Endoscope system, processor and endoscope

An endoscope system includes an endoscope and a processor. The endoscope includes: an actuator including a coil configured to cause a movable lens and a magnet to move by application of a drive signal; a position sensor configured to output a position detection signal showing a position of the movable lens according to a magnetic flux of the magnet; and an endoscope memory storing correction information for correcting crosstalk onto the position detection signal by the magnetic flux of the coil. The processor includes a drive controller configured to correct the position detection signal based on the drive signal and the correction information and output the drive signal based on a target position and the corrected position detection signal, to the actuator.

CROSS REFERENCE TO RELATED APPLICATION

This application claims benefit of Japanese Application No. 2018-218015 filed in Japan on Nov. 21, 2018, the entire contents of which are incorporated herein by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an endoscope system that adjusts an image forming state of an objective optical system by an actuator, a processor and an endoscope.

2. Description of the Related Art

Conventionally, in an image pickup apparatus such as a digital camera, focus adjustment and zoom adjustment have been performed using an actuator.

For example, Japanese Patent Application Laid-Open Publication No. 2015-88956 describes a technique for, at the time of driving a shake correcting member (an image sensor or a lens) by a driving coil in a digital camera, which is an image pickup apparatus, detecting a position of the shake correcting member by a magnetic sensor (a hall sensor). The magnetic sensor, however, not only detects magnetism corresponding to the position of the shake correcting member but also detects magnetism generated by the driving coil as noise. Therefore, a noise coefficient is calculated in advance from a drive signal and a detection signal of the magnetic sensor when the drive signal is outputted to the driving coil to remove a noise signal component corresponding to the magnetism generated by the driving coil, from the detection signal of the magnetic sensor.

At the time of performing measurement for calculation of the noise coefficient, the image sensor (a movable stage) is locked not to move or the measurement is performed before mounting the image sensor (the movable stage) so that the hall sensor is not influenced by change in a magnetic force of a magnet as described in paragraph [0051] and the like of the gazette.

SUMMARY OF THE INVENTION

An endoscope system according to one aspect of the present invention is an endoscope system including an endoscope and a processor to which the endoscope is connected, wherein the endoscope includes: an objective optical system configured to form a subject image; a movable lens configured to adjust an image forming state of the objective optical system; an actuator including a magnet configured to move integrally with the movable lens and a coil configured to cause the movable lens and the magnet to move by electromagnetic force by applying a drive signal; a position sensor configured to output a position detection signal showing a position of the movable lens according to a density of a magnetic flux generated by the magnet; and an endoscope memory storing at least one piece of correction information for correcting a crosstalk influence on the position detection signal given by a density of a magnetic flux generated by the coil to which the drive signal is applied; and the processor includes a controller configured to correct the position detection signal acquired from the position sensor, based on the drive signal and the at least one piece of correction information acquired from the endoscope memory, and output the drive signal generated by feedback control based on at least one target position of the movable lens and the position detection signal that is corrected, to the actuator.

A processor according to one aspect of the present invention is connected to an endoscope, the endoscope including: an objective optical system configured to form a subject image; a movable lens configured to adjust an image forming state of the objective optical system; an actuator including a magnet configured to move integrally with the movable lens and a coil configured to cause the movable lens and the magnet to move by electromagnetic force by applying a drive signal; a position sensor configured to output a position detection signal showing a position of the movable lens according to a density of a magnetic flux generated by the magnet; and an endoscope memory storing at least one piece of correction information for correcting a crosstalk influence on the position detection signal given by a density of a magnetic flux generated by the coil to which the drive signal is applied; and the processor including a controller configured to correct the position detection signal acquired from the position sensor based on the drive signal and the at least one piece of correction information acquired from the endoscope memory, and output the drive signal generated by feedback control based on at least one target position of the movable lens and the position detection signal that is corrected, to the actuator.

An endoscope according to one aspect of the present invention is connected to a processor, the endoscope including: an objective optical system configured to form a subject image; a movable lens configured to adjust an image forming state of the objective optical system; an actuator including a magnet configured to move integrally with the movable lens and a coil configured to cause the movable lens and the magnet to move by electromagnetic force by applying a drive signal; a position sensor configured to output a position detection signal showing a position of the movable lens according to a density of a magnetic flux generated by the magnet; and an endoscope memory storing at least one piece of correction information for correcting a crosstalk influence on the position detection signal given by a density of a magnetic flux generated by the coil to which the drive signal is applied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1 to 8show an embodiment of the present invention, andFIG. 1is a diagram showing a configuration of an endoscope system1in which an endoscope2and a processor3are attachably and detachably configured.

The endoscope system1as an image pickup apparatus in the present embodiment is configured, for example, as an electronic endoscope system that picks up an optical image of a subject and outputs an image pickup signal. Here, the endoscope system1may be any of endoscope systems for medical, industrial, academic and other purposes.

The endoscope system1is provided with the endoscope2and the processor3configured as a body separate from the endoscope2. The processor3is provided with a light source device4configured to emit illumination light, a video processor5configured to process an image pickup signal from the endoscope2, and a monitor6configured to display an endoscopic image based on a video signal outputted from the video processor5. Note that the monitor6is not limited to being included in the processor3, but a separate external monitor may be connected to the processor3and used. The light source device4may be configured integrally with the video processor5.

