1 b. Machine design - Prefered numbers, asthetic and ergonomic design

achine design - Prefered numbers, asthetic and ergonomic design

1. DESIGN OF MACHINE ELEMENT INTRODUCTION

2. With the acceptance of standardization, there is a need to keep the standard sizes or dimensions of any component or product in discrete steps. The sizes should be spread over the wide range, at the same time these should be spaced properly. For example, if shaft diameters are to be standardized between 10 mm and 25 mm, then sizes should be like : 10 mm, 12.5 mm, 16 mm, 20 mm, 25 mm and not like : 10 mm, 11 mm, 13 mm, 18 mm, 25 mm. This led to the use of geometric series known as series of preferred numbers or preferred series . Preferred serie s a r e serie s o f nu m b ers o b t aine d b y geome t r i c pr o g r e s si o n and rounded off. Preferred Numbers

3. There are five basic series with step ratios of: 8 5 10 , 10 10 , 20 10 , 40 10 & 10 These ratios are approximately equal to 1.58, 1.26, 1.12, 1.06 and 1.03. The f i v e bas i c s e ri e s of preferre d nu m b ers ( known a s preferre d series) are designated as: R5, R10, R20, R40, and R80. The examp l e s o f preferre d nu m b er serie s a r e: s t anda r d shaf t d iame t er s , power rating of coupling, center distances of standard gear boxes, etc. Preferred Numbers

4. The difference in two successive terms has a fixed percentage. It provides small steps for small quantities and large steps for large quantities. T he pr o duc t range i s c o v ered w i th m i n im u m n u mber of sizes without restricting the choice of the customers . Advantages Preferred Numbers

5. The difference in two successive terms has a fixed percentage. It provides small steps for small quantities and large steps for large quantities. T he pr o duc t range i s c o v ered w i th m i n im u m n u mber of sizes without restricting the choice of the customers . Advantages Preferred Numbers

6. R5 R10 R20 R40 1.00 1.00 1.00 1.00 1.06 1.12 1.12 1.18 1.25 1.25 1.25 1.32 1.40 1.40 1.50 1.60 1.60 1.60 1.60 1.70 1.80 1.80 1.90 2.00 2.00 2.00 2.12 2.24 2.24 2.36 2.50 2.50 2.50 2.50 2.65 2.80 2.80 3.00 3.15 3.15 3.15 3.35 3.55 3.55 3.75 4.00 4.00 4.00 4.00 4.25 4.50 4.50 4.75 5.00 5.00 5.00 5.30 5.60 5.60 6.00 6.30 6.30 6.30 6.30 6.70 7.10 7.10 7.50 8.00 8.00 8.00 8.50 9.00 9.00 9.50 10.00 10.00 10.00 10.00

7. In a present days of buyer's market, with a number of products available in the market are having most of the parameters identical, the appearance of product is often a major factor in attracting the customer. This is particularly true for consumer durables like: automobiles, domestic refrigerators, television sets, etc. Aesthetics is defined as a set of principles of appreciation of beauty. It deals with the appearance of the product. Appearance is an outward expression of quality of the product and is the first communication of the product with the user. For any product, there exists a relationship between the functional requirement and the appearance of a product. Aesthetic Considerations

8. The aesthetic quality contributes to the performance of the product, though the extent of contribution varies from the product to product. The following guidelines may be used in aesthetic design ( design for appearance ): The appearance should contribute to the performance of the product. The appearance should reflect the function of the product. The appearance should reflect the quality of the product. Aesthetic Considerations

9. The appearance should not be at too much of extra cost unless it is a prime requirement. The appearance should be suitable to the environment in which the product is used. The growing importance of the aesthetic considerations in product design has given rise to a separate disciple known as industrial design. The job of an industrial designer is to create new shapes and forms for the product which are aesthetically appealing – Form (Shape) , There are five basic forms of the products, namely, step, taper, shear, streamline and sculpture Aesthetic Considerations

10. Step form : The step form is a stepped structure having vertical accent It is similar to the shape of a multistorey building. Taper form The taper form consists of tapered blocks or tapered cylinders. Shear form The shear form has a square outlook. Streamline form The streamline form has a streamlined shape having a smooth flow as seen in automobile and aeroplane structures Sculpture form The sculpture form consists of ellipsoids, paraboloids and hyperboloids. Aesthetic Considerations

11. Aesthetic Considerations The sculpture and stream forms are suitable for mobile products like vehicles, while step and shear forms are suitable for stationary products

12. Colour Colour is one of the major contributors to the aesthetic appeal of the product. Many colours are linked with different moods and conditions. The selection of the colour should be compatible with the conventions. Morgan has suggested the colour code given in the following Table. Aesthetic Considerations Colour Meaning Red Danger, Hazard, Hot Orange Possible Danger Yellow Caution Green Safety Blue Caution-Cold Grey Dull

13. Material and Surface Finish The material and surface finish of the product contribute significantly to the appearance. The material like, stainless steel gives better appearance than the cast irons, plain carbon steels or low alloy steels. The brass or bronze give richness to the appearance of the product. The products with better surface finish are always aesthetically pleasing. The surface coating processes like: spray painting, anodizing, electroplating, etc. greatly enhances the aesthetic appeal of the product. Aesthetic Considerations

14. Ergonomics is defined as the scientific study of the man-machine-working environment relationship and the application of anatomical, physiological and psychological principles to solve the problems arising from this relationship The word ergonomic is formed from two Greek word: ergo means work and nomic mean natural laws. The final objective of the ergonomics is to make the machine fit for user rather than to make the user adapt himself or herself to the machine. It aims at decreasing the physical and mental stresses to the user. Psychology - Experimental psychologists who study people at work to provide data on such things as: Human sensory capacities, psychomotor performance, Human decision making, Human error rates, Selection tests and procedures, Learning and training. Ergonomic Considerations

15. Anthropometry - An applied branch of anthropology concerned with the measurement of the physical features of people. Measures how tall we are, how far we can reach, how wide our hips are, how our joints flex, and how our bodies move. Applied Physiology - Concerns the vital processes such as cardiac function, respiration, oxygen consumption, and electromyography activity, and the responses of these vital processes to work, stress, and environmental influences. Ergonomic Considerations

16. Ergonomic Considerations Man-Machine Closed Loop System

17. Ergonomic Considerations This man-machine closed loop system in influenced by the working environmental factors such as: lighting, noise, temperature, humidity, air circulation, etc. Ergonomic Considerations in Design of Displays Ergonomic Considerations in Design of Controls Working Environment. Lighting Noise Temperature Humidity and air circulation