Device and method for detecting position in a detection drive-sensing integrated camera module

Abstract

The present disclosure provides an apparatus and method for detecting a position in a drive-sensing integrated camera module. The position detection apparatus includes: a detector circuit that detects a detection signal including information about the position of a magnet from a coil, the coil being disposed in a housing and opposite to the magnet, the magnet being disposed on a lens barrel; and a control circuit that converts the detection signal into a count value, determines a conversion formula based on the count value and a change speed of the count value, and uses the determined conversion formula to detect a position value.

Description

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2019-0175324, filed with the Korean Intellectual Property Office on Dec. 26, 2019, the entire disclosure of which is incorporated herein by reference for all purposes. Technical Field

[0002] The following description relates to an apparatus and method for detecting a position in a drive-sensing integrated camera module. Background Art

[0003] Since mobile phones such as smartphones have been designed to have various functions, there has been a need to reduce the size of various circuits and components embedded in mobile phones.

[0004] There may be a need to reduce the size of a camera module using a drive-sensing integrated method in a smartphone.

[0005] A general camera module using a Hall sensing method may include an optical image stabilization (OIS) coil and a Hall sensor. In a camera module using such a Hall sensor, the Hall sensor may be disposed at a position where the magnetic field strength is the strongest to sense the magnetic field.

[0006] However, when using a Hall sensor, it may be difficult to reduce its size. Accordingly, a sensorless camera module has been developed that can drive an actuator and can use a coil to detect a position without using a Hall sensor.

[0007] However, in such a sensorless camera module, eddy currents can be generated by a magnetic field generated between a coil and a magnet, and the eddy currents can be used to detect a position.

[0008] A general position detection device in a sensorless camera module may perform a sensing operation based on an overlap between a magnet and a coil to sense a position for an autofocus (AF) function, and two detection coils may be used to detect forward and backward movement in the optical axis direction.

[0009] However, when using two detection coils and a single drive coil, there may still be limitations in reducing the size. Accordingly, when implementing a structure capable of performing both a driving operation and a detection operation using a single coil, there may be a problem in that it may be difficult to accurately distinguish between forward movement and backward movement in the optical axis direction. Summary of the Invention

[0010] This Summary of the Invention is provided to introduce a selection of concepts in a simplified form. These concepts are further described below in the Detailed Description. This Summary of the Invention is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to help determine the scope of the claimed subject matter.

[0011] An apparatus and method for detecting a position in a drive-sensing integrated camera module, which can accurately detect the position of a lens in a camera module having a drive-sensing integrated coil.

[0012] In one general aspect, a position detection apparatus includes: a detector circuit that detects a detection signal including information about the position of a magnet from a coil, the coil being disposed in a housing and opposite to the magnet, the magnet being disposed on a lens barrel; and a control circuit that converts the detection signal into a count value, determines a conversion formula based on the count value and a change speed of the count value, and uses the determined conversion formula to detect a position value.

[0013] The control circuit may include: a signal converter circuit that converts the detection signal into the count value; a formula determination circuit that determines the conversion formula based on an error between the count value and a target value and based on a change speed of the error; and a position detector circuit that converts the count value into the position value using the conversion formula determined by the formula determination circuit.

[0014] In a case where the count value is included in a predetermined monitoring range such that the error between the count value and the target value increases and the change speed of the error increases, the formula determination circuit may change a first conversion formula to a second conversion formula.

[0015] The detection range may be based on a center value corresponding to a center between a maximum count value and a minimum count value.

[0016] The first conversion formula may be: SP = b × D_CNT, where SP is the position value, b is a constant, and D_CNT is the count value.

[0017] The second conversion formula may be: SP = b × (2 × D_CNT - CT_CNT), where CT_CNT is the center value.

[0018] In another general aspect, a method for detecting a position includes: detecting a detection signal including information about the position of a magnet from a single coil disposed in a housing and opposite to the magnet, the magnet being disposed on a lens barrel; converting the detection signal into a count value; determining whether a condition for changing a conversion formula is satisfied based on the count value; when the condition for changing the conversion formula is not satisfied, maintaining a first conversion formula, and when the condition for changing the conversion formula is satisfied, changing the first conversion formula to a second conversion formula; and selectively using the first conversion formula or the second conversion formula to detect a position value.

