Lens device and image capturing apparatus

Abstract

The invention relates to a lens device and an image photographing apparatus. A lens apparatus includes a first focus lens, a second focus lens, a first actuator configured to drive the first focus lens, and a second actuator configured to drive the second focus lens. A predetermined inequality is satisfied.

Description

Technical Field

[0001] Aspects of the embodiments relate to a lens device and an image capture apparatus. Background Art

[0002] PCT International Publication WO 2020 / 170586 discloses a lens device in which two focusing lenses are driven separately by two actuators. Summary of the Invention

[0003] According to one aspect of the embodiment, a lens device includes: a first focusing lens; a second focusing lens; a first actuator configured to drive the first focusing lens; and a second actuator configured to drive the second focusing lens. The following inequality is satisfied:

[0004] VMAX1>VMAX2

[0005] k1>k2

[0006] Where VMAX1 is the maximum speed of the first focusing lens, VMAX2 is the maximum speed of the second focusing lens, k1 is the stroke within the operable range of the first focusing lens, and k2 is the stroke within the operable range of the second focusing lens. Alternatively, the following inequality is satisfied:

[0007] AMAX1>AMAX2

[0008] k1>k2

[0009] Where AMAX1 is the maximum acceleration of the first focusing lens, AMAX2 is the maximum acceleration of the second focusing lens, k1 is the stroke within the operable range of the first focusing lens, and k2 is the stroke within the operable range of the second focusing lens. An image capture device having the above lens arrangement also constitutes another aspect of the embodiment.

[0010] Further features of various embodiments of the present disclosure will become apparent from the following description of the embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 The configuration of the image capturing apparatus according to the first embodiment is shown.

[0012] Figure 2 The relationship between the positions of the first and second focusing lenses and time in the first and third embodiments is shown.

[0013] Figure 3 is a table showing parameter values in the first embodiment.

[0014] Figure 4 is a table showing parameter values in the second embodiment.

[0015] Figure 5 A configuration of an image capturing apparatus according to a third embodiment is shown.

[0016] Figure 6 is a table showing parameter values in the third embodiment. DETAILED DESCRIPTION

[0017] Referring now to the accompanying drawings, embodiments according to the present disclosure will be described in detail.

[0018] First embodiment

[0019] Now refer to Figure 1 , an image capturing apparatus 10 according to a first embodiment will be described. Figure 1 1 is a configuration diagram of the image capturing apparatus 10. The image capturing apparatus 10 includes a camera body 201 and a lens device 101 attachable to and detachable from the camera body 201. However, the present embodiment is not limited to this example and is also applicable to an image capturing apparatus in which a camera body and a lens device are integrated.

[0020] The lens device 101 includes a first (unit) lens barrel 444, an image stabilization lens barrel 445, an aperture (diaphragm) unit 405, a first focusing lens barrel 425, a fourth (unit) lens barrel 442, a second focusing lens barrel 434, and a sixth (unit) lens barrel 443. The first lens barrel 444 holds the first lens 401. The image stabilization lens barrel 445 holds the image stabilization lens 411. The first focusing lens barrel 425 holds the first focusing lens 404. The fourth lens barrel 442 holds the fourth lens 410. The second focusing lens barrel 434 holds the second focusing lens 413. The sixth lens barrel 443 holds the sixth lens 412. The lens held in each lens barrel is not limited to a single lens, but may be a lens unit including multiple lenses. These lenses and the aperture unit 405 constitute an imaging optical system.

[0021] The lens apparatus 101 also includes a gyro sensor 106 as a shake detector and a main CPU (lens control unit) 107 configured to perform overall drive control and calculations for the lens apparatus 101 .

[0022] The main CPU 107 drives the aperture unit 405 by issuing a command to the aperture drive source 109. The main CPU 107 also drives the first focus barrel 425 and the first focus lens 404 integrally by issuing a command to the first focus lens drive source 110. The main CPU 107 also drives the second focus barrel 434 and the second focus lens 413 integrally by issuing a command to the second focus lens drive source 111.

[0023] The first focusing lens 404 and the second focusing lens 413 are arranged along the direction of the optical axis x. During the focusing process, the first focusing lens 404 and the second focusing lens 413 move simultaneously in conjunction with each other.

[0024] The image stabilization lens barrel 445 is drivably held relative to the image stabilization base barrel 446 within a plane orthogonal to the optical axis x. During image stabilization control, the main CPU 107 calculates the amount of image stabilization using the detection value of the gyro sensor 106 and sends a command to the image stabilization drive source 108. The image stabilization drive source 108 performs image stabilization by driving the image stabilization lens barrel 445 in the y direction (yaw direction) and the p direction (pitch direction), which are axes orthogonal to the optical axis x. Thus, the image stabilization lens barrel 445 and the image stabilization drive source 108 function as an image stabilization unit.

