Method for the creation of tridimensional numerical models

• US 6,374,198 B1
• Filed: 03/08/1999
• Issued: 04/16/2002
• Est. Priority Date: 07/11/1996
• Status: Expired due to Fees

• Current Assignee: Hexagon Metrology Incorporated (Hexagon AB)
• Original Assignee: Mirai S.r.l.
• Inventors: Bacoccoli, Paolo, Schifa, Maurizio
• Primary Examiner(s): FREJD, RUSSELL WARREN
• Application Number:
  US09/214,991
• Time in Patent Office: 1,135 Days
• Field of Search: 703/1, 703/2, 703/6, 345/419, 345/420, 700/98, 702/152, 702/153, 356/601, 356/614
• US Class Current: 703/2
• CPC Class Codes: G06T 17/00 Three dimensional [3D] modelling, e.g. data description of 3D objects
• CPC Class Codes: G06V 30/144 using a slot moved over the image; using discrete sensing elements at predetermined points; using automatic curve following means

Abstract

A method for the creation of numerical models of surfaces by acquisition of points from a tridimensional actual model, comprises the steps of identifying a first group of points (X) on at least one boundary (12a, 13a, 14a) defined on the surface (11) of the actual model (10), acquiring the values of the spatial coordinates of the first group of points (X) by means of an acquisition system, and generating a numerical representation of a theoretical surface whose boundary is defined by these points (X). A subsequent step of the method comprises the operation of the acquisition system in order to acquire the coordinates of a second group of points of the actual model, directing it towards the estimated position of nodal points belonging to the theoretical surface. In a last step of the method, a numerical or mathematical representation of the surface of the actual model is generated which satisfies the condition of passing through at least the points of the second group. The method also preferably comprises a step of optimization of the path of the acquisition system, which can comprise contact or non-contact type probes, or even a processing module to identify data of actual points in a preliminarily defined point cloud.

Claims

1. A method for the creation of numerical models of surfaces by means of the acquisition of points from a tridimensional actual model, characterized in that it comprises the steps of:

a) identifying at least one boundary (12a, 13a, 14a) on the surface (11) of the actual model (10);

b) identifying a first plurality of points (X) on the at least one boundary (12a, 13a, 14a);

c) acquiring the values of the spatial coordinates of the first plurality of points (X) by means of an acquisition system;

d) generating a first numerical representation of at least one theoretical surface (16, 17, 18) having at least one boundary defined by the values of the spatial coordinates (20) of the first plurality of points (X);

e) determining values representing a second plurality of nodal points (23) belonging to the at least one theoretical surface (16, 17, 18);

f) operating the acquisition system to acquire the values of the spatial coordinates of a third plurality of actual points, directing the acquisition system towards the estimated positions of the nodal points (23) of the second plurality;

g) generating a second numerical representation of at least one theoretical surface which satisfies the condition of at least passing through the points of the third plurality.

2. A method according to claim 1, characterized in that in the second numerical representation, the at least one theoretical surface also satisfies the condition of passing through the points of the first plurality.

3. A method according to claim 1, characterized in that the method also comprises the step of identifying at least one boundary (15a) isolating predetermined areas of the surface (11) of the model, in particular discontinuous areas, and the further step of including certain points on the isolation boundary (15a) in the first series of points (X).

4. A method according to claim 3, characterized in that the acquisition system is programmed to ignore, during the acquisition step f), points on the surface (11) of the model which correspond to nodal points situated within a theoretical boundary (19) defined by the values of the spatial coordinates of the points of the first plurality (X) belonging to the isolation boundary (15a).

5. A method according to claim 1, characterized in that the values representing the second plurality of nodal points (23) comprise values of spatial coordinates and values of the perpendiculars to the at least one theoretical surface (16, 17, 18) at the nodal points, the acquisition system being operated to approach each point on the surface of the model in a position defined by the spatial coordinates of each estimated point (23) according to an approach direction parallel to the value of the perpendicular to each nodal point.

6. A method according to claim 1, characterized in that it comprises an optimization step, prior to the acquisition step f), in which the second plurality of nodal points is ordered in a predetermined sequence to minimize the path and/or the acquisition time of the third plurality of points by the acquisition system in the acquisition step f).

7. A method according to claim 6, characterized in that the optimization step comprises the definition of one or more homogeneous groups of nodal points (23) of the theoretical surface, each group comprising nodal points in which the perpendiculars to the theoretical surface passing through the said nodal points have directions comprised within a predetermined spherical angle.

8. A method according to claim 5, characterized in that the acquisition system comprises at least one non-contact type probe, the optimization step comprising the definition of a path of the probe for the acquisition of the points of the third plurality whereby the approach of the probe to the surface of the model according to the perpendicular to the surface at the nodal point takes place programmatically according to positive or negative directions with respect to the orientation of the perpendicular itself.