[0019] It is possible to determine whether the condition for changing the conversion formula is satisfied based on the error between the count value and the target value and the rate of change of the error.

[0020] Determining whether the condition for changing the conversion formula is satisfied may include: determining whether the count value is included within a monitoring range; calculating the error between the count value and the target value; and when the error between the count value and the target value increases, determining whether the rate of change of the error increases.

[0021] The first conversion formula may be a basic formula.

[0022] The monitoring range may be determined based on a center value corresponding to the center between the maximum count value and the minimum count value.

[0023] In another general aspect, a camera module includes: a lens barrel including a magnet; a substrate including a coil disposed opposite to the magnet; and one or more circuits that detect a detection signal related to the position of the magnet from the coil, convert the detection signal into a count value, determine a conversion formula based on the count value, and use the determined conversion formula to detect a position value.

[0024] The one or more circuits may determine whether the conversion formula is a first conversion formula or a second conversion formula based on one or more values associated with an error in the count value; and may convert the count value into the position value using the determined first conversion formula or the second conversion formula.

[0025] The one or more values associated with the error in the count value may include the error between the count value and the target value and the rate of change of the error between the count value and the target value.

[0026] The first conversion formula may be a default conversion formula, and in a case where the error between the count value and the target value increases and the rate of change of the error increases, the one or more circuits may change the first conversion formula to the second conversion formula.

[0027] Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a diagram showing an example of a camera module.

[0029] Figure 2 is a diagram showing an example of a position detection device.

[0030] Figure 3 is a diagram showing Figure 2 an example of the control circuit shown in

[0031] Figure 4 is a diagram showing an example of a method for detecting a position.

[0032] Figure 5 is a diagram showing an example of a process for determining conditions for changing Figure 4 the conversion formula shown in

[0033] Figure 6 is a diagram showing an example of position 1 between a magnet and a single coil.

[0034] Figure 7 is a diagram showing an example of position 2 between a magnet and a single coil.

[0035] Figure 8 is a diagram showing an example of position 3 between a magnet and a single coil.

[0036] Figure 9 is a diagram showing an example of the moving position and the detection position of the magnet when the conversion formula is not changed.

[0037] Figure 10 is a diagram showing the error between the count value D_CNT and the target value T_CNT and the speed of change of the error.

[0038] Figure 11 is a diagram showing an example of the moving position and the detection position of the magnet when the conversion formula is changed.

[0039] Throughout the drawings and the detailed description, the same reference numerals indicate the same elements. The drawings may not be drawn to scale, and for clarity, illustration, and convenience, the relative dimensions, scales, and depictions of the elements in the drawings may be exaggerated. Detailed Description

[0040] The following detailed description is provided to assist the reader in obtaining a comprehensive understanding of the methods, devices, and / or systems described herein. However, various changes, modifications, and equivalents of the methods, devices, and / or systems described herein will be apparent to those of ordinary skill in the art. The order of operations described herein is merely exemplary and is not limited to the order of operations set forth herein, but rather, changes that will be apparent to those of ordinary skill in the art may be made, except for operations that must occur in a specific order. Additionally, descriptions of functions and structures well known to those of ordinary skill in the art may be omitted for increased clarity and brevity.

[0041] The features described herein can be implemented in various forms and should not be construed as limited to the examples described herein. Rather, the examples described herein are provided so that this disclosure will be thorough and complete and will convey the scope of this disclosure fully to those of ordinary skill in the art.

[0042] Here, it should be noted that the use of the term "may" with respect to an example or embodiment (e.g., what an example or embodiment may include or achieve) means that there is at least one example or embodiment that includes or achieves such a feature, and all examples and embodiments are not limited thereto.

[0043] Throughout the specification, when an element (such as a layer, region, or substrate) is described as "on" another element, "connected to" another element, or "coupled to" another element, it may be directly "on" the other element, directly "connected to" the other element, or directly "coupled to" the other element, or there may be one or more other elements therebetween. In contrast, when an element is described as "directly on" another element, "directly connected to" another element, or "directly coupled to" another element, there may be no other elements therebetween.

[0044] As used herein, the term "and / or" includes any one and any combination of any two or more of the associated listed items.

