JPH04315846A - Sensor output threshold value setting device - Google Patents

Abstract

PURPOSE:To set a sensor output threshold value corresponding to a sensor and the characteristics of an object to be detected. CONSTITUTION:The output of a light receiving part 6b is inputted to a CPU10 via an A/D conversion part 11. The CPU set the threshold value which is an intermediate value based on a detection output when the path of detection light 7 to the light receiving part 6b is blocked and the detection output when the path of the detection light 7 to the light receiving part 6b is not blocked. Thus, after this, an appropriate sensor detection is made available based on the threshold value.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to the starting edge (BO) of a magnetic tape.
The present invention relates to a sensor output threshold setting device that sets a threshold for sensor output detection based on the output from a sensor such as an optical detection unit at an end (T) or an end (EOT).

0002

2. Description of the Related Art Various types of sensors are used to detect the status of equipment, and FIG. It shows. In the DAT cassette pack 1 shown in FIG. 4, the magnetic tape T wound around the tape reel 3 is pulled out from the open portion of the lid 2 and runs in the direction of the arrow. In FIG. 4, reference numeral 4 indicates a reel shaft provided on the device side for driving the tape reel 3. The cassette pack 1 is provided with a prism 5, and the detection light 7 emitted from the light emitting part 6a of the photoreflector 6 enters the prism 5, is reflected, crosses the magnetic tape running part, and is emitted from the photoreflector 6. It is detected by the light receiving section 6b.

FIG. 5 shows the case where the light receiving section 6b is a phototransistor, and when the cassette pack 1 is not loaded or when the magnetic tape T blocks the detection light 7, a current flows through the resistor R. Otherwise, the current flowing becomes small and the output voltage from the light receiving section 6b becomes high. In addition, the EOT (or BOT) transparent tape detects light 7.
When the current is on the path R, current flows through the resistor R, and the resistor R
Due to the voltage drop due to
The output voltage from will drop. Conventionally, the light receiving section 6 shown in FIG.
A TTL-based threshold setting section is provided for the output from b, and when the output voltage is higher than this threshold value, it is determined that the light receiving section 6b is in a non-light receiving state, and the output voltage is lower than the threshold value. When the value is low, it is determined that the light receiving section 6b is in the light receiving state.

0004

However, in the structure of the light receiving section 6b shown in FIG. 5, the output voltage in the light receiving state varies from device to device due to variation in the resistance value of the resistor R, or variation due to environmental temperature. arise. In addition, the prism 5 provided in each cassette pack 1
Since there are individual variations in the transmittance of the LEDs, this also causes variations in the output voltage in the light receiving state. Furthermore, since the magnetic tape also has variations in light transmittance, the output voltage when the magnetic tape T blocks the detection light 7 also varies. As described above, since there are various factors that cause variations in the output voltage from the light receiving section 6b, if the threshold value is uniformly determined by TTL as in the conventional example,
The probability of false detection will increase. The present invention solves the above-mentioned conventional problems, and provides a sensor output that prevents false detection by making it possible to set a threshold according to the output of the light receiving section under each condition of each device. The object of the present invention is to provide a threshold setting device.

[0005]

[Means for Solving the Problems] The sensor output threshold setting device according to the present invention includes an A/D device in the output path from the sensor.
A conversion section is provided, and means is provided for setting a detection threshold of the sensor between the output when the sensor is OFF and the output when the sensor is ON, based on the A/D converted digital output. It is characterized by the presence of

[0006]

[Operation] In the above means, the output from the sensor is converted into a digital value, and the sensor output is detected by the control section mainly including the CPU in accordance with the output of the digital signal. In this control section, a threshold value is set based on an output value when the sensor is ON and an output value when the sensor is OFF, so that the threshold value becomes an intermediate value. It also becomes possible to change the threshold value as necessary.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings of FIGS. 1 to 3. FIG. 1 is a circuit block diagram of a sensor output section, FIG. 2 is a diagram illustrating a threshold voltage setting, and FIG. 3 is a flowchart for threshold setting. The light receiving section (sensor) 6b shown in FIG. 1 is provided in the magnetic tape detection section in the DAT shown in FIG. Figure 4
As explained as a conventional example based on
When the cassette pack 1 is loaded and the detection light 7 emitted from the light emitting section 6a and passed through the prism 5 is blocked by the magnetic tape T, the light receiving section 6b hardly receives any light. Furthermore, EOT of the cassette pack
(tape end) or BOT (tape start) when the transparent tape blocks the path of the detection light 7, the light receiving section 6b
can detect the detection light 7 that has passed through the transparent tape.