[0025] The aperture unit 405 is fixed to the aperture base 441. The lens device 101 is fixed to the camera body 201 via the mount 414, and an optical element (imaging optical system) in the lens device 101 forms an image on the image sensor 202 held in the camera body 201 to capture an object image.

[0026] The camera body 201 includes a main CPU (camera control unit) 203, a release button 204 as an operating element, a main power source 205, and an image recording medium 206. The release button 204 has a two-stage configuration, with the first stage designated SW1 and the second stage designated SW2. SW1 issues commands for resuming from imaging standby, starting image stabilization, starting autofocus (AF), starting light metering (photometry), and other imaging start preparations. SW2 issues commands for imaging and recording the image on the image recording medium 206. The main CPU 203 supplies power to the lens unit 101 via a contact block (not shown) provided on the mount 414 and communicates other imaging information with the main CPU 107 in the lens unit 101.

[0027] In this embodiment, the lens device 101 is a fixed focal length lens and does not perform a zoom operation. The lens device 101 has a fixed lens barrel (not shown) in which a first lens barrel 444, an image stabilization base lens barrel 446, an aperture base 441, a fourth lens barrel 442, and a sixth lens barrel 443 are fixed. However, this embodiment is not limited to this example and is also applicable to a lens device that performs a zoom operation.

[0028] The first focusing lens barrel 425 is supported by a guide rod fixed to the fixed lens barrel so as to be linearly movable in the optical axis direction. The second focusing lens barrel 434 is supported by a guide rod fixed to the fixed lens barrel so as to be linearly movable in the optical axis direction.

[0029] Next, the first actuator 421 will be described. The first actuator 421 is a linear actuator, such as a voice coil motor. However, the present embodiment is not limited to this example, and the first actuator 421 may be an actuator other than a linear actuator. The yoke 423 is fixed to the fixed lens barrel. Figure 1 As shown, the magnet 424 is bipolarly magnetized in a direction perpendicular to the optical axis x and is fixed to the yoke 423. The coil 422 is fixed to the first focusing lens barrel 425 by adhesive or the like and is arranged to surround the yoke 423 in a non-contact manner around the optical axis, as shown in FIG. Figure 1 In the space where the coil 422 is arranged, a magnetic flux flows in a direction orthogonal to the optical axis x due to the magnet 424 and the yoke 423 .

[0030] When a current flows through the yoke 423, which serves as the first focus lens drive source 110, in accordance with a command from the main CPU 107, a Lorentz force is generated, and depending on the direction of the current, a driving force is generated in the coil 422 on the object side in the optical axis direction or on the image plane side in the optical axis direction. As a result, the first focus barrel 425 and the first focus lens 404 held therein can be driven in the optical axis direction.

[0031] Next, the position encoder 426 will be described. The position encoder 426 is, for example, a giant magnetoresistance (GMR) sensor, but is not limited to this example. A sensor head 427 is fixed to the first focusing lens barrel 425. The magnetic scale of the position encoder 426 is fixed to the fixed lens barrel. An output corresponding to the position of the first focusing lens barrel 425 is transmitted from the sensor head 427, serving as the first focusing lens position encoder 112, to the main CPU 107, enabling the position of the first focusing lens barrel 425 to be detected. Based on this output, the main CPU 107 controls the current value applied to the first focusing lens drive source 110, thereby controlling the position of the first focusing lens 404.

[0032] The first focusing lens barrel 425 has an object-side end (object-side mechanical end) 425a and an image-side end (image-side mechanical end) 425b. The aperture base 441 has an end 441a corresponding to the object-side end 425a. The fourth lens barrel 442 has an end 442b corresponding to the image-side end 425b. This limits the drivable range (operable range) of the first focusing lens barrel 425 (i.e., the first focusing lens 404). In this embodiment, the operable range of the first focusing lens 404 is defined as the stroke (first focusing lens stroke) k1 of the first focusing lens 404. In this embodiment, the lens apparatus 101 is a single-focus lens and is in focus at infinity. As the first focusing lens 404 moves toward the image plane, it transitions to a close-range focused state, with the position closest to the object being the closest-range focused position, i.e., the shortest imaging distance of the lens apparatus 101.

[0033] Next, the second actuator (stepping motor) 431 will be described. The second actuator 431 is, for example, an actuator (stepping motor) that converts rotational force into driving force in the optical axis direction. However, this embodiment is not limited to this example, and the second actuator 431 may be an actuator other than a stepping motor.

[0034] The second actuator 431 includes a motor 433 and a lead screw 432. The second actuator 431 is secured to the fixed barrel via a metal plate or the like coupled to the motor 433. In this embodiment, the pitch of the thread of the lead screw 432 is 0.4. A rack 435 engages with the threaded portion of the lead screw 432. The rack 435 is held by the second focusing barrel 434 and is mounted so that the joint between the holding portion and the lead screw 432 absorbs any deviation from the ideal position of the second focusing barrel 434 (i.e., the second actuator 431).

