POPPEOVÁ Viera1,a, BULEJ Vladimír1,b, ZAHORANSKÝ Robert1,c, URÍČEK Juraj1,d
1University of Žilina, Univerzitná 1, 010 26 Žilina, Slovakia
aviera.poppeova@fstroj.uniza.sk, bvladimir.bulej@fstroj.uniza.sk,
crobert.zahoransky@fstroj.uniza.sk, djuraj.uricek@fstroj.uniza.sk
Keywords: parallel kinematic structure, NC control system, Sinamics S120
Abstract. This paper describes the design of machine tool based on the mechanism with parallel kinematic structure (PKS) called hexapod. The advantages of mechanisms with PKS predetermine them to the field of machining and robotics. Machine tool is designed like fully automated device contains system for automatic tool and part changing too. There was necessary to solve also a question of operation safety according to the real risk of injury. Some information about the design process, main requirements, the problems and the final solution can be found in this paper.
Introduction
Numerical control systems (NC or CNC) are used for the machines and mechanisms, in which the acquisition of specified position or motion along the defined path is needed. Most of them can be found in machine tools, forming and cutting machines, robots, handling etc. Apart from errorless program execution a comfortable operator interface is expected. Simulation module can be considered as a common feature of them. They are designed by several companies like Fanuc, Siemens, etc. in general. The main operating requirements are precise path planning, synchronized motion of multiple axes, sufficient power, high dynamic properties and accuracy. The role of machine’s control system is to ensure of programmed commands execution according to the specified algorithm, timing and precision.
Within the field of machine tools have their own special position the devices for high speed cutting (HSC). It appears to use the machines with parallel or hybrid kinematic structure for HSC better than machines with conventional serial kinematics. These mechanisms are characterized above all by higher stiffness and higher dynamic parameters (thanks to the reduced moving mass).
Few years ago also a research group at the University of Žilina was started to deal with this field.
During this period there were designed some construction concepts of PKS and different kind of simulation software for these types of mechanism. One of the well-known fully parallel manipulator in general is called Hexapod. Hexapod known as Stewart platform too, is multi-axis machining centre capable of full six degrees of freedom (DOFs) motion plus spindle rotation at the tool head.
This paper discusses about the application of hexapod mechanism in design of machine tool and about the control system designed special for it.
Structure and design of a machine tool
Designed machine tool can be divided into the 6 basic features or subsystems (fig. 3) [2]:
• main frame
• moving platform wit main milling spindle
• linear telescopic actuators with electrical motors
• system of automatic tool changing
• system of automatic part changing
• electrical switchbox with control and power part
In figure 1, there is shown a basic structure of designed machine tool, the connection points, places for part changing by operator, moving platform with main milling spindle, electrical switchgear, etc. The main feature is a mechanism with PKS (hexapod) located in the middle of whole machine tool.
Figure 1. The actuators, moving axis (A1 to A6) and Co-ordinate system (X, Y, Z) of hexapod mechanism inside a designed machine tool (Univesity of Zilina)
Description of moving mechanism. The “hearth” of a machine tool is a moving mechanism, in our case with parallel kinematic structure called hexapod (fig. 5). Main frame was designed as a welded construction made of thin-walled steel profiles square and rectangular sections. It contains six connection points for linear actuators connected to them by universal joints (each has 2 DOFs).
Main frame has to restrain any forces and couples propagated from moving platform to the frame by 6 independent guiding chains contained linear actuators. Each linear actuator can generate continuous force up to 4026 N by maximum linear velocity of extension 338 mm per second and accuracy under 0,01 mm. The dynamic behavior is significant. Therefore we decided to carry-out stiffness analysis of a main frame. The results of a simulation confirm that the stress and deformations are within a permitted range.
Figure 2. The actuators, moving axis (A1 to A6) and Co-ordinate system (X, Y, Z) of hexapod
mechanism inside a designed machine tool (Univesity of Zilina)
For transfer of forces from actuators to the moving platform and a base frame are used six upper and six lower universal joints with 2 or 3 DOFs. Moving platform is connected to six universal joints with 3 DOFs and it carry a main milling spindle with power 1,05 kW and revolutions up to 21 000 per minutes. This spindle is equipped by automatic tool clamping unit with pneumatic system for clamping and cleaning too. This configuration gives us totally 6 DOFs for positioning and orientation of the spindle within a defined workspace.
Architecture of designed control system
According to defined requirements was designed final conception of a control system for hexapod (fig. 3). The conception consists of professional control system which can control six motors 1FT7 according to the data generated by simulation program.
