Optics: measuring and testing – Position or displacement – Position transverse to viewing axis
Reexamination Certificate
2000-09-21
2003-12-30
Nguyen, Tu T. (Department: 2877)
Optics: measuring and testing
Position or displacement
Position transverse to viewing axis
Reexamination Certificate
active
06671058
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for determining the position and rotational position of an object in three-dimensional space.
The objects suitable for the invention are varied and are very different in their function and application. Examples of such objects are surgical microscopes and surgical tools in the medical sector, levelling staffs in geodetic surveying, gun barrels in the military sector or aerials, in particular directional aerials and radar aerials. In the case of such objects, their position in space plays an important role. This is determined in a specified coordinate system completely by six real position parameters which are composed of three parameters for the position (translation group) and three parameters for the rotational position (rotation group). The position of the object is given by the 3-dimensional coordinates of a point selected on the object. The rotational position of the object is generally described by the direction vector of a defined object axis and the angle of rotation of the object about the object axis. The direction vector of the object axis is a unit vector having the length
1
, i.e. the sum of the squares of its components is 1.
2. Description of the Background Art
WO 95/27918 describes an arrangement for determining the spatial position of a surgical microscope with the aid of coded light signals which are emitted by light emitting diodes, preferably in the infrared range, and received by light receivers. A surgical microscope is generally mounted on an arm by means of a cardan joint and can be moved translationally in three directions in space and rotated about three directions in space so that its position in space can be adjusted as desired. On the surgical microscope, the light emitting diodes or optical fibres which are fed with light from the light emitting diodes are mounted at specific points. Alternatively, reflectors may also be mounted on the surgical microscope. The light receivers are arranged at various points in space and receive the light signals specific to each of them. From this, the spatial position of the surgical microscope is determined. If the spatial position of the patient is simultaneously known, the coordinates of the operating site viewed through the surgical microscope are thus known, which is indispensable for microsurgery.
In geodetic surveying, levelling staffs are used for determining vertical points of reference and for topographical surveying. They are also used in construction surveying and in the construction of traffic routes. A levelling staff is sighted with the telescope optical system of the levelling instrument in order to measure the difference in height between levelling instrument and levelling staff. It is assumed that the levelling staff is aligned perpendicular to the optical axis of the telescope. Since the optical axis of the telescope is usually adjusted so that it is in a horizontal plane, an operator must keep the levelling staff aligned as far as possible perpendicular with the aid of the water levels mounted thereon. Tilting of the levelling staff results in an error in the height measurement.
With the advent of automated digital levelling instruments according to DE 34 24 806 C2, electronic reading of the staff became possible for the first time. For this purpose, the levelling staff has a code pattern comprising black and white elements, a part of which is produced as an image on a position-resolving detector with the aid of the telescope optical system of the electronic levelling instrument. Here, the code pattern information present in the field of view of the telescope is used to obtain the desired height measurement by comparison with the code pattern of the levelling staff, which pattern is stored as a reference code pattern in the levelling instrument. Although the measured code pattern is identified in this measurement and evaluation method, tilting of the levelling staff and the resulting contribution to the inaccuracy of measurement are not taken into account.
A specific code pattern is disclosed in DE 195 30 788 C1. A levelling staff having a rotationally symmetrical cross-section has, on its lateral surface, code elements which form lines closed rotationally symmetrically with respect to the longitudinal axis of the levelling staff. Consequently, the code pattern is visible from all sides.
DE 44 38 759 C1 describes a method for determining the tilt angle of coded levelling staffs in the measuring direction by means of an electronic levelling instrument. The tilt of the levelling staff is taken into account exclusively in the measuring direction, i.e. in the observation direction. The resulting recording of the code pattern on the detector is evaluated and the tilt angle is determined. Lateral tilting of the levelling staff, which thus takes place transversely to the observation direction of the levelling instrument, is however not taken into account. A one-dimensional diode array is therefore adequate as a detector.
Owing to a lateral tilt of the levelling staff, an error also occurs in the height and distance measurement. The point of intersection of the optical axis of the levelling instrument with a tilted levelling staff is further away from the bottom of the levelling staff than in the case of exactly perpendicular alignment of the levelling staff. An insufficiently perpendicular alignment due to inaccurate reading of the water level by the operator therefore leads to erroneous measurements. There is subsequently no possibility for correcting errors. Moreover, often only a single operator is used today, said operator operating the levelling instrument for surveying. The levelling staff standing alone is exposed to the wind, which leads to corresponding deviations in the surveying.
In the case of a gun barrel—and the following statement also applies analogously in the case of directional aerials and radar aerials—the primary concern is to determine its orientation in space or to rotate the gun barrel into a specific predetermined direction and to measure said rotation. The horizontal and vertical angular position (azimuth and elevation) of the gun barrel is controlled with the aid of encoders which are mechanically connected to the gun barrel. The encoders contain in general coded rotary discs which execute a rotational movement by means of a gear during rotation of the gun barrel and thus deliver electrical signals corresponding to the angles of rotation. The mechanical play is disadvantageous in the case of such controls. Moreover, the large thermal loads and shocks lead to inaccuracies and to increased wear.
SUMMARY OF THE INVENTION
It is the object of the invention to provide a method by means of which the position and the rotational position of an object in three-dimensional space can be determined quickly and without contact.
The object is achieved, according to the invention, by use of an optical measuring head including an imaging optical system and a detector which is position-resolving in two dimensions and is arranged in the focal plane of the imaging optical system. The object with its object structures is focused onto the detector by the imaging optical system. The object structures are known from the outset as a priori information. The object structures may contain the geometric shape of the object and its dimensions or may be marks at specific points on the object or they may be a code pattern which is applied to the object. The image of the object or of the object structures which is present in two-dimensional form on the detector is evaluated in an evaluation unit connected to the detector.
There are various possibilities for evaluating the two-dimensional image information. For example, the image of the object can be compared with calculated images. From the known geometry of the object or from existing marks on the object or from an existing code pattern on the object or from all these object structures together, the expected detector image can be calculated using the known properties
Aebischer Beat
Appius Raphael
Braunecker Bernard
Leica Geosystems AG
Nguyen Tu T.
Rothwell, Figg, Ernst & Manbeck pc
LandOfFree
Method for determining the position and rotational position... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for determining the position and rotational position..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for determining the position and rotational position... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3137716