[0035] The main CPU 107 issues a pulse drive command to the motor 433, which serves as the second focusing lens drive source 111, to drive the second focusing lens barrel 434, which holds the second focusing lens 413. In this embodiment, the motor 433 rotates once with 40 pulses. Depending on the direction of rotation, the second focusing lens barrel 434 is driven 0.4 mm toward the object side or the image side. The second focusing lens barrel 434 includes a light-shielding fin (not shown), and its reference position can be identified by a photointerrupter attached to the fixed lens barrel. By counting pulses from the reference position, the main CPU 107 controls the position of the second focusing lens barrel 434, which holds the second focusing lens 413, under power-on control.

[0036] The second focusing lens barrel 434 has an object-side end (object-side mechanical end) 434a and an image-plane-side end (image-plane-side mechanical end) 434b. The fourth lens barrel 442 has an end 442a corresponding to the object-side end 434a. The sixth lens barrel 443 has an end 443b corresponding to the image-plane-side end 434b. As a result, the drivable range (operable range) of the second focusing lens barrel 434 (i.e., the second focusing lens 413) is limited. In this embodiment, the operable range of the second focusing lens 413 is defined as the stroke (second focusing lens stroke) k2 of the second focusing lens 413.

[0037] The lens device 101 is a fixed focal length lens and is in focus at infinity. A gap is provided on the object side of the first focusing lens 404 and the second focusing lens 413 to allow for a focus margin at infinity. As the first focusing lens 404 and the second focusing lens 413 move toward the image plane, they transition to a state of focusing at close distances. When the first focusing lens 404 and the second focusing lens 413 are closest to the object, they are positioned in a focused position focused at the closest distance, which is the shortest imaging distance of the lens device 101.

[0038] Now assume that ES1 is the image plane movement per unit movement of the first focusing lens 404 (first focusing sensitivity), ES2 is the image plane movement per unit movement of the second focusing lens 413 (second focusing sensitivity), m1 is the mass of the first focusing lens 404 (first focusing lens mass), and m2 is the mass of the second focusing lens 413 (second focusing lens mass).

[0039] VMAX1 is the maximum speed of the first focus lens 404 driven by the first actuator 421 (first focus lens maximum speed). VMAX2 is the maximum speed of the second focus lens 413 driven by the second actuator 431 (second focus lens maximum speed). Here, maximum speed refers to the fastest drive speed among all drives executed by commands from the main CPU 107 in the combination of the lens device 101 and the camera body 201. In this embodiment, the magnetic circuit of the first actuator 421 is designed so that VMAX1 is 70 mm / s. This design is based on the mass of the movable unit including the first focus lens 404, the sliding load between the first focus barrel 425 (sliding member) and the guide rod, back electromotive force, and available power.

[0040] The second actuator 431 can be driven at a maximum speed of 3000 PPS (3000 pulses per second) without losing sync. Since 40 pulses per rotation result in 0.4 mm of advance, VMAX2 is 30 mm / s. In this embodiment, the inequality VMAX1 > VMAX2 is satisfied. The maximum speed difference between VMAX1 and VMAX2 can be more than twice (VMAX1 > 2 × VMAX2). In other words, VMAX1 can be more than twice VMAX2.

[0041] Figure 2 FIG2 shows the movement trajectory of each actuator in this embodiment within 0.1 seconds when it is driven at maximum output. Figure 2 In the figure, the vertical axis represents the position of each focusing lens (mm), and the horizontal axis represents time (s). Figure 2 , VCM represents the first actuator 421 , and STM represents the second actuator 431 .

[0042] The characteristic values of the first actuator 421 were calculated under the conditions of a movable unit mass of 0.2 kg, a maximum output of 0.1 N, and a velocity resistance coefficient of 1.143 N·s / m. The velocity resistance coefficient is a combination of the viscous resistance of the grease and the back electromotive force. It is assumed that L1 represents the movement distance (first maximum movable distance) per unit time (e.g., 0.1 seconds) when the first focus lens 404 is moved from a stopped state with the maximum driving force of the first actuator 421. In this embodiment, L1 is 5.85 mm.

[0043] The second actuator 431 has the following accelerations to achieve a maximum speed of 3000 PPS: 2 pulses at 500 PPS, 2 pulses at 1000 PPS, and 2 pulses at 2000 PPS. Now, let L2 be the moving distance (the second maximum movable distance) per unit time (e.g., 0.1 seconds) when the second focus lens 413 is moved from a stopped state using the maximum driving force of the second actuator 431. In this embodiment, L2 is 2.85 mm.

[0044] In this embodiment, the relationship L1 > L2 can be satisfied. L1 and L2 can differ by more than two times (L1 > 2 × L2). In other words, L1 can be more than twice the length of L2. Here, the maximum movable distance within "0.1 seconds" is compared because reducing focusing time is a key issue in image capture device development, and extending the driving distance within the short time of approximately 0.1 seconds is important.

