Abstract:
A medium detecting device determines whether a medium is set in a device. The medium detecting device includes an optical sensor irradiates a light towards a position where the medium is possibly set, collects a reflected light, and outputs a signal based on the reflected light. A temperature sensor measures temperature around the optical sensor. A threshold selecting unit selects a threshold from among a plurality of thresholds based on the parameter. A determining unit determines whether the medium is set based on comparison of the signal and the threshold selected.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a medium detecting device that detects using an optical sensor whether a medium is set in a device.  
         [0003]     2. Description of the Related Art  
         [0004]     Noncontact optical sensors that detect objects are used in various fields. Optical sensors are used to detect whether paper money is put in ATMs (automated teller machines), whether coins are inserted in automatic vending machines, whether tickets or commuter passes are inserted in automatic ticket gates, and so forth. In recording medium players, such as CD (compact disc) players or DVD (digital versatile disc) payers, optical sensors are often used to detect whether a CD (compact disc) or a DVD (digital versatile disc) is set in the players.  
         [0005]     For example, Japanese Patent Application Laid Open No. 2003-338112 discloses a recording-medium conveying device that includes an optical sensor and microswitches. The optical sensor includes a light emitting diode (LED) and a phototransistor. The optical sensor and the microswitches are used to detect whether the disc is a disc with an outer diameter of 12 centimeters (cm) such as a CD and a DVD, a pseudo disc in which a CD with an outer diameter of 8 cm is fitted in a circular adaptor with an outer diameter of 12 cm, or a CD with an outer diameter of 8 cm.  
         [0006]     When a disc is conveyed inside the device with a conveying roller, a medium detecting sensor, which is the optical sensor, detects the disc. The microswitches function as outline detecting sensors that detect the outline of the disc to thereby detecting whether the disc is a 12-cm disc or a 12-cm pseudo disc. During a predetermined masking time period that starts when the disc is detected, if a detection signal output from the medium detecting sensor does not change, then, from the output of the outline detecting sensor it is determined whether the disc is a 12-cm disc or a 12-cm pseudo disc.  
         [0007]     According to this conventional technology, a system controller provided with a microprocessor controls the recording-medium conveying device and a recording-medium playback device that includes the recording-medium conveying device. Output of the optical sensor is converted into digital values, and the digital values are binarized into detection signals, based on a predetermined threshold. Specifically, if the output of the optical sensor exceeds the threshold, it is converted to a high logical level (H) detection signal, and if the output is smaller than the threshold, it is converted to a low logical level (L) detection signal. The output of the optical sensor is low when a disc is not set and high when the disc is set. Accordingly, whether a disc is set can be detected using the threshold.  
         [0008]     However, output of the optical sensors fluctuates because of fluctuations in power supply and environmental temperature, irregular parts, aging, and so forth. Fluctuations in power supply affect the output as follows. If the power supply increases in the optical sensor, electric current passing through the LED increases and the LED emits a stronger light. As a result, when the phototransistor is turned on, photocurrent increases and corrector voltage decreases, resulting in a smaller value to be output from the optical sensor. On the other hand, if the power supply decreases in the optical sensor, the electric current passing through the LED decreases and the LED emits a weaker light. As a result, when the phototransistor is turned on, the photocurrent decreases and the corrector voltage increases, resulting in a larger value to be output from the optical sensor.  
         [0009]     Fluctuations in environmental temperature affect the output as follows. For example, the light emitted from the LED is stronger with lower temperature, and is weaker with higher temperature. On the other hand, sensitivity of the phototransistor decreases with lower temperature (lower photocurrent), and increases with higher temperature (higher photocurrent). When the LED is combined with the phototransistor, the phototransistor has greater influence than the LED. Thus, with higher temperature, the photocurrent increases when the phototransistor is turned on, resulting in a smaller value to be output from the optical sensor. With lower temperature, the photocurrent decreases when the phototransistor is turned on, resulting in a larger value to be output from the optical sensor. This description is applicable when the LED and the phototransistor are used together in the optical sensor. Other types of optical sensors might have different tendencies.  
