Design and manufacture of highly passable special-purpose mobile robots using modern CAD systems..
Design and manufacture of highly passable special-purpose mobile robots using modern CAD systems
Authors: Oleg Maslov, Andrey Puzanov, Konstantin Kuvanov, Oleg Platov (OAO SKB PA, Kovrov)
The mind undoubtedly seems weak when we think about the tasks facing it.
A. Einstein
Among the many activities aimed at ensuring the safety and security of society, issues related to the prevention of terrorist attacks using explosive devices (ED) aimed at the destruction of civilians, as well as the destruction of objects of human activity, occupy a particularly important place. Experts around the world are looking for effective ways to combat and counter terrorism, one of which is the development of mobile robots (MR) designed to detect and destroy ED.
It should be noted that the tasks of designing and creating such robots are quite successfully solved by foreign developers, as evidenced by the wide range of special equipment they offer. The advanced development of robotic equipment abroad is primarily due to extensive experience in the fight against terrorism. For modern Russia, such experience is relatively small. However, the events of recent years have forced domestic specialists to concentrate their efforts in the field of designing and manufacturing special-purpose mobile robots. In a short period, a number of domestic models of robotic equipment have appeared, differing in class, purpose and composition of the actuator equipment. «Vezdekhod-TM3» is one of such models, belonging to the ultra-light class of robots, the main purpose of which is visual and acoustic reconnaissance of terrain, premises, vehicles, inspection of hard-to-reach places, detection and destruction of explosive devices.
The mobile robot is capable of moving on slightly rugged terrain, overcoming threshold obstacles, water obstacles, moving on snow and grass. To increase maneuverability when the robot is working in a confined space (inside buildings and structures), an onboard turning method is used. The robot's working equipment includes a manipulator with two degrees of freedom, two-stage video camera guidance mechanisms and a hydrodynamic destroyer. Extending the telescopic rod allows you to inspect hard-to-reach places (the bottom of a car, trash cans, etc.), examine and destroy suspicious objects.
The customer of the MR was the CST of the FSB of Russia. The work was entrusted to specialists from the Research Institute of SM of the Bauman Moscow State Technical University (Moscow), who were responsible for creating the control system, as well as specialists from the Special Design Bureau of Instrument Making and Automation (JSC SKB PA, Kovrov), who were responsible for developing the MR design and preparing the design documentation for subsequent serial production of the product at the Kovrov Electromechanical Plant (JSC KEMZ, Kovrov).
The team of JSC «SKB PA» was faced with the task of developing the MR design in the shortest possible time, which meets the requirements of the technical specifications (TS), and developing and issuing design documentation (DD) for serial production of the product. It is obvious that the development and production of the product at a high quality level would be impossible without the use of modern software products.
One of the important stages in the formation of the future appearance of the MR was the development of its preliminary three-dimensional model in the Autodesk Inventor Series (AIS) environment of versions 5.3 and 9, as the most effective in terms of the simplicity of designing complex elements of the robot, as well as in terms of the ability to export 2D drawings to the AutoCAD environment. With the help of AIS, work was carried out to determine the main design features of the units and mechanisms of the future robot, issues related to the layout and placement of actuators, elements of the on-board remote control system, the main and auxiliary equipment of the robot were worked out (Fig. 1).
Fig. 1. Three-dimensional model of a mobile robot,
developed in the AIS9 environment
In the process of designing the manipulator and the MR guidance mechanisms, various AIS9 capabilities were used, such as adaptive design, positional assembly representations, and flexible nodes. This made it possible to work out the most important positions of the actuator equipment, obtaining a complete picture of the intersections of nodes and parts during operation, and to avoid their possible collisions, as well as to estimate the overall dimensions of the MR during the operation of the actuator equipment. In parallel with the development of the main version of the MR, a search was underway for alternative solutions for the design of the chassis of the robot, manipulator, and auxiliary equipment (Fig. 2, 3).
