Design of mechatronics application.

Djikic, Mahmud ; Cohodar, Maida ; Kulenovic, Malik 等

1. INTRODUCTION

Analysis of the total time required for production of workpieces in the typical metal machining batch factory shows that only 5% of its time has spent on the machine tool (Groover, 2007). But of this 5%, 70% is the time required for feeding machine, moving tool in contact with workpiece, positioning, clamping and other auxiliary activities. In other words, 98,5% of the total time of a workpiece is nonprocessing time. On the other side, 40% metal workers are involved in processes of component placements and sub-assembly operations; machine tool, conveyors, die-casting machine, jigs and fixture and other processes loading and unloading; machine-to-machine transfer; handling dangerous or toxic materials; paletisation and package, assembly operations, etc.

Automation of such processes plays very important rule. Firstly, automation provides decreasing of human-worker participation in realization of processes, which finally leads to:

* Increasing of productivity,

* Improving of product quality (accuracy, repeatability and consistency),

* Integration with automation,

* Continuous availability for work,

* Decreasing of production costs and

* Humanization of working places which is especially important in the case of hazard environment.

Attention in the paper is devoted to design 'pick and place' robot. Its function is automation one of above-mentioned activities--transfer of component from one to the other storage. The paper presents the integrated so-called mechatronic approaches to design of robot system involving electronic, pneumatic component, sensors and computing. In mechatronic applications, a bulky mechanical system has replaced by a much more compact microprocessor system, which is readily adjustable to give a greater variety of programs (Bolton, 2007). This leads to cheaper, simpler, more reliable and grater flexible products than their predecessors. There are two approaches to design control system of products (Bradley at al.,1996):

* using embedded real-time microprocessor system and

* using data processing application.

[FIGURE 1 OMITTED]

In the first one, control system can be realized by microprocessor system, which is subsystem of completed products. In the case of data processing application, microprocessor is built into an environmental designed for typical computer system such as personal computer or industrial microprocessor system--PLC, which is in most stand-alone devices. Control system of 'pick and place' robot is realized on the second proposed way using SIEMENS SIMATIC S7-200 Micro PLC. 'Pick and place' robot, described in the paper, is developed for education purpose, as well as research of different parameters--controlling pressure and position, activity and timing of control units, etc., and is placed in Laboratory of Automation and Robotics at Faculty of Mechanical Engineering in Sarajevo. Designer of system is the first author of the paper. In (Hesse, 2001) you can find a number of examples of pneumatic applications.

2. DESIGN OF 'PICK AND PLACE' ROBOT

Purpose of 'Pick and place' robot (Fig.1) is part transfer from one to the other storage. On this way, it bridges the gap between highly automated processes of machining and component handling. Transfer of components from one to the other place is repetitive operation, performed often under unpleasant and sometimes dangerous working conditions requiring little skill worker. Automation of such processes provides integration with other automated subsystems of the factory.

[FIGURE 2 OMITTED]

'Pick and place' robot system consists of four cylinders, as shown in Fig.2. Cylinder A transfers parts from storage S1 to the place below gripper G. Cylinder B lets down gripper G, which grasps part. After that, cylinder B lifts workpiece in upper position and then cylinder C translates component to position over storage S2. When cylinder B set down component, gripper G releases it.

All cylinders are double acting, which piston motion is bounded with proximity sensors. Festo's proximity sensors SME-8-S-LED-24 are mounted on cylinder's slots. They are contactless sensors with resistors, which are sensitive to magnet-fields. Magnet mounted on the cylinder piston changes the switching signal status, as soon as the cylinder piston moves around of sensors. Diffuse sensor with background suppression (Baumer FHDK 10P1101/KS35) detects presence of workpiece in storage S1. To start 'pick and place' robot a pushbutton switch is included in system. Finally, system is also equipped with four solenoid valves.