[0045] Assume that AMAX1 is the maximum acceleration of the first focusing lens 404, and AMAX2 is the maximum acceleration of the second focusing lens 413. In this case, satisfying L1>L2 is equivalent to satisfying AMAX1>AMAX2.

[0046] Figure 3 This is a table showing the parameter values used in this embodiment. Each value is as described above. The first focus lens stroke k1 is 22 mm, and the second focus lens stroke k2 is 16 mm. The first focus sensitivity ES1 is 3.3, and the second focus sensitivity ES2 is 2.6 (|ES1| > |ES2|). The first focus lens mass m1 is 12 g, and the second focus lens mass m2 is 6 g (m1 > m2). The actual moving unit mass is this value plus the moving unit of the focusing barrel and actuator.

[0047] The product of the first focus sensitivity ES1 and the first focus lens stroke k1, ES1 × k1, is 72.6. The product of the second focus sensitivity ES2 and the second focus lens stroke k2, ES2 × k2, is 41.6. In other words, in this embodiment, |ES1 × k1| > |ES2 × k2| is satisfied. Here, the product of the focus sensitivity and the focus lens stroke represents the amount of image plane movement of the focus lens.

[0048] The product m1×k1 of the first focusing lens mass m1 and the first focusing lens stroke k1 is 264. The product m2×k2 of the second focusing lens mass m2 and the second focusing lens stroke k2 is 96. In this embodiment, m1×k1>m2×k2 can be satisfied. Here, the product of the focusing lens mass and the focusing lens stroke represents the workload required when driving the lens device in the upward lifting direction, for example.

[0049] The effects of this embodiment will now be described. In this embodiment, for example, a voice coil motor is used for the first actuator 421, and a stepper motor is used for the second actuator 431. In this embodiment, at least one of the inequalities VMAX1>VMAX2 and k1>k2, or AMAX1>AMAX2 and k1>k2 is satisfied.

[0050] For example, when a stepper motor is used for the first actuator 421, the focusing speed is lower than that of a voice coil motor, and the focusing time increases. In particular, the difference in maximum speed affects the driving time for the search drive speed that moves the entire focusing stroke from the infinite object distance to the close object distance.

[0051] In the configuration for focusing by driving two focus lenses, as in this embodiment, the focus lenses move at a speed approximately equal to the ratio of the first focus lens stroke k1 to the second focus lens stroke k2. Therefore, when using two actuators with approximately the same maximum speed, the side that must move faster (the first focus lens 404 in this embodiment) is limited, and the second focus lens 413 must move more slowly. This increases focusing time. Even if the focus lenses do not move their full stroke, they must move at a speed approximately equal to the ratio of the first focus lens stroke k1 to the second focus lens stroke k2.

[0052] Therefore, even in short-range driving, the first focus lens 404 with a large stroke is moved quickly. As described above, the first maximum movable distance L1 and the second maximum movable distance L2 within 0.1 seconds from the stop position have a relationship of L1>L2, so that a focused state can be quickly achieved even in a narrow range of focus driving.

[0053] The first focusing lens stroke k1 can be 10 mm or longer. For example, in this embodiment, the first focusing lens stroke k1 is 22 mm, which is a relatively long distance. When the first focusing lens stroke k1 is short, even if the maximum speed of the first actuator 421 is low, the focusing time can be reduced without significant difference. On the other hand, when the stroke is long, 10 mm or longer, as in this embodiment, the configuration of this embodiment significantly contributes to reducing the focusing time.

[0054] Conventionally, there is known a configuration in which voice coil motors are used for both the first actuator 421 and the second actuator 431. In this case, the voice coil motor has a position encoder for control, which requires space and cost, and the size and cost of the lens device increase.

[0055] In the case of a voice coil motor, the coil needs to be constantly energized to maintain its position, which increases power consumption. Furthermore, when the voice coil motor is driven, high-frequency magnetic noise is generated from the coil, which can negatively impact image sensor 202 and the imaging results. As a countermeasure, an LC filter consisting of a coil and a capacitor is incorporated into the circuit to filter out unnecessary high-frequency magnetic noise. However, because the coil of the LC filter generates magnetic noise, it should be placed in front of the lens, away from the image sensor. Consequently, the space for the LC filter, including wiring, is used on the front side of the lens, increasing the size of the lens assembly. Furthermore, the first actuator 421 is typically more expensive than the second actuator 431.

[0056] In this embodiment, for example, a voice coil motor is used as first actuator 421, and a stepping motor is used as second actuator 431, based on the characteristics of the focus lens. This reduces the cost and size of the lens assembly and shortens focusing time. Furthermore, suppressing power consumption increases the number of images captured and reduces environmental impact.

