JPH01320433A - Linear encoder - Google Patents

Abstract

PURPOSE:To improve the detecting accuracy of the title encoder by using a plate-shaped permanent magnet which is composed principally of specific elements and multipolarly magnetized and magnetic sensors confronted by the magnet. CONSTITUTION:This linear encoder for measuring displacement is constituted of a multipolarly magnetized plate-shaped permanent magnet 101 and magnetic sensors 102 which detect the magnetic field of the magnet 101. The permanent magnet 101 is composed principally of R (at least one kind of rate earth elements including Y), M (at least one kind of transition metals), and X (at least one kind of IIIb group elements) which are used as the basic component alloy, melting and casting an alloy of fundamental components for improving the magnetic characteristics at need, condensing the magnetic phase of the magnet by removing the R-rich liquid phase which is a nonmagnetic substance from the principal components by heat-working the cast ingot so that the magnetic anisotropy and mechanical orientational property is applied. Therefore, the detecting accuracy of this linear encoder is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a linear encoder that detects linear displacement using a multi-pole magnetized permanent magnet.

[Prior Art] Generally, the structure of a linear encoder is similar to the linear encoder of the present invention whose cross-sectional view is shown in FIG. (
The linear displacement is measured by detecting changes in the magnetic field with a Hall element, MR element, etc. 102.

Conventionally, ferrite magnets have often been used as permanent magnets in linear encoders.

[Problems to be Solved by the Invention] However, conventional linear encoders using ferrite magnets have the following drawbacks: (1) Since ferrite magnets have a small residual magnetic flux density Br, the magnetic field necessary for detection cannot be obtained. There were major limitations in resolution and accuracy.

(2) Sintered ferrite magnets are easily broken, requiring careful handling when assembling the linear encoder.

Furthermore, when using a linear encoder, there is a possibility that the magnet may be damaged if care is not taken when handling it.

(3) Ferrite magnets other than sintered magnets, such as resin-bonded ferrite magnets and rubber ferrite magnets, are less likely to break, but their magnetic properties are inferior to sintered ferrite magnets, resulting in changes in properties due to temperature changes, mechanical deformation, etc. There are many problems with this method, and it has not been applied to high-precision linear encoders.

Therefore, the present invention aims to solve these problems.
The purpose is to add R-M- to the linear encoder.
X (R is at least one rare earth element including Y, M is at least one transition metal, X is III b
By using a cast magnet (at least one of the group elements), the problems that conventionally occurred when using ferrite magnets are avoided, and a highly accurate and unbreakable linear encoder can be provided at a low price.

[Means for Solving the Problems] The linear encoder of the present invention is a linear encoder in which a permanent magnet is magnetized with multiple poles, a magnetic sensor detects the magnetic field of the permanent magnet, and a displacement is measured.(a) R (however, R is at least one kind of rare earth elements including Y), M (however, at least one kind of transition metals)
Species) and
casting, and then hot working the cast ingot to drop the magnetic phase by excluding the liquid phase of the non-magnetic R-rich phase from the basic components, thereby improving the magnetic anisotropy and mechanical orientation. A flat permanent magnet with multi-polar magnetization. It is characterized by comprising a magnetic sensor installed opposite to the permanent magnet.

[Example] Table 1 shows the alloy composition of the permanent magnet used in the linear encoder according to the present invention.

Table 1 Weigh rare earth metals (P,), transition metals (F,), boron (B) and copper (C,) in the two compositions shown in Table 1,
The magnetic properties of magnets obtained by casting after being melted in an induction heating furnace are shown in Table 2.For reference, the upper limit for ferrite magnets is generally about (B H) , =: 5. Further, for alnico magnets, the upper limit is iH=22 types.

The above-mentioned linear encoder that uses the RM-Xu magnet in its magnetic circuit can obtain a sufficient magnetic field even if the magnetization pitch is extremely fine due to the excellent magnetic properties of the magnet, and therefore it is better than the conventional one. In comparison, it is possible to achieve extremely high resolution. The present R-M-X cast magnet can be expected to further improve its magnetic properties by subjecting it to appropriate hot consolidation and heat treatment after casting, and the process is shown in FIG.

Table 2 As an example of hot working, an example of hot pressing is shown in FIG. 3, and an example of hot rolling is shown in FIG. 4. In FIG.
301 is a magnet alloy, 302 is an easy magnetization direction, 303 is a stamp, and 304 is a substrate.

In this example, hot pressing was performed at 1000° C. to orient the magnets. During processing, the speed of the stamp 3 was adjusted so that the strain rate was as low as possible. As a result, the direction of easy magnetization after processing was parallel to the direction in which pressure was applied. Next, hot rolling was performed as shown in FIG.

