Control device, endoscope system, and position detection method

Abstract

A control device (26) is provided with a processor (26a). The processor (26a): selects candidate coordinates of a magnetic field generation element (22); calculates a candidate vector (Gk) and a vector norm error (e1) on the basis of the coordinates of a magnetic field detection element (23), the candidate coordinates, and a detection signal; if the vector norm error (e1) is smaller than the minimum value in the past, updates maximum likelihood coordinates to the current candidate coordinates; determines whether or not the vector norm error (e1) is within the first range; and selects new candidate coordinates if the vector norm error is not within the first range.

Description

Control device, endoscope system, and position detection method

[0001] The present invention relates to a control device, an endoscope system, and a position detection method that detect the position of an endoscope using a magnetic field.

[0002] Endoscope devices have been conventionally used in various fields such as the medical field, the industrial field, the academic field, etc. When an endoscope is used, an insertion portion is inserted into a subject to observe the inside of the subject.

[0003] For example, in the medical field, there is an increasing demand for colonoscopic examinations. The insertion procedure in colonoscopic examinations is highly difficult. Therefore, a technology has been proposed that uses an endoscope insertion shape detection device (UPD) to grasp the shape of the endoscope's insertion portion, thereby enabling the insertion procedure to be performed smoothly.

[0004] An endoscope insertion shape detection device, for example, arranges multiple transmitter coils in the insertion portion of the endoscope and places multiple receiver coils in an antenna outside the body cavity. The transmitter coils generate a magnetic field, and detect the voltage generated in the receiver coils by the generated magnetic field, thereby estimating the position and direction of the transmitter coils. If the positions and directions of the multiple transmitter coils arranged in the insertion portion can be estimated, the shape of the insertion portion of the endoscope can be estimated.

[0005] For example, Japanese Patent No. 5231681 describes an example of a shape detection device using a magnetic field. The shape detection device calculates a candidate vector indicating the direction of a transmitter coil based on a search coordinate set (assumed three-dimensional coordinates) of the transmitter coil and the measured voltage of a certain receiver coil group. The shape detection device then determines, as a solution (estimated coordinates), a coordinate set that minimizes the sum of errors between the estimated electromotive voltage of another receiver coil group calculated based on the search coordinate set and the candidate vector and the measured voltage of the other receiver coil group. This method reduces the amount of calculation and search, making it possible to quickly obtain an estimated result (the position and direction of the transmitter coil).

[0006] However, with the technology described in Japanese Patent No. 5231681, if the calculation result of the candidate vector is far from the true value, the solution may fall into a local minimum (a minimum value of the evaluation function that differs from the true value) and converge to a point completely different from the true value. Convergence of the solution to a point completely different from the true value may occur, for example, when a transmitting coil is placed at the proximal point of the receiving coil. For this reason, the technology described in Japanese Patent No. 5231681 is not suitable for cases where the antenna with the receiving coil is placed at the proximal point of the endoscope.

[0007] On the other hand, in principle, the greater the distance between the transmitting coil, which is a magnetic field generating element, and the receiving coil, which is a magnetic field detecting element, the greater the influence of noise and the lower the detection accuracy.

[0008] Therefore, there is a need for a technology that can improve detection accuracy by preventing the solution from converging to a point that is completely different from the true value even when the distance between the magnetic field generating element and the magnetic field detecting element is reduced.

[0009] The present invention has been made in consideration of the above circumstances, and aims to provide a control device, an endoscope system, and a position detection method that can quickly estimate the relative position and direction of a magnetic field detection element and a magnetic field generating element located in a wide range including the near point of the magnetic field detection element with a small amount of calculation.

[0010] A control device according to one aspect of the present invention includes a processor that selects candidate coordinates of a magnetic field generating element, calculates a candidate vector based on the coordinates of the magnetic field detection element, the candidate coordinates, and a detection signal that the magnetic field detection element detects and transmits when the magnetic field generated by the magnetic field generating element, calculates a vector norm error based on the candidate vector, and if the calculated vector norm error is smaller than the minimum value of the vector norm errors calculated in the past, updates the most likely coordinate to the current candidate coordinate, determines whether the vector norm error is within a first range, and if the vector norm error is not within the first range, selects a new candidate coordinate.

[0011] An endoscopic system according to one aspect of the present invention comprises an endoscope, a magnetic field generating element that generates a magnetic field, a magnetic field detection element that detects the magnetic field and transmits a detection signal, and a processor that processes the detection signal, wherein the processor selects candidate coordinates of the magnetic field generating element, calculates a candidate vector based on the coordinates of the magnetic field detection element, the candidate coordinates, and the detection signal, calculates a vector norm error based on the candidate vector, and if the calculated vector norm error is smaller than the minimum value of the vector norm errors calculated in the past, updates the most likely coordinates to the current candidate coordinates, determines whether the vector norm error is within a first range, and if the vector norm error is not within the first range, selects new candidate coordinates.

[0012] A position detection method according to one aspect of the present invention generates a magnetic field using a magnetic field generating element, detects the magnetic field using a magnetic field detection element and transmits a detection signal, selects candidate coordinates of the magnetic field generating element, calculates a candidate vector based on the coordinates of the magnetic field detection element, the candidate coordinates, and the detection signal, calculates a vector norm error based on the candidate vector, and if the calculated vector norm error is smaller than the smallest value of the vector norm errors calculated in the past, updates the most likely coordinates to the current candidate coordinates, determines whether the vector norm error is within a first range, and if the vector norm error is not within the first range, selects new candidate coordinates.

[0013] FIG. 1 is a diagram showing a configuration of an endoscope system according to a first embodiment of the present invention. FIG. 1 is a diagram showing a configuration example in which a magnetic field generating element is arranged in an endoscope and a magnetic field detection element is arranged in an antenna external to the endoscope according to the first embodiment. FIG. 2 is a diagram showing a configuration example in which a signal detected by a receiver coil having a magnetic field detection element is amplified, converted into a digital signal, and transmitted to a magnetic field detection unit according to the first embodiment. FIG. 3 is a diagram showing a configuration of a position detection system according to the first embodiment. FIG. 4 is a diagram showing an example in which one of a plurality of lattice point coordinates within a predetermined spatial range centered on a search center coordinate is selected as a candidate coordinate in the first embodiment. FIG. 5 is a flowchart showing a part of a transmitter coil coordinate estimation process according to the first embodiment. FIG. 6 is a flowchart showing a stage 1 process that is a part of the transmitter coil coordinate estimation process according to the first embodiment. FIG. 7 is a flowchart showing a stage 2 process that is a part of the transmitter coil coordinate estimation process according to the first embodiment. FIG. 8 is a diagram showing a configuration example in which a magnetic field detection element is arranged in an endoscope and a magnetic field generating element is arranged in an antenna external to the endoscope according to a second embodiment of the present invention. FIG. 9 is a diagram showing a configuration example in which a magnetic field detection element is arranged in an endoscope and a magnetic field generation element is arranged in an antenna external to the endoscope according to a third embodiment of the present invention. It is a diagram showing the configuration of a position detection system according to a fourth embodiment of the present invention. It is a flowchart showing stage 1 processing which is a part of the transmitter coil coordinate estimation processing according to the fourth embodiment of the present invention. It is a flowchart showing stage 2 processing which is a part of the transmitter coil coordinate estimation processing according to the fourth embodiment of the present invention.

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments described below.

[0015] In the drawings, the same or corresponding elements are appropriately designated by the same reference numerals. It should be noted that the drawings are schematic, and that the length relationships, length ratios, and quantities of elements within a single drawing may differ from reality in order to simplify the description. Furthermore, there may be cases where the length relationships, ratios, quantities, and the like differ between multiple drawings. [First Embodiment]

[0016] 1 to 9 show a first embodiment of the present invention. Fig. 1 is a diagram showing the configuration of an endoscope system 1 according to the first embodiment.