The endoscope2is provided with an elongated insertion portion11to be inserted into a subject, an operation portion12provided on a proximal end side of the insertion portion11, and a universal cord13extended, for example, from a side portion of the operation portion12, and is configured as an electronic endoscope as described later. However, the endoscope2is not limited to an electronic endoscope but may be an optical endoscope if the endoscope2is configured to drive an objective optical system21(seeFIGS. 2 and 3, and the like) by an actuator23(seeFIGS. 2 and 3, and the like) described later.

The insertion portion11is provided with a distal end portion11a, a bending portion11band a flexible tube portion11cin that order from a distal end side toward the proximal end side. Note that though a case where the endoscope2is a flexible endoscope is given as an example here, the endoscope2may be a rigid endoscope.

Inside the distal end portion11a, the objective optical system21, an image pickup device22(seeFIG. 2), the actuator23, magnets24(seeFIGS. 2 and 3, and the like), a position sensor25(seeFIGS. 2 and 3, and the like) and the like are arranged.

The operation portion12is provided with a forceps opening12a, a grip portion12band a user operation portion12c.

The forceps opening12ais an opening portion on a proximal end side of a forceps channel provided in the insertion portion11. An opening portion on a distal end side of the forceps channel is arranged at the distal end portion11a. By inserting a treatment instrument such as forceps from the forceps opening12aand causing the treatment instrument to project from the distal end portion11a, various kinds of treatment for a subject by the treatment instrument can be performed.

The grip portion12bis a part that a surgeon who operates the endoscope2grasps by his hand.

The user operation portion12cis a part for the surgeon to perform various kinds of operations for the endoscope system1including the endoscope2.

The user operation portion12cis provided with two bending operation portions14, an air/water feeding button15, a suction button16and a switch portion17.

One of the two bending operation portions14is for performing a bending operation of the bending portion11bin a vertical direction, and the other is for performing a bending operation of the bending portion11bin a horizontal direction. It is possible to perform a bending operation of the bending portion11bin a desired direction by combining vertical bending and horizontal bending.

The air/water feeding button15is an operation button for performing air/water feeding to the distal end portion11aside, for example, via the forceps channel described above.

The suction button16is an operation button for performing suction from the distal end portion11aside, for example, via the forceps channel described above.

The switch portion17is configured being provided with a plurality of switches17a, and mainly operations related to image pickup are performed by the switch portion17. For example, a certain switch17ais adapted to function as a release button for picking up a still image; another certain switch17ais adapted to function as a freeze button for freezing video that is being observed on the monitor6; and still another certain switch17ais adapted to function as a focus button for adjusting a focus position of the objective optical system21(or a zoom button for adjusting a zoom position).

The universal cord13includes a light guide bundle and a signal line. Here, the light guide bundle is for transmitting illumination light generated by the light source device4to radiate the illumination to a subject from an illumination window on the distal end portion11a. The signal line is used for transmission of various kinds of signals related to image pickup of the image pickup device22, various kinds of signals related to driving of the actuator23and position detection, and endoscope information, and the like.

A scope connector13ato be detachably connected to the light source device4is provided on a proximal end of the universal cord13. By connecting the scope connector13ato the light source device4, a state in which illumination light can be supplied to a proximal end of the light guide bundle is entered.

For example, from a side portion of the scope connector13a, the scope cable13bthat includes the signal line described above is extended. An electrical connector13cto be detachably connected to the video processor5is provided on a proximal end of the scope cable13b. By connecting the electrical connector13cto a connector receptacle5aof the video processor5, an electrical circuit of the endoscope2and an electrical circuit of the video processor5are connected via the signal line. Note that the scope cable13bmay be attachable to and detachable from the scope connector13a, or the universal cord13and the scope cable13bmay be integrally configured.

The video processor5supplies power to the endoscope2to control an electrical configuration of the endoscope2. The video processor5also processes an image pickup signal obtained from the image pickup device22of the endoscope2to generate a video signal.

The monitor6is configured, for example, as a color monitor and is connected to the video processor5. The monitor6receives a video signal processed by the video processor5and displays an endoscopic image. Furthermore, the monitor6is adapted to be capable of displaying various kinds of information and the like related to the endoscope system1.

FIG. 2is a diagram showing main parts of electrical and optical configurations of the endoscope2and the processor3related to driving of the objective optical system21. Note that, inFIG. 2, thin arrows show a flow of a digital signal, and normal-thickness arrows show a flow of an analog signal (however,FIG. 2shows a mere example of classification of the digital signal and the analog signal).

The endoscope2is provided with the objective optical system21, the image pickup device22, the actuator23, the magnets24, the position sensor25and the user operation portion12cas described above and is further provided with a sensor amplification circuit26and an endoscope memory27.

The objective optical system21forms an optical image of a subject (a subject image) on an image pickup surface of the image pickup device22. The objective optical system21is provided with a movable lens21aand a fixed lens21b(seeFIG. 3). The movable lens21ais for adjusting an image forming state of the objective optical system21. The movable lens21ais movable in a direction of an optical axis O of the objective optical system21, facing the fixed lens21b. When the movable lens21amoves in the direction of the optical axis O, the image forming state of the objective optical system21is adjusted, and, for example, the focus position (which may instead be the zoom position) is changed. Therefore, the movable lens21afunctions, for example, as a focus lens (or a zoom lens). Note that though the movable lens21ais given as an example of a movable optical element here, the movable optical element is not limited to a lens, but other optical elements such as an optical filter, an optical diaphragm and a mirror are also possible.