In the embodiment shown in FIG. 1, the output voltage of the light receiving section (phototransistor) 6b is input to the A/D conversion input section 11 of the CPU 10. The output voltage from the light receiving section 6b is A
A/D converter 11 performs A/D conversion to obtain a digital value, and this digital signal is processed by the CPU to perform sensor detection and threshold setting. Above CPU
Reference numeral 10 is for controlling the operation of the mechanism section of the DAT drive device. For example, the CPU detects the output voltage from the light receiving section 6b, and thereby controls, for example, the reel motor drive section 12.

Next, the output voltage detection operation and threshold setting operation in the CPU 10 of the above embodiment will be explained with reference to FIGS. 2 and 3. From left to right, FIG. 2 shows the output voltage from the light receiving section 6b and the threshold value to be set or changed at each time point after the power is turned on, the cassette pack 1 is loaded, and the magnetic tape is running. They are shown in order. Although the output voltage detection and threshold setting in the CPU are performed using digital values, in FIG. 2, for convenience of explanation, the output voltage and the threshold value are explained as voltage values.

As shown in the flowchart shown in FIG. 3, when the power is turned on, it is determined in step (a) whether or not the cassette pack 1 is loaded. This judgment is made when the output from the detection switch of the cassette pack (not shown) is D/
The determination is made by A conversion and input to the CPU 10. In step (a) of FIG.
When it is determined that the is not loaded, step (
In b), the output voltage of the light receiving section 6b at this time is converted to A/D.
The CPU detects the converted signal. When the cassette pack is not loaded, the detection light 7 is transmitted to the light receiving section 6.
It is assumed that the output voltage of the light receiving section 6b at this time is 5 volts, although it is not detected by the light receiving section 6b, ignoring the external light (see (b) of FIG. 2). Next, in step (c) of FIG. 3, a threshold value is set. This threshold is determined by step (b
), and for example, if the detection output when the cassette is not loaded is 5 volts as described above, as shown in FIG. Set a threshold equal to half the voltage, 2.5 volts.

Next, in step (d), the device waits for the cassette pack 1 to be loaded. Whether or not the cassette pack 1 is loaded is determined by the output of a cassette pack detection switch provided in the device. cassette pack 1
When the magnetic tape T is loaded, as shown in FIG. 4, the magnetic tape T blocks the detection light 7, but at this time, the light receiving output of the light receiving section 6b is detected in step (e1). Assume that the output from the light receiving section 6b when the magnetic tape T blocks the optical path of the detection light 7 is, for example, 4 volts (see (e) in FIG. 2). At this time, in step (f1), the threshold value is changed based on the detection output of 4 volts when the magnetic tape is present. For example, by changing this threshold value,
As shown in (f), a threshold of 2 volts, half of 4 volts, is set.

Next, in step (g), it is waited to see if EOT (end of tape) is detected. When the EOT transparent tape passes through the path of the detection light 7, the light receiving section 6b detects the light and its output voltage decreases. Due to this decrease in the output voltage, the CPU determines that EOT has been detected. At this time, assume that the output voltage from the light receiving section 6b is, for example, 1 volt, as shown in FIG. 2(g). At this stage, the threshold value is changed again in step (h). As shown in FIG. 2(h), the threshold value at this time is changed by the output of 4 volts from the light receiving section 6b when the magnetic tape is interposed in the path of the detection light 7, and when the EOT is detected. It is set to 2.5 volts, which is half the output value of 1 volt.