[0017] As shown in FIG. 1 , the endoscope system 1 includes a position detection system 2 , an endoscope 3 , a light source device 4 , a video processor 5 , and a monitor 6 .

[0018] The endoscope 3 includes an insertion section 11 that is inserted into the subject, and an operation section 12 that is provided at the proximal end of the insertion section 11 .

[0019] The insertion section 11 is assumed to be a type having a flexible tube section and a curved section, that is, a type that can change shape. An objective lens 15 and an image sensor 16 are disposed at a tip section 14 of the insertion section 11.

[0020] Furthermore, a magnetic field generating element 22 is disposed in the insertion section 11 including the tip portion 14. The magnetic field generating element 22 generates a magnetic field MF (see FIG. 2, etc.). The magnetic field generating element 22 includes, for example, a plurality of transmitting coils C1 to Cn. The plurality of transmitting coils C1 to Cn are arranged at predetermined intervals along the longitudinal direction of the insertion section 11 in order from the tip side.

[0021] The operation unit 12 is provided with various switches 12 a for operating the endoscope 3 .

[0022] Furthermore, a memory 17 is provided in the operation unit 12 of the endoscope 3, for example (however, it may be in a portion other than the operation unit 12 as long as it is within the endoscope 3). The memory 17 stores various pieces of information related to the endoscope 3 in a non-volatile manner. Examples of information stored in the memory 17 include the model number and serial number of the endoscope 3, and parameters unique to the endoscope 3. The memory 17 is connected to the video processor 5, and transmits various pieces of information related to the endoscope 3 to the video processor 5.

[0023] The operation unit 12 also includes a bending operation knob and the like for bending the bending portion.

[0024] The endoscope 3 has a light guide 13 arranged along the longitudinal direction from the distal end 14 of the insertion section 11. The proximal end of the light guide 13 is connected to the light source device 4. The light guide 13 transmits illumination light supplied from the light source device 4 and irradiates the illumination light from the distal end 14 onto the subject.

[0025] The objective lens 15 forms an optical image of the subject illuminated with the illumination light on the image sensor 16. The image sensor 16 captures the optical image of the subject and transmits an image signal to the video processor 5.

[0026] The video processor 5 receives an imaging signal from the imaging element 16, and generates a video signal by image processing the imaging signal based on various information related to the endoscope 3 received from the memory 17. The video processor 5 transmits the video signal to the monitor 6.

[0027] The monitor 6 receives the video signal transmitted from the video processor 5 and displays an endoscopic image of the subject.

[0028] The position detection system 2 includes a position detection device 21, a magnetic field generating element 22, and a magnetic field detection element 23. That is, the magnetic field generating element 22 is disposed, for example, inside the endoscope 3, and constitutes a part of the position detection system 2.

[0029] The position detection device 21 includes a drive signal transmission unit 24 , a magnetic field detection unit 25 , and a control unit 26 .

[0030] The drive signal transmitting unit 24 transmits a drive signal for generating a magnetic field MF (for example, an AC signal for generating an AC magnetic field) to the magnetic field generating element 22 under the control of the control unit 26 .

[0031] For example, the drive signal transmitter 24 simultaneously transmits AC signals of different frequencies to the transmitting coils C1 to Cn. As a result, the transmitting coils C1 to Cn generate AC magnetic fields of different frequencies. In this case, it is possible to distinguish which of the transmitting coils C1 to Cn has generated the magnetic field MF based on the frequency of the AC magnetic field.

[0032] The drive signal transmitter 24 may also transmit an AC signal to one of the transmitter coils C1 to Cn sequentially by switching between the transmitter coils C1 to Cn that transmit the AC signal. In this case, it is possible to distinguish which of the transmitter coils C1 to Cn has generated the magnetic field MF based on the time at which the AC magnetic field is generated.

[0033] FIG. 2 is a diagram showing an example of a configuration in which the magnetic field generating element 22 is arranged in the endoscope 3 and the magnetic field detecting element 23 is arranged in an antenna 28 outside the endoscope 3 in the first embodiment.

[0034] The magnetic field detection element 23 detects the magnetic field MF and transmits a detection signal. As shown in Fig. 2, the magnetic field detection element 23 is configured as an antenna 28 (a receiving antenna in the example of Fig. 2) that can be moved, for example, using casters. The antenna 28 is placed in the examination room, for example, near an examination table on which a subject is placed (outside the body cavity). Note that the coordinates of the magnetic field detection element 23 after the antenna 28 is placed are known.

[0035] The magnetic field detection element 23 includes a plurality of receiving coil groups, and in this embodiment, an example is shown in which the magnetic field detection element 23 includes four receiving coil groups 23g1 to 23g4. The four receiving coil groups 23g1 to 23g4 are arranged at different positions on the antenna 28.

[0036] 3 is a diagram showing an example of the configuration of the magnetic field detection element 23 according to the first embodiment. In FIG. 3, the xyz coordinate system is a three-dimensional orthogonal coordinate system. The xyz coordinate system is also called a global coordinate system or a world coordinate system.

[0037] The receiver coil group 23g1 includes a set of three coils: an x-direction receiver coil SCx1 whose central axis is parallel to the x-axis direction, a y-direction receiver coil SCy1 whose central axis is parallel to the y-axis direction, and a z-direction receiver coil SCz1 whose central axis is parallel to the z-axis direction. The x-direction receiver coil SCx1, y-direction receiver coil SCy1, and z-direction receiver coil SCz1 detect magnetic field components in the orthogonal x-, y-, and z-axis directions, respectively.

[0038] That is, the x-direction receiver coil SCx1 generates an electromotive force corresponding to the x-axis component of the magnetic field MF generated by the transmitter coils C1 to Cn at the position of the x-direction receiver coil SCx1. The y-direction receiver coil SCy1 generates an electromotive force corresponding to the y-axis component of the magnetic field MF generated by the transmitter coils C1 to Cn at the position of the y-direction receiver coil SCy1. The z-direction receiver coil SCz1 generates an electromotive force corresponding to the z-axis component of the magnetic field MF generated by the transmitter coils C1 to Cn at the position of the z-direction receiver coil SCz1.

[0039] Similarly, the receiver coil group 23g2 includes a set of three coils: an x-direction receiver coil SCx2, a y-direction receiver coil SCy2, and a z-direction receiver coil SCz2, and generates electromotive voltages according to the magnetic field components in each direction.

[0040] Similarly, the receiver coil group 23g3 includes a set of three coils: an x-direction receiver coil SCx3, a y-direction receiver coil SCy3, and a z-direction receiver coil SCz3, and generates electromotive voltages according to the magnetic field components in each direction.

[0041] Similarly, the receiver coil group 23g4 includes a set of three coils: an x-direction receiver coil SCx4, a y-direction receiver coil SCy4, and a z-direction receiver coil SCz4, and generates electromotive voltages according to the magnetic field components in each direction.

[0042] In the following description, any one of the receiving coils SCx1 to SCz4 will be simply referred to as a receiving coil SC.

[0043] FIG. 4 is a diagram showing an example of a configuration in which a signal detected by a receiving coil SC of the magnetic field detection element 23 is amplified, converted into a digital signal, and transmitted to the magnetic field detection unit 25 in the first embodiment.

[0044] When the magnetic field MF penetrating the receiving coil SC changes over time, a time-varying electromotive voltage is generated across the receiving coil SC, causing a current (AC) to flow.

[0045] The electromotive voltage generated across the receiving coil SC is detected and amplified by an amplifier 38, converted into a digital signal by an analog-to-digital converter (ADC) 39, and transmitted to the magnetic field detection unit 25 as a detection signal.

[0046] At least one of the amplifier 38 and the ADC 39 may be provided within the position detection device 21 (for example, within the magnetic field detection unit 25), or may be provided within the antenna 28. For example, if the amplifier 38 and the ADC 39 are provided within the position detection device 21, the antenna 28 can have a simple and inexpensive configuration.