[0045] Although terms such as "first", "second", and "third" may be used herein to describe various components, elements, regions, layers, or sections, these components, elements, regions, layers, or sections are not limited by these terms. Rather, these terms are only used to distinguish one component, element, region, layer, or section from another component, element, region, layer, or section. Thus, a first component, first element, first region, first layer, or first section as referred to in the examples described herein may also be referred to as a second component, second element, second region, second layer, or second section without departing from the teachings of the examples.

[0046] For ease of description, spatial relationship terms such as "above", "upper", "below", and "lower" may be used herein to describe the relationship of one element to another as shown in the accompanying drawings. Such spatial relationship terms are intended to include different orientations of the device in use or operation in addition to the orientation depicted in the accompanying drawings. For example, if the device in the accompanying drawings is flipped, an element described as "above" or "upper" relative to another element will subsequently be "below" or "lower" relative to the other element. Thus, the term "above" includes both the orientations of "above" and "below" depending on the spatial orientation of the device. The device may also be positioned in other ways (e.g., rotated 90 degrees or in other orientations), and the spatial relationship terms used herein will be interpreted accordingly.

[0047] The terms used herein are for the purpose of describing various examples only and are not intended to limit the disclosure. Unless the context clearly dictates otherwise, the singular forms are also intended to include the plural forms. The terms "comprises", "comprising", and "having" list the presence of the stated features, quantities, operations, components, elements, and / or combinations thereof, but do not preclude the presence or addition of one or more other features, quantities, operations, components, elements, and / or combinations thereof.

[0048] Due to manufacturing techniques and / or tolerances, variations in the shapes shown in the accompanying drawings may occur. Thus, the examples described herein are not limited to the specific shapes shown in the accompanying drawings, but include changes in shape that occur during manufacturing.

[0049] The features of the examples described herein may be combined in various ways that will be apparent after understanding the disclosure of this application. In addition, although the examples described herein have various configurations, other configurations that will be apparent after understanding the disclosure of this application are also possible.

[0050] Figure 1 is a view showing an example of a camera module.

[0051] Referring to Figure 1 , the camera module 100 may include a housing 110, a case 120, a lens barrel 130, a magnet 180, and a single coil 150.

[0052] The housing 110 may be coupled to the case 120. The case 120 may be coupled to the housing 110 and may include an accommodation space.

[0053] As an example, the housing 110 may include a metal material or may be formed using a metal material, and may be grounded to a ground pad of a substrate disposed below the case 120 (e.g., in the -Z direction). Thus, the housing 110 may shield electromagnetic waves generated when the camera device is driven.

[0054] The lens barrel 130 can be disposed in the accommodation space of the housing 120, and the lens module 140 disposed along the optical axis (e.g., the Z-axis direction) can be disposed in the lens barrel 130.

[0055] The magnet 180 can be disposed on the outer side of the lens barrel 130. As an example, the magnet 180 can be configured as a member including a magnetic material, or can be configured as a dielectric material or a conductive material.

[0056] A single coil 150 can be mounted on the substrate 190, and the substrate 190 is disposed in the housing 120 and opposite to the magnet 180. The single coil 150 can be used for both driving operations and detection operations.

[0057] As an example, the single coil 150 can be spaced apart from the magnet 180 by a specific gap, and when a driving current flows in the single coil 150, a driving force can be transmitted to the magnet 180 through the electromagnetic force generated by the single coil 150, so that the magnet 180 can move. Accordingly, the lens module 140 disposed in the lens barrel 130 to which the magnet 180 is attached can move in the X-axis direction.

[0058] In this case, the inductance value of the single coil 150 can be changed by the magnetic force acting between the single coil 150 and the magnet 180, and the position of the magnet 180 can be detected based on the change in inductance.

[0059] Figure 2 is a diagram showing an example of a position detection device.

[0060] Refer to Figure 2 , the position detection device can include a detector circuit 300 and a control circuit 400. The position detection device can also include a driver circuit 200.

[0061] The detector circuit 300 can detect a detection signal Sd including information about the position of the magnet 180 from the single coil 150, and the single coil 150 is disposed in the housing 120 and opposite to the magnet 180 disposed in the lens barrel 130.

[0062] The control circuit 400 can convert the detection signal Sd into a count value D_CNT, can determine a conversion formula based on the count value D_CNT and the change speed of the count value D_CNT, and can use the determined conversion formula to detect a position value SP.