         [0010]     In recent years, highly transmissible C-thru discs have been developed. When a C-thru disc is inserted, the light emitted from the LED is irradiated to the phototransistor. As a result, the output of the optical sensor does not change much, whether the C-thru disc is inserted or not.  
         [0011]      FIG. 1  is an example of fluctuations in output of an optical sensor (currents output from the optical sensor). The output fluctuations are assumed to be caused by fluctuations in power supply and environmental temperature, irregular parts, and aging. Transmittance of a C-thru disc is also taken into consideration. A fluctuation range  100  is a range in which the output of the optical sensor fluctuates when the disc is set, and a fluctuation range  120  is a range in which the output of the optical sensor fluctuates when the disc is not set. An operable range  110  is a range in which a threshold to detect the disc is set, located between the fluctuation range  100  and the fluctuation range  120 .  
         [0012]     A threshold SH 1  appropriate under low temperature is applicable for room temperature but with very small margin, and is inapplicable for high temperature. On the other hand, a threshold SH 3  appropriate under high temperature is applicable for room temperature but with very small margin, and is inapplicable for low temperature. A threshold SH 2  appropriate under room temperature is applicable for high and low temperatures but with very small margins. Failures can increase if the threshold margin is small.  
         [0013]     Thus, it is difficult to determine a single threshold with the conventional technology, under the conditions described above.  
         [0014]     One approach is to screen out the parts that cause the fluctuation to suppress fluctuations, so that the operable range becomes wider under both high and low temperature conditions, however, this approach leads to increased cost.  
       SUMMARY OF THE INVENTION  
       [0015]     It is an object of the present invention to at least solve the problems in the conventional technology.  
         [0016]     According to an aspect of the present invention, a medium detecting device determines whether a medium is set in a device, and includes an optical sensor that irradiates a light towards a position where the medium is possibly set, collects a reflected light, and outputs a signal based on the reflected light collected; a measuring unit that measures a parameter related to the optical sensor; a threshold selects unit that selects a threshold from among a plurality of thresholds based on the parameter measured; and a determining unit that determines whether the medium is set based on a comparison of the signal and the threshold selected.  
         [0017]     According to another aspect of the present invention, a recording-medium playback device determines whether a medium is set using the above medium detecting device.  
         [0018]     According to still another aspect of the present invention, a medium detecting method is a method of determining whether a medium is set in a device, and includes irradiating a light from an optical sensor towards a position where the medium is possibly set, collecting at the optical sensor a reflected light, and outputting a signal from the optical sensor based on the reflected light collected; measuring a parameter related to the optical sensor; selecting a threshold from among a plurality of thresholds based on the parameter measured; and determining whether the medium is set based on a comparison of the signal and the threshold selected.  
         [0019]     According to still another aspect of the present invention, a computer-readable recording medium stores therein a computer program that causes a computer to implement the above medium detecting method.  
         [0020]     The other objects, features, and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  is a relationship between thresholds and fluctuations in output of an optical sensor in a conventional technology;  
         [0022]      FIG. 2  is a block diagram of a recording-medium playback device that includes a medium detecting device according to a first embodiment of the present invention;  
         [0023]      FIG. 3  is a detailed block diagram of the medium detecting device shown in  FIG. 2 ;  
         [0024]      FIG. 4  is an example of a threshold table used in the first embodiment;  
         [0025]      FIG. 5  is a relationship between thresholds based on temperature and fluctuations in output of an optical sensor according to the first embodiment of the present invention;  
         [0026]      FIG. 6  is a flowchart of an operation of the medium detecting device shown in  FIG. 3 ;  
         [0027]      FIG. 7  is a detailed block diagram of a medium detecting device according to a second embodiment of the present invention;  
         [0028]      FIG. 8  is an example of a threshold table used in the second embodiment;  
         [0029]      FIG. 9  is a relationship between thresholds based on voltage and fluctuations in output of an optical sensor according to the second embodiment of the present invention;  
         [0030]      FIG. 10  is an example of a medium detecting device according to a third embodiment of the present invention; and  
         [0031]      FIG. 11  is an example of a threshold table used in the third embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0032]     Exemplary embodiments of the present invention will be described below with reference to accompanying drawings.  