We had to pay attention especially to its ability to control six axes (motors) simultaneously with sufficient power and accuracy. Given requirements were fulfilled by several systems from different manufacturers. We decided to deploy the below-mentioned drive system made by co. Siemens - SINAMICS S120. Systems offered by co. Siemens were able to give us a complex solution which contains hardware components for drive control, software components as well as communication interfaces. This system is able to exchange data at the required qualitative level with sufficient speed, which makes this system more robust. It is not needed to adapt of system units (control system, motors, frequency invertors, display unit, a communication interface) in mechanical meaning and compatibility of signals as well. The structure of the controller and the drive subsystem is shown in figure 3. The main controller is a PLC Siemens S7-317T. The main drive unit is CU320 with SINAMICS S120.
Thus, the proposed structure of the drive control subsystem allows both, the fully automatic and manual mode too. In automatic mode is whole process controlled by master PC where the control program is running and it generates trajectories and motion for the defined kinematics. In the second case (manual mode) is system without influence of the master system and the programs are stored in the PLC.
Figure 3. Designed block schema of control system for hexapod machine tool
The main parts of control system for hexapod are:
• the superior (panel) PC, that contain simulation program,
• panel PC (graphic panel), used to manual control and displaying of input and output parameters
• control box containing PLC (Programmable Logic Controller) Siemens S7-300, control units and frequency invertors Sinamics for motors, graphic panel for displaying data (LCD) and input - output devices (I/O) with associated manual control,
• circuits for system of automatic part changing (APC) and automatic tool changing (ATC), hexapod motors M1-M6 and his action elements.
Figure 4. Simulation software for hexapod machine tool
Data from control PC are calculated in the simulation software (figure 4), or manually set by operator. Then they are sent to PLC via OPC server (Object Linking and Embedding for Process Control), which is a communication standard in industrial applications. There is used communication card and Profibus interface. I / O module contains 48 inputs and 48 outputs. PLC can control the power section and pneumatic circuits of the systems APC and ATC through this module. There are also connected the end sensors, incremental position sensors, safety devices such as doors’ sensors, the "Central stop" buttons or buttons for simple manual control into the I/O module. Basic data processed by the PLC will be displayed through graphic panel (19'' CD monitor).
All data processed by the PLC and also interpolation parameters are sent via PROFIBUS for motor control unit Sinamics, which directly controls all motors of Hexapod.
This concept is still just working and given that the project is in the process of solution, any occurred problems are solved simultaneously as well as the concept is subsequently modified by them.
a) b)
Figure 5. Structure of drive control system Siemens Sinamics S120 (a) [3] and structure of OPC Server objects (b) [2, 4]
Drive system Sinamics S120. SINAMICS S120 is a newly developed modular drive system (including frequency invertors) for demanding and high-performance applications. SINAMICS S120 provides powerful single drives and coordinated drives (multiple-axis applications) supporting vector or servo functions. It covers the 0.12 to 4,500 kW performance range. SINAMICS S120 can be combined with system SINUMERIK. All SINAMICS S120 components, including motors and sensors are connected via a common serial interface called DRIVE-CliQ. In figure 5 we can see the drive system structure containing a central control unit, power unit, motor drives and three electric motors.
System Sinamics S120 consists of the following modules [3]:
• Control Unit CU320, which is designed just for multi-axis control,
• AC power supply module, changes voltage DC to power the motor modules. Input voltage:
380 ÷ 400 V AC. The output voltage of 600V DC,
• Motor modules are the ultimate controls and are directly related to the motors. They are powered with DC voltage from the power module. For our case, the proposed three motor modules. Each module is able to control two motors.
Interface OPC server. Data transfer between the master system and PLC is provided by OPC interface implemented within the master PC. OPC (Object Link Embedding for Process Control) is a communication standard based on OLE / COM technology defined by company Microsoft. It provides the access to process data for applications connected in an industrial network. One of them can be for example a PLC controller (programmable logic controller) or any other control systems.
The primary objective of this communication standard is to provide an open interface for designers of industrial applications, so that they can easily communicate with different nodes within the industrial network. OPC does not replace the individual technologies of industrial networks which are still primarily designed for direct communication between devices in real time. It only represents an open platform for applications and automatic devices, which is an independent vendor-specific automation technology.
a) b)
Figure 6. Simatic NET – communication card PCI Profibus and software Simatic NET PC ACCESS [4] (a) and measured data in communication window of OPC client with OPC server (b).
OPC communication interface for Siemens Profibus is represented by package Simatic NET (Fig.