Fig. 2. MR vehicle
with variable geometry of the wheel drive
Fig. 3. Alternative version of the MP manipulator
In accordance with the requirements set by the customer for the transport module MR, it should be a means of delivering executive equipment to the place of the operation, possessing small weight and size characteristics, low energy consumption of the executive drives of the wheeled propeller, high cross-country ability and maneuverability, capable of withstanding impact loads. Fulfillment of these requirements required the developers to carry out a whole range of calculation and design work. It was based on our own methodology for designing high-cross-country wheeled vehicles in combination with the MSC.visualNastran.4D 2004 software environment. The developed methodology allowed:
- to supplement and clarify existing methods of designing ground vehicles (TV), taking into account the features inherent in MV of the ultra-light and light classes;
- to determine the geometric parameters of the vehicle based on the possible relief of the supporting surface;
- to carry out traction-dynamic calculations of the vehicle taking into account the type and characteristics of traction drives, loading conditions of the wheels of a multi-axle vehicle, environmental conditions in which the MV operates, to determine the energy consumption of the vehicle for movement and maneuvering;
- to study the dynamic stability of the future MR during its interaction with the supporting surface, to assess the influence of the vehicle parameters on its stability;
- to justify the choice of the type of supporting structure of the TM based on the volume of the elements of the SDU to be placed, the location of the attachments, the type and type of wheel drives.
An integral part of the methodology are mathematical models developed using computer modeling tools (for example, using the Matlab, Simulink simulation programs), which made it possible not only to quickly and efficiently carry out design and calculation work to determine the main parameters of the MR vehicle, but also to conduct a number of scientific studies (Fig. 4, 5). At the same time, the required studies were carried out taking into account the nonlinearity of the forces acting on the vehicle wheels, which made it possible to avoid distortion of the results obtained due to simplification of the models in order to obtain their analytical solution.
Fig. 4. Mathematical model for studying the
dynamic stability of a MR vehicle
when interacting with a
single obstacle
Fig. 5a — disturbing effects
acting on the vehicle when hitting an obstacle;
Fig. 5b — linear acceleration of the vehicle when driving on asphalt;
Fig. 5c — linear velocity and displacement of
the vehicle when interacting with an obstacle;
Fig. 5d — distribution of normal reactions of the support surface on the wheels of the vehicle on an incline
Fig. 5. Examples of the results of calculation and design
works carried out on the basis of the developed mathematical
models:
To carry out design work on selecting the final type of vehicle propulsion and modeling the operation of the actuator, the preliminary 3D model of the MR was transferred to the MSC.visualNastran.4D 2004 environment (Fig. 6).
Fig. 6. Exporting a 3D model of a mobile robot
to the MSC.visualNastran.4D 2004 environment
One of the most difficult tasks facing the developers was to select the optimal chassis that would meet the requirements for overcoming typical obstacles. To obtain the optimal type of propulsion unit, it was necessary to develop three-dimensional models in the AIS9 environment, which were subsequently exported to MSC.visualNastran.4D 2004 for the purpose of conducting their comparative modeling, including:
- modeling of the classic wheel propulsion unit (Fig. 7);
- modeling of a wheel-walking propulsion unit;
- modeling of a small-sized tracked mover;
- modeling of a wheeled mover with independent swinging suspension and twin wheels;
- modeling of a wheeled mover with forced swinging suspension and twin wheels (Fig. 8);
- modeling of the strength characteristics of various mover options when interacting with the supporting surface (Fig. 9).
Fig. 7. Simulation of the movement of a mobile robot downhill
Fig. 8. Simulation of overcoming a typical
obstacle for vehicles with different types of propulsion
Fig. 9. Modeling of dynamic strength
characteristics of the gearbox housing of a wheel
mover with a swinging suspension
under various conditions of overcoming an obstacle
The simulation results showed that the wheeled propeller is the most acceptable option for the ultra-light class MR vehicle, due to its small weight and size characteristics in combination with sufficient cross-country ability and simplicity of the design scheme. At the same time, the use of variable geometry in the design of the wheeled propeller does not always improve the cross-country ability of the MR and can lead to a significant complication of both the vehicle and the MR control system as a whole. Therefore, an all-wheel drive wheeled propeller with actuators located inside the vehicle body was chosen as the main option.
The most difficult and interesting part of testing the operation of the actuator equipment was the modeling of a shot from a hydrodynamic destroyer when simulating the destruction of a VU. Simulation of a shot in the MSC.visualNastran.4D 2004 environment by two types of destroyers of recoilless and recoil action allowed us to evaluate the impact of impact loads on the MR (Fig. 10).