[0063] The driver circuit 200 can drive the camera module 100 in response to a control signal SC received from the control circuit 400.

[0064] In the drawings, unnecessary repetitive descriptions of the same reference numerals and the same functions will not be provided, and the differences between the examples in the drawings will be mainly described.

[0065] Figure 3 is a diagram showing Figure 2 an example of the control circuit shown in

[0066] Referring to Figure 3 , the control circuit 400 may include a signal converter circuit 410, a formula determination circuit 420, and a position detector circuit 430.

[0067] The signal converter circuit 410 may convert the detection signal Sd into a count value D_CNT. As an example, the signal converter circuit 410 may count the detection signal Sd using a reference clock signal and may generate a count value D_CNT.

[0068] The formula determination circuit 420 may determine a conversion formula based on the error between the count value D_CNT and the target value T_CNT and the rate of change of the error.

[0069] The position detector circuit 430 may convert the count value D_CNT into a position value SP using the conversion formula determined by the formula determination circuit 420.

[0070] For example, when the count value D_CNT is included in a predetermined monitoring range CT_CNT ± a (a is a constant) such that the error between the count value and the target value increases and the rate of change of the error increases, the formula determination circuit 420 may change the first conversion formula determined as the basic formula to the second conversion formula.

[0071] The monitoring range CT_CNT ± a may be predetermined based on a center value CT_CNT corresponding to the center between the maximum count value and the minimum count value.

[0072] As an example, the first conversion formula may be represented by the following Equation 1.

[0073] [Equation 1]

[0074] SP = b × count value D_CNT

[0075] In Equation 1, "SP" is the position value, "b" is a constant, and "D_CNT" is the count value.

[0076] As an example, the second conversion formula may be represented by the following Equation 2.

[0077] [Equation 2]

[0078] SP = b × (2 × count value D_CNT - center value CT_CNT)

[0079] In Equation 2, "SP" is the position value, "b" is a constant, "D_CNT" is the count value, and "CT_CNT" is the center value. For example, b may be "1", but the example is not limited thereto.

[0080] Figure 4 It is a diagram showing an example of a method for detecting a detection position.

[0081] In the following description, a method for detecting a position will be described according to an example.

[0082] In the description of the method for detecting the position of the camera module, the same description of the operations described with reference to Figures 1 to 3 can be applied, and therefore, no repeated description will be provided in the description of the position detection device.

[0083] With reference to Figure 4 , in the operation of detecting a signal (S410), a detection signal Sd including information about the position of the magnet 180 can be detected from a single coil 150, and the single coil 150 is provided in the housing and is opposite to the magnet 180 provided in the lens barrel 130. As an example, the detection signal (S410) can be executed by the signal detector circuit 300.

[0084] In the operation of converting a signal (S420), the detection signal Sd can be converted into a count value D_CNT. As an example, the conversion of the signal (S420) can be executed by the signal converter circuit 410 of the control circuit 400.

[0085] In the operation of determining a condition for changing a conversion formula (S430), it can be determined whether the condition for changing the conversion formula is satisfied based on the count value D_CNT. As an example, the determination of the condition for changing the conversion formula (S430) can be executed by the formula determination circuit 420 of the control circuit 400. As an example, in the operation of determining the condition for changing the conversion formula (S430), it can be determined whether the condition for changing the conversion formula is satisfied based on the error between the count value D_CNT and the target value T_CNT and the rate of change of the error.

[0086] In the operation of determining a conversion formula (S440), when the condition for changing the conversion formula is not satisfied, the first conversion formula can be maintained (operation S441), and when the condition for changing the conversion formula is satisfied, the first conversion formula can be changed to the second conversion formula (operation S442). As an example, the determination of the conversion formula (S440) can be executed by the formula determination circuit 420 of the control circuit 400.

[0087] In the operation of detecting a position value SP (S450), the first conversion formula or the second conversion formula can be used to detect the position value SP. As an example, the detection of the position value SP can be executed by the position detector circuit 430 of the control circuit 400.

[0088] In operation S460, it is determined whether the detection of the position is completed. If it is determined that the detection of the position is completed, the process is completed. If it is determined that the detection of the position is not completed, the process returns to operation S410.