[0057] In this embodiment, the first actuator 421 is a voice coil motor serving as a linear actuator, but other types of linear actuators, such as linear ultrasonic motors and electromagnetic linear motors, may also be used. In this embodiment, the second actuator 431 is a stepper motor serving as an actuator configured to convert a rotational force into a driving force in the optical axis direction, but other types of actuators configured to convert a rotational force into a driving force in the optical axis direction may also be used.

[0058] Second embodiment

[0059] A second embodiment will now be described. Figure 4 is a table showing parameter values in this embodiment. Figure 1 The basic configurations of the image capturing apparatuses in the described first embodiment are similar, so the common description will be omitted.

[0060] If the second focusing lens stroke k2 can be less than the second focusing lens stroke of the first embodiment, the total focusing time can be reduced. In the optical system envisioned here, in order to reduce the second focusing lens stroke k2, the second focusing sensitivity ES2 will be increased. This is because: the value of the second focusing sensitivity ES2 × the second focusing lens stroke k2 (i.e., the image plane movement amount of the second focusing lens 413) does not change significantly. Therefore, by increasing the second focusing sensitivity ES2, the second focusing lens stroke k2 can be reduced.

[0061] In order to increase the second focusing sensitivity ES2, the optical power of the second focusing lens 413 needs to be increased. In order to increase the optical power of the second focusing lens 413, the number of lenses in the second focusing lens 413 needs to be increased. In this case, the mass m2 of the second focusing lens tends to increase. When the mass m2 of the second focusing lens increases and the second actuator 431 with the same driving force is used, the maximum speed of the stepping motor needs to be reduced. In a stepping motor where the lead screw converts the rotational force into an axial driving force, the main load is the rotational sliding loss, so even if the mass of the movable unit increases, the maximum speed will not decrease at that rate.

[0062] In this embodiment, the maximum speed is 2600 PPS, and the maximum speed VMAX2 of the second focusing lens is 26 mm / s. The second actuator 431 has the following accelerations to reach the maximum speed of 2600 PPS: an acceleration of 2 pulses at 500 PPS, an acceleration of 2 pulses at 1000 PPS, and an acceleration of 2 pulses at 2000 PPS. Now assume that L2 is the moving distance per unit time (e.g., 0.1 second) when the second focusing lens 413 starts to move from a stopped state with the maximum driving force of the second actuator 431 (the second maximum movable distance). In this embodiment, L2 is 2.48 mm.

[0063] According to Figure 4 the table shown, in this embodiment, it satisfies the first focusing lens maximum speed VMAX1 > the second focusing lens maximum speed VMAX2. In addition, the relationship between the first maximum movable distance L1 and the second maximum movable distance L2 is L1 > L2. This is equivalent to AMAX1 > AMAX2.

[0064] The relationship between the first focusing lens stroke k1 and the second focusing lens stroke k2 is k1 > k2. The first focusing lens stroke k1 is more than twice the second focusing lens stroke k2 (k1 ≥ 2 × k2). In this embodiment, it satisfies |ES1| < |ES2| and m1 < m2. In addition, in this embodiment, it satisfies |ES1 × k1| > |ES2 × k2|. Here, the product of the focusing sensitivity and the focusing lens stroke represents the image plane movement amount of the focusing lens.

[0065] In this embodiment, m1×k1>m2×k2 is satisfied. Here, the product of the focus lens mass and the focus lens stroke represents a workload required in the case of driving the lens device in the upward lift direction, for example.

[0066] Similar to the second embodiment, in the first embodiment, the total drive time is limited by driving the second actuator 431 when searching for the full stroke. When the search time is calculated by including both acceleration and deceleration, the search time in the first embodiment is short, namely 0.54 seconds, and the search time in the second embodiment is also short, namely 0.345 seconds. Therefore, even in the case where |ES1| < |ES2|, the actuator with a larger product of focus sensitivity and focus lens stroke can be set to a voice coil motor with a higher maximum speed, while the actuator with a smaller product can be set to a stepping motor. Thus, this embodiment can provide a lens device with a short focusing time.

[0067] Even when m1 < m2, the actuator with a larger product of focus lens mass and focus lens stroke can be set to a voice coil motor with a higher maximum speed, while the actuator with a smaller product can be set to a stepping motor. Thus, this embodiment can provide a lens device with a short focusing time.

[0068] Third embodiment

[0069] Next, a third embodiment will be described. Figure 5 1 is a configuration diagram of an image capturing apparatus 20 according to the present embodiment. In the present embodiment, description of portions common to the image capturing apparatus 10 according to the first embodiment will be omitted.