Fig. 10. Modeling the behavior of the MR when firing a VU destroyer
Based on the results of the calculation and design work, the deficiencies of the preliminary design of the MR were identified and eliminated, the expected functional capabilities of the MR were confirmed, the traction characteristics of the developed actuators of the wheel mover, manipulator and guidance mechanisms were checked, and the reactive rigidity of the design was increased. The finally approved version of the MR design made it possible to move on to the volumetric stage of preparation and release of the design documentation with subsequent preparation of production for serial production of the product, which we will discuss in the next article.
At the stage of developing the technological process for manufacturing the MR, design features were identified in a number of parts that did not allow them to be manufactured using the existing equipment and cutting tool. The design of these parts required the use of electrical discharge machines, which the company does not have, or the use of a special cutting tool, the manufacture of which is long, expensive and extremely labor-intensive.
To solve this problem, it was decided to manufacture these parts on CNC machines equipped with a rotary device (with 4 controlled axes). When developing control programs for processing, the EdgeCAM 9 CAM system was used, into which 3D models of parts created in Autodesk Inventor were loaded. This allowed for quick regeneration of the control program for CNC machines, due to the close integration of these systems, so EdgeCAM 9 automatically redefines the cutter trajectory in accordance with changes in the 3D model, which was impossible when working with two-dimensional geometries. (Fig. 11, 12).
Fig. 11. Blank of the manipulator support
with the contour of the future part in the EdgeCAM 9 environment
Fig. 12. Visualization of milling rough
machining of the manipulator support in EdgeCAM 9
The translation of the geometry of parts from AIS9 to EdgeCAM 9 was carried out with the preservation of associative links. This allowed for the rapid regeneration of the control program for CNC machines, thanks to the ability of EdgeCAM 9 to automatically redefine the cutter trajectory according to the modified 3D model, which was impossible when working with two-dimensional geometries.
In parallel with the creation of the CP, work was carried out on the design and preparation of a two-dimensional design documentation for the MR. The preparation of the two-dimensional design documentation was carried out using the software of the company «Intermech» (Minsk), intended for automated design and technological design. This software allows design and technological departments to work in a single information space and significantly accelerates the process of technical preparation of production. The preparation and design of the MR drawings were carried out in the CadMech2000 environment, which is compatible with the most common CAD systems and contains a wide reference and information base and a base of standard elements of parts and assembly units (Fig. 13).
Fig. 13. Drawing of a mobile robot in the CadMech2000 environment based on AutoCAD 2002 (side view)
Fig. 14. Electronic copies of the CD
for the mobile robot in the Search8 archive
The required views, sections and cross-sections were prepared in the AIS9 environment, saved in DWG format and then formatted in accordance with the Unified System for Design Documentation (ESKD) in CadMech2000. The prepared DD was submitted to the Search8 electronic archive, which serves as a repository for any type of electronic document and is the main link between the design, technological and management services of the enterprise (Fig. 14).
The final stage of the work was the manufacture of a prototype MR and its subsequent testing in order to check and confirm the operability of both the entire sample as a whole and the units and mechanisms included in it (Fig. 15, 16). During the testing, the obtained design results were also practically confirmed and, consequently, the correctness of the developed design methods.
Fig. 15. Destruction of an object simulating a VU
Fig. 16. Mobile robot «Vezdekhod-TM3»
In conclusion, it should be said that the use of software from AutoDesk, InterMech, PathTrace, MSC allowed not only to significantly reduce the development time of the MR, eliminate unnecessary material costs for the manufacture of a model, development and implementation of design documentation into production, but also to implement a systematic approach in the field of designing special-purpose mobile robotics, to carry out the entire range of necessary technical calculations, and to perform scientific research. All licensed software was purchased from the Russian Industrial Company (Moscow), technical and advisory support was provided by specialists of this company throughout the entire period of implementation and use of the packages.
You can get detailed consultations and demo versions of the software from specialists of the Russian Industrial Company:
in Moscow (095) 744-0004, Yekaterinburg (343) 359-87-59, St. Petersburg (812) 164-54-08. Centralized order acceptance service: info@cad.ru, tel. (095) 744-0004.
CAD/CAM/CAE Observer
Issue # 2 (20) 2005