Lars Lindner

Mobile robot vision system using continuous laser scanning for industrial application

Purpose The purpose of this paper is the presentation and research of a novel robot vision system, which uses laser dynamic triangulation, to determine three-dimensional (3D) coordinates of an observed object. The previously used physical operation principle of discontinuous scanning method is substituted by continuous method. Thereby applications become possible that were previously limited by this discretization. Design/methodology/approach The previously used prototype No. 2, which uses stepping motors to realize a discontinuous laser scan, was substituted by the new developed prototype No. 3, which contains servomotors, to achieve a continuous laser scan. The new prototype possesses only half the width and turns out to be significantly smaller and therefore lighter than the old one. Furthermore, no transmissions are used, which reduce the systematic error of laser positioning and increase the system reliability. Findings By using a continuous laser scan method instead of discontinuous laser scan method, dead zones in the laser scanner field can be eliminated. Thereby, also by changing the physical operation principle, the implementation of applications is allowed, which previously was limited by the fixed step size or by the object distance under observation. By using servomotors instead of stepping motors, also a significant reduced positioning time can be accomplished maintaining the relative positioning error less than 1 per cent. Originality/value The originality is based on the substitution of the physical operation principle of discontinuous by continuous laser scan. The previously used stepping motors discretized the laser scanner field and thereby produced dead zones, where 3D coordinates cannot be detected. These stepping motors were substituted by servomotors to revoke these disadvantages and provide a continuous laser scan, where dead zones in the field of view get eliminated and the step response of the laser scanner accelerated.

Continuous 3D scanning mode using servomotors instead of stepping motors in dynamic laser triangulation

A novel principle of dynamic triangulation with a laser scanner was developed at the institute of engineering UABC. This coordinate measurement method uses stepping motors for positioning a laser in a defined field of view. The present paper describes the substitution of these stepping motors with robust controlled servomotors in open- and closed-loop configuration. This approach converts the discontinuous (i.e. discrete steps) scanning method into a continuous one, to eliminate dead zones in the field of view and to accelerate the step response of the laser scanner.

An approach for dynamic triangulation using servomotors

A novel principle of dynamic triangulation was developed at the institute of engineering UABC. This method of coordinate measurement uses stepping motors for laser positioning and an open loop controlled DC motor for signal detection. The present paper describes an approach for use of servomotors in cascade control loop, optimized with the amplitude optimum in the frequency domain. These approach results in a short rising time of the step response without overshoot. Simulations of the complete system approves the theoretically values.

Optical Cyber-Physical System Embedded on an FPGA for 3D Measurement in Structural Health Monitoring Tasks

Abstract This paper presents the description of a cyber-physical system embedded on an FPGA for 3D measurement in structural health monitoring tasks. The implementation technique and performance evaluation demonstrate the contribution of this paper to the mathematical fundamentals adaptation of an on-site rotatory scanning system to a cyber-physical system. In particular, it is described in detail the design of a virtual angle measurement soft sensing technique based on the information conversion of an optoelectronic signal provided by a rotatory scanning system through an FPGA. Behaving the FPGA as the sensor controller and the actuator in the scanning system. Using the measurement of angles through the proposed embedded system, it can be calculated the coordinates and displacement of specific indicators distributed over a structure under observation. Providing online data exchange from on-site measurement to a remote computational station for real-time or posteriorly data analysis.

Exact laser beam positioning for measurement of vegetation vitality

Purpose The purpose of this paper is to present a novel application for a newly developed Technical Vision System (TVS), which uses a laser scanner and dynamic triangulation, to determine the vitality of agriculture vegetation. This vision system, installed on an unmanned aerial vehicle, shall measure the reflected laser energy and thereby determine the normalized differenced vegetation index. Design/methodology/approach The newly developed TVS shall be installed on the front part of the unmanned aerial vehicle, to perform line-by-line scan in the vision system field-of-view. The TVS uses high-quality DC motors, instead of previously researched low-quality DC motors, to eliminate the existence of two mutually exclusive conditions, for exact positioning of a DC motor shaft. The use of high-quality DC motors reduces the positioning error after control. Findings Present paper emphasizes the exact laser beam positioning in the field-of-view of a TVS. By use of high-quality instead of low-quality DC motors, a significant reduced positioning time was achieved, maintaining the relative angular position error less than 1 per cent. Best results were achieved, by realizing a quasi-continuous control, using a high pulse-width modulated duty cycle resolution and a high execution frequency of the positioning algorithm. Originality/value The originality of present paper is represented by the novel application of the newly developed TVS in the field of agriculture. The vitality of vegetation shall be determined by measuring the reflected laser energy of a scanned agriculture zone. The paper’s main focus is on the exact laser beam positioning within the TVS field-of-view, using high-quality DC motors in closed-loop position control configuration.