[0070] The image capture device 20 includes a camera body 201 and a lens unit 102 that is attachable and detachable relative to the camera body 201. The lens unit 102 includes a first (unit) lens barrel 544, an image stabilization lens barrel 545, an aperture (diaphragm) unit 505, a first focusing lens barrel 525, a (2a) (unit) lens barrel 542, a second focusing lens barrel 534, and a (2b) (unit) lens barrel 543. These lens barrels respectively retain the first lens 501, the image stabilization lens 511, the first focusing lens 504, the (2a) (unit) lens 510, the second focusing lens 513, and the (2b) (unit) lens 512. The image stabilization lens barrel 545 is drivably retained relative to an image stabilization base barrel 546 in a plane orthogonal to the optical axis x. The aperture unit 505 is fixed to the aperture base 541.

[0071] The lens device 102 according to this embodiment includes a zoom lens and can perform a zoom operation (to change the focal length). The lens device 102 includes a guide barrel and a cam ring (not shown). A roller provided on the first lens barrel 544 engages with a cam groove in the cam ring and a linear groove in the guide barrel. As the zoom ring rotates in conjunction with the cam ring, the first lens barrel 544 advances and retracts along the optical axis.

[0072] Next, the second unit 547 will be described. The second unit 547 includes a second unit base (movable barrel) 548 that is movable in the optical axis direction according to changes in focal length. The 2a lens 510, the aperture base 541, the image stabilization base barrel 546, and the 2b lens 512 are fixed to the second unit base 548.

[0073] The first focusing lens barrel 525 is supported by a guide rod fixed to the second unit base 548 so as to be linearly movable in the optical axis direction. The second focusing lens barrel 534 is supported by a guide rod fixed to the second unit base 548 so as to be linearly movable in the optical axis direction.

[0074] The roller provided on the second unit base 548 engages with the cam groove in the cam ring and the linear groove in the guide barrel. Thus, as the zoom ring rotates in conjunction with the cam ring, the second unit 547 moves back and forth in the optical axis direction.

[0075] Next, the first actuator 551 will be described. In this embodiment, the first actuator 551 is, for example, a linear vibration motor (ultrasonic motor). The first actuator 551 is held by the second unit base 548. A slider 552 is fixed to the second unit base 548. The vibrator 553 is made of a piezoelectric element and is driven by pressing a contact portion against the slider 552 and applying an ultrasonic voltage to the slider 552. The rack 554 serves to connect the vibrator 553 and the first focusing lens barrel 525 and to absorb any deviation from the ideal position.

[0076] Next, the position encoder 526 will be described. A sensor head 557 is fixed to the second unit base 548. An optical scale 558 is fixed to the first focusing lens barrel 525. An output corresponding to the position of the first focusing lens barrel 525 is sent from the sensor head 557, which serves as the first focusing lens position encoder 112, to the main CPU 107, and the position of the first focusing lens barrel 525 can be detected. The main CPU 107 controls the position of the first focusing lens 504 by controlling the current value applied to the first focusing lens driving source 110 based on the output.

[0077] The first focusing lens barrel 525 has an object-side end 525a and an image-side end 525b. The aperture base 541 has an end 541a corresponding to the object-side end 525a. The image stabilization base barrel 546 has an end 546b corresponding to the image-side end 525b. Thus, the driving range of the first focusing lens barrel 525 that holds the first focusing lens 504 is limited, and this range is defined as the first focusing lens stroke k1. Figure 5 The lens device 102 in FIG. 1 is a zoom lens and is in a focused state at infinity at the WIDE end. The first focus lens stroke k1 is ensured so that the focused state can be achieved from infinity to close distances throughout the entire zoom range.

[0078] Next, the second actuator 531 will be described. The second actuator is, for example, a stepping motor and is held by the second unit base 548. The second actuator 531 includes a motor engine 533 and a lead screw 532. The second actuator 531 is fixed to the fixed lens barrel by a metal plate or the like connected to the motor engine 533. In this embodiment, the pitch of the thread of the lead screw 532 is 0.4. A rack 535 engages with the threaded portion of the lead screw 532. The rack 535 is held by the second focusing lens barrel 534 and is installed so that the engagement between the holding portion and the lead screw 532 absorbs any deviation from the ideal position of the second actuator 531 and the second focusing lens barrel 534.

[0079] The second focusing lens barrel 534 has an object-side end 534a and an image-side end 534b. The second unit base 548 has an end 548a corresponding to the object-side end 534a. The 2a unit barrel 542 has an end 542b corresponding to the image-side end 534b. Thus, the driving range of the second focusing lens barrel 534 that holds the second focusing lens 513 is limited, and this range is defined as the second focusing lens stroke k2.

[0080] Figure 5 The lens device 102 in FIG. 1 is a zoom lens and is in a focused state at infinity at the WIDE end. The second focusing lens stroke k2 is ensured so that the focused state can be obtained from infinity to close distance in the entire zoom range.

