Autofocus device of a camera and method

• US 5,860,032 A
• Filed: 06/24/1997
• Issued: 01/12/1999
• Est. Priority Date: 09/07/1994
• Status: Expired due to Term

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Iwane, Toru
• Primary Examiner(s): Adams, Russell
• Assistant Examiner(s): Mahoney, Christopher E.
• Application Number:
  US08/881,490
• Time in Patent Office: 567 Days
• Field of Search: 354/400-408, 396/95, 396/125, 396/104, 348/352, 352/140
• US Class Current: 396/95
• CPC Class Codes: G02B 7/102 controlled by a microcomputer cameras with interchangeable lenses G03B17/14
• CPC Class Codes: G02B 7/28 Systems for automatic generation of focusing signals

Abstract

An autofocus device and method for a camera that can process statistically the tracking and focusing of an object in high velocity motion. The device and method corrects the acceleration of the motion and computes a lens forwarding amount and an absolute position of the object. This is achieved by a camera system including a camera body and a focus lens. The camera body includes an autofocus detector, an autofocus processor section and a main CPU. The focus lens includes a lens, a lens driving gear, a lens CPU, and a motor. This structure, having an improved autofocus processor, enables highly accurate prediction tracking and autofocus control that accommodates fluctuations in an autofocus operation.

Claims

1. An autofocus device for a camera, comprising:

a defocus amount detector;

a memory to store a plurality of consecutive immediate past data sets including detection amount data obtained from the defocus amount detector and data corresponding to a lens forwarding amount; and

an autofocus processor section to process the data stored in the memory to predict a future predicted image composition plane at a specific time based on a specific function that includes a term that is the square root of the image plane velocity statistically manipulated from past data sets, and current movement of the image composition plane, wherein a change in a position of the image composition plane is defined by the specific function derived from regression analysis of image plane movement described by the consecutive immediate past data sets so that driving of a focus lens can be controlled based on the future predicted image composition plane and the current movement of the image composition plane.

2. The autofocus device according to claim 1, wherein exposure is performed continuously for a moving object in such a manner that the image composition plane during a next exposure is predicted by the autofocus processor section and the focus lens is driven to allow the object image to coincide with the predicted image composition plane during exposure.

3. The autofocus device according to claim 1, wherein the autofocus processor section predicts the future image composition plane using a reciprocal function as the specific function.

4. The autofocus device according to claim 1, wherein the autofocus processor section predicts the future image composition plane using a first order hyperbola as the specific function.

5. The autofocus device according to claim 1, wherein the autofocus processor section predicts the future image composition plane using the following function as the specific function when an image plane position is below a vertical midline of a curve defining the image composition plane:

##EQU12## where y is a y-intercept position, a is a slope of the function, t₀ is a time at which a peak of the specific function defining the image composition plane occurs, t is the time lapsed until that time, and c is an offset constant.

6. The autofocus device according to claim 1, wherein the autofocus processor section predicts the image composition plane using the following function as the specific function:

##EQU13## where y is a y-intercept position, a is a slope of the function, v is the current image plane velocity, and c is an offset constant.

7. The autofocus device of claim 1, wherein the autofocus processor section computes a specific function for a plurality of image plane velocities obtained from the plurality of past data sets and a linear regression equation for the data corresponding to the plurality of lens forwarding amounts, the position of the image plane at a specific time being predicted by the autofocus processor section based on a correlation between the specific function and the linear regression, driving of a focus lens being executed based on the correlation.

8. The autofocus device of claim 1, wherein the autofocus processor section predicts the image composition plane based on the detection amount data, change in the position of the image plane is considered to be the specific function, a regression line is obtained by the autofocus processor section using the data stored in the memory to fit the specific function to movement of the image plane described by the plurality of past data sets based on the regression line, and movement of the image plane is predicted using the specific function.

9. The autofocus device according to claim 8, wherein the specific function includes a term that is the square root of the image plane velocity.

10. An autofocus device according to claim 8, wherein the autofocus processor section computes a correlation between a plurality of image plane velocities or their corresponding function transformation values and the data corresponding to a plurality of lens forwarding amounts, and, based on the correlation, the autofocus processor section computes absolute values of the plurality of lens forwarding amounts.

11. The autofocus device according to claim 10, wherein the specific function includes a term that is the square root of the image plane velocity.

12. An autofocus device for a camera, comprising:

a defocus amount detector;

a memory to store a plurality of consecutive immediate past data sets including detection amount data obtained from the defocus amount detector and data corresponding to a lens forwarding amount; and

an autofocus processor section to process the data stored in the memory to predict a future image composition plane based on the detection amount data, wherein the autofocus processor section obtains a regression line from the stored consecutive immediate data sets using a function having a term that is the square root of the image plane velocity and, based on a forwarding amount at a certain time, including the current time, one or more of an image plane velocity at that time, an absolute image plane position, and an image plane acceleration is computed.

13. The autofocus device according to claim 12, wherein the autofocus processor section predicts a future image plane position and an image plane velocity after a specified time based on a previously obtained image plane velocity, image plane position and image plane acceleration.

