Patent Application
20230074396
The disclosure relates to a control system and a method for compensating a disturbance force acting on an actuator causing a gravity imbalance, and in particular to a lens control system and a method for compensating a gravitational disturbance force acting on an actuator of a lens group of an optical assembly.
Digital camera systems create two-dimensional images by collecting and geometrically controlling the spatial alignment of incoming light rays onto an array of image sensor picture elements (pixels). By changing exposure parameters such as aperture, focus, shutter speed, and International Organization for Standardization (ISO) film sensitivity, the captured image can be manipulated to fit an artistic expression.
Highly automated camera functions require the camera processors to precisely synchronize the movement of lens groups with the image acquisition. Lens control processors of such cameras utilize closed-loop control techniques based on linear lens positions of the lens groups and based on voice coil current measurements to smoothly move the lens groups to their target positions.
Camera processors may have inertial measurement unit (IMU) sensors which are provided to keep the camera display in an upright or horizontal position as the user rotates the camera body and the gravity angle changes.
U.S. Pat. No. 10,739,551 B1 describes techniques to compensate for changes in a depth of field of a camera caused by changes in orientation of the camera (e.g., tilt) and changes in the temperature of the camera. However, conventional control systems, such as the system described in U.S. Pat. No. 10,739,551 B1 do not track performance of position and velocity commands based on gravity information to optimize general performance of the lens control system.
Therefore, it has been a continuing need for improving the position and velocity command tracking performance of an optical system by using knowledge of the earth's gravitational force acting on an optical assembly to optimize the tuning of the closed-loop control system.
It is therefore an object of the present disclosure to improve an optical assembly position and velocity command tracking performance of a lens control system by compensating a disturbance force acting on at least one lens group of an optical assembly of the lens control system.
The object is achieved by adjusting closed-loop tuning parameters of an actuator of a lens group based on a pitch angle to compensate a disturbance force acting on the actuator.
According to an aspect of the disclosure, the pitch angle is obtained from an IMU. According to another aspect of the disclosure, the pitch angle is estimated by extracting a force acting on the actuator due to gravity from a commanded and measured voice coil current.
The lens control system for compensating the disturbance force acting on the at least one lens group of the optical assembly includes a camera controller. The optical assembly includes the at least one lens group on which the disturbance force acts and at least one actuator. The at least one lens group defines an optical axis and the at least one actuator is configured to move the at least one lens group along the optical axis in response to an optical lens position command received from the camera controller.
The lens control system further includes an optical assembly controller in communication with the camera controller. The optical assembly controller includes a power driver configured to apply an electrical energy to the at least one actuator to produce a force that acts on the at least one lens group to move the at least one lens group to a commanded position, a current sensor configured to measure a current flowing through the at least one actuator in response to the electrical energy applied to the at least one actuator, and a position sensor configured to generate position information by measuring an actual position of the at least one lens group.
According to an aspect of the disclosure, the optical assembly controller further includes a closed loop controller configured to determine a correct amount of the electrical energy required to move the at least one lens group to the commanded position based on gravity orientation information and the position information.
According to a further aspect of the disclosure, the camera controller includes an inertial measurement unit. The inertial measurement unit provides the gravity orientation information.
According to yet another aspect of the disclosure, the gravity orientation information can also be determined by extracting a component of an entirety of forces acting on the at least one actuator created by gravity without an inertial measurement unit. In other words, according to this aspect of the disclosure, the gravity orientation information is determined by the optical assembly controller without relying on information external to the optical assembly controller.
According to a further aspect of the disclosure, the entirety of forces is directly proportional to the current flowing through the at least one actuator. The disturbance force includes a gravitational force, and electrical and mechanical forces result from a change in the operating conditions.
According to an aspect of the disclosure, the change in the operating conditions includes a change in temperature and a change in a power source capacity. According to yet another aspect of the disclosure, the electrical energy includes a first component required to change the position of the at least one actuator to the commanded position, and a second component required to compensate the disturbance force. According to a further aspect of the disclosure, the at least one actuator includes a linear voice coil actuator.
The object of the disclosure is further achieved by a method for compensating a disturbance force acting on at least one lens group of an optical assembly, the at least one lens group defining an optical axis, the optical assembly further including at least one actuator configured to move the at least one lens group along the optical axis in response to an optical lens position command received from a camera controller, the method including applying an electrical energy to the at least one actuator to produce a force that acts on the at least one lens group to move the at least one lens group to a commanded position, measuring, by a current sensor, a current flowing through the at least one actuator in response to the electrical energy applied to the at least one actuator, and generating, by a position sensor, position information by measuring an actual position of the at least one lens group.