[0047] Furthermore, the electromotive force generated in the receiving coil SC decreases as the distance from the transmitting coils C1 to Cn to the receiving coil SC increases. For this reason, if the amplifier 38 and the ADC 39 are provided, for example, within the antenna 28, signal distortion and noise contamination can be reduced when the signal generated in the receiving coil SC is transmitted from the antenna 28 to the position detection device 21.

[0048] The magnetic field detection unit 25 separates the average received voltage amplitude over a certain period of time (obtained by Fourier transforming the voltage) transmitted from the receiving coil SC via the amplifier 38 and ADC 39, i.e., the detection signal, for example, by frequency separation (or separation according to time), and divides it into signals for each of the receiving coil groups 23g1, 23g2, 23g3, and 23g4, and transmits them to the control unit 26.

[0049] The control unit 26 is a control device and includes, for example, a processor 26a and a memory 26b. That is, the control unit 26 is configured such that the processor 26a, such as an ASIC (Application Specific Integrated Circuit) including a CPU (Central Processing Unit) or an FPGA (Field Programmable Gate Array), loads and executes a processing program stored in a storage device (or recording medium) such as the memory 26b, thereby performing the functions of each unit described below. However, the configuration of the control unit 26 is not limited to this, and each unit may be configured as a dedicated electronic circuit that performs the function of that unit, for example.

[0050] The processor 26a processes the detection signals received from the magnetic field detection unit 25. The processor 26a performs processing to detect the positions and directions of the transmitting coils C1 to Cn based on the detection signals, as will be described later.

[0051] The arrangement of the transmitting coils C1 to Cn along the longitudinal direction within the insertion portion 11 is known. Therefore, once the position and direction of each of the transmitting coils C1 to Cn is known, the processor 26a can detect the shape of the insertion portion 11.

[0052] The position detection device 21 is connected to the video processor 5. Based on the detected shape of the insertion portion 11, the position detection device 21 generates, for example, an image showing the shape of the insertion portion 11, insertion support information, etc., and transmits the generated information to the video processor 5. The video processor 5 displays the information received from the position detection device 21 on the monitor 6 together with the endoscopic image, thereby providing insertion support, etc.

[0053] FIG. 5 is a diagram showing the configuration of the position detection system 2 according to the first embodiment.

[0054] As shown in FIG. 5, the control unit 26 includes, as functional units, a candidate coordinate selection unit 31, a candidate vector calculation unit 32, a candidate vector norm error calculation unit 33, an estimated electromotive voltage calculation unit 34, a normalized voltage error calculation unit 35, and an estimated coordinate acquisition unit 36.

[0055] The candidate coordinate selection unit 31 selects candidate coordinates of the magnetic field generating element 22 .

[0056] The candidate vector calculation unit 32 calculates the candidate vector G based on the coordinates of the magnetic field detection element 23, the candidate coordinates of the magnetic field generation element 22, and the detection signal received from the magnetic field detection unit 25. k Calculate.

[0057] The candidate vector norm error calculation unit 33 calculates the candidate vector G k Based on the above, a candidate vector norm error e1 (for simplicity, also referred to as a vector norm error) (first evaluation function) is calculated.

[0058] The estimated electromotive voltage calculation unit 34 calculates the candidate vector G k Based on this, an electromotive voltage (estimated electromotive voltage) estimated to be generated in the magnetic field detection element 23 is calculated.

[0059] The normalized voltage error calculation unit 35 calculates an electromotive force error, which is the difference between the estimated electromotive force and the measured voltage obtained from the detection signal. Furthermore, the normalized voltage error calculation unit 35 normalizes the electromotive force error based on the measured voltage to calculate a normalized electromotive force error e (second evaluation function).

[0060] When the normalized electromotive voltage error e 2 is within the second range, the estimated coordinate acquisition unit 36 ​​acquires the current most likely coordinate as the estimated coordinate of the magnetic field generating element 22 .

[0061] The operation of each functional unit of the control unit 26 shown in FIG. 5 will be described in more detail with reference to the flowcharts of FIGS. 7 to 9, also with reference to FIG.

[0062] Fig. 6 is a diagram showing an example in which one of a plurality of lattice point coordinates p1 to p26 within a predetermined spatial range centered on a search center coordinate p0 is selected as a candidate coordinate in the first embodiment. Fig. 7 is a flowchart showing a part of the transmit coil coordinate estimation process in the first embodiment. Fig. 8 is a flowchart showing stage 1 processing, which is a part of the transmit coil coordinate estimation process in the first embodiment. Fig. 9 is a flowchart showing stage 2 processing, which is a part of the transmit coil coordinate estimation process in the first embodiment.

[0063] The transmit coil coordinate estimation process shown in FIGS. 7 to 9 is mainly performed by the processor 26a operating as each functional unit shown in FIG. 5 in accordance with a computer program stored in the memory 26b.

[0064] In the main processing (not shown), the processor 26a executes the processing shown in FIG. 7 every time it receives a detection signal from the magnetic field detection unit 25.

[0065] When the process shown in FIG. 7 starts, the processor 26a initializes each parameter (step S1).

[0066] In the transmission coil coordinate estimation process shown in FIGS. 7 to 9, a candidate vector G indicating the direction of the magnetic field generating element 22 (hereinafter referred to as the transmission coil C as appropriate) is mainly used. k The process of stage 1 for estimating the candidate vector G k and stage 2 processing for estimating the position of the transmitting coil C based on the above.

[0067] In the initialization of step S1, the processor 26a sets a value ST1 indicating stage 1 to a parameter ST indicating the current stage. The processor 26a sets 0 to a counter j that counts the number of processed lattice point coordinates (see FIG. 6) within a predetermined spatial range. The processor 26a sets 0 to a counter i that counts the number of times a search center coordinate p0 has been selected (i.e., the number of times a lattice point coordinate (see FIG. 6) centered on the search center coordinate p0 has been set), as will be described later. The processor 26a sets a candidate vector norm error e1 to e1, and the maximum value e that can be taken for e1. 1max The processor 26a inputs the maximum value e that can be taken as e into the normalized electromotive voltage error e. 2max Put in.

[0068] Then, the processor 26a detects the electromotive voltage (measurement voltage) generated in the magnetic field detection element 23 from the detection signal transmitted from the magnetic field detection unit 25 (step S2).

[0069] The memory 26b stores in advance information about the spatial range (entire range) in which the position can be detected by the magnetic field detection element 23. Specifically, the memory 26b stores, for example, the maximum and minimum values ​​of each x, y, and z coordinate in the entire range.

[0070] The processor 26a selects one of the three-dimensional coordinates of points contained within the entire range stored in the memory 26b as the search center coordinates p0 (step S3).

[0071] The processor 26a sets a plurality of lattice point coordinates within a predetermined spatial range centered on the search center coordinate p0. When setting the lattice point coordinates, the processor 26a sets the lattice point interval and rotates the lattice point coordinate system (step S4).

[0072] When step S4 is performed for the first time since the start of the process of FIG. 7 , the lattice point interval is set longer than when step S4 is performed for the second or subsequent times. Thereafter, when selecting a new search center coordinate p0 (i.e., when the maximum likelihood coordinate approaches the true value (the true coordinate of the magnetic field generating element 22) and it becomes acceptable to narrow the search range), the processor 26a reduces the specified spatial range to set a shorter lattice point interval and rotates the lattice by an appropriate angle (e.g., 30° around a specified rotation axis). However, it is not necessary to change the lattice point interval each time the process of step S4 is performed. For example, the lattice point interval may not be changed while the current stage is stage 1, and may be changed after the current stage becomes stage 2.

[0073] 6 is a diagram showing an example of grid point coordinates set by the processor 26 a. In the example shown in Fig. 6, in an x'y'z' coordinate system, which is a local three-dimensional orthogonal coordinate system, 3x3x3 grid point coordinates are set in the x'-axis direction, y'-axis direction, and z'-axis direction, with search center coordinate p0 as the center.

