Abstract
Positioning technologies are useful in a great number of applications, which are oriented for pick and place robots, manipulation of machine tools, especially on machines oriented for artificial vision and detection systems, such as vision-guided robotic systems and object existence in a limited environment. Due to the high demand of those applications, this chapter presents digital control theory application using a laser positioner, which obtains 3D coordinates in a defined field of view. Using the LM629N-8 motion controller, representing the main digital controller for the motion task of the laser positioner as an active element, which is analyzed via modeling and simulation using Matlab-Simulink. Additionally, this chapter focuses on some of the principal sources of uncertainties that exist in a laser scanning system and mainly on the receptive part of such system, which is driven by a brushed DC motor. The processed signal will be analyzed in different environmental conditions to analyze how it is affected by the instability characteristics of this main actuator.
TopIntroduction
In accordance to positioning technologies which nowadays represent a principal part for vision-guided mobile robotics, this chapter explains methodologies and techniques to obtain three-dimensional coordinates using a vision system. The conception of a single-sensor high speed and low cost scanning system called Technical Vision System (TVS) to obtain data of space coordinates of any surface of an object under observation using a Laser Positioner (LP), which defines accuracy measurements when positioning a laser beam in the mobile robots. Especially, this chapter presents detailed information about the Technical Vision System (TVS), which has two principal parts, namely the Laser Positioner (LP) as the active element and the Scanning Aperture (SA) as the passive element. Both systems collectively obtain data about the limited surrounding environment in a field-of-view of TVS using 3D laser mapping. The TVS has different applications like automatic inspection, quality control of industrial processes, health monitoring of crops and structures.
Thus, this chapter focuses on the components LP and SA. The Laser Positioner is constituted for different components particularly, this system works with an implementation in closed-loop (Atkinson, 2012), that is a precision motion control which integrates the embedded digital controller (Wescott, 2006), LM629N-8 made by Texas Instrument. In fact, this controller represents the main device to execute arbitrary angular displacements of the actuator, that is a high quality brushed DC motor of the LP-TVS. Also this controller is commanded by a Graphic User Interface (GUI) developed in LabVIEW using an Arduino Mega as gateway between the LM629N-8 and the GUI. The GUI includes all available commands of the LM629N-8. The Scanning Aperture (SA) principles and elements are then presented as a useful way to receive signals generated by a light emitter sources, such as the LP first presented in this chapter. In addition to the utility of the SA in Laser Scanner Systems, uncertainty factors of the driving conditions in the SA, due to the signal processing characteristics of the system, may affect the resolution of the detected coordinate (angle). Thus, a closed-loop control system is proposed for the SA DC motor. The final part of this chapter shows experimentation with both the LP and the SA. Therefore, this chapter has been written for engineering students, engineers, and new researchers that are interested in machine vision applied for mobile robotics taking into account, the operation of the principal components of an optoelectronic device (Bass, et al., 2009) named Technical Scanner System.
Background
Digital Control Theory Application (DCTA) and Signal Processing (SP) are topics considered for Discrete-Time Systems (DTS), due to those analyze and interpret mathematically physical phenomenon behavior. With DCTA and SP new knowledge about approaches and limitation of DTS is created. Currently, the tools used in DCTA are more capable to perform complex tasks in comparison as they were before. Examples of these tools are some single-board computers such as Raspberry Pi, Jaguar One, Orange Pi, pcDuino4, among others. Furthermore, new Integrated Development Environments (IDE’s) maximizes the productivity of the designer during the software development for high-performance microcontrollers such as the Intel® Quark™ microcontroller D2000, Arduino Ethernet, Arduino DUE, Arduino Mega 2560. Due to the powerful features of these processors it is possible to develop complex control algorithms to handle automatic systems. The SP is necessary for control methodologies, due to signal processing operations main task is to convert physical signals to electric signals which can be fed back to the automatic systems. This can be done by the implementation of different elements such as filters, transducers, analogic-to-digital converters, as well as mathematical, computational algorithms and statistical methods (Madisetti, 2009). The wide variety of tools and methodologies used to SP and DCTA gives the opportunity to develop more specialized, efficient and low-cost systems. Thus, in this chapter the DCTA and SP are applied in the development of the TVS used for Mobile Robotics.
Key Terms in this Chapter
Trapezoidal Velocity Profile: This is a defined concept as an internal control variable in some precise motion controllers, where the acceleration and deceleration have equal rates, the trapezoidal velocity is integrated mathematically to obtain the final angular position.
Specular Reflection: Is the mirror like reflection, also known as regular, considered this way when any kind of wave (in this case light), reflect as a mirror from a surface.
Microcontroller: This is a digital embedded electronic microcircuit generally is packaging, it contents various modules to process basic or complex tasks due to has a central process unit, memories, inputs/outputs ports, and like minimum a system bus, to run developed algorithms to give some specific solution. Currently, this device has a great relationship between performance and low-cost.
Active Node (of the System): The active node of the system is the one in charge of emitting a signal, in the TVS case the active node y emitting a laser beam, that works as primordial element for the triangulation.
Power Driver: This electronic circuit which represents a switch-mode power amplifier for driving DC Motors. It is essential to transmit power (voltage nominal and electrical current) for the applied actuator in a motion control system.
Diffuse Reflection: Phenomenon when light waves reflect from a surface in a scattered way in several angles rather than just one (specular).
Mixed Reflection: A reflection that is both diffuse and specular, this is the kind of reflection that most of the material present.
Passive Node (of the System): This node is considered passive due to always be waiting for a signal to be received, this subsystem of the TVS works as the feedback for the entire triangulation.
Laser Positioner: This is a capable optoelectronic device to move a laser beam in a precise form, using different methods, these Laser Positioner are used in Laser scanning systems as a principal active element of them.
Motion Control System: This is integrated by a group of different components, these components are of different disciplines such as mechanical, electronic, control, and programming, to obtain a control variable, which is elemental in mechatronics discipline due to these systems are responsible to process control signals to move joints and mechanical systems.