Analyses of Key Variables to Industrialize a Multi-Camera System to Guide Robotic Arms

Purpose – To describe a new vision‐based co‐ordinate measuring machine (CMM) developed in France by ActiCM, which has undergone successful trials with car maker Renault.Design/methodology/approach – The vision‐based CMM uses intelligent vision devices (IVDs) which are mounted on a robot arm. Each IVD has two high‐definition CCD cameras, a visible LED illumination source and a white light projector. Up to eight sensors can work simultaneously on the same part which the IVDs' cameras can image from two different and known positions. These two views are then geometrically manipulated by the device software using photogrammetry to extract 3D data.Findings – Trials at a Renault car production plant have shown that the system can validate a car's body shape in significantly less time than is possible with conventional CMMs. The time for a 2,000‐element validation has been reduced from around 10 to 2 h, with a dimensional accuracy of 300 μm.Originality/value – This illustrates that vision‐based CMMs are able to ...

For manufacturing of high-value components, such as in the aerospace, automotive, shipbuilding and nuclear power industries, there is a significant demand for integrated traceable measurement to provide fast feedback during the manufacturing processes. Most modern machine tools are equipped with a probing system. However, one of the key challenges is that the traceability of measurement on a machine tool is not ensured yet, and therefore, the measurement results are not reliable for process control and product geometry verification. A laser tracker is a portable optical measurement system and capable of performing high accuracy and long range 3D measurements. As such, it is a suitable alternative solution for large component measurement. The aim of this paper is to test measurement uncertainties for a large component using different methods, including use of tactile on-machine tool probing and optical laser tracker, in ‘shop floor’ conditions. The measurement results have been verified using a large gantry coordinate measuring machine (CMM).

This paper presents a practical approach to fully automated kinematic calibration of an industrial manipulator. The approach is based on the principle of plane constraint. The electrical signal is used to fix the moment of contact between the conductive tool and the flat surface. The measurement data are manipulator configurations (joint angles) at the moment of contact. A modification of the algorithm to deal with the scaling problem is also proposed. This approach provides both high calibration accuracy and lower cost of the experimental setup compared to coordinate measuring machines (CMMs), laser trackers, and vision systems. The article examines the impact of various methods of kinematic parameterization of manipulators: the Denavit – Hartenberg agreement (DH), product of exponentials (POE), as well as the complete and parametrically continuous model (CPC) on the calibration accuracy. A comparison is made of the open-loop and the proposed closed-loop calibration methods on the Puma 560 model known in the literature. POE parameters were converted to DH and CPC to compare accuracy after calibration based on these parameterizations. The method of computing POE-CPC transformation as a solution to a certain optimization problem is proposed. The problem of identifying geometric parameters in the presence of restrictions is solved by gradient optimization methods. Experiments have been carried out on an ABB IRB 1600 industrial manipulator with an installed conductive probe and an ABB IRBP A-500 robotic positioner with a conductive metal flat surface. A technique for indirectly checking the accuracy of calibration of kinematic parameters is proposed based on a study of the accuracy of manipulation when using these parameters.

Coordinate measuring machines (CMMs) with continuous-contact scanning capabilities are experiencing more and more use in a wide variety of discrete-part manufacturing industries. Many users of these CMMs, if asked, will say that their metrology requirements include high density scans at high speeds with high accuracy. These requirements are in conflict, as there will be some point at which the accuracy of the scanned data begins to decrease with an increase in the scanning speed. This paper addresses the effects of scanning speed on the performance of different CMMs using contact sensors. The use of a family of artifacts is proposed in order to evaluate the relative scanning performance as a function of scanning speed and the direction of the scan within the CMM volume. The artifacts that are developed for these tests have a sinusoidal waveform superimposed on a flat surface. This paper describes a series of experiments that utilize these artifacts and assess the ability of these tests to capture how a scanning CMM will perform when measuring actual parts.

This paper presents an automated calibration method for industrial robots, based on the use of (1) a novel, low-cost, wireless, 3D measuring device mounted on the robot end-effector and (2) a portable 3D ball artifact fixed with respect to the robot base. The new device, called TriCal, is essentially a fixture holding three digital indicators (plunger style), the axes of which are orthogonal and intersect at one point, considered to be the robot tool center point (TCP). The artifact contains four 1-inch datum balls, each mounted on a stem, with precisely known relative positions measured on a Coordinate Measuring Machine (CMM). The measurement procedure with the TriCal is fully automated and consists of the robot moving its end-effector in such as a way as to perfectly align its TCP with the center of each of the four datum balls, with multiple end-effector orientations. The calibration method and hardware were tested on a six-axis industrial robot (KUKA KR6 R700 sixx). The calibration model included all kinematic and joint stiffness parameters, which were identified using the least-squares method. The efficiency of the new calibration system was validated by measuring the accuracy of the robot after calibration in 500 nearly random end-effector poses using a laser tracker. The same validation was performed after the robot was calibrated using measurements from the laser tracker only. Results show that both measurement methods lead to similar accuracy improvements, with the TriCal yielding maximum position errors of 0.624 mm and mean position errors of 0.326 mm.