[0074] The lattice point coordinates to be set are not limited to 3x3x3, and may be, for example, 5x5x5, etc. However, in order to quickly obtain the estimated coordinates of the magnetic field generating element 22 with a small amount of calculation, it is preferable not to increase the number of lattice point coordinates.

[0075] A total of 27 lattice point coordinates are arranged within a predetermined spatial range, including lattice point coordinates p1 to p26 and search center coordinate p0. The x'y'z' coordinate system, which is the local coordinate system, and the xyz coordinate system, which is the global coordinate system, are related using a rotation matrix in three-dimensional space.

[0076] The processor 26a (candidate coordinate selection unit 31) selects, for example, one of the lattice point coordinates shown in Figure 6 as a candidate coordinate (step S5). When performing step S5 for the first time after starting the process of Figure 7, the search center coordinate p0 may be selected as the candidate coordinate, or one of the lattice point coordinates p1 to p26 may be selected as the candidate coordinate. Furthermore, when performing step S5 for the second or subsequent times, the search center coordinate p0 has already been selected as a candidate coordinate, so one of the lattice point coordinates p1 to p26 will be selected as the candidate coordinate.

[0077] The processor 26a (candidate vector calculation unit 32) calculates the candidate vector G based on the selected candidate coordinates. k is calculated (step S6).

[0078] While the above description has been given of an example in which there are four sets of receiving coils, ie, receiving coil groups 23g1 to 23g4, the following description will be given more generally assuming that there are l sets of receiving coils (l is an integer equal to or greater than 2). Furthermore, any set number from 1 to l will be represented by k (k=1, 2, ..., l). In the example shown in Figures 2 and 3, l=4.

[0079] The electromotive force vector v is generated from the electromotive force generated in the magnetic field detection element 23 of the group k by the magnetic field MF generated from the transmitting coil C. k is the direction vector g (unit vector) of the transmitting coil C and the matrix B k and a constant ξ, it is expressed in principle by (Equation 1). (Equation 1)

[0080] Here, the electromotive force vector v k is the electromotive voltage v generated in the x-direction receiving coil SCxk of the set k xk and the electromotive voltage v generated in the y-direction receiving coil SCyk of the set k. yk and the electromotive voltage v generated in the z-direction receiving coil SCzk of the set k.zk Using the above, it is expressed by (Equation 2). (Equation 2)

[0081] The direction vector g of the transmitting coil C has an x-direction component g x , y-direction component g y , z-direction component g z Using the above, it is expressed by (Equation 3). (Equation 3)

[0082] The value of the constant ξ is determined by the gain of the entire transmission / reception system, which includes the transmission system (such as the magnetic field generating element 22 and the drive signal transmission unit 24) that transmits the magnetic field MF and the reception system (such as the magnetic field detection element 23 and the magnetic field detection unit 25) that receives the magnetic field MF transmitted from the transmission system. The value of the constant ξ is determined by, for example, the characteristics of the transmission coil C and the characteristics of the reception coil. The constant ξ is pre-stored in the memory 26b.

[0083] matrix B k is matrix A k and matrix R k Using the above, it is expressed by (Equation 4). (Equation 4)

[0084] Matrix R in (Equation 4) k is expressed by (Equation 5). (Equation 5)

[0085] Matrix element r of (Equation 5) xk , r yk , r zk is expressed by (Equation 6). (Equation 6)

[0086] In (Equation 6), x Rk , y Rk , z Rk represent the x, y, and x coordinates of the receiving coil SCk of the set k, respectively, and x T , y T , z T represent the x, y, and x coordinates of the transmitting coil C, respectively. xk , r yk , r zk represent the distance in the x direction, the distance in the y direction, and the distance in the z direction between the receiving coil SCk and the transmitting coil C, respectively.

[0087] Also, the matrix A in (Equation 4) k is expressed by (Equation 7). (Equation 7)

[0088] The matrix elements of (Equation 7) are expressed by (Equation 8).

[0089] That is, matrix A k is determined based on the x, y, and z coordinates of the receiving coil SCk and the x, y, and z coordinates of the transmitting coil C.

[0090] Therefore, matrix A k and matrix R k and the matrix B calculated by (Equation 4) k is calculated based on the xyz coordinates of the receiving coil SCk of the set k (the coordinates of the magnetic field detection element 23) and the candidate coordinates (the candidate coordinates of the magnetic field generating element 22) (each xyz coordinate of the transmitting coil C).

[0091] In the above principle, the matrix B is calculated using the candidate coordinates as the coordinates of the transmitting coil C. k Calculate the electromotive force vector v k By using the measured values ​​as k The candidate vector G k is the candidate vector G k The directional vector g (indicating a candidate direction of the transmitting coil C) is multiplied by a constant ξ (Equation 9).

[0092] Next, the processor 26a determines whether the value of the parameter ST is ST1, that is, whether the current stage is stage 1 (step S7).

[0093] If the value of the parameter ST is ST1, the process proceeds to the stage 1 process in FIG. 8 (step S8).

[0094] When the stage 1 process of FIG. 8 begins, the processor 26a (candidate vector norm error calculation unit 33) calculates the candidate vector G kBased on this, a candidate vector norm error e1 is calculated as expressed by (Equation 10) (step S11). Note that in (Equation 10) (and (Equation 11) and (Equation 12) described later), the two vertical lines surrounding the vector represent the norm (specifically, the length of the vector (Euclidean norm)). (Equation 10)

[0095] Each time a new candidate vector norm error e1 is calculated, the processor 26a compares it with the minimum value of the candidate vector norm errors e1 calculated in the past (step S12).

[0096] That is, the processor 26a stores the minimum value of the candidate vector norm error e calculated after starting the process shown in Fig. 7 in, for example, the memory 26b. Then, the processor 26a compares the minimum value of the candidate vector norm error e stored in the memory 26b with the newly calculated candidate vector norm error e.

[0097] If the newly calculated candidate vector norm error e is smaller than the smallest value of the previously calculated candidate vector norm errors e, the processor 26a updates the current candidate coordinate to the most likely coordinate (the coordinate estimated to be closest to the true value (the true coordinate of the magnetic field generating element 22) at this point in time) (step S13). The memory 26b stores the most likely coordinate.

[0098] The processor 26a determines whether the candidate vector norm error e is greater than or equal to a predetermined threshold e 1th It is determined whether the value is less than the first threshold value e (step S14). 1th The processor 26a stores a predetermined threshold value e 1th is read out and the determination in step S14 is performed.

[0099] As shown in (Equation 10), the candidate vector norm error e1 takes a value equal to or greater than 0. Therefore, the first range is equal to or greater than 0 and equal to or less than e 1th The range is less than.

[0100] Here, the candidate vector norm error e is a predetermined threshold e 1thIf it is not less than p, the processor 26a determines whether the counter j has reached a predetermined value p (step S15). The predetermined value p is the total number of candidate coordinates in a predetermined spatial range centered on the search center coordinate p0.

[0101] 6, except for when the search center coordinate p0 is selected initially after starting the process shown in FIG. 7, the candidate coordinates are the lattice point coordinates p1 to p26 (because, as described above, the search center coordinate p0 selected the second time or later is a coordinate for which the candidate vector norm error e1 (or normalized electromotive voltage error e2, which will be described later) has already been calculated). Therefore, in step S15, the processor 26a determines whether the process has been completed with all of the lattice point coordinates p1 to p26 as candidate coordinates, depending on whether the counter j has reached a predetermined value p=26.

[0102] In step S15, if the counter j has not reached the predetermined value p, the processor 26a increments the counter j (step S16) and proceeds to the processing of step S5 in Fig. 7. In step S5, the processor 26a selects a lattice point coordinate that has not yet been selected from among the lattice point coordinates p1 to p26 as a new candidate coordinate, and performs the processing described above. Therefore, the processor 26a selects a new candidate coordinate if the candidate vector norm error e1 is not within the first range.