6 - a). It contains Profibus PCI communication card PC 5613 and OPC server software package PC ACCESS. If we want to use the OPC server and Profibus for communication between master system and PLC Simatic S7-300, it is necessary to:
• connect the card into the PCI slot of main control PC,
• install the SIMATIC NET software into the PC,
• and configure Profibus communication interface using the PG / PC interface.
After these initial configurations is OPC server and Profibus interface ready for using.
The OPC Server integrated into the Windows platform can work with any application designed in different programming languages (Delphi, C + +, Visual Basic, etc.) or SCADA systems (Supervisory Control and Data Acquisition) at the dispatcher level. Then the OPC server provide the communication and data transfer between the software application and drive control system of mechanism with parallel kinematic structure.
The Class "Siemens OPC DAAutomation" represented by SOpcDaAuto.dll library is available to any developer application after installing of Simatic NET (Fig. 5 - b). The connection to the OPC server can be programmed by referencing to this library in following steps:
• create an object MyOPCServer,
• establish a connection with OPC server "OPC.SimaticNET" by calling the Connect method
• create group class MyGroups,
• create a specific group MyGroup inside a group class MyGroups and set the parameters IsSubscribed and IsActive,
• create item class MyItems,
• assign each item "DB1, INT100" inside item class where the DB1 is data block number, INT (integer) define a variable type, and 100 is the address of the variable in memory. Or
"I8.1" for input (I-Input) and "O8.1" for output (O-Output), where 8 indicates a figure of eight, bit 1 indicates the specific bit within the eight,
• initialize the variable class using the method AddItems.
The application can communicate with the server via the OCP PLC and mutually exchange data in either synchronous or asynchronous mode directly after the initialization step. Therefore, the object MyOPCServer, group MyGroup supported events AsyncRead, AsyncWrite, SyncWrite and DataChange.
Synchronous communication is approaching the periodic OPC client to change data on the OPC server. If the last query was changed data is sent to the OPC client. Synchronous mode transmission channel more burdensome than asynchronous and furthermore does not follow rapid changes in values - if the frequency is approaching as 1 second and the data are changed several times per second, so in OPC client comes only the last value for a time interval of 1 s.
Acknowledgement
This article was created by the solution of project - code ITMS 26220220046: “The Development of Parallel Kinematic Structure Prototypes for Application in the Area of Machine Tools and Robots” supported by operational program Development and research, financed from European foundation for regional progress.
Conclusions
Hexapod can be considered as a general parallel mechanism with complex DOFs because it produces 6 DOF of a general rigid body motion. This article presented a specialized control system designed for machine tool based on parallel kinematic structure called hexapod. Currently the designed control system, simulatiuon software and algorithms are tested at the authors’ workplace.
Every part was developed according to the requirements defined at the beginning of this project.
References
[1] ĎURICA J.: Vývoj riadiaceho systému pre paralelnú kinematickú štruktúru. Disertation thesis, University of Žilina, Slovakia, 2009.
[2] www.siemens.com
[3] SIEMENS: Sinamics S120 – Commisioning Manual 11/2009. Siemens AG, 2009. ,p. 215, Order number: 6SL3097-4AF00-0BP0
[4] SIEMENS: Simatic S7-300 CPU 31xT Manual 07/2010. Siemens AG, 2010. ,p. 96, Order number: A5E01672599-02
Modeling and Analysis of The Biorobotics Mechanism
Ing. Ladislav Kárník, Ph.D.
VŠB – Technical University of Ostrava, Faculty of Mechanical Engineering, Department of Robotic 17. listopadu 15, 708 33 Ostrava-Poruba, Czech Republic
E-mail: ladislav.karnik@vsb.cz
Keywords: biorobotics mechanism, service robot, locomotion mechanism, analyse, simulation.
Abstract. The paper is intended to provide innovation learning texts for technical subjects in regards to biorobotics. The innovation is concerned with making learning texts electronic and supplementing the modulus specialized for other biorobotics mechanisms, including a simulation and analysis biorobotic mechanism.
Introduction
Scientific subjects oriented on biorobotics are specialized as to their content in several areas. The first area is specialized on defining and determining basic concepts in biorobotics. The next area describes mobile robots which use all types of bio-locomotion. The content is specialized on describing single structural units, the procedures for designing drives, practical applications, a description of 3D models, etc.
Because the area is presently developing quickly it is necessary to update the content. The third area is specialized on the creation of a 3D model of a biorobotics mechanism using the Creo system.
