Magnetic type digital-analogic position-sensing device

A magnetic type digital-analogic position-sensing device utilizes plural magnetic strips and plural digital sensing readers to perform position-sensing operation. One of the magnetic strips is provided with an analogic sensing reader. After being finely divided, the signal outputted from the analogic sensing reader can cooperate with the signals outputted from the digital sensing readers to obtain the displacement of the sensor. By such arrangements, the position-sensing device can both have high environment adaptability and high resolution.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a program control system for a magnetic recording media, and more particularly to a magnetic type digital-analogic position-sensing device.

2. Description of the Prior Art

The existing sensing devices for measuring a displacement of a rotary or linear displacement device for a motor or a linear motor can be divided into two types: magnetic type and optical type. The optical type sensing devices are better than the magnetic type sensing devices in precision, so the industries which seek high precision will adopt the optical type sensing devices. A conventional optical sensing device, as shown inFIG. 1, consists of an optical scale A and a sensor B. The optical scale A includes four parallel-arranged elongated scale elements A1, A2, A3, A4, and each of the scale elements A1, A2, A3, A4includes plural through holes A11, A21, A31, A41. The length of the through holes A11, A21, A31, A41of the respective scale elements A1, A2, A3, A4is the same and identical to the distance between each pair of neighboring through holes A11, A21, A31, A41of the respective scale elements A1, A2, A3, A4. Further as shown inFIG. 2, the length of the through holes A11of the first scale element A1is two times as long as that of the through holes A21of the second scale element A2, the length of the through holes A21of the second scale element A2is two times as long as that of the through holes A31of the third scale element A3, and the length of the through holes A31of the third scale element A3is two times as long as that of the through holes A41of the fourth scale element A4. The sensor B is provided with four digital sensing readers B1, B2, B3, B4opposite the respective four scale elements A1, A2, A3, A4. The respective sensing readers B1, B2, B3, B4will output a high or low signal depending on if there are the through holes of the respective scale elements A1, A2, A3, A4or not. The signals outputted from the four sensing readers B1, B2, B3, B4are integrated as shown inFIG. 3, so that the relative distance between the sensing device B and the optical scale A can be known from the signals of that time.

Since the length of the through holes A11, A21, A31, A41of the respective scale elements A1, A2, A3, A4and the distance between each pair of neighboring through holes A11, A21, A41of the respective scale elements A1, A2, A3, A4determine the resolution of the sensing device B (the resolution is the minimum value to measure the displacement of the sensor B). The length of through holes A11, A21, A31, A41and the distance between each pair of neighboring through holes A11, A21, A31, A41of the respective scale elements A1, A2, A3, A4of the optical scale A in the optical type sensing device can be finely formed by adopting the nano technology, so that the precision is relatively high. On the contrary, the magnetic sensing device uses the magnetic scale in which N poles and S poles are alternately arranged to make the sensing reader to output a high or low signal. Since the distance between the N pole and S pole of the magnetic type sensing device cannot achieve the normal precision of the optical type sensing device, the high precision industries will select the optical type sensing devices.

However, the more precise the optical type sensing device is, the better the working environment is needed (if the working environment is not good enough, the dust or particles are likely to obstruct the through holes of the scale elements to greatly lower the precision). Since the general industries cannot provide the location with better working environment satisfying the requirements of the optical type sensing device, they can only adopt the magnetic type sensing devices which cannot be affected by the environment condition, consequently, the corresponding precision is greatly reduced.

SUMMARY OF THE INVENTION

The primary objective of the present invention is to provide a magnetic type digital-analogic position-sensing device, which has both high environment adaptability and high resolution.

In order to achieve the above objective, the magnetic type position-sensing device in accordance with the present invention comprises a magnetic scale and a sensor. The magnetic scale includes plural magnetic strips, and each of the magnetic strips includes plural magnetic zones. Each of the magnetic zones equally includes an S pole and an N pole. The plural magnetic zones on the same magnetic strip have the same length, and the magnetic zones on any two of the magnetic strips have the different lengths. The sensor is located on the magnetic scale and provided with plural digital sensing readers opposite the magnetic strips of the magnetic scale. The sensor is further provided with an analogic sensing reader opposite one of the magnetic strips. The sensing readers are used to sense the magnetic polarity of the opposite magnetic strips.

When the sensor moves along the magnetic scale, the digital sensing readers will sense the magnetic polarity of the magnetic zones of the magnetic strips to output high or low signals, in addition, the analogic sensing reader will sense the magnetic polarity of the opposite magnetic strip to output a sinusoidal signal. After being finely divided, the signal outputted from the analogic sensing reader will be used to obtain the relative position of the sensor and the magnetic scale or the displacement of the sensor by integrating the signals outputted from the digital sensing readers. By such arrangements, the magnetic type position-sensing device in accordance with the present invention can have the high environment adaptability of the magnetic-type sensing device and the high resolution achieved by using the analogic sensing reader.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIGS. 4-5, a magnetic type position-sensing device in accordance with a preferred embodiment of the present invention comprises a magnetic scale10and a sensor20.