A plurality of pixels are arrayed on an image pickup surface of the image pickup device22, and the image pickup device22generates an image pickup signal configured with a plurality of pixel signals by performing photoelectric conversion of a subject image formed by the objective optical system21by each pixel. Note that an image pickup system of the image pickup apparatus is configured including the objective optical system21and the image pickup device22.

The actuator23moves the movable lens21ain the direction of the optical axis O and is specifically configured as a voice coil motor (VCM) configured to cause driving force to be generated by electromagnetic force.

The magnets24are configured with permanent magnets or the like and are arranged to move in the direction of the optical axis O integrally with the movable lens21a. Magnetic fields generated by the magnets24are used for the position sensor25to detect a position of the movable lens21athat moves integrally with the magnets24.

Furthermore, the magnets24of the present embodiment are not only used for position detection but also configured to also serve as a part of the voice coil motor in order to miniaturize the distal end portion11a. Therefore, the actuator23configured as the voice coil motor includes the magnets24and coils23aand23b(seeFIG. 3and the like) described later.

Here,FIG. 3is a cross-sectional view showing configurations of the objective optical system21and the actuator23. Note that, inFIG. 3, a left side indicates a distal end side (an object side) and a right side indicates a proximal end side (an image side). An observation window not shown is provided on a distal end side of the objective optical system21.

The movable lens21ais held, for example, by a movable barrel51that is movable in the direction of the optical axis O within a predetermined range. The fixed lens21bis, for example, held by a lens barrel52and then fixed to a fixed barrel53. Furthermore, the fixed barrel53is fixed to a distal end portion body54provided in the distal end portion11aof the insertion portion11.

The magnets24are fixed to the movable barrel51, and the coils23aand23bof the actuator23are attached to a fixed portion such as the fixed barrel53.

In the configuration example shown inFIG. 3, the magnets24are provided at two positions on the distal end side and the proximal end side in the direction of the optical axis O, respectively, and magnetized in a radial direction around the optical axis O. Magnetization directions of the magnet24on the distal end side and the magnet24on the proximal end side are opposite to each other. More specifically, an outer diameter side and an inner diameter side of the magnet24on the distal end side are an S-pole and an N-pole, respectively; and an outer diameter side and an inner diameter side of the magnet24on the proximal end side are an N-pole and an S-pole, respectively.

The coil23ais provided facing the magnet24on the distal end side, and the coil23bis provided facing the magnet24on the proximal end side. Both of the coils23aand23bare wound in a circumferential direction around the optical axis O. Furthermore, in response to the magnetization directions of the magnet24on the distal end side and the magnet24on the proximal end side being opposite to each other, a direction of a current applied to the coil23aand a direction of a current applied to the coil23bare opposite directions around the optical axis O (if one is a clockwise direction around the optical axis O, the other is a counterclockwise direction around the optical axis O).

At a middle position between the coils23aand23bin the direction of the optical axis O on an outer peripheral side of the coils23aand23b, the position sensor25is fixed to the distal end portion body54. In other words, the position sensor25is arranged on the fixed portion side, facing the magnets24, with the coils23aand23bbeing sandwiched between the position sensor25and the magnets24.

The position sensor25outputs a position detection signal showing the position of the movable lens21aaccording to a density of a magnetic flux generated by the magnets24. More specifically, the position sensor25is configured using a magnetic sensor such as a hall element configured to output a position detection signal (a hall detection signal) according to the magnetic flux density of a magnetic field generated by the magnets24. In other words, since the density of the magnetic flux that enters the position sensor25changes when the magnets24move facing the position sensor25, it is possible to, by detecting a voltage (a hall voltage) of a position detection signal, know positions of the magnets24, therefore, the position of the movable lens21athat moves integrally with the magnets24.

However, as seen from the arrangement inFIG. 3, the position sensor25is arranged close to the coils23aand23bin the small-size actuator23arranged in the distal end portion body54of the endoscope2. Therefore, a density of a magnetic flux generated when a current is applied to the coils23aand23b(indicated by arrows inFIG. 3) is also detected by the position sensor25.

In other words, when a current is applied to the coils23aand23bto move the movable lens21a, a voltage obtained by a change in a hall voltage by the density of the magnetic flux generated from the coils23aand23bbeing added to a hall voltage by the density of the magnetic flux generated from the magnet24is the hall voltage detected by the position sensor25.

Thus, a signal due to the magnetic flux from the coils23aand23b(appropriately referred to as a leakage magnetic flux) is superimposed on a position detection signal outputted from the position sensor25, in addition to an original signal showing the position of the movable lens21a. The signal due to the leakage magnetic flux becomes a noise signal (a false signal) at the time of detecting the position of the movable lens21a.

The noise signal due to the leakage magnetic flux not only causes position detection accuracy to decrease but also influences stability at the time of performing feedback control. Therefore, correction information for correcting the noise signal is determined and stored in the endoscope memory27as described later. In the feedback control, influence of the leakage magnetic flux (a false signal component) included in the position detection signal is corrected using the correction information read from the endoscope memory27.

Here, the magnitude of the noise signal (the false signal) due to the leakage magnetic flux differs according to each individual endoscope2because of mechanical variation, electrical variation and assembly variation among endoscopes2. Therefore, for each individual endoscope2, a correction coefficient K (see Formula 1 and the like described later) that gives a relationship between a current for a drive signal applied to the coils23aand23band a position detection signal outputted from the position sensor25when the current is applied is acquired as the correction information.