[0089] Figure 5 It is a diagram showing an example of a process for determining conditions for changing the Figure 4 conversion formula shown in.

[0090] Refer to Figure 5 In the operation (S430) of determining the conditions for changing the conversion formula, it is possible to determine whether the count value D_CNT is included in a predetermined monitoring range CT_CNT ± a (a is a constant) (S431). The error between the count value D_CNT and the target value T_CNT can be calculated (S432). It is possible to determine whether the rate of change of the error increases when the error between the count value D_CNT and the target value T_CNT increases (S433).

[0091] As an example, in the operation (S440) of determining the conversion formula, when the conditions for changing the conversion formula are satisfied, the first conversion formula determined as the basic formula can be changed to the second conversion formula.

[0092] As an example, the monitoring range CT_CNT ± a can be predetermined based on the center value CT_CNT corresponding to the center between the maximum count value and the minimum count value.

[0093] The first conversion formula can be Equation 1 as described above, and the second conversion formula can be Equation 2 as described above.

[0094] Figure 6 It is a diagram showing an example of position 1 between the magnet and the single coil. Figure 7 It is a diagram showing an example of position 2 between the magnet and the single coil. Figure 8 It is a diagram showing an example of position 3 between the magnet and the single coil. Figure 9 It is a diagram showing an example of the moving position and the detection position of the magnet when the conversion formula is not changed.

[0095] Refer to Figures 6 to 9 When the magnet 180 moves between position 1 and position 2 and moves to position 3, in Figure 6 position 1 in and in Figure 8 position 3 in, the overlapping area between the magnet 180 and the single coil 150 can be the same. Therefore, the detected count value D_CNT may be the same, making it difficult to accurately detect the position.

[0096] Figure 10 It is a diagram showing the error between the count value D_CNT and the target value T_CNT and the rate of change of the error.Figure 11 This is a diagram showing an example of the moving position and detection position of a magnet when the conversion formula is changed.

[0097] Referring to Figure 10 , when the count value D_CNT corresponding to the currently detected position becomes close to the target value T_CNT (target position), the error can be reduced and the error rate (e.g., the slope of the error change) can also be reduced.

[0098] When the magnet 180 approaches Figure 7 the position 2 in Figure 10 and position 3 cannot be detected but the position 3' of a reference single coil 150 is detected, different from

[0099] the detected position may be far from the actual target value (target position). In this case, the error may increase and the error rate may also increase.

[0100] Therefore, as described above, when the detected position is included in the monitoring range such that the error between the detected count value D_CNT and the target value T_CNT increases and the error rate also increases, the initially determined first conversion formula can be changed to the second conversion formula.

[0101] The control circuit of the position detection device in the example can be implemented in a computing environment where a processor (e.g., a central processing unit (CPU), a graphics processing unit (GPU), a microprocessor, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA)), a memory (volatile memory (e.g., RAM), non-volatile memory (e.g., ROM and flash memory)), an input device (e.g., a keyboard, a mouse, a pen, a voice input device, a touch input device, an infrared camera, a video input device, etc.), an output device (e.g., a display, a speaker, a printer, etc.) and a communication connection device (e.g., a modem, a network interface card (NIC), an integrated network interface, a radio frequency transmitter / receiver, an infrared port, a USB connection device, etc.) are interconnected (e.g., peripheral component interconnect (PCI), USB, firmware (IEEE1394), an optical bus structure, a network, etc.).

[0102] The computing environment can be implemented as a personal computer, a server computer, a handheld or laptop device, a mobile device (e.g., a mobile phone, a PDA, a media player, etc.), a multiprocessor system, a consumer electronic device, a minicomputer, a mainframe computer, a distributed computing environment including the aforementioned random systems or devices, but the embodiments are not limited thereto.

[0103] According to the foregoing example, in a camera module having a drive-sensing integrated coil, the position of the lens can be accurately detected, and using a single drive-sensing integrated coil, the overlapping area between the magnet and the coil and the direction of the magnet and the coil can be sensed, so that the size of the camera module can be reduced, and the manufacturing cost can be reduced by structural simplification.

[0104] Therefore, a stable timing margin can be obtained, and the manufacturing performance and stability can be increased.