In this way, the output voltage when the magnetic tape T blocks the path of the detection light (sensor OFF) and the output voltage when the light transmitted through the transparent tape of the EOT is detected by the light receiving section 6b are as follows. The threshold value is set to half the output voltage. After that, when the output from the light receiving section 6b is D/A converted and input to the CPU, the CPU detects the output level based on the finally set threshold value, and detects whether the magnetic tape T is transparent or not. The tape detection operation is now performed accurately.

Next, if the cassette pack 1 is loaded when the power is turned on, the process moves from step (a) to step (e2) in FIG. The output voltage is detected when the Assuming that the output voltage at this time is 4 volts as shown in FIG. 2(e), the threshold value is set to 2 volts in step (f2) (see FIG. 2(f)). Then, the threshold value is set to 2.5 volts, which is between the output voltage (for example, 1 volt) when EOT is detected and the detected voltage of 4 volts when magnetic tape is detected.

[0015] Also, when loading the cassette pack,
When the end of the tape is located in the path of the detection light 7,
The detection value of the light receiving section 6b is, for example, 1 as shown in FIG. 2(g).
When the magnetic tape T is rewound, the magnetic tape T blocks the optical path and an output of 4 volts is obtained, for example, as shown in FIG. 2(e). In this case, the threshold value is first set to 2.5 volts, which is half of both output voltages, and there is no need to change it. Furthermore, as shown in FIG. 4, the embodiment described above shows the output of the light receiving section 6b provided at the pull-out part of the magnetic tape pulled out from the tape reel 3 on the supply side. The same applies to the installed detection unit. For example, if the detection voltage of the light transmitted through the beginning of the tape when loading the cassette is 1 volt, then when the magnetic tape is wound and the magnetic tape T blocks the light, the detection voltage is 1 volt. When the output voltage is 4 volts, the threshold value of this detection section is set to 2.5 volts, for example.

In the above embodiment, the threshold value is set to half the voltage according to the previous detection output at the time of setting, and
Alternatively, the threshold setting point does not necessarily have to be half of the output voltage, and the threshold setting point can be set at the most favorable point considering the characteristics of the device. . Further, the output voltage shown in FIG. 2 is shown as an example, and the actual output voltage does not necessarily match that shown in FIG. The above threshold values are set and changed each time the cassette pack 1 is loaded. Therefore, the most accurate threshold value is set depending on the transmission characteristics of the prism 5 provided in the cassette pack and the transmission characteristics of the magnetic tape T.

Furthermore, although the illustrated embodiment has been described with respect to a cassette pack having a prism 5, it does not have a prism and a light source is inserted inside the magnetic tape T, and the light is positioned outside the running part of the magnetic tape. A similar threshold setting is performed even when the light is detected by a light receiving section. Furthermore, the threshold setting device of the present invention is not limited to detecting the edge of a magnetic tape using optical detection, but can also be implemented in an optical detection unit and a magnetic detection unit in other devices.

[0018]

As described above, according to the present invention, the threshold level of the sensor output is set based on the actual detection output from the sensor, so that the optimum threshold value can be set without false detection. It becomes possible.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram showing a sensor output threshold setting device according to the present invention;

FIG. 2 is an explanatory diagram of output showing sensor output and threshold value;

[Fig. 3] Flowchart showing threshold setting and change control;

FIG. 4 is a plan view showing the optical detection section of the cassette pack;

[
FIG. 5 is a circuit diagram of the light receiving section.

[Explanation of symbols]

1　Cassette pack 3 Tape reel T Magnetic tape 5 Prism 6 Photo reflector 6a　Light emitting part 6b Light receiving part 7 Detection light 10 CPU 11 A/D conversion section

Claims (1)

[Claims] [Claim 1] An A/D converter is provided in the output path from the sensor, and based on the A/D converted digital output, the output is set between the output when the sensor is OFF and the output when the sensor is ON. 1. A sensor output threshold setting device, comprising means for setting a detection threshold of a sensor.