14. A method of accurately predicting tracking of a moving object in an autofocus device of a camera having a focusing lens, a defocus amount detector, a memory to store a plurality of past data sets including detection amount data obtained from the defocus amount detector and data corresponding to a lens forwarding amount, a driving control, and an autofocus processor section to process the data stored in the memory, the method comprising the steps of:

(a) obtaining a predetermined plurality of defocus amounts from the defocus detector taken at predetermined intervals of time and storing the predetermined plurality of defocus amounts in the memory;

(b) obtaining relative lens forwarding amount data, one for each of the predetermined intervals of time;

(c) normalizing and standardizing the lens forwarding amounts data as position data c_n ;

(d) computing an image plane velocity from at least two previous defocus amounts, two corresponding lens forwarding amounts taken at the same time as the defocus amounts, and the actual time at each defocus amount detection;

(e) converting the lens position data c_n and the computed image plane velocity to a unified dimension;

(f) storing a square root of the image plane velocity (v_n) of a specified number of data sets in the memory;

(g) performing linear regression on the position data c_n and the square roots of the image plane velocity v_n to statistically determine a slope and a y-intercept of a function defining the image plane velocity;

(h) obtaining current image plane velocity by substituting a current lens forwarding amount into the function defining the image plane velocity determined in step (g);

(i) determining the current image plane acceleration from the current image plane velocity obtained in step (h);

(j) obtaining a predicted image plane velocity from the current image plane velocity and the current image plane acceleration determined in steps (h) and (i);

(k) obtaining a current defocus amount from the latest defocus amount, the lens forwarding amount from the time when the latest defocus amount was obtained until the current time, and the image plane velocity;

(l) outputting the current defocus amount and the predicted image plane velocity to the driving control; and

(m) controlling the velocity of the focus lens using the driving control based on the outputted current defocus amount and the predicted image plane velocity.

15. The method of claim 14, wherein the step of linear regression to statistically determine the slope and the y-intercept includes:

computing averages c_m, v_m for the standardized position data c_n and the square root of the image plane velocity v_n ;

summing the product of the differences of each data c_n, v_n from the computed averages c_m, v_m ;

computing the total sum of the square of the differences between the standardized position data c_n and the average c_m ; and

determining the slope and y-intercept of a specific function from the previous summing steps.

16. The method of claim 14, further comprising a step of checking the data sets to determine suitability of the data within the data sets.

17. The method of claim 16, wherein the step of checking is performed by determining whether the memory contains a specified number of data sets.

18. The method of claim 16, wherein the step of checking is performed by determining whether an oldest of the data sets in the memory was obtained after a specified time.

19. An autofocus device for a camera, comprising:

a defocus amount detector means for detecting a defocus amount;

a memory means for storing a plurality of consecutive immediate past data sets including detection amount data obtained from the defocus amount detector means and data corresponding to a lens forwarding amount; and

an autofocus processor means for processing the consecutive immediate data sets stored in the memory to predict a future predicted image composition plane at a specific time based on a specific function that includes a term that is the square root of the image plane velocity statistically manipulated from past data sets, and current movement of the image composition plane, wherein a change in a position of the image composition plane is defined by the specific function derived from regression analysis of image plane movement described by the consecutive immediate past data sets so that driving of a focus lens can be controlled based on the future predicted image composition plane and the current movement of the image composition plane.

20. The autofocus device according to claim 19, wherein the autofocus processor means computes a specific function for a plurality of image plane velocities obtained from the data sets and a linear regression equation for the data corresponding to the plurality of lens forwarding amounts, the position of the image plane at a specific time being predicted by the autofocus processor means based on a correlation between the specific function and the linear regression, driving of a focus lens being executed based on the correlation.

21. The autofocus device of claim 19, wherein the autofocus processor means computes a specific function for a plurality of image plane velocities obtained from the data and a linear regression equation for the data corresponding to the plurality of lens forwarding amounts, the position of the image plane at a specific time being predicted by the autofocus processor means based on a correlation between the specific function and the linear regression, driving of a focus lens being executed based on the correlation.

22. The autofocus device of claim 19, wherein the autofocus processor means predicts the image composition plane based on the defocus amount detector means detected data, change in the position of the image plane is considered to be a specific function, a regression line is obtained by the autofocus processor means using the data stored in the memory means to fit the specific function to movement of the image plane described by the data based on the regression line, and movement of the image plane is predicted using the specified function.

23. An autofocus device for a camera, comprising:

a defocus amount detector;

a memory to store a plurality of past data sets including detection amount data obtained from the defocus amount detector and data corresponding to a lens forwarding amount; and

an autofocus processor section to process the data stored in the memory to predict a future predicted image composition plane at a specific time based on a specific function, statistically manipulated from past data sets, and current movement of the image composition plane, wherein a change in a position of the image composition plane is defined by the specific function derived from regression analysis of image plane movement described by the past data sets so that driving of a focus lens can be controlled based on the future predicted image composition plane and the current movement of the image composition plane,

wherein the autofocus processor section predicts the image composition plane using the following function as the specific function when an image plane position is below a vertical midline of a curve defining the image composition plane;

##EQU14## where y is a y-intercept position, a is a slope of the function to is a time at which a peak of the specific function defining the image composition plane occurs, t is the time lapsed until that time, and C is an offset constant.