Attention is specialized especially on mobile robots with movement underwater which using crawl, and are used in the health service industry, etc. Creating 3D models connects areas which are involved in importing into the environment of the MSC/ADAMS system. They are practically in the environment of MSC/ADAMS simulation and analysis specialized on checking the basic parameters of the designed biorobotics mechanisms. Further they check the movement characteristics of robots over a defined terrain with obstacles. The results of the analysis done will be feedback for the modification of a 3D model in design phase of a biorobotics mechanism.
Tutorial texts specialized on the area of biorobotics
The special multimedia texts with the title „ The simulation and analysis of biorobotics mechanisms" will be placed on university nets in the form of html pages and they are intended firstly for the graduate study subject „Robotics" at our Technical University of Ostrava , the Faculty of Mechanical Engineering. In terms of studying these subjects there will be multimedia texts presented as special background papers for subjects such as, for example „Biorobotics", „Service robots", „Robotization in non - engineering areas", etc. These multimedia texts are possible to be used for students of the mechanical faculties of other technical universities in the Czech and Slovak Republics, specialized on the study, development, research, design and checking of the proposed 3D model specialized on biorobotics, service robotics, mechatronics, etc. These texts can be used by specialized workers in the industry too, who are engaged in robotics (biorobotics), etc. Furthermore, they can be appropriate as study material for experimental workers from this field and other specialists from the wide public.
In multimedia texts they are summarized as a universal contemporary piece of knowledge from the specialization biorobotics which is needed in phase of designing and developing a product. They present specific selected examples of a 3D model of a biorobotics mechanism created in the Creo system. Examples represent a single type of design of a biorobotics mechanism according to type of locomotion. Furthermore, it solves the problems of analysing and synthesizing the designed 3D model in the simulation system MSC/ADAMS in specific examples. The results of the simulation are presented in the form of animation, graphs, etc.
The multimedia texts offer needed information for designing a biorobotics mechanism including a summary of a presently applied design in an indoor and outdoor environment. From the point of type locomotion it is concerned with the walking and jumping biorobotics mechanism, with sneaking movement, flying robots, swimming robots and special robots. In more detail it defines the problems of the biorobotics mechanism with crawling movement, flying robots, moving underwater and using prosthetic upper and lower limbs. Attention is devoted to a biorobotics mechanism with an artificial muscle and anthropomorphic gripper too [2, 3].
Students have the possibility of using practical examples of 3D models created in Creo systems and MSC/ADAMS systems or designs created to verify theoretic knowledge and to design their own constructions during semester projects and diploma work.
From the point of the content of multimedia texts it is possible to classify the main chapters according to their name:
• Classification and the basic concepts of a biorobotics mechanism.
- Models of biorobotics mechanism - Walking robots
- Jumping robots - Climbing robots
- Mobile robots with crawling movement - Flying biorobots
- Robots moving underwater - Atypical construction robots.
• Checking models of the biorobotics mechanism.
• Anthropomorphic gripper.
• Artificial upper and lower limbs.
• Biorobotics mechanisms specialized in the areas of health care.
Innovation and new approaches
The problems have not been worked out yet in a compact form in the form of available multimedia texts. The content completion of recently prepared multimedia texts include upgraded chapters about new contemporary pieces of knowledge and supplementary information about new chapters. This expansion is concerned mainly with robots with crawling movement, the of application artificial muscles in biorobotics mechanisms and anthropomorphic grippers. The new direction is concerned with checking the modulus of service robots in the MSC/ADAMS system and the creation of a modulus for underwater robots. There are newly processed findings from the areas of artificial upper and lower limbs and biorobotics mechanisms applied in health service.
The new approaches to teaching technical subjects specialized on biorobotics presents different sorts of tutorial materials. In multimedia texts there are references to Internet pages which solve existing problems abroad, pictures, videos, etc. Furthermore it includes pieces of knowledge obtained while completing projects at the Department and diploma and other works. The texts include a series of specific examples of the modulus of a biorobotics mechanism including a practical analysis and simulation with the presentation of exemplary procedures and instructions [6, 7].
The total content completion of multimedia texts is usable in theoretic teaching and practical teaching during exercises. The prepared multimedia texts correspond to the required standards and it is possible to use them for the distance form of studies. The presented choice of examples constitute only a possible solution from a wide spectrum of possible applications [6, 7].
Areas of practical use
The range of the practical usage of the theoretical pieces of knowledge which is presented in multimedia texts is specialized on work with a physically made model. Whereas, in the Department of Robotics there are several physically made prototypes of the biorobotics mechanism which can