part storage system carousel of vtl by low cost automation

Proceedings of the 2nd

International Conference on Current Trends in Engineering and Management ICCTEM -2014

17 – 19, July 2014, Mysore, Karnataka, India

239

PART STORAGE SYSTEM (CAROUSEL) OF VTL BY LOW COST

AUTOMATION

MALATESHA S KRISHNA1, KRISHNAMURTHY L

2, AJITH KUMAR G

3, PRAKASH K R

4

1, 2, 4

(Department of Mechanical Engineering, the National Institute of Engineering, Mysore, India) 3(Design and Development, Ace Designers Private Limited, Bangalore, India)

ABSTRACT

Part storage systems (carousel) are the enablers for unattended cell operation. Unattended time of the

manufacturing cell depends upon the ability of the storage system to store the number of unfinished part. Using

conventional methods like circular and square layouts it is difficult to increase the storage capacity. This paper mainly

addresses the concept of increasing the storage capacity of Inverted Vertical Turret Lathe by using layouts of different

shapes by using double rod cylinder with hook mechanism. It has been proposed in this paper, to employ this concept to

reduce the number of cylinders required and other hardware components which would lead to low cost automation.

Keywords: Computer Numerical Control (CNC), Part Storage System (Carousel), Vertical Turret Lathe (VTL).

I. INTRODUCTION

Computer Numerical Control (CNC) Lathes are classified into two types; Vertical and Horizontal. Many

modern horizontal CNC turning centers are of the slant bed design. Advantage of the slant bed includes: easy access for

loading and unloading and measuring; allowance for the chips to fall free; minimum floor space utilization; easy and

quickness of tool change; better strength and rigidity [1].

Vertical CNC turning centers are modern versions of the manual Vertical Turret Lathe (VTL). Although

principally designed for larger and difficult to handle work pieces, vertical turning center advanced considerably in terms

of state-of-art technology [1]. In VTLs there are two versions; a) Spindle facing upwards b) Spindle facing downwards.

At present, very few manufacturers are providing layouts in VTL. It has to be emphasized here that the use of layouts

becomes imperative since it increases the storage capacity.

Horizontal and Vertical CNC are well-known single cell manufacturing cells, which are being extensively used

in present day industries. Further, Computer Numerical Controlled machines are employed for mass production by

replacing conventional lathes to improve productivity and quality. However recently machine tool manufacturers have

found solutions for automatic loading and unloading to reduce the fatigue of labor and reduce cycle time, increasing

productivity [2].

Need for auto loading and unloading includes expensive gantry, robot with loading system, machine guarding

consisting of ladder and automatically operated by only M-codes through CNC controller [3].

Part Storage System (Carousel) is the integrated subsystems of automatic loading and unloading. The part

storage system and automatic transfer of parts between the storage system (Carousels) & the processing station are the

necessary condition for an automated cell that operates unattended for extended period of time. If all of the parts are

identical and requires the same, then unattended time UT of operation is given by [4].

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UT = np Tc (1)

Where np is the capacity of the part storage system, Tc = Cycle time for the given part.

In the conventional carousel systems on can use the drives and mechanism like

1. Stepper motor and Servo drives

2. CAM mechanisms

3. Indexing mechanisms like Ratchet pawl, Rack and pinion, Geneva wheel [4].

To increase the capacity of the parts storage system here is a necessity of different shaped layouts consisting of

T, L, and O shapes. The schematic representation of the layouts is shown in Fig.1, Fig.2 and Fig.3 respectively. The

rectangle indicates the pallets carrying the work piece; arrow indicates circulation of the pallets which carries the along

the shape of the layout. The cross symbol indicates the pick-up site in the layout by inverted spindle with hydraulic

chuck. Here hydraulic chuck performs two functions namely

1. Automatic pick-up of the work piece from part storage (carousel).

2. Turning operation of the work piece takes place in the same hydraulic chuck itself.

Fig. 1: T- Shaped Layout Fig. 2: L- Shaped Layout

Fig. 3: O-Shaped Layout

This paper converges to part storage system (carousel), not on the automatic loading and unloading. The shape of the

layout depends upon the storage capacity, external shape of the VTL and space availability

In this paper further discussions are carried out by taking L-shaped layout into consideration because pallets are

shifted in 6 directions which are indicated by arrows.