According to an aspect of the disclosure, the method further includes determining, by a closed loop controller, a correct amount of the electrical energy required to move the at least one lens group to the commanded position based on gravity orientation information and the position information.
According to yet another aspect of the disclosure, the method further includes determining the gravity orientation information by extracting a component of an entirety of forces acting on the at least one actuator created by gravity without an inertial measurement unit.
The invention will now be described with reference to the drawings wherein:
Exemplary embodiments of the disclosure will be explained below with reference to the accompanying schematic figures. Features that coincide in their nature and/or function may in this case be provided with the same designations throughout the figures.
The terms “exhibit”, “have”, “comprise” or “include” or any grammatical deviations therefrom are used in a non-exclusive way. Accordingly, these terms can refer either to situations in which, besides the feature introduced by these terms, no further features are present, or to situations in which one or more further features are present. For example, the expression “A exhibits B”, “A has B”, “A comprises B” or “A includes B” may refer both to the situation in which no further element aside from B is provided in A (that is to say to a situation in which A is composed exclusively of B) and to the situation in which, in addition to B, one or more further elements are provided in A, for example element C, elements C and D, or even further elements.
Furthermore, the terms “at least one” and “one or more” and grammatical modifications of these terms or similar terms, if they are used in association with one or more elements or features and are intended to express the fact that the element or feature can be provided singly or multiply, in general are used only once, for example when the feature or element is introduced for the first time. When the feature or element is subsequently mentioned again, the corresponding term “at least one” or “one or more” is generally no longer used, without restriction of the possibility that the feature or element can be provided singly or multiply.
Also, the terms “preferably”, “in particular”, “by way of example” or similar terms are used in conjunction with optional features, without alternative embodiments thereby being restricted. In this regard, features introduced by these terms are optional features, and there is no intention to restrict the scope of protection of the claims, and in particular of the independent claims, by these features. In this regard, the invention, as will be recognized by a person of ordinary skill in the art, can also be carried out using other configurations. Similarly, features introduced by “in one embodiment of the invention” or “in one exemplary embodiment of the invention” are to be understood to be optional features, without this being intended to restrict alternative refinements or the scope of protection of the independent claims. Furthermore, all possibilities of combining the features introduced by these introductory expressions with other features, whether optional or non-optional features, are intended to remain unaffected by said introductory expressions.
Changes in the pitch angle 155 are orthogonal to changes in the yaw angle 135 and the roll angle 155, and result in the optical assembly 110 tilting up or down. A rotation about the yaw axis 130 is a rotation of a plane defined by the pitch axis 150 and the roll axis 140 and is also orthogonal to the pitch axis 150 and the roll axis 140.
Linear voice coil actuators 200 are a type of direct drive mechanism that provides extremely precise positioning of a lens group over small displacements. Like linear motors, linear voice coil actuators 200 work on the principle of a permanent magnet field and a coil winding. When a current is applied to the coil 210, a force is generated (known as the Lorentz force). Operationally, the force produced by a voice coil causes the moving part 220 or linear bearing to travel, e.g., from a first position shown in
As shown in
The optical assembly 310 further includes imager 330, shutter 333, and iris 335. Shutter 333 is operated by stepper motor 343 and iris 335 is operated by stepper motor 345. Further, optical assembly 310 includes 350 to place the second lens group 325 in a park position. As also shown in
The optical assembly controller 315 uses closed-loop control of a linear lens position and a voice coil current to smoothly move either lens group. The camera controller 305 also includes an IMU sensor 310 which is conventionally used to maintain the image shown on display 306 in an upright position as the user rotates the camera body 120.
The first and second lens groups 323, 325 can be independently positioned along the optical axis which corresponds to the roll axis 140. The optical assembly controller 315 receives optical lens position commands from the camera controller 305 via Serial Peripheral Interface (SPI) 393 for each lens group in units of diopters and converts the optical lens position commands to linear lens position commands. Using closed-loop position control of each lens group 323, 325, an electrical current is produced to control the force necessary to move the voice coil with linear bearings 220 that support the lens groups 323, 325 to the desired position measured by a sensor.
