistance, which in this case faces the return path, so there is a high plate 54 on the AND gate 70, there through the recessed segment 34 of the signal, and if furthermore to the same AND gate magnetic resistance at the location of the read head 35 70 from the trailing read head 40 b ' has increased a high signal. The lines of force lead through the result, the AND gate 70 is opened, and the return plate 54 to the shaft 10 and back to the output of the OR gate 74 creates a south pole of the magnetic code disk 24. As a result of the binary signal 2 ¹ . As can be seen from this, the shielding effect of the return plate 54 is provided in the event that the read head 40 α is opposed to an effectively enforce no magnetic lines of force 40 segment of low magnetic flux density and a 64 generates the core 41, whereby this generates its low high signal, the reading head 40 b interrogated, remanence state and remains unsaturated and the while in the other case, in which the reading head 40 a winding 42 with respect to the output line 50 assumes a lower inductance than a segment of high magnetic flux density. stands, the read head 40 b emits no signal. That's why Of course, the specific polarization of the 45 is an inverted signal from the read head 40 α bemagnetischen code wheel 24 is shown only as an example, exploited to the trailing read head retrieve information 40 b ', and it is also the opposite way gen Toggle. The same principle is in the same Way on the reversible. The sleeve 22 is applied in this particular following higher places and is in the embodiment a fairly high magnetic single resistance in U.S. Patent 3,056,956 and is written as a factor of 50.
Resistance. Other factors to be considered are the air gap between the inference claims:
plate 54 and the shaft 10, the distance between the magnetic cores 41 and the code disk 24 and 1. Magnetic encoder, consisting of likewise the distance between the cover plate 36 and 55 a magnetizing perpendicular to its surface Shaft 10. Therefore, if the sleeve 22 opposite th rotatable code disk with multiple tracks the other factors have a relatively high, fixed, ma-different importance, each one represents magnetic resistance, so have smaller multitudes of segments with alternating high Variations in these other factors include only one and low magnetic flux, so proportionately little effect on the overall read heads for the 60 as from the tracks resistance, and you always get a fairly stable determination of the different magnetic flux reading signals, strengthen, characterized by a den F i g. 8 shows a typical, in connection with magnetic leakage flux from the read heads (40) this coding device used reading circuit, in the shielding return element (54) (F i g 1). a 60 kHz generator 65 simultaneously to each of the 65 2nd coding device according to claim 1, characterized in that Reading heads e 40 α to 40 g, both on the front indicates that the code tracks from raised on the trailing side as well as a (32) and recessed (34) segments AC signal generated and with each input (Fig. 3). 3. Coding device according to claim 1 or 2, characterized in that the reading heads (40) from a saturable iron core (41) with two possible remanence states, one of which when scanning a segment (32) with high magnetic flux, the other when scanning a Segment (34) occurs with low magnetic flux (Fig. 3 and 4). 4. Coding device according to claim 3, characterized in that the iron cores (41) with windings (42) are provided, the inductance of which varies according to the remanence state of the iron core changes (Fig. 2). Considered publications:
U.S. Patent No. 3,056,956. For this purpose 2 sheets of drawings 809 537/508 3.68 © Bundesdruckerei Berlin