3. CONTROL SYSTEM

The SIMATIC S7-200 Micro PLC, design as stand-alone CPU, coordinates all actions of transfer of components. It offers real-time control with Boolean processing speeds of 0,37 (is per instruction. (http://www.automation.siemens.com)

Between two possible programming options for connecting computer to S7-200, which SIEMENS provides, a direct connection with USB/PPI Multi Master cable RS485 is applied herein. The S7-200 is based on central processing unit CPU222 with 8 in/ 6 out and in order to cover 'pick and place' robot application which requires 10 inputs and 8 outputs, it is expanded by adding I/O expansion module EM223 with 4DI/4DO.

4. PROGRAMMING OF SYSTEM

All applied sensors are binary--0 and 1 to indicate whether or not a cylinder piston has reached the end position. The inputs to the controller are signals from eight limit switches, the pushbutton and the diffuse sensor. The central processing unit (CPU) of PLC executes the various logic and sequencing functions depending on state of inputs as well as program instructions determining the appropriate output signals. They are on/off signals to operate solenoid valves which provide corresponding actions of cylinders (Table 1).

Sequences of actions of 'pick and place' robot with denoted activated sensors and produced outputs are shown in Fig.3.

The programming method, used in the paper, is based on the ladder diagram. The V. 4.0. STEP 7 MicroWIN SP2 programming package provides user-friendly environment to develop program sequences (System Manual, SIMATIC S7200; Berger, 2006).

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

Start position of 'pick and place' robot is depicted in Fig.2. Sensors I0.2, I0.3, I0.4, I0.5 and I0.1 with condition that there are parts in the storage, are activated and produce 1--signals. This start position is called home position and it is represented with network 1 on ladder diagram, Fig.4. In this start position when start pushbutton is activated for start operation of 'pick and place' robot system, six normally open contacts, arranged in series, will be closed and output will be energized.

Such designed system can be integrated very easily in complex automated production system. Also, if it is required, system can be simply reprogrammed for different sequences of activities.

5. CONCLUSION

The main purpose of the paper is to point out an importance of mechatronics approach to the design of technical system. Replacing a bulky mechanical control system with a microprocessor system gives an answer for mechanical problem with a little space.

Mechatronics approach based on integration of computer digital technique through electronic and electric interfaces with mechanical system leads to flexible, compact, modular, cheaper, simpler and more reliable solution.

These mentioned properties of mechatronic solution are considered on the example of 'pick and place' robot system with SIMATIC s7-200 MicroWin PLC as control system. It is developed (by M.Djikic) and placed in Laboratory for Automation and Robotics at Faculty of Mechanical Engineering in Sarajevo. On this way, students have a very nice example and opportunity that, through exercises, would be introduced with basis of mechatronic systems and their programming.

6. REFERENCES

Berger, H. (2006). Automating with SIMATIC: Controllers, Software, Programming, Data Communication Operator Control and Process Monitoring, Wiley-VCH; 3 Revised edition; ISBN-13: 978-3895782763

Bolton, W. (2004). Mechatronics, Electronic Control Systems in Mechanical and Electrical Engineering, Prentice Hall; 3 ed., ISBN-13: 978-0131216334

Bradley, D.A.; Dawson, D.; Burd, N.C. & Loader A.J. (1996). Mechatronics, Electronics in products and processes, Chapman & Hall; ISBN: 0 412 58290 2

Groover, M.P. (2007). Automation, Production Systems, and Computer Integrated Manufacturing, Prentice Hall; 3 ed., ISBN-13: 978-0132393218

Hesse, S. (2001). 99 Examples pf Pneumatic Applications, FESTO AG & Co., D-73734 Esslingen, Germany, www.festo.com

http://www.automation.siemens.com/bilddb/index.asp7aktPrim =0&nodeID=5000646&lang=en&foldersopen=-1225-1224-1223-1222 -1226-1228-1229-1231-&jumpto=1231 Accessed: 2008-07-2

System Manual Edition 08/2005, SIMATIC S7-200 Programmable Controller,

Tab. 1. The outputs from the controller

 Outputs

Actuator Symbol - +

Cylinder 1 A Q 0.2 Q 0.0
Cylinder 2 B Q 0.4 Q 0.1
Cylinder 3 C Q 0.5 EQ 1
Gripper G EQ 0 Q 0.3