Electricity: electrical systems and devices – Control circuits for electromagnetic devices – Systems for magnetizing – demagnetizing – or controlling the...
Reexamination Certificate
2002-06-05
2004-02-03
Jackson, Stephen W (Department: 2836)
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
Systems for magnetizing, demagnetizing, or controlling the...
C361S139000, C361S146000
Reexamination Certificate
active
06687111
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electromagnetic mark device for a magnetic encoder, and, particularly, to a device, which can generate a magnetic field by way of the current to make magnetic marks much easily, such that it is possible to reduce the pitch between any two neighboring magnetic marks greatly so as to enhance the accuracy of the magnetic encoder in addition to the magnetic field being set up reliably with stable magnetic flux.
2. Description of Related Art
Generally, a technical application of an encoder is to measure the relative position, the velocity and the angular velocity of an object such that the object can be located more accurately. The principle thereof is to fix a series of magnetic marks equidistantly on a base, and a magnetic resistance element is utilized to pass through the magnetic lines of force on each magnetic mark so as to sense a change of signal for determining a relative position of a moving object. A measure apparatus thereof is usually called an encoder, wherein, the apparatus used for measuring a linear position of the object is called a linear encoder and for measuring a rotational angle of the object is called an angular encoder.
A conventional encoder as shown in
FIG. 1
comprises a stationary ruler body
101
, two opposite guard layers
102
,
103
disposed at the upper and the lower ends of the ruler body
101
, and a sensor
104
. A plurality of magnetic marks N, S, N, S, . . . with a constant pitch arranged on the ruler body
101
in a way of adjacent magnetic poles of the magnetic marks being disposed alternately. The sensor
104
is fixedly attached to a moving mechanism and provided with two magnetic resistance sensing elements
104
A,
104
B. When the moving mechanism carries the sensor
104
to move along the ruler body with a relative constant velocity, the sensing elements
104
A,
104
B have different resistances during passing through different magnetic fields on the ruler body
101
. Signals on the sensing elements
104
A,
104
B as shown in
FIG. 2
includes a signal approximate sine wave and a signal approximate cosine wave respectively. The signals can be treated and figured out the number of pulse waves such that it is possible to find out the displacement of the moving mechanism relative to the stationary mechanism. Wherein, in case of the moving mechanism displacing in a direction designated as
105
A, the sensing element
104
A phase-leads the sensing element
104
B, and, in case of the moving mechanism displacing in a direction designated as the sensing element
104
A phase-lags the sensing element
104
B. Hence, it is possible to determine if the moving mechanism is turning forward or turning inversely based on the state of phase thereof.
It can be learned from the preceding analysis that the encoder has the resolution thereof to be determined by way of the capability of picking up the signal from the sensor and the accuracy of the magnetic marks on the ruler body. But, problems caused by both of the magnetization technique and the magnetic material result in that it is hard to shorten the pitch between magnetic poles. The prior art mostly emphasizes on the improvement of the capability of picking up the signal of sensor such as the selection of magnetic resistance material and the arrangement of signals in the sensor, or on the improvement of the manufacturing process to the sensibility of flux, the anti-noise of flux and the characteristics of temperature change. However, the prior art provides less improvement on the ruler body making and the mode for producing the magnetic marks.
For producing the magnetic marks on the ruler body, the magnetic material in the prior art is mostly utilized to coat the ruler body and then the magnetic marks are produced by way of magnetization. Theoretically, the smaller the graduations of the magnetic marks are, the higher the resolution will be, but, smaller graduations of magnetic marks may confront many problems. Firstly, the magnetization work is required to up-grade for meeting the needed accuracy such that it becomes more difficult to produce the magnetic marks and the production cost for the magnetic marks increases considerably. Next, a smaller pitch may increase the error percentage of the magnetic marks under the condition of same error such that it requires a higher working accuracy for maintaining the same error percent. Hence, the density of coating on the magnetic material has to be increased relatively. Further, it is hypothesized that the ruler body is made of homogeneous material at the time of being designed and the hypothesis is proper in case of the pitch being much greater than the grain size of the magnetic material. While the pitch is shortened to be close to the grain size of the magnetic material, it may affect the intensity of magnetic field to generate noise if the magnetic material is not so homogeneous as the original hypothesis. In order to avoid the noise generated from the material, a smaller grain size and a more strict homogeneity have to be reached synchronously with the reduced pitch such that the material is required to provide a better homogeneity as soon as the graduations of the magnetic marks become smaller. In practice, the magnetic marks of the ruler body usually are magnetized on a magnetic rubber and the pitch is restricted in a range of 5 mm to 10 mm due to being affected by the grain size and the homogeneity of the material. If the pitch is required to reduce further, a special magnetic material has to be plated on a hard base plate as a medium for magnetic marks. However, the special magnetic material mostly is made of alloy so that, on the one hand, it is not easy to be coated on the magnetic material and, on the other hand, it is easy to be scratched. Moreover, the surface of the special material may crack because of the factor of temperature. Unfortunately, the signal of the encoder may arise noise regardless the crack or the scratch. Secondly, in addition to the limitation concerning the characteristics of the material, the smaller the magnetic graduation is, the stricter the control with regard to the density and the accuracy of the magnetization is required. Hence, the accuracy of the magnetic marks on the ruler body is hard to be enhanced due to the restricted technique of magnetization.
Besides, the permanent magnetic material is normally utilized to produce the magnetic marks on the ruler body but in case of being adsorbed with magnetic dust, being not uniform at the interior thereof, being scratched at the outer surface thereof, or being interfered by the foreign magnetic field, the permanent magnetic material may generate the noise. Further, the smaller magnetic graduation needs a small corresponding signal but the noise still remains unchanged. Moreover, the smaller magnetic graduation may results in a smaller signal
oise ratio and the incorrect signal will be generated undesirably. Further, the permanent magnetic material can be demagnetized by the interference of a more powerful external magnetic field but the smaller magnetic graduation may result in a smaller magnetic flux and a smaller magnetic force needed for the demagnetization. Hence, Once strong lines of magnetic force exist in the work environment, the magnetic marks has an increased possibility of being demagnetized relatively so that it has a certain limit to reduce the graduation. In practice, a lot of uncertain lines of magnetic force may distribute over around an environment in which motors are in use in addition to many magnetic material being able to generate dust such that extraordinary magnetic marks may be influenced by the apertures in the magnetic material, scratches on the ruler body, the adsorption of the magnetic dust and the interference of the magnetic field to produce incorrect signal. Furthermore, the reduced magnetic graduation may result in the permanent magnetic material being demagnetized or magnetized improperly and it may cause the permanent damage if the ruler body is care
Chang Hsin Ming
Huang Chuan Fu
Jiang Shyh Biau
Lee Dong Liang
Yang Chi Ming
Connolly Bove Lodge & Hutz
Jackson Stephen W
View Move Technologies, Inc.
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