Turning now to
As shown in
A linear voice-coil actuator 320 is a type of direct-drive linear motor. The current flowing through the coil assembly 210 interacts with the permanent magnetic field and generates a force vector (torque) perpendicular to the direction of the current, along the lens transport axis of motion which corresponds to the roll axis 140. Voice coil motors are generally brushless and do not utilize commutation. Their structural stability can support high positioning resolutions.
The linear voice-coil actuator 320, 322 has a non-commutated motor construction which increases reliability. The direct coupling of the linear voice-coil actuator 320, 322 to the load, i.e., the lens group 323, 325 allows for fast acceleration/deceleration such that very high speeds and accelerations can be easily achieved. Closed-loop control of the voice coil current by the current loop 405, which generates a torque or force, overcomes the bandwidth limitations of voice coil electrical resistance and inductance and improves load disturbance rejection. In other words, the current loop 405 normalizes all of the torque disturbances, i.e., the disturbance forces acting on the lens group 323, 325 and/or on the linear voice-coil actuator 320, 322. This includes a torque disturbance or disturbance force, or a component thereof, due to gravity.
Although the current loop 405 may normalize torque disturbances in any gravity orientation, it has been shown that normalization of torque disturbances in a horizontal gravity orientation, i.e., when the optical assembly 110 is rotated around the pitch axis 150, significantly improves operation of the camera functions, e.g., the zoom function. Thus, by dynamically changing the tuning of the control loops based on the gravity orientation information 460, stability of the system can be improved.
Closed-loop control of the lens transport position by the position loop 410 is needed to overcome static and dynamic frictional and inertial loads.
The position loop 410 includes closed loop controller 445. The closed loop controller 445 is configured to determine a correct amount of the electrical energy required to move the at least one lens group 325 to the commanded position based on gravity orientation information 460 and position information generated by the position sensor 440. As shown in
The position loop 410 is called every 25 μsec when a timer interrupt occurs. It takes 6 passes for all of the calculations to generate a new current and output to each actuator 455.
On the 1st pass, the actual lens actuator positions are read via an analog/digital (A/D) converter and a position trajectory for each lens group 323, 325 (in the optical diopter space) is generated. This makes it possible for both lens groups 323, 325 to synchronously maintain a contrast or phase focus mode. On the 2nd pass, the lens positions are converted from millimeters (mm) to diopters. On the 3rd pass, the commanded position of the first of two lens groups 323 is subtracted from the actual (feedback) position and the error is multiplied by the PID loop compensation. The output is converted to a duty cycle and applied to the actuator 322.
On the 4th pass, a commanded position of the second lens group 325 is subtracted from the actual (feedback) position and the error is multiplied by the PID loop compensation. The output is converted to a duty cycle and applied to the actuator 320. Nothing happens on the 5th pass. On the 6th pass, the phase counter is reset so the entire cycle can be repeated.
On the 3rd pass, the current gravity orientation angle is compared to a threshold which determines if horizontal, vertical up, or vertical down tuning of the first lens group 323 should be applied. On the 4th pass, the current gravity orientation angle is compared to a threshold which determines if horizontal, vertical up, or vertical down tuning of the second lens group 325 should be applied.
As discussed above, as the camera body 100 and the optical assembly 110 are physically tilted up or down about the pitch axis 150, a disturbance force acts upon the lens actuator 320, 322 and the lens group 323, 325 due to the earth's gravitational field. The disturbance force includes a gravitational force, and electrical and mechanical forces resulting from a change in operating conditions. More significantly, it has been determined that the disturbance force differs substantially depending on the gravity orientation of the optical assembly 110. When the optical assembly 110 is in a straight up position (i.e., the pitch angle 155 is at an angle Φ=90.0 degrees), the force to slide or move the lens group 325 is maximum in the direction towards the imager 330. This maximum equals the sliding mass times the acceleration due to gravity. Without any counter force from the voice coil 455, the lens group 325 will side to the end nearest the imager 330.
As the pitch angle 155 decreases towards a horizontal position (pitch angle Φ=0.0 degrees), the force to slide the lens group 325 decreases by sin(Φ). The lens stops moving when this force is less than the frictional force to slide the lens.
In the horizontal position (pitch angle Φ=0.0 degrees), there is no force to slide the lens group.
As the pitch angle 155 decreases towards a straight down position (pitch angle Φ=−90.0 degrees), the force to slide the lens group increases by sin(Φ). The lens group starts moving when this force is larger than the frictional force to slide the lens group. Without any counter force from the voice coil, the lens group will slide to the end farthest from the imager 330.
