System for detecting rotational angle of objective pattern

• US 4,876,732 A
• Filed: 05/18/1987
• Issued: 10/24/1989
• Est. Priority Date: 06/04/1986
• Status: Expired due to Fees

• Current Assignee: Fuji Electric Company Limited (Fuji Electric Systems Company Limited)
• Original Assignee: Fuji Electric Company Limited (Fuji Electric Systems Company Limited)
• Inventors: Ishizaka, Yutaka, Shimomura, Shoji, Miyagawa, Michiaki
• Primary Examiner(s): Boudreau, Leo H.
• Application Number:
  US07/050,578
• Time in Patent Office: 890 Days
• Field of Search: 382/8, 382/27, 382/28, 382/41, 382/45, 382/46, 340/727, 364/463, 364/559
• US Class Current: 382/288
• CPC Class Codes: G06V 30/1478 of characters or characters lines

Abstract

A system and method for determining a rotational angle of an objective pattern which involves calculating the area A and linear moments M_x and M_y of the pattern from binary picture elements formed after optically sensing the pattern. The picture elements are stored in the memory in binary form. The center of gravity of the objective pattern is calculated on the basis of the area A and the linear moments M_x and M_y, and a circular or ring-like search region (a window) is formed about that center of gravity. Thereafter, significant picture information in the search region is extracted from the picture information stored in the memory (in either an inverted or non-inverted state). The rotational angle of the objective pattern is then determined either by using a moment of inertia method or a inter two-gravity centers method calculation. The selection between the moment of inertia method and the inter two-gravity centers method can be performed by means of pre-set switch state information.

Claims

1. A method for detecting a rotational angle of an objective pattern comprising the steps of:

(a) optically sensing an objective pattern by a picture sensor to form a sense signal;

(b) binary coding said sense signal into picture elements;

(c) calculating an area of said objective pattern and a plurality of linear moments of said objective pattern from said picture elements;

(d) calculating a center of gravity of said objective pattern from said area and said linear moments;

(e) storing said area, linear moments, center of gravity and said binary-coded picture elements into a memory;

(f) calculating a displacement of said center of gravity corresponding to a difference between a center of gravity of a predetermined picture sample and said center of gravity of said objective pattern;

(g) determining an appropriate search region from among said binary-coded picture elements and reading out data corresponding to said search region;

(h) normalizing a position of said search region;

(i) calculating a rotational angle for said objective pattern based on predetermined mathematical formulae and utilizing said stored information; and

(j) storing predetermined data for determining whether said logic state of said picture information is to be inverted, and as to which one of said methods of calculation are to be used in detection of said rotational angle of said objective pattern.

2. The method of claim 1, further including the step of forming a search region by using a normalization process.

3. A system for detecting a rotational angle of a two-dimensional objective pattern converted into binary picture information, said system comprising:

memory means for storing said picture information;

first feature extraction means for extracting an area and a moment of inertia of said objective pattern from said picture information;

center of gravity means for determining a center of gravity of said objective pattern from said area and said moment of inertia of said objective pattern;

region forming means performing a search region having a predetermined shape about said center of gravity of said pattern;

second feature extraction means for extracting a selective portion of said picture information out of said memory means, whereby said rotational angle of said objective pattern is detected on the basis of said extracted portion by using a selected one of a moment of inertia method or an inter two-centers of gravity method of calculation; and

predetermined data storage means for determining whether said logic state of said picture information is to be inverted, and as to which one of said methods of calculation are to be used in detection of said rotational angle of said objective pattern.

4. A system for detecting rotational angle of an objective pattern according to claim 3, in which said search region is formed by using a normalization process.