In the configuration as described above, the movable lens21a, the movable barrel51and the magnets24constitute a movable portion, and other portions constitute a fixed portion. The fixed portion is fixed to the distal end portion11aand holds the movable portion such that the movable portion can move in the direction of the optical axis O within a predetermined range.

By applying a current to the coils23aand23bthat are in a magnetic field generated by the magnets24, a Lorentz force occurs in the coils23aand23b, and the movable portion moves in the direction of the optical axis O due to reaction of the Lorentz force because the fixed barrel53is fixed.

Note that a reason why the moving magnet type voice coil motor is adopted here is that it is possible to more easily miniaturize the actuator23by the configuration of applying a current to the fixed portion side than by a configuration of applying a current to the movable portion side (because it is necessary to use, for example, a flexible printed circuit board and the like to apply a current to the movable portion side the position of which moves). Therefore, adoption of a moving coil type voice coil motor is not prohibited.

The sensor amplification circuit26shown inFIG. 2is configured as a differential amplification circuit configured to amplify a hall voltage of an analog position detection signal outputted from the position sensor25.

The endoscope memory27is a nonvolatile memory storing correction information for correcting an error that occurs in a position detection signal for each individual endoscope2.

More specifically, the endoscope memory27stores such correction information for correcting crosstalk influence on a position detection signal given by the density of the magnetic flux generated by the coils23aand23bto which a drive signal has been applied as described above. Here, a shift of a position detection signal due to the crosstalk influence (a noise signal component) not only differs according to models of endoscopes2but also differs for each individual endoscope2even among endoscopes2of the same model. Therefore, as described later, the correction information is measured for each individual endoscope2and stored in the endoscope memory27.

Further, the endoscope memory27stores a correction factor α with a value larger than 0 and equal to or smaller than 1, which is preferably determined according to characteristics of the actuator23(therefore, the correction factor α differs for each of models of endoscopes2, and, furthermore, may differ for each production lot if the mounted actuator23is changed according to the manufacture lot of endoscope2).

In addition, the endoscope memory27further stores model information (such as a model number) and a serial number of the endoscope2, other various kinds of information related to the endoscope2, and the like.

As described above, the user operation portion12cis provided with the switches17afor adjusting the image forming state (the focus position, the zoom position and the like) of the objective optical system21as described above. In other words, by a user operating the user operation portion12c, an instruction signal showing a target position of the movable lens21ais transmitted from the user operation portion12cto the processor3side. As an example, it is set which of a far-point focus position (a normal position) and a near-point focus position (a near position) is to be selected as the target position of the movable lens21aby the user operation portion12c(however, the setting is not limited to two-point focusing of far-point and near-point focusing, and it is, of course, possible to continuously change the focus position (or the zoom position)).

Note that though manual focusing by setting from the user operation portion12chas been described here, focusing is not limited to the manual focusing, but auto-focusing or the like based on an image pickup signal obtained from the image pickup device22may be performed.

As described above, the endoscope2is attachable to and detachable from the processor3by detachably connecting the scope connector13ato the light source device4and detachably connecting the electrical connector13cto the connector receptacle5aof the video processor5.

A signal transmitted/received between the endoscope2and the processor3via the electrical connector13cand the connector receptacle5ais, for example, as follows.

The endoscope2transmits an instruction signal from the user operation portion12c, a position detection signal from the sensor amplification circuit26and data such as the correction information in the endoscope memory27to the processor3. Further, the endoscope2receives a drive signal to the actuator23, power supply and a reference voltage signal to the sensor amplification circuit26, and a hall element current signal to the position sensor25, from the processor3. Furthermore, the endoscope2is adapted to, when a predetermined operation condition, a calibration mode as a specific example, is set, receive correction information calculated by the processor3and store the correction information into the endoscope memory27.

The processor3controls the endoscope system1to emit illumination light by the light source device4and acquires an image pickup signal from the endoscope2. The video processor5processes the image pickup signal to generate a video signal, outputs the video signal to the monitor6to causes an endoscopic image and the like to be displayed on the monitor6. Since publicly known techniques can be appropriately used for the above configuration and operation related to the processor3, detailed description will be omitted.

As components related to driving of the objective optical system21, the processor3is provided with a driver circuit31, a current detection circuit32, an ADC33, an ADC34, a sensor driving circuit35, a reference voltage circuit36and a drive control circuit38.

The driver circuit31outputs a drive signal to the actuator23to drive the actuator23, based on control by the drive control circuit38. More specifically, by the driver circuit31applying a drive signal with a predetermined current value to the coils23aand23b, the movable portion including the movable lens21aand the magnets24is moved by electromagnetic force.

The current detection circuit32detects the current value of the drive signal supplied from the driver circuit31to the actuator23and outputs an analog current detection signal.

The ADC33is an analog/digital converter (an A/D converter) configured to convert an analog current detection signal outputted from the current detection circuit32to a digital current detection signal.

The ADC34is an analog/digital converter (an A/D converter) configured to convert an analog position detection signal acquired from the position sensor25and amplified by the sensor amplification circuit26to a digital position detection signal.

The sensor driving circuit35is a constant current circuit configured to supply a hall element current, which is a constant current, to the position sensor25configured, for example, as a hall element.

The reference voltage circuit36supplies an offset voltage signal to be a reference voltage, to the sensor amplification circuit26configured, for example, as a differential amplification circuit.