In the straight down position (pitch angle Φ=−90.0 degrees), the force to slide the lens group is maximum in the direction away from the imager 330. Thus, the lens control system 400 improves the optical assembly position and velocity command tracking performance by using the camera's pitch angle 155, obtained from the IMU 310 to adjust the closed-loop tuning parameters of the lens group 323 and lens group 325 linear voice coil actuator of actuators 320 and 322, respectively. This is a new utilization of IMU 310 sensor measurements which, as discussed above, are traditionally only used to keep the camera display horizontal as the gravity angle changes.
This is in particular different from the related art because knowledge of camera pitch angle 155 for tuning enables the same camera performance independent of gravity orientation. In other words, “best” closed-loop actuator tracking performance is realized when control loop tuning parameters adjust the actuator system frequency response to increase low frequency gain and bandwidth while maintaining adequate stability margins. Since a torque disturbance changes the frequency response and changing the gravity orientation of a portable camera causes a torque disturbance, fixed tuning parameters will not yield the same performance at different gravity orientations.
Using pitch angle 155, commanded position, velocity and servo error measurements to dynamically adjust tuning parameters ensures stability margins are maintained. By applying thresholds to the measured pitch angles which correspond to significant changes in the frequency response, simple efficient tuning adjustments can normalization tracking performance over a wide range of pitch values.
In addition, there is no need to dynamically stabilize the camera movement. Only the pitch information is needed. Roll angle 145 and yaw angle 135 have no effect on the control system because their forces are orthogonal to the optical assembly movement. Thus, the lens control system 400 is configured to dynamically select and transition to optimized tuning parameters as the system undergoes gravity orientation changes.
The third exemplary embodiment shown in
Thus, unlike in the first exemplary embodiment shown in
All of the information needed to extract the gravity orientation from the voice coil current is locally available to the control system. By using commanded position, velocity and servo error measurements, tuning parameters can be dynamically adjusted to ensures stability margins are maintained.
By applying thresholds to the measured pitch angles 155 which correspond to significant changes in the frequency response, simple efficient tuning adjustments can normalization tracking performance over a wide range of pitch values.
As a result, there is no need to dynamically stabilize the camera movement which makes high-quality performance of the automatic zoom function, for example, possible. Only the pitch information is needed fort this control operation. Roll and Yaw have no effect on the control system because their forces are orthogonal to the optical assembly movement.
Turning now to
The frequency response graphs show that the magnitude of the closed-loop tracking response below 40 Hz for horizontal orientation has the lowest gain and results in the worst lens positioning performance.
As shown in
Turning now to
As shown in
Changes in gravity orientation result in deterministic mechanical imbalance forces or disturbance forces in the lens control system 300.
Using Newton's second law of motion, all forces on the center of mass of the optical assembly 110, 310 acting along the optical axis under the influence of gravity can be calculated:
F
D
=F
G*SIN(Φ)=M*A*SIN(Φ),
wherein M is the lens group mass/weight, A is the acceleration due to gravity which is 9.8 meters/sec2, and Φ is the tilt angle between the mechanical optical axis and horizontal plane normal to gravity.
In the absence of any force produced by the voice coil (FVC), at a pitch angle 155 of Φ=0 degrees, (horizontal position) static friction keeps the lens from moving.
F
D
=F
G*SIN(0)=0<FSF
As the pitch angle 155 Φ increases towards 90 degrees (vertical-UP), at same angle Φ=ΦSLIDE, the static bearing force (FSF) is exceeded by the force on the optical assembly 110, 310 due to acceleration by gravity along the axis of movement (FD) and the lens group 323, 325 starts to slide.
F
D
=M*A*SIN(ΦSLIDE)>FSF
For the closed-loop control system to position the lens group in the desired position, a restoring force is needed:
F
VCclosed-loop
=F
D
−F
SF
Assuming the coefficient of friction is the same, as the pitch angle Φ decreases from horizontal towards −90 degrees (vertical-DOWN), at tilt angle Φ=−ΦSLIDE, the static bearing force (FSF) is again exceeded by the force on the lens assembly due to acceleration by gravity along the axis of movement (FD) and again the lens starts to slide, as shown in
In the vertical-down position shown in
−FVCclosed-loop=FD−FSF
It is understood that the foregoing description is that of the exemplary embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.