[0103] Furthermore, if counter j has reached a predetermined value p in step S15, the processor 26a determines whether counter i has reached a predetermined value m1 (step S15A). Here, the predetermined value m1 is greater than 0 and less than a predetermined value m (see step S28 in FIG. 9 ), which will be described later. The memory 26b stores the predetermined value m1. The processor 26a reads the predetermined value m1 from the memory 26b and performs the determination in step S15A. Here, if counter i has reached the predetermined value m1, the processor 26a proceeds to the processing of step S18, which will be described later. If counter i has not reached the predetermined value m1 in step S15A, the processor 26a increments counter i and resets counter j to 0 (step S17), and proceeds to the processing of step S3 in FIG. 7. In step S3, the processor 26a selects the three-dimensional coordinates of another point included in the entire range stored in memory 26b as search center coordinates p0, and performs the above-described processing.

[0104] That is, even if all of the plurality of grid point coordinates p1 to p26 are selected as candidate coordinates, if the candidate vector norm error e1 is not within the first range, the processor 26a selects a new search center coordinate p0.

[0105] On the other hand, in step S14, the candidate vector norm error e is set to a predetermined threshold value e 1th If it is less than the predetermined value, the processor 26a sets the value ST2 indicating stage 2 to the parameter ST indicating the current stage (step S18).

[0106] Then, the processor 26a updates the search center coordinate p0 to the current most likely coordinate (step S19), proceeds to the process of step S4 in FIG. 7, and further performs the processes up to step S6.

[0107] Therefore, if the candidate vector norm error e1 is within the first range in step S14, the processor 26a selects the current most likely coordinate as the new search center coordinate p0 in step S19, and selects one of the multiple lattice point coordinates p1 to p26 within a predetermined spatial range centered on the search center coordinate p0 as the candidate coordinate in step S5.

[0108] Since the value ST2 is entered into the parameter ST in step S18, the processor 26a determines in the subsequent step S7 that the value of the parameter ST is not ST1, and proceeds to the stage 2 processing of FIG. 9 (step S9).

[0109] When the stage 2 process of FIG. 9 begins, the processor 26a (estimated electromotive voltage calculation unit 34) calculates the matrix B k and candidate vector G k+1 Based on this, the estimated electromotive force B k G k+1 (See the second term in the norm of the numerator in the right-hand side sigma of (Equation 11)) is calculated (step S21).

[0110] Furthermore, the processor 26a (normalized voltage error calculation unit 35) calculates the estimated electromotive voltage B k G k+1 and the electromotive force vector v obtained from the detection signal k (measured voltage) and the electromotive voltage error (see the norm of the numerator in the sigma on the right side of (Equation 11)), which is the error between k The measured voltage is normalized to calculate the normalized electromotive voltage error e2 as expressed by (Equation 11) (Step S22). (Equation 11)

[0111] In addition, on the right side of (Equation 11), sigma is the sum of k=1 to l, but the candidate vector G k+1 The subscript (k+1) of takes the value "1" when k=l.

[0112] Each time a new normalized electromotive voltage error e2 is calculated, the processor 26a compares it with the minimum value of the normalized electromotive voltage error e2 calculated in the past (step S23).

[0113] That is, the processor 26a stores the minimum value of the normalized electromotive voltage error e calculated after starting the process shown in Fig. 7 in, for example, the memory 26b, and then compares the minimum value of the normalized electromotive voltage error e stored in the memory 26b with the newly calculated normalized electromotive voltage error e.

[0114] If the newly calculated normalized electromotive force error e is smaller than the smallest value of the previously calculated normalized electromotive force error e, the processor 26a updates the most likely coordinate to the current candidate coordinate (step S24). The memory 26b stores the most likely coordinate.

[0115] The processor 26a determines whether the normalized electromotive voltage error e2 is greater than or equal to a predetermined threshold value e 2th It is determined whether the value is less than the predetermined threshold value e (second range) (step S25). 2th The processor 26a stores a predetermined threshold value e 2th is read out and the determination in step S25 is performed.

[0116] As shown in (Equation 11), the normalized electromotive voltage error e2 takes a value equal to or greater than 0. Therefore, the second range is equal to or greater than 0 and equal to or less than e 2th The range is less than.

[0117] Here, the normalized electromotive voltage error e2 is a predetermined threshold value e 2th If it is not less than p, the processor 26a determines whether the counter j has reached a predetermined value p (step S26).

[0118] In step S26, if the counter j has not reached the predetermined value p, the processor 26a increments the counter j (step S27) and proceeds to the processing of step S5 in Fig. 7. In step S5, the processor 26a selects a lattice point coordinate that has not yet been selected from among the lattice point coordinates p1 to p26 as a new candidate coordinate, and performs the processing described above. Therefore, the processor 26a selects a new candidate coordinate when the normalized electromotive voltage error e2 is not within the second range.

[0119] If the counter j has reached the predetermined value p in step S26, the processor 26a determines whether the counter i has reached the predetermined value m (step S28). The memory 26b stores the predetermined value m. The processor 26a reads the predetermined value m from the memory 26b and performs the determination in step S28.

[0120] If the counter i has not reached the predetermined value m in step S28, the processor 26a increments the counter i and resets the counter j to 0 (step S29).

[0121] Furthermore, the processor 26a updates the search center coordinate p0 to the current most likely coordinate (step S30), proceeds to the process of step S4 in FIG. 7, and then performs the process of step S5.

[0122] Therefore, if the normalized electromotive force error e2 is not within the second range even when all of the multiple lattice point coordinates p1 to p26 are selected as candidate coordinates, the processor 26a selects the current most likely coordinate as the new search center coordinate p0, and selects one of the multiple lattice point coordinates p1 to p26 within a predetermined spatial range centered on the search center coordinate p0 as the candidate coordinate.

[0123] As described above, when the processor 26a selects new search center coordinates p0, it reduces the predetermined spatial range and shortens the grid point interval.

[0124] On the other hand, in step S25, the normalized electromotive voltage error e2 is set to a predetermined threshold value e 2th If it is less than the predetermined value m, or if the counter i has reached the predetermined value m in step S28, the processor 26a (estimated coordinate acquisition unit 36) acquires the current most likely coordinate as the estimated coordinate (step S31).

[0125] That is, when the normalized electromotive voltage error e2 is within the second range, the processor 26a acquires the current most likely coordinates as the estimated coordinates of the magnetic field generating element 22.

[0126] In this embodiment, the normalized electromotive voltage error e2 is set to a predetermined threshold value e 2th Even if the counter i has not yet reached the predetermined value m, when the counter i reaches the predetermined value m, the processor 26a obtains the current most likely coordinate as the estimated coordinate.

[0127] Furthermore, the direction vector g indicating the direction of the magnetic field generating element 22 (the direction of the transmitting coil C) whose estimated coordinates have been acquired is the candidate vector G k The vector sum of the above is normalized as a unit vector and is expressed by the following (Equation 12).

[0128] Here, the candidate vector G used in (Equation 12) k is the x, y, x coordinates of the receiving coil SCk of the set k. Rk , y Rk , z Rk and recalculated using (Equation 4) to (Equation 9).

[0129] Therefore, the direction vector g (estimated vector) expressed by (Equation 12) is the maximum likelihood vector corresponding to the maximum likelihood coordinates that are the basis of the estimated coordinates.

[0130] After the process of step S31 is performed, the process returns to the main process (not shown).

[0131] According to the first embodiment, in stage 1, the candidate vector G k is made to approach a likely vector, and the candidate vector norm error e is made to fall within a predetermined threshold e 1th When the value of the candidate vector G is less than 1, the process proceeds to stage 2, where the candidate coordinates are made closer to the most likely coordinates. k does not deviate far from the true value, and it is possible to avoid the estimated coordinates from approaching the true value and falling into a local minimum.