[0105] Although the present disclosure includes specific examples, it will be apparent to those of ordinary skill in the art that various changes in form and detail can be made in these examples without departing from the spirit and scope of the claims and their equivalents. The examples described herein will be considered only in a descriptive sense and not for purposes of limitation. The description of a feature or aspect in each example will be considered applicable to a similar feature or aspect in other examples. Appropriate results can be obtained if the described techniques are performed in a different order, and / or if the components in the described systems, architectures, devices, or circuits are combined in a different manner and / or replaced or supplemented with other components or their equivalents. Therefore, the scope of the present disclosure is not limited by the specific embodiments, but by the claims and their equivalents, and all variations within the scope of the claims and their equivalents will be construed as being included in the present disclosure.

Claims

1. A position detection device, comprising: A detector circuit configured to detect a detection signal including information related to the position of a magnet provided in a lens barrel, wherein the information related to the position of the magnet is based on the inductance value of a coil provided in a housing and opposite to the magnet; and A control circuit configured to convert the detection signal into a count value, determine a conversion formula based on an error between the count value and a target value and a change rate of the error, and detect a position value using the determined conversion formula, wherein The control circuit includes: A signal converter circuit configured to convert the detection signal into the count value; A formula determination circuit configured to determine the conversion formula based on the error between the count value and the target value and based on the change rate of the error; and A position detector circuit configured to convert the count value into the position value using the conversion formula determined by the formula determination circuit, wherein, when the count value is included in a predetermined monitoring range such that the error between the count value and the target value increases and the change rate of the error increases, the formula determination circuit changes a first conversion formula to a second conversion formula, wherein the monitoring range is based on a center value corresponding to the center between a maximum count value and a minimum count value.

2. The position detection device according to claim 1, wherein The first conversion formula is: SP = b × D_CNT, wherein SP is the position value, b is a constant, and D_CNT is the count value.

3. The position detection device according to claim 2, wherein, The second conversion formula is: SP = b × (2 × CT_CNT - D_CNT), wherein CT_CNT is the center value.

4. A method for detecting a position, the method comprising: Detecting a detection signal including information related to the position of a magnet provided in a lens barrel, wherein the information related to the position of the magnet is based on the inductance value of a coil provided in a housing and opposite to the magnet; Converting the detection signal into a count value; Determining whether a condition for changing a conversion formula is satisfied based on the count value; When the condition for changing the conversion formula is not satisfied, maintaining the first conversion formula, and when the condition for changing the conversion formula is satisfied, changing the first conversion formula to the second conversion formula; and Selectively using the first conversion formula or the second conversion formula to detect a position value, wherein it is determined whether the condition for changing the conversion formula is satisfied based on an error between the count value and a target value and a change rate of the error.

5. The method according to claim 4, wherein, Determining whether the condition for changing the conversion formula is satisfied includes: Determining whether the count value is included in a monitoring range; Calculating an error between the count value and the target value; and When the error between the count value and the target value increases, determining whether the change rate of the error increases.

6. The method according to claim 5, wherein, The first conversion formula is a basic formula.

7. The method according to claim 6, wherein, The monitoring range is determined based on a center value corresponding to the center between a maximum count value and a minimum count value.

8. The method according to claim 7, wherein The first conversion formula is: SP = b × D_CNT, where SP is the position value, b is a constant, and D_CNT is the count value.

9. The method according to claim 8, wherein The second conversion formula is: SP = b × (2 × CT_CNT - D_CNT), where CT_CNT is the center value.

10. A camera module, comprising: a lens barrel including a magnet; a substrate including a coil disposed opposite to the magnet; and one or more circuits configured to detect a detection signal related to the position of the magnet and based on the position of the coil, convert the detection signal into a count value, determine a conversion formula based on an error between the count value and a target value and a change rate of the error, and use the determined conversion formula to detect a position value.

11. The camera module according to claim 10, wherein, The one or more circuits are configured to: determine whether the conversion formula is a first conversion formula or a second conversion formula based on the error between the count value and the target value and the change rate of the error; and convert the count value into the position value using the determined first conversion formula or second conversion formula.

12. The camera module according to claim 11, wherein, The first conversion formula is a default conversion formula, and wherein the one or more circuits are further configured to: change the first conversion formula to the second conversion formula in response to an increase in the error between the count value and the target value and an increase in the change rate of the error.

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