The drive control circuit38is configured, for example, including an arithmetic processing circuit such as a CPU and a memory, and is adapted to fulfill a function as each processing portion. Here, in the memory of the drive control circuit38, model information (such as a model number) and a serial number of the processor3, a processing program executed by the processor3, various kinds of parameters used in the processor3, set values set for the endoscope system1by the user, other various kinds of information related to the processor3and the like are stored.

The drive control circuit38is a controller configured to control the driver circuit31so that the position of the movable lens21ashown by a position detection signal corresponds to a target position shown by an instruction signal from the user operation portion12c.

More specifically, the drive control circuit38includes a correction factor changing portion41, a variable filter portion42, a correction information calculating portion43, a correcting portion44, a feedback controller45, a target position setting portion46, a superimposed signal generating portion47and a drive amount adding portion48.

The correction factor changing portion41reads the correction information and the correction factor α from the endoscope memory27and adaptively changes the correction factor α acquired from the endoscope memory27so that the value is smaller in the case of prioritizing stability of feedback control than in the case of prioritizing accuracy of a position detection signal. Then, the correction factor changing portion41outputs the correction information read from the endoscope memory27and the correction factor α that has been adaptively changed, to the correcting portion44. Note that if the correction factor α is not adaptively changed, the correction factor changing portion41may be omitted.

The variable filter portion42performs filter processing (low-pass filter processing) of causing a signal component with a frequency equal to or below a cutoff frequency to pass through and reducing a signal component with a frequency higher than the cutoff frequency, for a position detection signal acquired from the position sensor25, and outputs the position detection signal to the correcting portion44. The variable filter portion42is configured to be capable of causing the cutoff frequency to change at this time.

The variable filter portion42sets a first cutoff frequency lower than a frequency of a superimposed signal when the predetermined operation condition (the calibration mode or the like) is not set, and sets a second cutoff frequency higher than the frequency of the superimposed signal if the predetermined operation condition is set.

When the predetermined operation condition (the calibration mode or the like) is set, the correction information calculating portion43calculates correction information.

More specifically, if the predetermined operation condition is set, the correction information calculating portion43acquires a position detection signal from the position sensor25via the variable filter portion42and acquires a current detection signal showing a current value of a drive signal (including a superimposed signal) to be applied to the actuator23, from the ADC33. Furthermore, the correction information calculating portion43extracts a current value component of the superimposed signal in the current detection signal and detects an amplitude of a signal component synchronized with the superimposed signal, in the position detection signal. Then, the correction information calculating portion43calculates a ratio of the amplitude of the signal component synchronized with the superimposed signal, in the position detection signal to an amplitude of the current value component of the superimposed signal (more specifically, the correction factor K described later) as the correction information.

When the predetermined operation condition (the calibration mode or the like) is set, the correction information calculated by the correction information calculating portion43is stored into the endoscope memory27.

Based on the drive signal (more specifically, the current value of the drive signal acquired from the ADC33) to the actuator23and the correction information acquired from the endoscope memory27, the correcting portion44corrects a noise signal component due to the density of the magnetic flux generated from the coils23aand23b, in the position detection signal acquired from the position sensor25. More specifically, the correcting portion44corrects the position detection signal by subtracting a signal obtained by multiplying the drive signal by the correction information (the correction coefficient K described later) from the position detection signal.

Note that if the correction factor changing portion41described above is provided, the correcting portion44further corrects the correction information (the correction factor K described later) acquired from the endoscope memory27using the correction factor α changed by the correction factor changing portion41, and corrects the position detection signal acquired from the position sensor25based on the corrected correction information and the drive signal.

The feedback controller45outputs a drive signal generated by feedback control based on the target position of the movable lens21aand the position detection signal corrected by the correcting portion44, to the actuator23, and the feedback controller45constitutes a part of the controller.

More specifically, the feedback controller45generates a control signal for causing the driver circuit31to output a drive signal with such a constant current value that a difference between a current position of the movable lens21ashown by the position detection signal outputted from the correcting portion44and the target position of the movable lens21ashown by an instruction signal from the user operation portion12cbecomes 0.

Further, when the predetermined operation condition (the calibration mode or the like) is set, the feedback controller45generates a drive signal for performing servo control so that the target position is a certain position (the target position is kept at a certain position).

The target position setting portion46sets the target position of the movable lens21abased on the instruction signal from the user operation portion12c.

When the predetermined operation condition (the calibration mode or the like) is set, the superimposed signal generating portion47generates and outputs a superimposed signal which is an alternating current signal (for example, a sine-wave alternating current signal) with an amplitude and a frequency for a shift amount of the position of the movable lens21ato be a shift amount that the feedback controller45regards as a stoppage.

Here,FIG. 4is a chart showing a relationship between a frequency of an alternating current drive signal applied to the actuator23and an amplitude that occurs on the movable portion that has been driven.FIG. 4shows a state of the amplitude that occurs on the movable portion when an alternating current with a constant amplitude is applied to the actuator23while the frequency is changed.

The voice coil motor has a characteristic of being difficult to move when a frequency of an applied current becomes high. More specifically, when an alternating current with a constant amplitude is applied to the actuator23, and a frequency of the applied alternating current is increased, an amplitude of an oscillation that occurs on the movable portion gradually decreases as shown inFIG. 4. (Note that since the amplitude of the oscillation that occurs on the movable portion increases if the amplitude of the alternating current is increased in a state of the frequency being fixed,FIG. 4shows frequency characteristics when the amplitude is constant.)

