Clamping fixtures in cell manufacturing.

Kostal, Peter ; Matusova, Miriam ; Charbulova, Marcela 等

1. INTRODUCTION

Cell manufacture is characterized by wide economical effect, which is nearly the same as economical effect of mass or high series production. Cell production also ensures flexible change of manufacturing assortment, which can be changed following to the market requirements.

Modern production cells has in many aspect inbuilt intelligent control system on different level. This intelligent control system ensures better using of such devices. It also ensures manufacturing costs minimization, as well as manufacturing quality increasing. Such intelligence in these days includes various control algorithms. Such algorithms are able to optimise manufacturing cell activity following to the various actual external factors. These factors are influencing to the manufacturing process inside of the cell and in connection with manufacturing process, can these factors influence to the whole factory and its parts. Very important parts of intelligent manufacturing cells are its peripheral devices, such as for example clamping devices. These devices have to design, that they are not able to limit abilities of whole manufacturing cell. Better say, whole design process of all peripheral devices have to simple integration of new intelligent functions in to the manufacturing cell and also to the manufacturing process. Such peripheries have to be equipped by proper actuators and sensors to be able effective cooperate with manufacturing cell control system. We are building such manufacturing cell on our department. This cell will ensure manufacturing and assembly operations and we are also developing some peripheral devices such as clamping device with some intelligent functions.

2. MODULAR CLAMPING SYSTEM

The modular clamping system contains a group of normalized parts. From these parts is possible making the compact unit for needed part clamping. The clamped part is usually more complex.

The standard structure of modular clamping system is defined by part list. Number and type of used parts is changeable according a concrete disposition, workpieces set, manufacturing conditions and manufacturing organization.

[FIGURE 1 OMITTED]

The modular clamping system parts construction is optimized to part number minimizing and maximizing of usability. According of this optimization we achieve the short upsetting time of clamping fixture and higher rigidity of clamping too. The final effect of these achievements is higher accuracy of machining. (Matusova & Hruskova 2007) The using of modular clamping systems is one from more important rationalization process in flexible manufacturing. These kind of clamping fixtures are successfully used in industry and helps achieve more effective manufacturing (Fig. 1). Their advantages are shown mainly in small and medium batch production. Possibility of their usage is given by its flexibility. (Danisova et al 2006)

3. INTELLIGENT CLAMPING FIXTURE DESIGN

A robotic work place is realized in laboratories of institute. This work place is equipped by SMC industrial robot with storage system. Both this systems are connected with feeding rotary device. The system is equipped by automated gripper changing system and it is also equipped by pneumatic clamping system, which will contain some basic functions of intelligent clamping system.

Pneumatic driven clamping device will be placed in the working area of industrial robot. This device will be designed by these requirements:

* Clamped dimension to the 70mm--there will be no manipulation with parts, which will overreach this dimension. Robotic arm bearing capacity is 100N.

* Synchronized clamps movement--this requirement is necessary because of rotary parts clamping

* Open clamps signalisation--to prevent manipulation with clamped part, or to prevent putting the part in the fixture, when there is one part already

* Part clamped in fixture device signalisation--prevent to the collision of part which are placed in the fixture and which are gripped in robotic arm

* Clamped shapes variability--clamping of various shapes--cylinder, square

* Using of changeable clamps--clamps will be changed with help of the gripper

* Proper clamps on the fixture signalisation--to prevent clamping of oval shaped part with clamps not used for oval shaped parts

* Clamping force regulation ability--it is necessary to use various clamping force for various types of pars. According to these requirements was chosen the pneumatic base for proper clamping device. The basic building element of the fixture will be double clamp fixture with marking MHF2. Firm SMC produced the fixture. The design of the fixture is known as design with synchronized, parallel driven clamps movement. Chosen fixture has maximal clamping dimension 80 mm. More precisely we chose clamping fixture MHF2 20D2 (Fig. 2.)