[0132] For example, at the periapsis, the candidate vector G k is likely to deviate from the true value. Here, the near point is the point closest to the magnetic field detection element 23 within the range (entire range) of space in which the position can be detected by the magnetic field detection element 23. In contrast, in this embodiment, as shown in (Equation 10), the candidate vector G k The candidate vector norm error e1 is based on the vector norm obtained by dividing by a constant ξ (i.e., a norm close to the value 1, which is the norm of a unit vector). k Therefore, in this embodiment, the likelihood of the candidate vector norm error e1 can be accurately determined even at the near point, and the candidate vector G k can be brought closer to the true value.

[0133] Furthermore, since the electromotive force becomes large at the near point, even a small coordinate error can easily cause a large voltage error between the estimated electromotive force and the measured voltage. In contrast, in this embodiment, as shown in (Equation 11), the electromotive force error is normalized based on the measured voltage, and the normalized electromotive force error e2 is set to a predetermined threshold value e 2th Therefore, in this embodiment, the error rate between the estimated electromotive voltage and the measured voltage can be accurately determined even at the near point, and the estimated coordinate can be made closer to the true value.

[0134] In stage 2 shown in Fig. 9, the process may return to step S4 or step S5 in Fig. 7, but it will not return to step S3 in Fig. 7. In other words, in stage 2, another point included in the entire range stored in memory 26b is not selected as the search center coordinate p0. In this way, in stage 2, only lattice point coordinates p1 to p26 are searched for, with the maximum likelihood coordinate obtained in stage 1 as the search center coordinate p0, so that estimated coordinates can be obtained quickly with a small number of search points (i.e., a small amount of calculation).

[0135] In this way, the relative positions and directions of the magnetic field generating elements 22 in a wide range including the near point of the magnetic field detecting element 23 and the magnetic field detecting element 23 can be estimated quickly with a small amount of calculation.

[0136] Furthermore, when the search center coordinate p0 and the grid point coordinates are reset, the grid point interval is shortened, so that estimated coordinates can be obtained with high accuracy.

[0137] Furthermore, the magnetic field generating element 22 is disposed inside the endoscope 3, and the magnetic field detecting element 23 is disposed in the antenna 28 outside the endoscope 3. This allows for a high degree of freedom in the placement of the receiving coil groups 23g1 to 23g4 in the magnetic field detecting element 23. Therefore, as shown in FIG. 2, the receiving coil groups 23g1 to 23g4 can be placed away from noise sources, for example, and the accuracy of the detection signal can be increased. [Second embodiment]

[0138] 10 is a diagram showing a configuration example in a second embodiment of the present invention in which a magnetic field detection element 23 is arranged in the endoscope 3 and a magnetic field generation element 22 is arranged in an antenna 28 outside the endoscope 3. In the second embodiment, parts that are the same as those in the first embodiment are given the same reference numerals, and descriptions thereof will be omitted as appropriate. In the second embodiment, differences from the first embodiment will be mainly described.

[0139] In the first embodiment, the magnetic field generating element 22 is arranged inside the endoscope 3, and the magnetic field detecting element 23 is arranged in an antenna 28 (a receiving antenna in the example of FIG. 2) outside the endoscope 3. In contrast, in the second embodiment, the magnetic field generating element 22 is arranged in an antenna 28 (a transmitting antenna in the example of FIG. 10) outside the endoscope 3, and the magnetic field detecting element 23 is arranged inside the endoscope 3.

[0140] In this way, the magnetic field generating element 22 (specifically, transmitting coils C1 to Cn) and the magnetic field detecting element 23 (specifically, receiving coil groups 23g1 to 23g4) may be arranged in the opposite manner to the configuration shown in the first embodiment.

[0141] According to the second embodiment, substantially the same effects as those of the first embodiment described above are achieved.

[0142] Furthermore, the current value of the detection signal transmitted by the magnetic field detection element 23 after detecting the magnetic field MF is generally smaller than the current value of the drive signal transmitted by the drive signal transmission unit 24 to the magnetic field generation element 22. Therefore, according to the second embodiment, the amount of heat generated from the coils in the endoscope 3 can be reduced more than in the first embodiment, and the temperature rise of the endoscope 3 can be suppressed. This makes it possible to reduce, for example, the generation of thermal noise in the image pickup element 16 due to the temperature rise. Furthermore, the burden on the patient caused by the temperature rise of the endoscope 3 can also be reduced. [Third Embodiment]

[0143] 11 is a diagram showing an example of a configuration in a third embodiment of the present invention in which a signal detected by a receiving coil SC of a magnetic field detection element 23 is amplified with a changeable amplification factor, converted into a digital signal, and transmitted to a magnetic field detection unit 25. In the third embodiment, parts that are the same as those in the first and second embodiments are given the same reference numerals, and descriptions thereof will be omitted as appropriate. In the third embodiment, differences from the first and second embodiments will be mainly described.

[0144] The position detection system 2 further includes first to n-th amplifiers 38-1 to 38-n that amplify the signal generated by the magnetic field detection element 23 upon detecting the magnetic field MF and transmit the detection signal.

[0145] A plurality of (n) amplifiers 38-1, 38-2, ..., 38-n are connected in parallel to both ends of the receiving coil SC. The n amplifiers 38-1, 38-2, ..., 38-n each detect an electromotive voltage across both ends of the receiving coil SC and amplify it by a respective gain.

[0146] If the gain of the first amplifier 38-1 is G1, the gain of the second amplifier 38-2 is G2, ..., and the gain of the nth amplifier 38-n is Gn, then each amplifier is configured so that the relationship G1<G2< ...<Gn holds, for example.

[0147] The first amplifier 38-1 is connected to the ADC 39-1, which transmits to the magnetic field detector 25 a digital detection signal containing information about the voltage V1 amplified by the first amplifier 38-1 with a gain G1.

[0148] The second amplifier 38-2 is connected to the ADC 39-2. The ADC 39-2 transmits to the magnetic field detector 25 a digital detection signal including information about the voltage V2 amplified by the second amplifier 38-2 with a gain G2.

[0149] The same applies to the other amplifiers, and the n-th amplifier 38-n is connected to the ADC 39-n. The ADC 39-n transmits a digital detection signal including information on the voltage Vn amplified by the n-th amplifier 38-n with a gain Gn to the magnetic field detection unit 25.

[0150] The magnetic field detection unit 25 receives detection signals containing information on the voltages V1 to Vn from the n ADCs 39-1 to 39-n. As described above, the gains have the relationship G1<G2< ... <Gn, so the voltages generally have the relationship V1<V2< ... <Vn.

[0151] The magnetic field detection unit 25 detects a threshold voltage V1 for each of the voltages V1 to Vn. th ~Vn th The electromotive voltage V generated across the receiving coil SC is obtained as follows:th ~Vn th may be implemented as hardware in the magnetic field detection unit 25, or may be stored in a memory (not shown) in the magnetic field detection unit 25, or in the memory 26b in the control unit 26.

[0152] The magnetic field detection unit 25 first sets the voltage V1 to a threshold voltage V1 th Compared with V1>V1 th In this case, the electromotive voltage V is calculated by V=V1 / G1.

[0153] Also, V1≦V1 th In this case, the magnetic field detection unit 25 sets the voltage V2 to the threshold voltage V2 th Compared with V2>V2 th At this time, the electromotive voltage V is calculated by V=V2 / G2.

[0154] V2≦V2 th In this case, the magnetic field detection unit 25 performs the same process for the voltages V3 and onwards, and V(n-1)≦V(n-1) th When this happens, the voltage Vn is set to the threshold voltage Vn th Compared with Vn>Vn th At this time, the electromotive voltage V is calculated by V=Vn / Gn.

[0155] Note that Vn≦Vn th In this case, the magnetic field detection unit 25 may transmit an error signal to the control unit 26. In this case, the control unit 26 determines that the magnetic field MF has not been detected by the magnetic field detection unit 25, and suspends the execution of the process shown in FIG. 7 until the control unit 26 receives the next detection signal from the magnetic field detection unit 25.

[0156] Or, Vn≦Vn th Even in this case, the magnetic field detection unit 25 may calculate the electromotive voltage V by V=Vn / Gn.