At this time, the roll 401 is
Adjusted the speed. As a result, the easy magnetization direction after processing is
parallel to the direction of pressure. Figure 5 (a), (b)
.

(c) is an explanatory diagram of the action of hot working, and 501 is PrFe.
In the CuB phase particles, 502 is an a-Fe phase, 503 is an R-rich phase, and 504 is an R-rich liquid phase. FIG. 5(a) shows the state of the main phase of the cast ingot, and as shown in the figure, a small amount of α-Fe phase is embedded within the PrFeCuB phase particles. The space between the PrFeCuB phase particles is filled with a nonmagnetic R-rich phase. Figure 5(b)
1 shows the state during hot working, where the R-rich phase melts to become an R-rich liquid phase and is expelled to the outside. Further, the α-Fe phase diffuses and disappears.

The PrFeCuB phase particles are made finer during processing, and the principal axis of the crystal is oriented in a certain direction. FIG. 5(C) shows the state of the magnet, where the excluded R-rich phase part is cut off and the central part where fine PrFeCuB phase particles are oriented is used.

As described above, hot processing improves magnetic properties, and although the properties after processing differ depending on the processing conditions, the maximum energy product (BHmax) can be improved to about 4 times compared to before processing. was confirmed.

FIG. 1 shows an embodiment of the linear encoder of the present invention. A magnet 101 is multi-pole magnetized on one side, and the magnetic sensor 10
2 are placed facing each other.

It should be noted that the magnet compositions shown as examples are some of the composition examples for which good results were obtained through experimental confirmation. A typical example is shown in which praseodymium (Pr) is used as the rare earth metal and iron (F, ) is used as the transition metal. Although specific composition examples, performance, etc. are omitted, it has been confirmed that the coercive force of the magnet increases by replacing a portion of P with dysprosium (Dll). In addition, cerium (C,
), it is also possible to replace a part of P with neodymium (Na).For transition metals, part of F can be replaced with cobalt (C
.

), the temperature characteristics of the magnet were significantly improved, and it was confirmed that it could withstand use at considerably high temperatures. Furthermore, by substituting a part of F with nickel (N1), the coercive force of the magnet was increased.

[Effects of the Invention] As described above, the linear encoder of the present invention has many advantages over conventional ones.

To summarize the technical points of the present invention, cast magnets with high impact resistance are suitable for linear encoders, but alnico magnets, which are typical of conventional cast magnets, have various problems in terms of magnetic properties. Therefore, its application to linear encoders has not been realized. Furthermore, conventionally known rare earth magnets are expensive, and sufficient magnetic properties cannot be obtained by casting. Therefore, by using the RM-XM magnet, it has become possible to realize a linear encoder with a good balance between functionality and price (cost performance).

Specifically, the linear encoder of the present invention is extremely excellent in the following points.

(1) Since the magnet has excellent magnetic properties, a sufficient magnetic field can be obtained and detection accuracy is good.

(2) Low cost because cast magnets are used.

(3) Since cast magnets are used, they are less likely to break, so the magnets are less likely to be damaged when assembling and using linear encoders.Linear encoders are expected to be subjected to shocks during use (machine tools, robots, etc.) Therefore, it is extremely effective to use cast magnets with high mechanical strength.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view 101 of the linear encoder of the present invention.
... Magnet 102 ... Magnetic sensor 103 ... Yoke Fig. 2 is a diagram of the manufacturing process of the magnet Fig. 3 is an illustration of hot pressing processing Fig. 4 is an illustration of hot rolling processing Fig. 5 is an illustration of hot rolling processing Illustration of the action of processing Applicant Seiko Epson Co., Ltd. Agent Patent attorney Kizobe Suzuki and 1 other person Figure 1 2) 7' Figure 3 Figure 4

Claims (2)

[Claims] (1) In a linear encoder in which a permanent magnet is magnetized with multiple poles and a magnetic sensor detects the magnetic field of the permanent magnet to measure displacement, R (where R is at least one of rare earth elements including Y).
A flat permanent magnet which has basic components of M (species), M (at least one transition metal), and X (at least one group IIIb element) and is multipolarized, and the permanent magnet A linear encoder characterized by comprising a magnetic sensor installed facing the. (2) The permanent magnet is produced by dissolving and casting the alloy as the basic component, and then hot working the cast ingot to eliminate the liquid phase of the R-rich phase, which is a non-magnetic substance, from the basic component. 2. The linear encoder according to claim 1, wherein the magnetic phase is concentrated to impart magnetic anisotropy and mechanical orientation.