[0081] Now, let ES1 be the image plane movement amount per unit movement amount of the first focus lens 504 (first focus sensitivity), and ES2 be the image plane movement amount per unit movement amount of the second actuator 431 (second focus sensitivity). Furthermore, m1 is the mass of the first focus lens 504 (first focus lens mass), and m2 is the mass of the second focus lens 513 (second focus lens mass).

[0082] VMAX1 is the maximum speed (first focus lens maximum speed) of the first focus lens 504 driven by the first actuator 551. VMAX2 is the maximum speed (second focus lens maximum speed) of the second focus lens 513 driven by the second actuator 531. Here, the maximum speed refers to the fastest driving speed among all the driving operations executed by commands from the main CPU 107 in the combination of the lens device 102 and the camera body 201.

[0083] In this embodiment, the output characteristics of the first actuator 551 are designed and controlled so that VMAX1 is 100 mm / s. Generally, a linear ultrasonic motor can be driven at high speed with a higher output than a stepping motor. This design will be based on the mass of the movable unit including the first actuator 551, the sliding load between the first focusing lens barrel 525 as a sliding member and the guide rod, and the available power.

[0084] The second actuator 531 can be driven at a maximum speed of 3000 PPS (3000 pulses per second) without losing sync. Since 40 pulses per rotation result in 0.4 mm of advance, VMAX2 is 30 mm / s. At this point, VMAX1 > VMAX2, and the maximum speed difference between the two actuators is at least twice (VMAX1 ≥ 2 × VMAX2). In other words, VMAX1 is at least twice VMAX2.

[0085] In this embodiment, the first actuator 551 has the characteristic of being able to move at 12700 mm / s 2 The output of the movable unit, including the second focusing lens barrel 534 holding the second focusing lens 513, is accelerated. At maximum output, it reaches a maximum speed of 100 mm / s within 0.0079 seconds from a stopped state. L1 is the movement distance (first maximum movable distance) per unit time (e.g., 0.1 seconds) when the second focusing lens barrel 534 is moved from a stopped state at the maximum driving force of the first actuator 551. In this embodiment, L1 is 9.21 mm.

[0086] Figure 2 The STM in the graph represents the second actuator 531. The second actuator 531 has the following accelerations to achieve a maximum velocity of 3000 PPS: 2 pulses at 500 PPS, 2 pulses at 1000 PPS, and 2 pulses at 2000 PPS. Now, let L2 be the movement distance (the second maximum movable distance) per unit time (e.g., 0.1 seconds) when the second focus lens 413 is moved from a stopped state using the maximum driving force of the second actuator 531. In this embodiment, L2 is 2.85 mm.

[0087] In this embodiment, the relationship L1 > L2 is satisfied (i.e., AMAX1 > AMAX2), and the difference between the two maximum movable distances is at least twice (L1 ≥ 2 × L2). In other words, the length of L1 is at least twice that of L2. Here, the maximum movable distance within "0.1 seconds" is compared because reducing focusing time is a major issue in the development of image capture devices, and it is important to extend the driving distance within the short time of approximately 0.1 seconds.

[0088] Figure 6 This is a table showing the parameter values used in this embodiment. Each value is as described above. The first focus lens stroke k1 is 5.9 mm, and the second focus lens stroke k2 is 3.6 mm. The first focus sensitivity ES1 is 1.98, and the second focus sensitivity ES2 is 1.81. The first focus lens mass m1 is 14.2 g, and the second focus lens mass m2 is 4.4 g. The actual moving unit mass is this value plus the moving unit mass of the focusing barrel and actuator.

[0089] The product of the first focus sensitivity ES1 and the first focus lens stroke k1, ES1×k1, is 11.7. The product of the second focus sensitivity ES2 and the second focus lens stroke k2, ES2×k2, is 6.5, thus satisfying |ES1×k1|>|ES2×k2|. Here, the product of the focus sensitivity and the focus lens stroke represents the amount of image plane movement caused by the focus lens.

[0090] The product m1×k1 of the first focusing lens mass m1 and the first focusing lens stroke k1 is 83.8. The product m2×k2 of the second focusing lens mass m2 and the second focusing lens stroke k2 is 15.8, satisfying m1×k1>m2×k2. Here, the product of the focusing lens mass and the focusing lens stroke represents the workload required when driving the lens device in the upward lifting direction, for example.

[0091] The effects of this embodiment will now be described. In this embodiment, a linear vibration motor is used for the first actuator, and a stepping motor is used for the second actuator. In this embodiment, the relationships k1 > k2 and VMAX1 > VMAX2 are satisfied. For example, when a stepping motor is used for the first actuator, the focusing speed is lower than that of a linear vibration motor, resulting in a longer focusing time.

[0092] There are also conventional examples of using a linear vibration motor for both the first actuator and the second actuator. In this case, the linear vibration motor requires a position encoder for control, which requires space and costs, and increases the size and cost of the lens device.