[FIGURE 2 OMITTED]

Fixture device is pneumatic driven. Two double acting cylinders realize fixture acting. One pressed air input will open the clamps and other one input will close them. Clamps synchronization movement is ensured by geared transfer mechanism. One or two sensors can monitor clamps position. Sensors can be mounted to the fixture with help of grooves. Chosen pneumatic actuator advantages are for example simple design, safeties, reliability, vide clamping dimension, undemanding maintenance, high lifetime small sizes and low costs. Working pressure can be set up from 0,1 to the 0,7 MPa, what means that clamping forces will rise from 30N to the 220N on each clamp. (Danisova & Zvolensky 2006)

3.1 Clamps presence scanning

Also design of monitoring system of claps presence on the fixture body, was created following to some conditions. Most important conditions influenced to the design are sensor sizes, sensor simplicity, its reliability, lifetime, rapid and exact scanning.

For actual needs (it is only important to scant clamps presence, not the type of clamps) is the most proper solution, using of micro switchers. Micro switchers will be placed at clamps holder. Biggest advantage of such scanning is price of micro switchers. Sensors will be placed on the pneumatic fixture body. But we cannot do any holes in to the actuator body, that why switchers will be glued. In the future, after design finishing phase, after short fixture running, switchers will be replaced by other more complicated and effective system, which will ensure the clamps presence scanning. (Kostal & Velisek 2007)

3.2 Workpiece presence scanning

There are different ways how to scan presence of work piece in the fixture clamping area. Various types of sensors such as optical sensor, inductive sensor, camera scanning system and so on can scan this position. Most effective solution is using of optic sensor, which will be placed in the middle of clamping dimension. Big advantage of optic sensor against to the inductive sensor or against to the capacity sensor is its longer scanning range and there is also a possibility of various material kinds scanning. Camera scanning systems are for this solution vain complicated. For this concrete solution there will be used optical reflex sensor with axial optic, with advantage of optical beam regulation.

[FIGURE 3 OMITTED]

Optical reflex sensors are working at principle of optical performance scanning. They are comparing set optical performance value with actual value coming from the environment. Such sensors are able to scan object of various sizes and complexity. Sensor will be placed on the fixture device with help of assembly clip, which will be glued on the side of the fixture device body. (Kos al et al 2007)

4. CONCLUSION

Intelligent clamping systems can help to increase reliability of some operations. Automated manufacture can be done more flexible. Such clamping systems are more expensive and complex as classical fixtures, because they have integrated some automated control and measuring units. Intelligent clamping systems are able to prevent to some failures, which are created during the production in automated manufacture and assembly. Designed intelligent sensors will equip pneumatic clamping system. Sensors will scan clamps presence, working product presence; clamps placement and also clamping force regulation.

The best way to workpiece detection is by our meanings to use of an optical sensor. The capacitive or inductive sensors have small range of detection, and detection by camera is very complicated and expensive solution for this case.

Acknowledgment

The research has been supported by VEGA MS and SAV of the Slovak Republic within the project: VEGA 1/3164/06--Using of intelligent fixtures in manufacturing and assembly processes.

5. REFERENCES

Danisova, N; Pastierovie, M. & Fidler, B. (2006) Nove generacie upinaeov vo vyrobnom procese. (New generation of clamping fixtures in production) Vedecke prdce MtF STU v Bratislave so sldlom v Trnave. pp. 21-26 ISSN 1336-1589.--E. 21 (2006),

Danisova, N.; Zvolensky, R. (2006) Automated flexible manufacturing systems. Proceedings of KOD 2006, pp. 253-256, ISBN 86-85211-92-1, Palic, 30-31. maj 2006.--Novi Sad : Fakultet tehniekih nauka

Kos al, P.; Matusova, M. & Velisek, K (2007) Modeling of clamping fixtures. Academic Journal of Manufacturing Engineering. pp.65--68, ISSN 1583-7904.--Vol. 5, No. 2

Kostal, P.; Velisek, K. (2007) Intelligent clamping fixtures for box shaped workpieces. Proceedings of 7th. International Multidisciplinary Conference. ISSN 1224-3264.--Vol. XXI Baia Mare, Romania, May 17-18, 2007 (2007).--Baia Mare : North University of Baia Mare, 355-358, I. diel

Matusova, M.; Hruskova, E (2007) Database of fixture mechanisms. Proceedings of RaDMI 2007 pp. 613-617 ISBN 86-83803-22-4 , 16-20 September 2007.--Trstenik: High Technical Mechanical School of Trstenik,