JPS6228496B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a capacitive column sensor for detecting the state of a magnetic tape in a tape buffer section of a magnetic tape device.

Generally, a magnetic tape device is equipped with a column sensor to detect the amount of tape in a vacuum column of a tape buffer section. This column sensor is a necessary detector to control the reel motor and maintain the appropriate amount of tape in the vacuum column in response to the detected signal. It must always vary depending on the amount of tape in the column. The column also requires an emergence detector to detect when the magnetic tape enters the column's emergence region. This is because it is necessary to quickly detect that the magnetic tape is about to come off the column, stop unnecessary tape feeding or winding, and prevent damage to the tape just before it comes off the column.

In most conventional magnetic tape devices, the column sensor and the emergence sensor are configured separately, and when attempting to detect the emergence using the column sensor signal, the column sensor's straight line Because it is necessary to strictly suppress individual variations in gender and other characteristics, it is necessary to manufacture them with considerable precision. Alternatively, instead of allowing individual variations, it is necessary to adjust the volume or the like to compensate. In any case, the use of a column sensor and an emergency sensor in a conventional magnetic tape device is not only expensive but also unreliable in terms of handling and performance.

The object of the present invention is to eliminate the above-mentioned drawbacks, to enable accurate detection of the emergence state without making any corrective adjustments, and to provide a capacitive type that is simple to handle, economical, and reliable. The purpose of the present invention is to provide a column sensor.

According to the present invention, two fixed electrode plates each having an air hole are placed in parallel with a distance therebetween;
a flexible electrode foil placed between these fixed electrode plates, an air chamber on one side of the flexible electrode foil is separated into a servo area and an emergency area, and the other side is combined into one air chamber; , the servo area and the column are connected by a sensor groove, the emergency area and the column are connected by an emergency detection hole, and depending on the pressure difference between the air chambers on one side and the other side,
If the loop of the magnetic tape is in the servo area of the column, the flexible electrode foil surrounding the air chamber of the servo area is moved; if the loop of the magnetic tape is in the emergence area of the column, the emergence area is moved. A capacitive column sensor for a magnetic tape device is obtained, which detects a change in capacitance between the fixed electrode plate and the flexible electrode foil by touching the surrounding flexible electrode foil.

Next, embodiments of the column sensor according to the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of the front structure on the side of the vacuum column in the embodiment. In this diagram,
The magnetic tape 3 passes from the supply reel 1 through the supply side vacuum column 6, passes through the magnetic head 4 and the capstan 5, and then passes through the take-up side vacuum column 6' and is wound onto the take-up reel 2. The supply side column 6 and the take-up side column 6' have column sensor grooves 8, 8', upper emergency detection holes 9,
9' and lower emergence detection holes 10, 10', and two column sensors corresponding to the supply side column 6 and the winding side column 6' are attached to the back side of these holes, respectively. Further, there are vacuum suction holes 7 and 7' at the bottom of each column, which suck the magnetic tape 3 downward to form tape loops 3a and 3a'.

FIG. 2 is a perspective view showing the electrode structure of the column sensor in this embodiment. In the figure, the electrode is composed of three sheets, with a thin flexible electrode foil 26 with a lead wire 25 attached and an insulated surface in the center, and transparently drawn electrodes 26 on both sides. Thin insulating plates 27 and 27' cut out as shown in the dotted lines are stacked on top of each other,
Furthermore, a fixed electrode plate 2 is provided with lead wires 23 and 23' having a plurality of air holes 24 on its outer surface on both sides.
2 and 22' are superimposed. The fixed electrode plate 22 side of the electrode foil 26 includes column sensor grooves 8, 8', emergency detection holes 9, 9', and 1.
0 and 10', and the other fixed electrode plate 22' side is connected to the column sensor pressure intake port 14 and connected to an air chamber 30 maintained at an appropriate pressure. It is installed in a sealed manner.