[0093] A linear vibration motor requires a transformer and an inductor. The transformer is an electrical component used to boost voltage, while the inductor is an electrical component used to suppress electrical noise. Each transformer and inductor includes a coil. However, when the linear vibration motor is driven, magnetic noise is generated from the coil, which can negatively impact the image sensor 202 and degrade imaging results. As a precaution, the transformer and inductor are positioned in front of the lens, away from the image sensor. Therefore, space is required on the second unit base 548 that holds the first and second actuators for the transformer and inductor, including their wiring.

[0094] Second unit base 548 is a movable unit that moves during zooming. Therefore, space for a transformer and an inductor, including wiring, must be secured within a limited space, and the size of second unit base 548, which includes the optical system, must be increased. Consequently, the size of the lens device tends to increase. On the other hand, this embodiment, which uses a stepping motor as the second actuator, can reduce the space required for the transformer and inductor, including wiring, on second unit base 548, providing a reduced-size lens device.

[0095] Generally, the first actuator 551 is more expensive than the second actuator 531. On the other hand, in this embodiment, by using a stepping motor for the second actuator, the cost can be suppressed.

[0096] Even in the zoom lens according to this embodiment, a linear vibration motor is used for the first actuator and a stepping motor is used for the second actuator, depending on the characteristics of the focus lens. This embodiment can provide a lens device that is reduced in size and cost, and has a shorter focusing time.

[0097] Although the present disclosure describes example embodiments, it should be understood that the present disclosure is not limited to the example embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications and equivalent structures and functions.

[0098] Various embodiments may provide a lens arrangement with reduced size and reduced focusing time.

Claims

1. A lens device comprising: a first focusing lens; a second focusing lens; a first actuator configured to drive a first focusing lens; and a second actuator configured to drive a second focusing lens, It is characterized by satisfying the following inequality: VMAX1>VMAX2 k1>k2 Wherein, VMAX1 is the maximum speed of the first focusing lens, VMAX2 is the maximum speed of the second focusing lens, k1 is the stroke within the operable range of the first focusing lens, and k2 is the stroke within the operable range of the second focusing lens.

2. A lens device comprising: a first focusing lens; a second focusing lens; a first actuator configured to drive a first focusing lens; and a second actuator configured to drive a second focusing lens, It is characterized by satisfying the following inequality: AMAX1>AMAX2 k1>k2 Wherein, AMAX1 is the maximum acceleration of the first focusing lens, AMAX2 is the maximum acceleration of the second focusing lens, k1 is the stroke within the operable range of the first focusing lens, and k2 is the stroke within the operable range of the second focusing lens.

3. The lens device according to claim 2, wherein: The following inequality is satisfied: L1>L2 Here, L1 is the maximum movable distance per unit time when the first focus lens is moved from a stopped state by the driving force of the first actuator, and L2 is the maximum movable distance per unit time when the second focus lens is moved from a stopped state by the driving force of the second actuator.

4. The lens device according to claim 1, wherein: The first actuator is a linear actuator, and the second actuator is an actuator configured to convert a rotational force into a driving force in the optical axis direction.

5. The lens device according to claim 4, wherein: The first actuator is a voice coil motor or a vibration type motor, Wherein, the second actuator is a stepping motor.

6. The lens device according to claim 1, wherein: The following inequality is satisfied: m1×k1>m2×k2 m1 is the mass of the first focusing lens, and m2 is the mass of the second focusing lens.

7. The lens device according to claim 1, wherein: The following inequality is satisfied: |ES1×k1 |>|ES2×k2| Wherein, ES1 is the focus sensitivity of the first focusing lens, and ES2 is the focus sensitivity of the second focusing lens. 8 . The lens device according to claim 1 , further comprising a position encoder configured to detect a position of the second focusing lens.

9. The lens device according to claim 1, wherein: During the focusing process, the first focusing lens and the second focusing lens move simultaneously in conjunction with each other.

10. The lens device according to claim 1, wherein: The following inequality is satisfied: |ES1|>|ES2| Wherein, ES1 is the focus sensitivity of the first focusing lens, and ES2 is the focus sensitivity of the second focusing lens.

11. The lens device according to claim 1, wherein: The following inequality is satisfied: m1>m2 Wherein, m1 is the mass of the first focusing lens, and m2 is the mass of the second focusing lens.

12. The lens device according to claim 1, wherein: The stroke of the first focusing lens is greater than 10 mm.

13. The lens device according to claim 1, wherein: The following inequality is satisfied: k1≥2×k2.

14. The lens device according to claim 1, wherein: The first focusing lens and the second focusing lens are arranged along the direction of the optical axis.

15. The lens device according to any one of claims 1 to 14, further comprising a movable lens barrel movable in the optical axis direction according to a change in focal length, It is characterized by: The first actuator and the second actuator are held by the movable barrel.

16. An image capturing device comprising: The lens device according to any one of claims 1 to 15; and Image sensor.

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