The shift amount that the feedback controller45regards as a stoppage is, for example, a shift amount corresponding to a signal value below accuracy of bit conversion by the ADC34(corresponding to an upper limit threshold M1of the amplitude inFIG. 4). In other words, when an amplitude of a position detection signal outputted by the position sensor25and amplified by the sensor amplification circuit26becomes below the bit conversion accuracy of A/D conversion by the ADC34, the feedback controller45regards the movable lens21aas being stopped from a viewpoint of measurement accuracy.

Thus, the superimposed signal generating portion47generates a superimposed signal with a certain amplitude and a frequency higher than F1so that the amplitude of the oscillation that occurs on the movable portion becomes the shift amount that the feedback controller45regards as a stoppage (a shift amount smaller than the upper limit threshold M1). Here, F1is a frequency threshold corresponding to the upper limit threshold M1.

Note that the shift amount that the feedback controller45regards as a stoppage is not limited to the above. For example, even in the case of a shift amount equal to or above the accuracy of bit conversion by the ADC34, the bit value of which fluctuates, the shift amount may be treated as the shift amount regarded as a stoppage if the bit value fluctuation is within a certain range, and the feedback controller45regards the bit value fluctuation as an error.

The drive amount adding portion48superimposes the superimposed signal outputted from the superimposed signal generating portion47on a drive signal outputted from the feedback controller45and outputs the drive signal on which the superimposed signal is superimposed, to the actuator23via the driver circuit31, and the drive amount adding portion48constitutes a part of the controller.

FIG. 5shows charts showing examples of a position detection signal when a drive signal has a low frequency and a position detection signal when the drive signal has a high frequency.

Low frequency fields inFIG. 5show a state in which, when an alternating current signal with a frequency lower than the frequency threshold F1described above is applied to the actuator23, a noise signal (a false signal) f2due to the leakage magnetic flux from the coils23aand23bis superimposed on an actual position detection signal f1indicating the position of the movable lens21a. (A left field shows f1and f2separately, and a right field shows a position detection signal f obtained by superimposing f2on f1.)

High frequency fields inFIG. 5show a state in which, when a superimposed signal, which is an alternating current signal with a frequency higher than the frequency threshold F1(for example, a frequency of about 10 K(Hz) in the characteristic diagram inFIG. 4) is superimposed on a drive signal for servo-controlling the movable lens21ato a certain target position, and the drive signal on which the superimposed signal is superimposed is applied to the actuator23, a noise signal (a false signal) f2due to the leakage magnetic flux from the coils23aand23bis superimposed on an actual position detection signal f1indicating the position of the movable lens21a. (A left field shows f1and f2separately, and a right field shows a position detection signal f obtained by superimposing f2on f1.) As seen fromFIG. 5, the actual position detection signal f1indicates that the movable lens21ais at the certain target position, that is, a signal value indicating movement of the movable lens21adoes not fluctuate. Therefore, an amplitude of the position detection signal f becomes an amplitude of the noise signal (the false signal) f2, and it is possible to easily extract only the amplitude of the noise signal (the false signal) f2.

Note that a method is also conceivable in which, without providing the superimposed signal generating portion47or the drive amount adding portion48, the target position is caused to change by a sine wave with a frequency higher than the frequency threshold F1by the target position setting portion46. In this case, however, since such control is performed that the target position of the movable lens21aforms a sine wave, a drive signal outputted from the driver circuit31does not necessarily become an accurate sine wave, and the measurement accuracy may decrease. Therefore, by providing the superimposed signal generating portion47and the drive amount adding portion48so that the drive signal outputted from the driver circuit31becomes an accurate sine wave, the measurement accuracy is improved.

FIG. 6is a flowchart showing an actuator control process in the endoscope system1.

When the processor3connected to the endoscope2is powered on or when the endoscope2is connected to the processor3that is powered on, the actuator control process is executed from a main process not shown, the main process being executed by the processor3after various kinds of initialization is performed.

When the process starts, the drive control circuit38acquires the correction factor α from the endoscope memory27first (step S1) and judges whether or not to enter the calibration mode (step S2).

Here, it is judged to enter the calibration mode if correction information has not been recorded in the endoscope memory27yet, and it is judged not to enter the calibration mode if correction information has already been recorded. However, whether or not to enter the calibration mode is not limited to the above. Even if the correction information has been already recorded in the endoscope memory27, the calibration mode may be set at the time of maintenance or the like.

If it is judged at step S2that the calibration mode is to be entered, calibration control is performed (step S3).

Here,FIG. 7is a flowchart showing details of the calibration control at step S3inFIG. 6.

When the process is entered, the correction factor changing portion41changes the correction factor α to 1 (that is, 100%) irrespective of a value of the correction factor α acquired at step S1(step S11).

Furthermore, the variable filter portion42sets the cutoff frequency to the second cutoff frequency that is higher than a frequency of an alternating current superimposed signal generated by the superimposed signal generating portion47(step S12). Here, since the frequency of the superimposed signal is higher than the frequency threshold F1as described above, the second cutoff frequency is naturally higher than the frequency threshold F1.

Note that if noise with a frequency higher than the frequency of the superimposed signal does not influence the position detection accuracy, the low-pass filter processing by the variable filter portion42may be turned off (all-pass characteristics may be set) instead of setting the second cutoff frequency.

Then, the superimposed signal generating portion47generates and outputs a superimposed signal (step S13). Note that, for the frequency and amplitude of the superimposed signal, particular values applicable to any of endoscopes2of respective models, or the frequency and amplitude may be adaptively set according to the kind of the actuator23mounted on the endoscope2.