The optical triangulation probe (OTP), which consists of a light spot projector and a camera, has found widespread applications for three-dimensional (3D) measurement and quality control of products in the industrial manufacturing. The OTP calibration is an extremely important issue, since the performances such as high accuracy and repeatability are crucially depended on the calibration results. This paper presents a flexible approach for modeling and calibration of the OTP, which only requires planar patterns observed from a few different orientations and light spots projected on the planes as well. For the calibration procedure, the structure parameters of the OTP are calculated, such as the camera extrinsic and intrinsic parameters which include the coefficients of the lens distortion, and the directional equation for the light axis of the projector. For the measuring procedure, the formulations of 3D computation are concisely described using the calibration results. Experimental tests of the real system confirm the suitable accuracy and repeatability. Furthermore, the technique proposed here is easily generalized for the OTP integration in robot arms or Coordinate Measuring Machines (CMMs).

A modular space frame for assessing the performance of co-ordinate measuring machines (CMMs)

Coordinate Measuring Machines (CMM) are widely used in industry, mainly for assessing product’s compliance to geometrical specifications. They are a de-facto standard for such a control, owing to their high accuracy and flexibility in catering to different measurement tasks with fast and easy setup change. One of the key aspects of any CMM inspection plan, affecting accuracy and cost, is the choice of the measurement strategy, namely the definition of the number and the location of the points sampled on the part’s surface. In the industrial practice, such important decisions are usually left to the experience of qualified operators. A method is presented here, based upon an innovative application of Kriging models to coordinate metrology, that defines an adaptive sampling strategy with the goal of obtaining accurate estimates of form errors using relatively small samples. Exploitation of kriging models (originated for geostatistics investigations, then successfully applied to the sector of Computer Experiments) in dimensional metrology entails however some adjustments. Two practical cases of form error estimation have been investigated, the first dealing with flatness verification, and the second with roundness.

Metrology, the science of measurement, has significantly evolved to meet the demands of modern industries. This paper explores the historical significance, technological advancements, and contemporary applications of metrology, highlighting key technologies like laser trackers, photogrammetry, interferometers, optical fibres, coordinate measuring machines (CMM), coordinate measuring Arms (CMA), electromagnetic distance measurement (EDM), and digital metrology tools. Each technology’s unique capabilities, such as high precision, long-range measurement, and data integration, are compared, emphasizing their roles in fields like aerospace and manufacturing. The comparative analysis provides insights into the advantages and limitations of these technologies, offering guidance for selecting appropriate metrology solutions. Additionally, the potential future advancements in metrology, driven by innovations in sensor technology, artificial intelligence, and digital twins, are discussed. This paper accentuates metrology’s pivotal role in enhancing measurement accuracy, reliability, and efficiency in various engineering and manufacturing processes.

The Extreme Ultraviolet Imager (EUI) instrument for the Solar Orbiter mission will image the solar corona in the extreme ultraviolet (17.1 nm and 30.4 nm) and in the vacuum ultraviolet (121.6 nm). It is composed of three channels, each one containing a telescope. Two of these channels are high resolution imagers (HRI) at respectively 17.1 nm (HRI-EUV) and 121.6 nm (HRI-Ly∝), each one composed of two off-axis aspherical mirrors. The third channel is a full sun imager (FSI) composed of one single off-axis aspherical mirror and working at 17.1 nm and 30.4 nm alternatively. This paper presents the optical alignment of each telescope. The alignment process involved a set of Optical Ground Support Equipment (OGSE) such as theodolites, laser tracker, visible-light interferometer as well as a 3D Coordinates Measuring Machine (CMM). The mirrors orientation have been measured with respect to reference alignment cubes using theodolites. Their positions with respect to reference pins on the instrument optical bench have been measured using the 3D CMM. The mirrors orientations and positions have been adjusted by shimming of the mirrors mount during the alignment process. After this mechanical alignment, the quality of the wavefront has been checked by interferometric measurements, in an iterative process with the orientation and position adjustment to achieve the required image quality.

Under the laser tracker measurement of angle subsystem environment,signal acquisition system of laser tracker incremental encoder based on FPGA was designed in this paper. The FPGA in this system was mainly responsible for the encoder signal acquisition, processing, and generating timing signals, data caching mechanism and asynchronous output of the data. This paper detailedly introduced quadrupler frequency, phase discrimination, counting, latches, and UART asynchronous serial port output sub-modules in the process of signal acquisition of FPGA, which was implemented by Verilog HDL language. Online logic analyzer of the Quartus software acquired the value of encoder signal in real time, and the rationality of the design was verified ultimately.