         [0033]     It is known that output of an optical sensor fluctuates because of various parameters, such as fluctuations in temperature around the optical sensor or in power supply voltage supplied to the optical sensor. In a medium detecting device according to the present invention, a threshold used to detect whether a disc is set in a device, can be variably set according to various parameters.  
         [0034]     Specifically, a plurality of thresholds corresponding to various levels of temperature or power supply voltage is predetermined. Immediately before the disc is detected, the temperature or the power supply voltage is measured, and a threshold is selected from among the predetermined thresholds based on the measured temperature or power supply voltage. Accordingly, the output of the optical sensor can be prevented from being affected by the fluctuations in temperature or power supply voltage, so that the disc can be detected accurately.  
         [0035]     A first embodiment according to the present invention is described with reference to FIGS.  2  to  7 .  FIG. 2  is a block diagram of a recording-medium playback device  9  according to the first embodiment. The recording-medium playback device  9  includes a medium detecting device  1  and a playback processing section  91 . The medium detecting device  1  detects whether a disc  4 , which is a recording medium such as a CD or a DVD, is set. After the medium detecting device  1  detects the disc  4 , the playback processing section  91  loads the disc  4  to perform playback processing.  
         [0036]      FIG. 3  is a detailed block diagram of the medium detecting device  1  shown in  FIG. 2 . The medium detecting device  1  includes an optical sensor  2 , a temperature sensor  3 , and a microcomputer  5 .  
         [0037]     The optical sensor  2  includes an LED (not shown) and a phototransistor (not shown). Light emitted from the LED controls the phototransistor to turn on/off. The optical sensor  2  outputs a corrector voltage, which is an output of the phototransistor, as an optical sensor output SV, to the microcomputer  5 .  
         [0038]     The temperature sensor  3  can be a thermistor, a resistance thermometer, a temperature-sensitive ferrite, and so forth. The temperature sensor  3  measures a temperature of or around the optical sensor  2 , converts the temperature measured to a voltage, and outputs the voltage as a temperature sensor output TO, to the microcomputer  5 .  
         [0039]     The microcomputer  5  includes two digital-analogue converters (hereinafter, “A/D converter”)  51 ,  52 , a detection processing section  53 , and a storage section  54 . The microcomputer  5  executes a computer program stored in a program memory (not shown), to realize a function of the detection processing section  53 . The microcomputer  5  monitors the optical sensor output SV and the temperature sensor output TO, to determine whether the disc  4  is set in the medium detecting device  1 .  
         [0040]     The A/D converter  51  converts the optical sensor output SV into a digital value, and the digital value is output as an optical sensor output SV 1  to the detection processing-section  53 . The A/D converter  52  converts the temperature sensor output TO into a digital value, and the digital value is output as a temperature sensor output TO 1  to the detection processing section  53 .  
         [0041]     The storage section  54  includes a ROM (read only memory) and a RAM (random access memory), and so forth, and stores a threshold table shown in  FIG. 4 . The threshold table defines a threshold for each of a plurality of temperatures, such as a threshold SH 11  for low temperature, a threshold SH 12  for room temperature, and a threshold SH 13  for high temperature. These thresholds are determined beforehand based on fluctuations in the optical sensor output SV 1 , caused by fluctuations in power supply and environmental temperature, irregular parts, aging, and transmittance of a C-thru disc. As shown in  FIG. 5 , a fluctuation range  100  is a range in which the output of the optical sensor fluctuates when a disc is set. A fluctuation range  120  is a range in which the output of the optical sensor fluctuates when a disc is not set. An appropriate threshold is to be set in an operable range  110 , located between the fluctuation range  100  and the fluctuation range  120 .  
         [0042]     The detection processing section  53  selects a threshold from the threshold table stored in the storage section  54 , based on the temperature sensor output TO 1 . The detection processing section  53  compares the threshold selected with the optical sensor output SV 1 , to determine whether a disc  4  is set in the medium detecting device  1 .  