Next, the structure and operation thereof will be explained in more detail with reference to FIG. 3, which shows the structure of the column sensor in cross section. Front wall 11 and rear wall 1
In the column chambers 6, 6' surrounded by 3, the tape 3 is inserted into the vacuum suction holes 7,
It is pulled downward by suction from 7', forming a loop 3a. The column rear wall 13 has the above-mentioned emergency detection holes 9, 9', column sensor grooves 8, 8', and lower emergence detection holes 10, 1.
0', and a column sensor is attached to the back surface thereof, which has regions 31, 32 and 33 corresponding to each hole and groove and separated from each other by insulating plates 27, 27' and a separating plate 28. . If the pressure in the concave column chamber 12 of the tape loop 3a is P ₁ and the pressure in the convex column chamber 12' drawn by the vacuum is P ₂ (P ₁ >P ₂ ), then the flexible electrode foil 26 Areas 31, 32, 3
The air chamber 30 on the opposite side facing 3 has a pressure (P ₁
Add +P ₂ )/2. That is, the magnitude of the pressure is the pressure P ₁ of the concave column chamber 12 (air chamber 31)
>Pressure of air chamber 30 P ₁ +P ₂ /2 > Convex column chamber 12
′ is related to the pressure P ₂ . Therefore, the concave column chamber 1
The flexible electrode foil corresponding to the part 2 is brought to the fixed electrode plate 22' side, and the flexible electrode foil corresponding to the part of the convex column chamber 12' is brought to the fixed electrode plate 22 side. Therefore, when the tape loop is in the servo area, the length and area of the attracting portion between each electrode changes depending on the column position of the tape loop, and C=ε ₀ S/d (ε ₀ : dielectric constant, S: The capacitance between the flexible electrode foil 26 and the fixed electrode plates 22 and 22' changes depending on the counter electrode area (d: distance between the counter electrodes). Thus, the difference between the capacitance between electrodes 26 and 22 and the capacitance between electrodes 26 and 22' is handled electrically, thereby maintaining the proper position of the tape loop of the vacuum. , can control the reel motor. Next, when the loop position of the tape passes the emergence detection holes 9, 9' and enters the emergence area as shown in 3b, the entire tape including the flexible electrode foil moves to the electrode plate 22 side, and the loop position 3c, after passing the emergence detection holes 10, 10', all the flexible electrode foils are attached to the fixed electrode plate 2.
It is attracted to the 2' side.

As mentioned above, when the tape loop enters the emergence region, the flexible electrode foil does not move so as to have a suction area proportional to the column position of the tape loop as in the servo region, but instead moves to the flexible electrode foil that is in contact with the emergence region. The entire area of is impressed at once. FIG. 4a shows how the capacitance changes suddenly when the tape loop passes through the emergence hole according to this embodiment, where the horizontal axis shows the moving distance of the loop and the vertical axis shows the voltage detected by the electrode. By using the jump points as shown in the figure, the emergence level can be set to a high position as shown by the dotted line.
The position of the tape loop does not change even if there are variations in the parts (indicated by the dashed line).

By the way, in the conventional column sensor, Fig. 4b
As shown in Figure 2, when attempting to detect emergence, the characteristics change as shown by the solid line and the dashed line due to variations in the parts, and the tape loop position at which emergence is detected is at point b for the same emergence level. It changes as shown at point a. Therefore, in conventional column sensors, it is necessary to suppress variations in parts or adjust the emergency level using a volume or the like.

In addition, in the above embodiment, the larger the adsorption area of the flexible electrode foil in the emergence area, the larger the change in capacitance, which allows the emergence level to be increased, so the tolerance range due to component variations becomes larger. Needless to say.

As is clear from the above description, according to the present invention, by separating the air chamber on one side of the flexible electrode into the servo area and the emergence area, large variations in manufacturing can be tolerated. Since the emergency level can be determined without electrical adjustment of the volume or the like, it is easy to handle, economical, and highly effective in improving reliability.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the front structure of an embodiment according to the present invention, FIG. 2 is a perspective view showing the structure of an electrode of a column sensor according to the present invention, and FIG. 3 is a side cross-sectional view showing the structure of an embodiment according to the present invention. 4a and 4b are diagrams showing the voltage versus tape loop position variation characteristics of the column sensor of the present invention and the conventional column sensor, respectively. In the figure, 1 is the supply reel, 2
is a take-up reel, 3 is a magnetic tape, 4 is a magnetic head, 5 is a capstan, 6, 6' are vacuum columns, 7, 7' are vacuum suction holes, 8, 8' are column sensor grooves, 9, 9' 10 and 10' are upper emergence detection holes, 10 and 10' are lower emergence detection holes, 11 and 13 are column walls, 12 is a concave column chamber, 12' is a convex column chamber, 14 is a pressure intake port for column sensor, 22, 22 ' is a fixed electrode plate, 24
is an air hole, 27, 27' is an insulating plate, 28 is a separator, 26 is a flexible electrode foil, 30 is an air chamber,
31 and 33 are emergency areas, and 32 is a servo area.

Claims (1)

[Claims] 1.Equipped with two fixed electrode plates each having an air hole placed in parallel with an interval, and a flexible electrode foil placed between these fixed electrode plates, and an air chamber on one side of the flexible electrode foil is controlled by a servo. Separate the region and the emergence region, and set the other side to 1.
Further, the servo area and the column are connected by a sensor groove, the emergency area and the column are connected by an emergency detection hole, and the pressure difference between the air chambers on one side and the other side is connected to the air chambers. Accordingly, if the loop point of the magnetic tape is in the servo area of the column, the flexible electrode foil surrounding the air chamber of the servo area is moved; if the loop point of the magnetic tape is in the emergent area of the column, A capacitive column sensor for a magnetic tape device, wherein a capacitance change between the fixed electrode plate and the flexible electrode foil is detected by touching the flexible electrode foil surrounding the emergence region.