Quality Control (QC) is one of the most important phases in the production process. In tradition, the workpiece must be inspected for dimension and shape errors in the QC lab or Coordinate Measuring Machine (CMM) after being machined, which is time-consuming and labor-intensive, especially for large scale parts. Thus the only practical way to do that is to migrate the critical primary inspection operations upstream from the QC lab or CMM to the production floor, and that’s what On-Machine Measurement (OMM) does. OMM technology can inspect the workpiece on its operating station by motion control and the position detection function of CNC machine tool, by which the measuring error caused by the misalignment between measuring datum and manufacturing datum can be avoided accurately. Therefore, it is a feasible way to achieve the real-time control of the manufacturing process and improve the manufacturing accuracy and efficiency. The servo axes of multi-axis CNC machine tool might be redundant for being used in OMM, which will result in that one measurement task could be done by different servo motion schemes. In addition, the map between the machine accuracy and measuring accuracy has not been found out previously. Thus, how to determine metering schemes to measure a workpiece with high accuracy and efficiency is one of the most important problems and also a hotspot for everybody. To solve this problem, a generation method of task-oriented OMM scheme is proposed. Utilizing multi-body system theory and transformation of homogeneous coordinates, a function relationship between the geometrical characteristic of workpiece as independent variables and motions of machine tool as dependent variables is established. All possible metering schemes are obtained by analyzing the solution of functional equation. Then the performance of measurement scheme can be evaluated by comparing the measuring errors of each scheme after building a mapping relationship between the machine tool volumetric errors and measuring errors. In the end, a case study was accomplished, and the correctness and efficiency of the methodology has been verified.

<div class="section abstract"><div class="htmlview paragraph">Industrial robots have been around since the 1960s and their introduction into the manufacturing industry has helped in automating otherwise repetitive and unsafe tasks, while also increasing the performance and productivity for the companies that adopted the technology. As the majority of industrial robotic arms are deployed in repetitive tasks, the pose accuracy is much less of a key driver for the majority of consumers (e.g. the automotive industry) than speed, payload, energy efficiency and unit cost. Consequently, manufacturers of industrial robots often quote repeatability as an indication of performance whilst the pose accuracy remains comparatively poor. Due to their lack in accuracy, robotic arms have seen slower adoption in the aerospace industry where high accuracy is of utmost importance. However if their accuracy could be improved, robots offer significant advantages, being comparatively inexpensive and more flexible than bespoke automation. Extensive research has been conducted in the area of improving robotic accuracy through re-calibration of the kinematic model. This approach is often highly complex, and seeks to optimise performance over the whole working volume or a portion thereof, rather than optimising performance of a particular task. In this paper, a method for iteratively teaching poses on a standard industrial robot is presented, and an investigation into the limits on the achievable pose accuracy and the required recalibration period is conducted. Through experimental work on a KUKA KR 240 R2900 ultra robot equipped with a drilling end-effector and measured in 3DoF using a laser tracker, it is demonstrated that the achievable accuracy approaches the stated repeatability of the robot. Finally, investigation results into the accuracy of the robot over short distances to allow small corrections to be applied from these taught poses to compensate for work-piece alignment or thermal effects are presented.</div></div>

Three dimensional (3-D) geometric shape measurements have found wide applications in the fields of industrial manufacturing, fast reverse engineering, quality control, biomedical sciences, etc. In the present paper we focus our attention on Reverse engineering. It starts from an existing product, and creates a CAD (Computer Aided Design) model, for modification or reproduction of its design. This kind of process is usually undertaken in order to redesign a system for better maintainability or to obtain a copy of a system without access to design from which it was originally produced. There are many different methods for acquiring shape data. Tactile methods represent a popular approach to shape capture. The most commonly known forms are Coordinate Measuring Machines (CMMs) and mechanical or robotic arms with a touch probe sensing device. Non-contact methods use light, sound or magnetic fields to acquire shape from objects. In the case of contact and non-contact, an appropriate analysis must be performed to determine the positions of points on objects surface. The aim of this paper is to present a new reconstruction method of three-dimensional measuring system for objects acquisition:reverse engineering based on structured light system. This technique consists in projecting a known pattern of pixels (structured light) on an object: the way in which this pattern is deformed encountering the object surfaces, allows vision systems (a couple of monochromatic digital cameras) to calculate depth information necessary for surfaces digitization. The subsequent application of this methodology has been to reengineer an aeronautical component that has changed over time and divergent from initial project. At last have been studied proposals and possible solutions that ensure an higher quality of manufactured products and a substantial savings in costs of production system of the product itself.

The development of a layer based machining system