Gewindestangen mit Messmarken für Photogrammetrische 3D-Veremssung

screw sleeves

Photogrammetry

Fastening anchors are recessed into the ground at the installation site for mounting and secure fastening of a machine. The tolerances specified by the design are not observed and there is a risk of distortion of the assembly work due to the unsuitable screw positions in the concrete foundation to the connection points on the machine.

After mounting 24 screw sleeves in a concrete foundation, the exact pose (= position & orientation) of the sleeves is not known.

For further planning purposes, all Poses screw sleeves embedded in the machine foundation are required. Only on the basis of the exact measurement data and the results that can be presented in CAD can further delays caused by later changes that were not planned in the planning process be avoided.

The measurement takes place outdoors, at the future installation site of the machine. The measurement is carried out very quickly, without any further infrastructure on the part of the client (electricity, protective hall, etc.).

After successful measurement and evaluation of the data, the customer can adapt the machine mountings constructively on the basis of the determined actual values so that no delays occur during subsequent assembly.


customer requirements:

In order to avoid time delays due to subsequent reworking during the subsequent set-up process, the pose of each screw sleeve is measured with an accuracy of ±0.5mm / ±2mm/m and output in a CAD format (step) for further processing. This means that the machine mounting can be adapted to the actual situation before setting up and there is no delay in setting up the machine.

Method of measurement:

Principle of short-range photogrammetry

Photogrammetry is a measuring technique in which the object is measured with the help of many 2D images.

The 3D coordinates can be determined from any point visible in multiple images from different viewing directions.

Prerequisite for the calculation of 3D coordinates is:

  • Fixed interior orientation of the camera (main image point, focal length)
  • At least five identical dots on each image
  • At least two (better: four) images per measuring point
  • Recordings from different locations

Measuring system used:

Evaluation computer with evaluation software

Digital camera with 12 million pixels

900 mm scale embodiment made of CFRP for traceability to the international length standard

Coded link points

Measuring aids used

Hemispherical measuring adapters signal the position of the screw sleeve in the outlet area.

Screwed-in threaded rods with an uncoded measuring mark on the upper side provide a second measuring point for determining the direction (oblique position).

Execution of the measurement

The measurement is carried out with a total of 35 individual images from different perspectives. In order to obtain the best possible cutting angle, the camera is held at different heights.

Due to daylight with changing bilight conditions, several test images must be taken beforehand to adjust the camera settings with regard to brightness and image sharpness.

evaluation

By means of the evaluation software AICON 3D Studio a classical photogrammetric evaluation with the following steps is carried out:

  • Image measurement (measurement of the 2D image coordinates of all measuring points in each image)
  • Pre-orientation of the measurement images using approximation methods
  • Point assignment of identical measuring points (via coded measuring points)
  • 3D coordinate calculation using bundle triangulation

The coordinates of the measuring points are then transferred from the AICON software to a graphics software for graphical control and point assignment.

outcomes

In order to better illustrate the pose of the individual screw sleeves, the position and inclination of the sleeves in the concrete foundation were calculated on the basis of the thread dimensions and passed on to the customer as a STEP file with the nominal sleeve diameter.

The software Polyworks Modeler was used to process the 3D point data. The STEP data was then generated with the SolidWorks design software. The customer has taken over the CAD data of the actual situation into his design program and adapted the machine mounts on this basis.

Statistics:

Dimensions Accuracy (RMS)

  • x: 800 mm x : 0,022 mm
  • y: 700 mm y : 0.021 mm
  • z: 300 mm z: 0, 026 mm

Time needed

  • Signalling: 30 min
  • Image acquisition: 20 min
  • Processing: 10 min
  • Analysis of results: 75 min
  • Total: 135 min

Summary of the

When selecting the measuring system, we opted for the photogrammetry system because its mobility and robustness allow us to achieve high accuracy even under changing weather conditions in the open air. The set-up time with the complex attachment of the measuring marks is usually a disadvantage of photogrammetry, but here, with the very few measuring points, it had no decisive influence on the measuring time.

The customer's wish for fast and thus cost-saving measurements could be easily realized with the extremely mobile measuring system.

During the evaluation of the measurement, an attempt was also made to achieve a directly usable result for the customer with just a few steps. He was able to load the STEP data record supplied directly into his CAD system and make the necessary adjustments to the machine elements.