[0157] As described above, the voltage is checked in the order V1 → V2 → ... → Vn because if the amplification factor is too large compared to the signal magnitude, the voltage value will exceed the upper limit of the ADC's detectable range, and the voltage cannot be detected correctly.

[0158] In this way, the first to n-th amplifiers 38-1 to 38-n function as amplifiers that can change the amplification factor in accordance with the voltage of the signal.

[0159] 11 shows an example in which a plurality of amplifiers 38 with different gains and a plurality of ADCs 39 connected to each of the plurality of amplifiers 38 are provided, but the configuration is not limited to this. For example, a single amplifier 38 with a variable gain and a single ADC 39 connected to the single amplifier 38 may be provided, and the gain of the amplifier 38 may be changed according to the voltage of the signal transmitted from the receiving coil SC.

[0160] In addition, the current value of the drive signal transmitted by the drive signal transmitting unit 24 to the magnetic field generating element 22 (and thus the strength of the magnetic field MF generated by the magnetic field generating element 22) may be changed so that the voltage of the signal transmitted from the receiving coil SC falls within a certain voltage range.

[0161] According to the third embodiment, substantially the same effects as those of the first and second embodiments are achieved. Furthermore, the third embodiment achieves the following effects.

[0162] 4 has limitations on the voltage detectable range (dynamic range) and resolution. For this reason, even if the algorithm is improved, it may not be possible to detect the position of the magnetic field generating element 22 over a wide range from the near point to the far point. Here, the far point is the point farthest from the magnetic field detecting element 23 within the spatial range (entire range) in which the position can be detected by the magnetic field detecting element 23.

[0163] In contrast, according to the third embodiment, the amplification factor of the amplifier can be changed according to the voltage of the signal generated by the magnetic field detection element 23 upon detecting the magnetic field MF, thereby widening the detectable voltage range. Alternatively, the current value of the drive signal can be changed so that the voltage of the signal generated upon detecting the magnetic field MF falls within a certain voltage range, thereby making it possible to constantly detect the magnetic field MF. This makes it possible to detect the position of the magnetic field generation element 22 over a wide range from the near point to the far point with high accuracy. [Fourth embodiment]

[0164] 12 to 14 show a fourth embodiment of the present invention. In the fourth embodiment, parts that are the same as those in the first to third embodiments are given the same reference numerals, and descriptions thereof will be omitted as appropriate. In the fourth embodiment, differences from the first to third embodiments will be mainly described.

[0165] FIG. 12 is a diagram showing the configuration of a position detection system 2 according to the fourth embodiment.

[0166] 5 , the position detection device 21 shown in Fig. 12 further includes an estimated coordinate use unit 41 connected to the estimated coordinate acquisition unit 36. The estimated coordinate use unit 41 is provided, for example, as a functional unit within the control unit 26. However, the estimated coordinate use unit 41 may also be provided outside the control unit 26.

[0167] The estimated coordinate use unit 41 receives the estimated coordinates (and estimated vectors as necessary; the same applies below) transmitted from the estimated coordinate acquisition unit 36. Based on the received estimated coordinates of the transmitting coils C1 to Cn, the estimated coordinate use unit 41 generates, for example, a shape detection image indicating the shape of the insertion unit 11. Furthermore, the estimated coordinate use unit 41 may generate insertion assistance information based on the received estimated coordinates.

[0168] The shape detection image, insertion support information, etc. generated by the estimated coordinate use unit 41 are transmitted to the video processor 5 connected to the position detection device 21 and displayed on the monitor 6 together with the endoscopic image.

[0169] Although not explicitly stated, the position detection system 2 according to the first to third embodiments may include the estimated coordinate use unit 41 .

[0170] FIG. 13 is a flowchart showing stage 1 processing, which is part of the transmitting coil coordinate estimation processing in the fourth embodiment.

[0171] The stage 1 processing shown in FIG. 13 is basically the same as the stage 1 processing shown in FIG. 8, but after performing the processing of step S17, the processor 26a further determines whether the counter i has reached a predetermined value m (step S41).

[0172] If the counter i has not yet reached the predetermined value m, the processor 26a proceeds to the process of step S3 in FIG.

[0173] On the other hand, if the counter i has reached the predetermined value m in step S41, the processor 26a proceeds to processing in step S42 in FIG. 14, which will be described later.

[0174] FIG. 14 is a flowchart showing stage 2 processing, which is part of the transmit coil coordinate estimation processing in the fourth embodiment.

[0175] 14 is basically the same as the stage 2 process shown in Fig. 9, except that if the counter i has reached the predetermined value m in step S28, the processor 26a does not update the estimated coordinates (step S42). Also, as described above, if the counter i has reached the predetermined value m in step S41 of the stage 1 process, the processor 26a does not update the estimated coordinates in step S42.

[0176] In this way, the processor 26a counts the number of times the search center coordinate p0 is selected using the counter i, and even if the count value reaches a predetermined value m, if the candidate vector norm error e1 is not within the first range or the normalized electromotive voltage error e2 is not within the second range, the processor 26a does not obtain the estimated coordinates of the magnetic field generating element 22.

[0177] Therefore, the estimated coordinates are acquired (updated) by the processing in step S31 after the transmitting coil coordinate estimation processing in FIG. 7 is called in the main processing and the candidate vector norm error e1 is calculated to be equal to or smaller than the predetermined threshold value e1 in step S14 of the stage 1 processing in FIG. 1th and the normalized electromotive voltage error e2 is less than the predetermined threshold value e2 in step S25 of the stage 2 processing of FIG. 2th This occurs when the amount is less than the specified amount.

[0178] When the endoscope 3 is moved, e<e 1th , and e2 < e 2thIn addition, if electromagnetic noise occurs, or if there is individual variation in the coils of the transmitting and receiving system that transmits and receives the magnetic field MF, the constant ξ, or the like, it may become difficult to estimate the position and direction.

[0179] Therefore, in this embodiment, even if the estimated coordinates are searched a predetermined number of times (the number of times until the counter i reaches a predetermined value m), e<e 1th , and e2 < e 2th If the above condition cannot be satisfied, the estimated coordinates are not updated. In this case, the estimated coordinates obtained the last time the transmitting coil coordinate estimation process in FIG. 7 was called in the main process are still used.

[0180] According to the fourth embodiment, substantially the same effects as those of the first to third embodiments described above are achieved.

[0181] Furthermore, according to the fourth embodiment, if estimated coordinates that are assumed to be correct cannot be acquired, the estimated coordinates are not updated, so that the estimated coordinate use unit 41 can be prevented from generating an inaccurate shape detection image or inaccurate insertion support information.

[0182] A fifth embodiment of the present invention will be described with reference to Figure 1 etc. In the fifth embodiment, parts that are the same as those in the first to fourth embodiments are given the same reference numerals, and descriptions thereof will be omitted as appropriate. In the fifth embodiment, differences from the first to fourth embodiments will be mainly described.

[0183] As described above, the value of the constant ξ used when calculating the candidate vector norm error e1 is determined by the gain of the entire transmission / reception system including the transmission system that transmits the magnetic field MF and the reception system that receives the magnetic field MF. For this reason, the value of the constant ξ may vary due to individual differences on the endoscope 3 side in which the magnetic field generating element 22 (or magnetic field detecting element 23) is provided, and further, the value of the constant ξ may vary due to individual differences on the position detection system 2 side in which the magnetic field detecting element 23 (or magnetic field generating element 22) is provided.

[0184] Therefore, a first correction value (individual adjustment value) for the constant ξ is stored in the memory 17 provided in the endoscope 3 in order to correct the influence of individual variations on the endoscope 3 side on the candidate vector norm error e1.

[0185] Furthermore, a second correction value (individual adjustment value) for the constant ξ to correct the influence of individual variations on the position detection system 2 side on the candidate vector norm error e1 is stored, for example, in a memory 26b provided in the position detection device 21.