After that, the feedback controller45sets a target position of the movable lens21a(step S14).

Here, it is more general to think that a magnitude of a noise signal due to the leakage magnetic flux that is included in a position detection signal differs according to the position of the movable lens21a.

Therefore, it is preferred to not only measure a magnitude of a noise signal when the movable lens21ais at one particular position but also measure magnitudes of noise signals when the movable lens21ais at a plurality of different particular positions. This is because it becomes possible thereby to determine a magnitude of a noise signal when the movable lens21ais at an arbitrary position by interpolation calculation or the like.

Therefore, the feedback controller45is adapted to set one or more (preferably a plurality of) target positions of the movable lens21ain the calibration mode. For example, in the case of performing the two-point focusing as described above, each of the far-point focus position (the normal position) and the near-point focus position (the near position) may be set as a target position.

Note that, in order to avoid the movable portion from hitting an end part of the movement range, each target position is set to be away from the end part of the movement range of the movable portion by a predetermined distance or more. Consequently, it is possible to prevent breakage and the like of the actuator23.

Furthermore, the feedback controller45performs servo control and calculates a drive amount of the driver circuit31so that the movable lens21ais maintained at a target position (step S15).

The drive amount adding portion48superimposes the superimposed signal from the superimposed signal generating portion47on a drive signal from the feedback controller45and outputs the drive signal on which the superimposed signal is superimposed, to the driver circuit31, and the driver circuit31drives the actuator23(step S16).

After that, the correction information calculating portion43acquires a position detection signal from the position sensor25via the variable filter portion42(step S17) and calculates correction information based on the acquired position detection signal and the current value of the drive signal acquired from the current detection circuit32via the ADC33(step S18).

More specifically, when an amplitude (an amplitude of a current value) of the superimposed signal on the drive signal applied to the actuator23from the driver circuit31is indicated by lamp, and an amplitude of a signal component synchronized with the superimposed signal, in the position detection signal acquired from the variable filter portion42is indicated by B amp, the correction factor K as the correction information is calculated by Formula 1 below:
K=Bamp/Iamp  [Formula 1]

Here, since the position detection signal that the correction information calculating portion43acquires from the position sensor25is a signal that has passed through a position detection signal transmission route such as the sensor amplification circuit26, the calculated correction factor K is such that responds to variation in characteristics of individual position detection signal transmission routes.

The correction information calculating portion43causes the correction factor K thus calculated to be stored into the endoscope memory27as correction information (step S19).

Note that since the correction information is information depending on each individual endoscope2, the process of calculating correction information and storing the correction information into the endoscope memory27is preferably performed at the time of inspection at factory shipment of the endoscope2.

After that, the feedback controller45judges whether there is a next target position or not (step S20). If judging that the next target position exists, the feedback controller45returns to step S14described above and sets the next target position of the movable lens21a.

In this way, the feedback controller45preferably sets a plurality of target positions to be servo-controlled; the correction information calculating portion43calculates a plurality of pieces of correction information for the set plurality of target positions, respectively; and the endoscope memory27stores the plurality of pieces of correction information in association with the plurality of target positions, respectively.

If the process is performed for all the target positions, it is judged at step S20that there is not a next target position.

At this time, the variable filter portion42sets the cutoff frequency to the first cutoff frequency that is lower than the frequency of the alternating current superimposed signal generated by the superimposed signal generating portion47(step S21). Consequently, removal of high-frequency noise from the position detection signal outputted from the ADC34is performed as usual.

Furthermore, after the correction factor changing portion41returns the correction factor α set to 1 at step S11to the value acquired from the endoscope memory27at step S1(step S22), the flow returns to the process ofFIG. 6.

Thus, if the calibration control at step S3ends, or it is judged at step S2not to enter the calibration mode, the correcting portion44acquires the correction information (more specifically, the correction factor K described above) from the endoscope memory27via the correction factor changing portion41(step S4).

Then, according to whether there is an instruction signal from the user operation portion12cor not and according to content of the instruction signal, it is judged whether or not a focus switching operation has been performed on the user operation portion12c. If the focus switching operation has been performed, it is further judged whether an instructed target position is the near-point focus position (the near position) or the far-point focus position (the normal position) (step S5). If the focus switching operation has not been performed, it is judged that the target position is another position.

Here, if it is judged that the operation of focus switching to the normal position has been performed, the target position setting portion46sets the target position to the normal position (step S6).

If it is judged at step S5that the operation of focus switching to the near position has been performed, the target position setting portion46sets the target position to the near position (step S7).

If it is judged at step S5that the target position is another position, the current target position is maintained as it is.

Then, feedback control for causing the movable lens21ato be close to the set target position is performed (step S8).

Here,FIG. 8is a flowchart showing details of the feedback control at step S8inFIG. 6.

When the process is entered, the correcting portion44acquires the position detection signal from the variable filter portion42(step S31) and corrects the position detection signal (step S32).

Here, when the position detection signal acquired from the variable filter portion42is indicated by P, and a current value of the drive signal acquired from the ADC33is indicated by I, the correcting portion44corrects the position detection signal P to calculate a corrected position detection signal P′ by specifically performing calculation as shown by Formula 2 below.
P′=P−α×K×I[Formula 2]

On a right side of Formula 2, K×I indicates a noise signal (false signal) component included in the position detection signal P when the drive signal with the current value I is applied to the coils23aand23bof the actuator23.