9. A method according to claim 8, characterized in that the approach of the non-contact type probe to each point on the surface of the model takes place alternatively according to positive and negative directions for consecutive points in the predetermined ordered sequence.

10. A method according to claim 1, characterized in that the surface of the tridimensional actual model is preliminarily defined by a high quantity of data grouped into at least one point cloud, the acquisition system comprising a processing module controlled programmatically to identify the values of the spatial coordinates of the third plurality of points in the at least one point cloud starting from the estimated position of the theoretical nodal points.

11. A system for the acquisition of data of surfaces of tridimensional models, characterized in that it comprises:

at least one non-contact type measurement band type probe (112),

actuating means (111, 113) for moving the probe (112), controllable by means of signals representing the coordinates of theoretical points (T),

transmission means (114) for transmitting the coordinates of the theoretical points (T) and for selectively receiving the data transmitted by the probe (112),

actuator means to selectively enable the reception of the data transmitted by the probe in correspondence with its arrival at positions determined univocally by the coordinates of the theoretical points (T).

12. A system according to claim 11, characterized in that the transmission and reception means comprise an electronic processor (114) connected to the probe (112) with the interposition of an interface (116), the actuator means comprising a circuit for the detection of an enabling signal for the selective transfer to the computer (114) of the signals coming from the probe.

13. A system according to claim 11, characterized in that the transmission and reception means comprise an electronic processor (114) connected to the probe (112), the actuator means comprising a register or memory location which memorizes data that can be selectively modified between a “

true”

value and a “

false”

value.

14. A system according to claim 11, characterized in that the probe (112) is a measurement band type laser probe.

15. A method for the acquisition of data of surfaces of tridimensional objects by means of non-contact type measurement band type probes, characterized in that it comprises the following steps:

a) identification of a first theoretical point (T1) defining a first univocal position of a measurement band type probe (112), situated at a distance from a first actual point (R1) on the surface of the object, the distance of the first actual point from the probe being included within the measurement band of the probe,

b) identification of a second theoretical point (T2) defining a univocal position of the probe situated at a distance from a second actual point (R2) included within the measurement band,

c) movement of the probe (112) from the first to the second theoretical point along a path during which the probe remains at a distance from the surface (110) of the object substantially included within the measurement band of the probe,

d) acquisition of the data transmitted by the probe (112), representative of the position of the second actual point (R2), on reaching the position defined by the second theoretical point (T2).

16. A method according to claim 15, characterized in that it comprises the additional steps of identification of an array of theoretical points (T), the acquisition of the data transmitted by the probe (112) in the movement from a position defined by one of the said theoretical points to the position defined by the subsequent theoretical point being inhibited.

17. A method according to claim 15, characterized in that it comprises an additional step of minimization or optimization of an open path joining all the theoretical points (T).

18. A method according to claim 15, characterized in that it comprises a continuous step of controlling the data transmitted by the probe (112) traveling from one position to the next, defined by consecutive theoretical points, to check that the distance between the probe and the actual surface (110) remains within the measurement band of the probe.

19. A system for the acquisition of surface data of tridimensional objects, characterized in that it comprises a point cloud type acquisition system generating a high quantity of data representing the points on the surface of a tridimensional object, a device for the acquisition of points on the tridimensional object supplying a computer with data identifying a reduced plurality of selected points from at least one predefined boundary on the surface of the tridimensional object, the computer being programmed to generate a numerical representation of at least one theoretical surface having a boundary defined by the data of the reduced plurality of points and defining a plurality of theoretical nodal points, the computer also being programmed to identify, within the point cloud data, the acquired actual nodal data which are closest to the data of the theoretical nodal points, the theoretical nodal points of the at least one theoretical surface being replaced by the acquired actual nodal data to define the numerical representation of the at least one surface of the tridimensional object.

20. A system for the creation of a numerical model representing a tridimensional actual model, characterized in that it comprises a measuring device for the acquisition of measurement data of the aforesaid actual model, processing means being connected to the measuring device to control the process of data acquisition, to receive identification data of actual points on the surface of the model acquired by the measuring device, and to create a numerical model of a surface passing through said actual points, the processing means also receiving initial data representing initial points situated on at least one predetermined boundary on the surface of the actual model and processing at least one set of data representing theoretical nodal points belonging to a theoretical surface with a boundary passing through the initial points, the processing means also controlling the measuring device in sequence towards positions and along directions defined by the theoretical nodal points for the acquisition of the actual points on the surface of the model in the neighborhood of the theoretical nodal points.