Auto focusing mechanism of surveying instrument

• US 7,361,874 B2
• Filed: 12/28/2005
• Issued: 04/22/2008
• Est. Priority Date: 02/25/2005
• Status: Active Grant

• Current Assignee: Topcon Corporation
• Original Assignee: Sokkia Co. Ltd. (Topcon Corporation)
• Inventors: Nishita, Nobuyuki, Nagao, Takashi, Shoji, Naoki
• Primary Examiner(s): Epps; Georgia
• Assistant Examiner(s): Sohn; Seung C
• Application Number:
  US11/319,204
• Publication Number:
  US 20060192074A1
• Time in Patent Office: 846 Days
• Field of Search: 250/201.2, 250/201.7, 356/4.03
• US Class Current: 250/201.2
• CPC Class Codes: G01C 15/00 Surveying instruments or accessories not provided for in groups G01C1/00 - G01C13/00
• CPC Class Codes: G02B 7/36 using image sharpness techniques , e.g. image processing techniques for generating autofocus signals image data processing per se G06T; in cameras having a solid state image sensor H04N23/67

Abstract

An auto focusing mechanism is provided in a surveying instrument, such as an electronic level, that is capable of automatically focusing a telescope on a sighted staff.

As a focusing lens (21b) is moved by a motor (41) along the optical axis of a telescope (20), the image of a staff (1) sighted by the telescope (20) is converted into an electrical signal by a line sensor (24). The output signal of the line sensor (24) is converted into a digital signal by an A/D converter (27) and stored in a RAM (28). Based on the data stored in the RAM (28), a microcomputer (3) monitors frequencies of the component signals, or wavelets, contained in the output signal of the line sensor (24) stored in the RAM (28). When a particular frequency of the output signal associated with the position of the focusing lens (21b) is detected a determination is made that the focusing lens (21b) is located at a focusing position, and the distance from the telescope (20) to the staff (1) is calculated.

Claims

1. An auto focusing mechanism for use with a surveying instrument equipped with a telescope having a collimating optical system that includes, between an objective lens and an eyepiece thereof, a focusing plate and a focusing lens for forming on said focusing plate an image of a staff serving as a targeted collimating object, said staff having thereon a multiple pattern marked at equal intervals, said auto focusing mechanism adapted to automatically focus said telescope on said staff, said auto focusing mechanism comprising:

drive means for moving said focusing lens in the direction of the optical axis of said collimating optical system;

position detection means for detecting the position of said focusing lens in said collimating optical system;

photoelectric conversion means for converting into an electric signal the image formed on said focusing plate;

frequency detection means for detecting the frequencies of said electric signal outputted from said photoelectric conversion means;

distance calculation means for calculating the distance from said telescope to said staff based on the output signal received from said photoelectric conversion means, said distance calculation means adapted to monitor the position of said focusing lens detected by said position detection means and the frequencies detected by said frequency detection means to thereby determine said distance when a particular frequency for a focusing position is detected by said frequency detection means during a process of varying the position of said focusing lens; and

drive control means for controlling said drive means to position said focusing lens at a focusing position based on the distance calculated by said distance calculation means and the position detected by said position detection means,

wherein said frequency detection means extracts, from the electric signal outputted from said photoelectric conversion means, only a particular frequency component that is presumably detectable for the dark-and-bright pattern of said staff when said focusing lens is positioned at the focusing position, and

wherein said distance calculation means includes;

moving average processing means for calculating the absolute values of pulse heights of said particular frequency components extracted by said frequency detection means, and performing moving average processing on the absolute values of pulses in a given preset staff sectional area;

decision means for making a decision as to whether the maximum value of the moving average obtained by said moving average processing exceeds a given threshold level or not;

staff area setting means for setting a staff sectional area in the output signal of said photoelectric conversion means when an affirmative decision is obtained in said decision, said staff sectional area having the same width as a region of photoelectric transducers centered at the transducer giving said maximum value; and

calculation means for calculating the distance from said telescope to said staff based on the period of said output signal of said photoelectric conversion means within said staff sectional area by regarding the period of cycle as the pitch of the pattern of said staff.

2. An auto focusing mechanism for use with a surveying instrument equipped with a telescope having a collimating optical system that includes, between an objective lens and an eyepiece thereof, a focusing plate and a focusing lens for forming on said focusing plate an image of a staff serving as a targeted collimating object, said staff having thereon a multiple pattern marked at equal intervals, said auto focusing mechanism adapted to automatically focus said telescope on said staff, said auto focusing mechanism comprising:

drive means for moving said focusing lens in the direction of the optical axis of said collimating optical system;

position detection means for detecting the position of said focusing lens in said collimating optical system;

photoelectric conversion means for converting into an electric signal the image formed on said focusing plate;

frequency detection means for detecting the frequencies of said electric signal outputted from said photoelectric conversion means;

distance calculation means for calculating the distance from said telescope to said staff based on the output signal received from said photoelectric conversion means, said distance calculation means adapted to monitor the position of said focusing lens detected by said position detection means and the frequencies detected by said frequency detection means to thereby determine said distance when a particular frequency for a focusing position is detected by said frequency detection means during a process of varying the position of said focusing lens; and

drive control means for controlling said drive means to position said focusing lens at a focusing position based on the distance calculated by said distance calculation means and the position detected by said position detection means,

wherein said frequency detection means extracts, from the electric signal outputted from said photoelectric conversion means, only a particular frequency component that is presumably detectable for the dark-and-bright pattern of said staff when said focusing lens is positioned at the focusing position, and

wherein said photoelectric conversion means includes multiple photoelectric transducers, and

said distance calculation means includes;

moving average processing means for calculating the absolute values of pulse heights of said particular frequency components extracted by said frequency detection means, and performing moving average processing on the absolute values of pulses within a given preset staff sectional area;

light intensity correction coefficient calculation means for calculating a light intensity correction coefficient based on the difference between the maximum light intensity obtained from the level of the electric signal within the staff sectional areas used in the moving average processing and the maximum light intensity obtained from the output signals of said multiple photoelectric transducers;

light intensity correction coefficient multiplication means for multiplying the moving average obtained by said light intensity correction coefficient calculation means;

decision means for making a decision whether the maximum value of the products obtained by said light intensity correction coefficient multiplication means exceeds a given threshold or not;

staff area setting means for setting a staff sectional area in association with said output signal of said photoelectric conversion means when an affirmative decision is obtained in said decision, such that said staff sectional area has the same width as a region of photoelectric transducers centered at the transducer giving said maximum value; and

calculation means for calculating the distance from said telescope to said staff based on said period of the output signal of said photoelectric conversion means within said staff sectional area by regarding said period of cycle as the pitch of the pattern of said staff.