Machine vision system for UAV navigation

Unmanned Aerial Vehicle (UAV) navigation requires Machine Vision Systems to determine physical values of near distanced objects. These machine vision systems must respond in sufficiently amount of time using less scanning data from the observed objects. A novel Technical Vision System (TVS), which uses DC motors and laser triangulation to determine spatial coordinates of these objects, is offered and used for UAV navigation. Present paper thereby shows the implementation of open-loop control algorithm, to position the TVS laser ray in the UAV Field of View (FOV). Issues of this implementation, experimental realization and results are presented, as the theoretical concept of a continuous FOV derived.

UAV remote laser scanner improvement by continuous scanning using DC motors

Previous research have shown the advantages of a novel Technical Vision System (TVS), developed at the Autonomous University of Baja California (UABC), which uses triangulation to determine spatial coordinates on any object under observation. Present paper proposes a new application for the TVS use on drones with remote laser scanner in agriculture to determine a vegetation index of scanned crops. Thereby the needed algorithm to position the laser ray in the TVS field-of-view are proposed, implemented using microcontroller and tested using various experimental factors. Experimentation results shows the advantages and disadvantages of every algorithm comparing the positioning errors after control.

Resolution improvement of accelerometers measurement for drones in agricultural applications

In agricultural tasks, monitoring of large fields is required. In the last years automatic/autonomous monitoring has been researched; where unmanned aerial vehicles (UAV)-commonly known as drones-are used. For these systems, constrains related with autonomy during flight arise. In order to control properly the UAVs during flight, they require to measure physical variables, in a fast and accurate way. Also, the weight of instruments must be reduced for improving autonomy. In general, aerial vehicles obtain parameters like position, velocity and acceleration using inertial navigation systems. Regarding to this concern, in this work application of a novel technique for measurements onboard UAVs-particularly inertial measurement unit or IMU-is proposed. There are accelerometers inside the IMU. These accelerometers have a frequency domain output. The speed and position are calculated by the INS from acceleration. The acceleration is obtained from frequency measurements of the accelerometers output. For this reason an accurate and fast frequency measurement method is required. In this work, for this particular application, frequency measurement using principle of rational approximations is proposed. This technique allows to measure frequency in short time and with high accuracy, using a few electronic components. Due this properties, it perfectly fits requirements for UAVs.

Photodiode and charge-coupled device fusioned sensors

Machine vision methods to provide spatial coordinates measurement has developed in a wide range of technologies for multiples fields of applications such as robot navigation, medical scanning, and structural monitoring. Each technology with specified properties that could be categorized as advantage and disadvantage according its utility to the application purpose. This paper presents the photodiode and charge coupled device sensors fusion as the base for those systems with non-lineal behavior supported by artificial intelligence techniques, which require the use of information from various sensors for pattern recognition to produce an enhanced output.

Machine vision system errors for unmanned aerial vehicle navigation

The use of laser scanners as machine vision systems in Unmanned Aerial Vehicle (UAV) navigation offers a wide range of advantages, when compared with camera-based systems. As one advantage, the measurement of real physical distances can be mentioned, which results in a reduction of measurement times and thereby fast image processing of the UAV surrounding medium. In previous work, a novel laser scanner namely Technical Vision System (TVS) was presented, which implements a continuous laser scan for determination of 3D coordinates of any object under observation. Also previous work has shown the advantage, when using high-quality instead of low-quality DC motors as actuators for positioning the laser ray in the TVS field-of-view. However, the static friction in the ball bearings of the motor shaft leads to a residual error not zero for the angular error in steady state. Present paper introduces a new approach of estimating this residual error by use of a friction model. Thereby, the friction model is described and used for simulation of the residual angular error when controlling the DC motor in open-loop configuration and validated by experimentation results.