         [0043]      FIG. 6  is a flowchart of an operation performed by the medium detecting device  1 . When a loading operation request to insert the disc  4  is received from the playback processing section  91 , the detection processing section  53  acquires the temperature sensor output TO 1  input from the A/D converter  52  (steps S 100  and S 110 ).  
         [0044]     The detection processing section  53  selects a threshold from the threshold table stored in the storage section  54 , based on the acquired temperature sensor output TO 1  (step S 120 ). Specifically, if the temperature sensor output TO 1  corresponds to a predetermined low temperature range, the threshold SH 11  is selected to detect whether the disc  4  is set. Likewise, thresholds SH 12  and SH 13  are selected when the temperature sensor output TO 1  corresponds to room and high temperature ranges, respectively.  
         [0045]     The detection processing section  53  acquires an optical sensor output SV 1  of the A/D converter  51  (step S 130 ). The detection processing section  53  compares the optical sensor output SV 1  with the threshold selected (step S 140 ). If the optical sensor output SV 1  is larger than the threshold, the detection processing section  53  outputs a detection signal that the disc  4  is set.  
         [0046]     Upon receiving the detection signal that the disc  4  is set, the playback processing section  91  loads the disc  4  and starts a playback processing (step S 150 ).  
         [0047]     The detection processing section  53  repeats the operation of comparing the selected-threshold with an optical sensor output SV 1 , until the optical sensor output SV 1  is larger than the threshold (steps S 130  and S 140 ).  
         [0048]     As described above, the threshold table is stored in the storage section  54 , the temperature sensor  3  measures the temperature before the disc  4  is detected, the detection processing section. 53  selects a threshold based on the temperature measured and the threshold table, compares the threshold with the optical sensor output SV 1  of the optical sensor  2  to detect whether the disc  4  is set. Therefore, the disc can be detected accurately, without having to screen out parts that cause fluctuations in the output. Moreover, cost is suppressed because the parts do not have to be screened.  
         [0049]     In the first embodiment, the medium detecting device  1  includes the temperature sensor  3 . However, if the recording-medium playback device  9  already includes a temperature sensor, it can be used. In other words, the temperature sensor  3  does not necessarily have to be provided inside the medium detecting device  1 , as long as information that identifies the temperature around the optical sensor  2  is input to the detection processing section  53 , such as the temperature sensor output TO or the temperature sensor output TO 1 .  
         [0050]     In the first embodiment, a threshold is selected according to temperature changes. However, fluctuations in output of the optical sensor are not only caused by variations in the temperature, but also caused by variations in the power supply voltage supplied to the optical sensor. In a second embodiment, the threshold is selected according to the power supply voltage.  
         [0051]      FIG. 7  is a block diagram of a medium detecting device la according to the second embodiment of the present invention. The structure of the medium detecting device la is almost the same as that of the medium detecting device  1  according to the first embodiment shown in  FIG. 3 , except that a power supply sensor  6  is provided instead of the temperature sensor  3 , and an A/D converter  55  is provided instead of the A/D converter  52 . Common components are denoted by the same reference numerals and overlapping descriptions are omitted.  
         [0052]     The power supply sensor  6  monitors the power supply voltage supplied to the optical sensor  2 , and outputs the power supply voltage as a power supply sensor output VO to the A/D converter  55 . The A/D converter  55  converts the power supply sensor output VO to a digital value, and the digital value is output as a power supply sensor output VO 1  to the detection processing section  53 .  
         [0053]     The storage section  54  stores a threshold table that includes a threshold for each of a plurality of levels of the power supply voltage as shown in  FIG. 8 . For example, a threshold SH 21  is for low power supply voltage, a threshold SH 22  is for medium power supply voltage, and a threshold SH 23  is for high power supply voltage. These thresholds are determined beforehand based on fluctuations in the optical sensor output SV 1 , caused by fluctuations in power supply and environmental temperature, irregular parts, aging, and transmittance of a C-thru disc. Specifically, an appropriate threshold is to be set in the operable range  110 , located between the fluctuation range  100  and the fluctuation range  120 , as shown in  FIG. 9 .  
         [0054]     Next, an operation of the medium detecting device la is described. When a loading operation request to insert the disc  4  is received from the playback processing section  91 , the detection processing section  53  acquires a power supply sensor output VO 1  from the A/D converter  55 .  