The magnetic scale10includes four magnetic strips11,12,13,14. The respective magnetic strips11,12,13,14include plural magnetic zones111,121,131,141. The respective magnetic zones111,121,131,141are equally divided into two parts that are N pole and S pole. The magnetic zones111,121,131,141on the respective magnetic strips11,12,13,14have the same length. The length of the magnetic zones111of the first magnetic strip11is two times as long as that of the magnetic zones121of the second magnetic strip12, the length of the magnetic zones121of the second magnetic strip12is two times as long as that of the magnetic zones131of the third magnetic strip13, and the length of the magnetic zones131of the third magnetic strip13is two times as long as that of the magnetic zones141of the fourth magnetic strip14, in other words, the magnetic zones of any two of the magnetic strips11,12,13,14have different lengths, and the length of the magnetic zones of one of every two neighboring magnetic strips is twice as long as that of the other one.

The sensor20is located on the magnetic scale10and includes four digital sensing readers21,22,23,24that are located opposite the magnetic strips11,12,13,14of the magnetic scale10, respectively, namely the first digital sensing reader21is opposite the first magnetic strip11, the second digital sensing reader22is opposite the second magnetic strip12, the third sensing reader23is opposite the third magnetic strip13, and the fourth sensing reader24is opposite the fourth magnetic strip14. The digital sensing readers21,22,23,24are used to sense the magnetic polarity of the respective magnetic strips11,12,13,14. The sensor20is further provided with an analogic sensing reader25opposite the fourth magnetic strip14to sense the magnetic polarity of the fourth magnetic strip14. The analogic sensing reader25and the fourth digital sensing reader24are located on the same magnetic poles of the neighboring magnetic zones141, for example, the analogic sensing reader25is located on an N pole of one of the magnetic zones141of the fourth magnetic strip14, and the fourth digital sensing reader24is located on an N pole of a magnetic zone141neighboring the one of the magnetic zones141of the fourth magnetic strip14.

When the sensor20moves along the magnetic scale10, the respective digital sensing readers21,22,23,24and analogic sensing reader25will move along the opposite magnetic strips11,12,13,14, and thus the digital sensing readers21,22,23,24and analogic sensing reader25will sense the magnetic zones11,121,131,141of the respective magnetic strips11,12,13,14one by one. The magnetic polarity sensed by the respective digital sensing readers21,22,23,24and the analogic reader25also changes from N pole to S pole alternately, for example, when the first sensing reader21moves along the first magnetic strip11, the first sensing reader21faces the N pole of one of the magnetic zones111of the first magnetic strip11, after a first displacement, the first sensing reader21will face the S pole of the one of the magnetic zones111of the first magnetic strip11, after a second displacement, the first sensing reader21will face the N pole of another of the magnetic zones111. As a result, it can be found that the magnetic polarity sensed by the respective sensing readers21,22,23,24and the analogic sensing reader25will change from N pole to S pole alternately. The respective digital sensing readers21,22,23,24will cooperate with the sensed N poles and S poles to output high and low signals, and the analogic sensing reader25will cooperate the sensed N poles or N poles to output a sinusoidal signal. The signals outputted from the respective digital sensing readers21,22,23,24and the analogic sensing reader25are integrated as shown inFIG. 6.

Hence, the relative position of the sensor10and the magnetic scale20and the displacement of the sensor10can be roughly known from the signals outputted from the respective sensing readers21,22,23,24. The analogic sensing reader25outputs the sinusoidal signal, and every sinusoidal wave represents 360 degrees, so that the sinusoidal wave can be divided into many parts as desired, the minimum value of every parts can be 1 degree, 0.1 degrees or 0.01 degrees. The rough positions of the digital sensing readers21,22,23,24cooperating with the position of the corresponding sinusoidal wave of the analogic sensing reader25can precisely determine the relative position of the sensor10and the magnetic scale20and the displacement of the sensor10, for example, in the outputted signals, the signal of the first digital sensing reader21is high, the signal of the second digital sensing reader22is lower, the signal of the third digital signal23is low, and the signal of the fourth sensing reader24is low, therefore, it can be found that the position is located within the sixth pair of sinusoidal waves of the analogic sensing reader25(one pair of sinusoidal waves of the analogic sensing reader25includes two sinusoidal waves that have a 90 degree phrase angle difference therebetween). In addition to the abovementioned, as long as the degree of the signal of the analogic sensing reader25is known, as shown inFIG. 6, the relative position a of the sensor10and the magnetic scale20and the displacement of the sensor10can be precisely obtained.

Therefore, it can be found that besides high environment adaptability, the magnetic type position-sensing device also has high resolution due to the analogic sensing reader25. The number of the magnetic strips and the number of digital sensing readers in accordance with the present invention are not limited to that described in the preferred embodiment.