At the time of performing normal-time feedback control for causing the movable lens21ato move to a target position, control stability is prioritized, and a result of multiplying the noise signal (false signal) component (K×I) by the correction factor α equal to or smaller than 1 (preferably smaller than 1) is subtracted from the position detection signal P. Note that since the current value I may be positive or negative according to whether the movable portion is moved to the object side or to the image side, a second term on the right side of Formula 2 may reduce or increase a value of a first term on the right side.

Here, in the case of performing the two-point focusing, if each of a correction factor corresponding to the near-point focus position (the near position) and a correction factor corresponding to the far-point focus position (the normal position) is stored in the endoscope memory27as the correction factor K, the necessity to perform interpolation calculation is eliminated, and a processing load is reduced. It is preferably possible to perform accurate correction.

In the case of performing multipoint focusing (or multipoint zooming) with three or more points or focusing to continuous positions (or zooming to continuous focal lengths), interpolation calculation or the like is performed from a plurality of correction factors K to determine a correction factor corresponding to a target position as necessary, and the correction factor is used for correction.

The position detection signal V corrected in this way is outputted from the correcting portion44to the feedback controller45.

The feedback controller45calculates such a drive signal that a position shown by the position detection signal P′ corresponds to the target position set by the target position setting portion46(step S33).

The drive signal calculated in this way is outputted from the feedback controller45to the driver circuit31via the drive amount adding portion48. During normal operation other than the calibration mode, since the superimposed signal generating portion47does not generate a superimposed signal, the driver circuit31applies a drive signal from the feedback controller45to the actuator23to drive the actuator23(step S34).

When the process of step S34is performed, the flow returns to the process shown inFIG. 6.

When the feedback control at step S8is performed in this way, it is judged whether or not to end the actuator control (step S9).

If it is judged not to end the actuator control, the flow returns to step S5described above, and feedback control according to focus switching is performed. The control from steps S5to S9is repeatedly performed for each predetermined sampling time period.

On the other hand, if it is judged to end the actuator control at step S9, the flow returns to the main process not shown.

According to the embodiment as described above, since a position detection signal is corrected based on a drive signal to the actuator23for driving the movable lens21aand correction information acquired from the endoscope memory27, a position of the movable lens21acan be more accurately acquired. As a result, it becomes possible to more accurately feedback-control the movable lens21ato move to a target position.

Further, when the calibration mode or the like is set, a superimposed signal for obtaining a shift amount regarded as a stoppage is generated, superimposed on a drive signal for causing the movable lens21ato be at a certain target position and outputted to the actuator23; and a ratio of an amplitude of a signal component synchronized with the superimposed signal, in the position detection signal to an amplitude of the superimposed signal is calculated as correction information and stored in the endoscope memory27. Therefore, a device or a mechanism for locking the movable portion is not required, and the correction information for correcting the position detection signal can be acquired in a state in which the movable portion is incorporated in the objective optical system21.

Furthermore, since the shift amount that the feedback controller45regards as a stoppage is a shift amount corresponding to a signal value below the accuracy of bit conversion by the ADC34configured to perform A/D conversion of the position detection signal, it is possible to regard the shift amount as a stoppage from a viewpoint of detection accuracy, without requiring a particular configuration or the like for controlling the shift amount regarded as a stoppage.

Since, by subtracting a signal obtained by multiplying a drive signal by the correction information acquired from the endoscope memory27, from a position detection signal acquired from the position sensor25, the position detection signal is corrected, it is possible to perform calculation with a low load at a high speed, and it is possible to improve real-time processing.

In addition, if a plurality of target positions are set, a plurality of pieces of correction information are calculated, and the plurality of pieces of correction information are stored in the endoscope memory27in association with the plurality of target positions, respectively, it becomes possible to obtain correction information for an arbitrary target position by interpolation calculation or the like.

Further, if the calibration mode or the like is not set, a first cutoff frequency lower than a frequency of a superimposed signal is set. Therefore, it is possible to suppress high-frequency noise and acquire a highly accurate position detection signal.

On the other hand, if the calibration mode or the like is set, a second cutoff frequency higher than a frequency of a superimposed signal is set. Therefore, a noise signal (false signal) component based on the superimposed signal does not attenuate, and it is possible to appropriately acquire correction information.

Furthermore, the correction factor α is adaptively changed so that the value is smaller in the case of prioritizing stability of feedback control than in the case of prioritizing the accuracy of a position detection signal. Therefore, it is possible to provide the endoscope system1in which both of highly accurate position detection and drive stability are enabled.

More specifically, since the correction factor α is set to 1 during correction information calculation in which the position detection accuracy is important, it is possible to highly accurately calculate correction information.

Further, since the correction factor α is set to a value determined according to the characteristics of the actuator23during normal feedback control in which drive stability of the actuator23is important, it is possible to perform stable driving.

Note that the process of each portion described above may be performed by one or more processors configured as hardware. For example, each portion may be a processor configured as an electronic circuit, or may be a circuit portion in a processor configured with an integrated circuit such as an FPGA (field programmable gate array). Alternatively, a processor configured with one or more CPUs may execute a function as each portion by reading and executing the processing program recorded in a recording medium.

Though description has been made above mainly on an endoscope system, an operation method for causing an endoscope system to operate as described above, a processing program for causing a computer to perform processes similar to processes of an endoscope system, a computer-readable non-transitory recording medium in which the processing program is recorded, and the like are also possible.