[0186] The processor 26a of the position detection device 21 corrects the constant ξ based on the first correction value read from the memory 17 of the endoscope 3 and the second correction value read from the memory 26b of the position detection device 21, and calculates the candidate vector norm error e1 using the corrected constant ξ.

[0187] According to the fifth embodiment, substantially the same effects as those of the first to fourth embodiments described above are achieved.

[0188] Furthermore, according to the fifth embodiment, the individual adjustment value of the constant ξ used in the process of calculating the candidate vector norm error e is stored in a memory on the side that transmits the magnetic field MF and a memory on the side that receives the magnetic field MF, respectively. Therefore, even if there is a large individual variation, it is possible to obtain an estimated position stably with high accuracy.

[0189] Furthermore, even when a different type of endoscope 3 is combined with the position detection system 2 (or when a different type of position detection system 2 is combined with an endoscope 3), the estimated position can be obtained stably and with high accuracy.

[0190] Although the present invention has been described above primarily in terms of a control device and an endoscope system, it is not limited thereto. For example, the present invention may be a position detection method that performs the same processing as the control device. The present invention may also be a computer program that causes a computer to perform the same processing as the control device. Furthermore, the present invention may also be a non-transitory computer-readable recording medium that records the computer program.

[0191] Examples of recording media for storing a computer program product include portable recording media such as flexible disks, CD-ROMs (Compact Disc Read Only Memory), DVDs (Digital Versatile Discs), and USB (Universal Serial Bus) memory, as well as recording media such as HDDs (Hard Disk Drives) and SSDs (Solid State Drives). The recording media may store only a portion of the computer program, not just the entire program. Furthermore, all or part of the computer program may be distributed or provided via a communications network. A user can install the computer program from the recording media onto a computer, or download and install the computer program via a communications network, whereby the computer reads the computer program, executes all or part of the operations, and performs the operations of the control device described above.

[0192] Furthermore, the present invention is not limited to the above-described embodiments. In the implementation stage, the components can be modified and embodied without departing from the spirit of the invention. Furthermore, various aspects of the invention can be formed by appropriately combining multiple components disclosed in the above embodiments. For example, some components may be deleted from all the components disclosed in the embodiments. Furthermore, components from different embodiments may be appropriately combined. In this way, it goes without saying that various modifications and applications are possible within the scope of the gist of the invention.

Claims

1. A control device comprising a processor, the processor: selects candidate coordinates of a magnetic field generating element; calculates a candidate vector based on the coordinates of a magnetic field detection element, the candidate coordinates, and a detection signal transmitted by the magnetic field detection element after detecting the magnetic field generated by the magnetic field generating element; calculates a vector norm error based on the candidate vector; if the calculated vector norm error is smaller than a minimum value of the vector norm errors calculated in the past, updates a maximum likelihood coordinate to the current candidate coordinate; determines whether the vector norm error is within a first range; and if the vector norm error is not within the first range, selects a new candidate coordinate.

2. The control device according to claim 1, characterized in that the processor selects, as the candidate coordinate, one of a plurality of lattice point coordinates within a predetermined spatial range centered on the search center coordinates.

3. The control device according to claim 2, characterized in that the processor selects new search center coordinates when the vector norm error is not within the first range even if all of the multiple lattice point coordinates are selected as the candidate coordinates.

4. The control device described in claim 2, characterized in that, when the vector norm error is within the first range, the processor selects the current maximum likelihood coordinate as the new search center coordinate, and selects one of the multiple lattice point coordinates within the specified spatial range centered on the search center coordinate as the candidate coordinate.

5. The control device according to claim 4, characterized in that, when the processor selects new search center coordinates, it reduces the specified spatial range and shortens the lattice point interval.

6. The control device according to claim 4, characterized in that the processor: when the vector norm error is within the first range, calculates a normalized electromotive force error based on the candidate vector; when the calculated normalized electromotive force error is smaller than a minimum value of the normalized electromotive force error calculated in the past, updates the maximum likelihood coordinate to the current candidate coordinate; determines whether the normalized electromotive force error is within a second range; and when the normalized electromotive force error is not within the second range, selects a new candidate coordinate.

7. The control device according to claim 6, characterized in that the processor: calculates an estimated electromotive force based on the candidate vector; calculates an electromotive force error which is the error between the estimated electromotive force and a measured voltage obtained from the detection signal; and normalizes the electromotive force error based on the measured voltage to calculate the normalized electromotive force error.

8. The control device described in claim 6, characterized in that, when the normalized electromotive force error is not within the second range even if all of the plurality of lattice point coordinates are selected as the candidate coordinates, the processor selects the current maximum likelihood coordinate as a new search center coordinate, and selects one of the plurality of lattice point coordinates within the specified spatial range centered on the search center coordinate as the candidate coordinate.

9. The control device according to claim 8, characterized in that, when the processor selects new search center coordinates, it reduces the specified spatial range and shortens the lattice point interval.

10. The control device according to claim 6, characterized in that the processor acquires the current maximum likelihood coordinates as estimated coordinates of the magnetic field generating element when the normalized electromotive voltage error is within the second range.

11. The control device described in claim 8, characterized in that the processor counts the number of times the search center coordinate is selected, and does not obtain the estimated coordinate of the magnetic field generating element if the vector norm error is not within the first range or the normalized electromotive voltage error is not within the second range even when the count value reaches a predetermined value.

12. An endoscope system comprising: an endoscope; a magnetic field generating element that generates a magnetic field; a magnetic field detection element that detects the magnetic field and transmits a detection signal; and a processor that processes the detection signal, wherein the processor selects candidate coordinates of the magnetic field generating element, calculates a candidate vector based on the coordinates of the magnetic field detection element, the candidate coordinates, and the detection signal, calculates a vector norm error based on the candidate vector, updates a maximum likelihood coordinate to the current candidate coordinate if the calculated vector norm error is smaller than a minimum value of the vector norm errors calculated in the past, determines whether the vector norm error is within a first range, and selects a new candidate coordinate if the vector norm error is not within the first range.

13. The endoscope system according to claim 12, further comprising an amplifier that amplifies a signal generated by the magnetic field detection element when the magnetic field is detected and transmits the detection signal, and the amplifier is capable of changing an amplification factor according to a voltage of the signal.

14. The endoscope system according to claim 12, characterized in that the magnetic field generating element is disposed inside the endoscope, and the magnetic field detecting element is disposed outside the endoscope.

15. The endoscope system according to claim 12, characterized in that the magnetic field generating element is disposed outside the endoscope, and the magnetic field detecting element is disposed inside the endoscope.

16. The endoscope system according to claim 12, characterized in that the endoscope is provided with a memory that stores a first correction value for correcting the effect of individual variations in the endoscope on the vector norm error.

17. The endoscopic system described in claim 12, characterized in that the magnetic field generating element, the magnetic field detecting element, and the processor are provided in a position detection system, and the position detection system is provided with a memory that stores a second correction value for correcting the effect on the vector norm error due to individual variations in the position detection system.

18. A position detection method comprising: generating a magnetic field by a magnetic field generating element; detecting the magnetic field by a magnetic field detection element and transmitting a detection signal; selecting candidate coordinates of the magnetic field generating element; calculating a candidate vector based on the coordinates of the magnetic field detection element, the candidate coordinates, and the detection signal; calculating a vector norm error based on the candidate vector; updating a maximum likelihood coordinate to the current candidate coordinate if the calculated vector norm error is smaller than a minimum value of the vector norm errors calculated in the past; determining whether the vector norm error is within a first range; and selecting a new candidate coordinate if the vector norm error is not within the first range.

19. The position detection method according to claim 18, characterized in that one of a plurality of lattice point coordinates within a predetermined spatial range centered on the search center coordinates is selected as the candidate coordinates.

20. The position detection method according to claim 19, further comprising the step of selecting new search center coordinates if the vector norm error is not within the first range even when all of the plurality of lattice point coordinates have been selected as the candidate coordinates.

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