         [0055]     Based on the acquired power supply sensor output VO 1  the detection processing section  53  selects a threshold from the threshold table stored in the storage section  54 . Specifically, if the power supply sensor output VO 1  corresponds to the low power supply range, the detection processing section  53  selects the threshold SH 21 . Likewise, the detection processing section  53  selects the threshold SH 22  when the power supply sensor output VO 1  corresponds to the medium power supply range, and selects the threshold SH 23  when the power supply sensor output VO 1  corresponds to high power supply ranges.  
         [0056]     The detection processing section  53  acquires an optical sensor output SV 1  from the A/D converter  51 . The detection processing section  53  compares the optical sensor output SV 1  with the threshold selected. If the optical sensor output SV 1  is larger than the threshold, the detection processing section  53  outputs a detection signal that the disc  4  is set.  
         [0057]     Upon receiving the detection signal that the disc  4  is set, the playback processing section  91  loads the disc  4  and starts a playback processing. The detection processing section  53  repeats the operation of comparing the selected threshold with an optical sensor output SV 1 , until the optical sensor output SV 1  is larger than the threshold.  
         [0058]     As described above, the threshold table is stored in the storage section  54 , the power supply sensor  6  measures the power supply voltage before the disc  4  is detected, the detection processing section  53  selects a threshold based on the power supply voltage measured and the threshold table, compares the threshold with the optical sensor output SV 1  of the optical sensor  2  to detect whether the disc  4  is set. Therefore, the disc can be detected accurately, without having to screen out parts that cause fluctuations in the output. Moreover, cost is suppressed because the parts do not have to be screened.  
         [0059]     In the second embodiment, the medium detecting device  1   a  includes the power supply sensor  6 . However, if the recording-medium playback device  9  already includes a power supply sensor, it can be used. In other words, the power supply sensor  6  does not necessarily have to be provided inside the medium detecting device la, as long as information that identifies,the power supply voltage supplied to the optical sensor  2  is input to the detection processing section  53 , such as the power supply sensor output VO or the or the power supply sensor output VO 1 .  
         [0060]     The parameters used to select the threshold in the first and second embodiments are temperature and power supply voltage, respectively. However, any other parameter that affects the output of the optical sensor can be used. Moreover, a plurality of parameters can be used in combination.  
         [0061]     An example shown in  FIG. 10  is a combination of  FIG. 3  and FIG.  7 , i.e., both the temperature sensor  3  and the power supply sensor  6  are included. Thus, the threshold table stored in the storage section  54  defines thresholds for each of a plurality of combinations of the temperature and the power supply voltage, as shown in  FIG. 11 . For example, a threshold SH 31  is for low temperature and low power supply voltage, a threshold SH 32  is for low temperature and medium power supply voltage, a threshold SH 33  is for low temperature and high power supply voltage, a threshold SH 34  is for room temperature and low power supply voltage, a threshold SH 35  is for room temperature and medium power supply voltage, a threshold SH 36  is for room temperature and high power supply voltage, a threshold SH 37  is for high temperature and low power supply voltage, a threshold SH 38  is for high temperature and medium power supply voltage, and a threshold SH 39  is for high temperature and high power supply voltage.  
         [0062]     When a loading operation request to insert the disc  4  is received, the detection processing section  53  acquires a temperature sensor output TO 1  from the A/D converter  52  and a power supply sensor output VO 1  from the A/D converter  55 , selects a threshold from the threshold table based on the temperature sensor output TO 1  and the power supply sensor output VO 1 , compares the optical sensor output SV 1  with the threshold selected. The threshold can be set more accurately using both the temperature and the power supply voltage as compared to the case when only one parameter is used.  
         [0063]     In the first and second embodiments, the medium detecting device  1  is used to detect whether the disc  4  is set in the recording-medium, playback device  9  that plays back discs such as DVDs and CDs. However, the medium detecting device  1  can be used to detect any medium in any device.  
         [0064]     According to the present invention, a disc can be detected accurately, and cost can be suppressed.  
         [0065]     Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.