241

II. OBJECTIVES

The core objectives of this paper includes (a) maximize the storage capacity of the part storage system

(carousel) (b) increase the unattended time of operation (c) low cost automation by reducing the number of elements i.e.

cylinders, sensors etc..

III. METHODOLOGY

Hook is the main part of the concept. Hook is equipped with torsion spring [5]. Hook is connected to the

cylinder by link. Hook deflects in the downward direction due to torsion spring and traces the path of the external

geometrical feature like Cam and followers. (Fig. 4, 5 and 7)

Fig. 4: Hook with Torsion Spring Fig. 5: Hook Moves in Downward Direction

During one side stroke (extending/retracting) hook engages/latches the pallet (which carries the work piece but,

the work piece is not shown in Figure) as shown in Fig. 6. Hook disengages pallet during the return motion (Fig. 7).

Fig. 6: Pallet Engaged by Hook Fig. 7: Hook Disengaging Movement

The following cross-sections of layout illustrates the impression behind the concept

Fig. 8: Hook Engages/Latches the Pallet Fig. 9: Pallets are Shifted by One Pallet Length

(stroke length of cylinder) through Hook which is

connected to Cylinder

Fig. 10: Disengaging Movement


International Conference on Current Trends in Engineering and Management ICCTEM

Sequence of operations: The pallets discussed above are positioned throughout the layout. Pallets get shifted by one pallet length which

is equal to stroke length of the cylinder in each direction. This sequence of operations required to deliver the new raw

material to the picking station is as explained below. The sequence of operation begins with the

vertical hydraulic chuck places the finished part. From

by moving the pallets in both X and Y directions.

Fig. 11(a):Placement of Finished Part after Machining

Fig. 11(c): Vertical Chuck Facilitating New

Work Piece for Machining

Fig. 11(e): Shifting of Pallets by One Pallet

Length in Y-Direction

International Conference on Current Trends in Engineering and Management ICCTEM


242

pallets discussed above are positioned throughout the layout. Pallets get shifted by one pallet length which


ation is as explained below. The sequence of operation begins with the

vertical hydraulic chuck places the finished part. From Fig. 11(b) to Fig. 11(j) depicts the further sequencing operations

irections.

Fig. 11(a):Placement of Finished Part after Machining Fig. 11(b): Supply of New Work Piece to Machining

Fig. 11(c): Vertical Chuck Facilitating New Fig. 11(d): Movement of Pallets in

Work Piece for Machining

Fig. 11(e): Shifting of Pallets by One Pallet Fig. 11(f): Shifting of Pallets by One Pallet

Length in X-Direction


19, July 2014, Mysore, Karnataka, India

pallets discussed above are positioned throughout the layout. Pallets get shifted by one pallet length which


Fig. 11(a) wherein

the further sequencing operations

Fig. 11(b): Supply of New Work Piece to Machining

Fig. 11(d): Movement of Pallets in the X-direction

Fig. 11(f): Shifting of Pallets by One Pallet

Direction




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Fig. 11(g): Movement of Pallet in Transverse Direction Fig. 11(h): Providing Space for New Work Piece by

One Pallet Length Shift in X- Direction

Fig. 11(i): Finished Work Part Ready for Movement Fig. 11(j): New Work Piece in Position

in the Transverse Direction

It can be observed that from the above sequence of operations, the pallets moves/circulates in opposite

directions as can be seen Fig. 11(d) & Fig. 11(h), Fig. 11(e) & Fig. 11(g). Hence the portion of the layout in which pallets

move in opposite directions can be identified. Pallets moving opposite direction can be controlled by one double acting

cylinder. This arrangement is as shown in the Fig. 12 & Fig. 13. During one side motion (extending/retracting), hook on

left side of the cylinder engages the pallet and hook on the right side moves without engaging the pallet (compare Fig.

11(d) & Fig. 13). The cylinder remains in this position until pallets as shown in Fig. 11(g) get shifted by another cylinder

(cylinder is not shown in figure). During motion opposite to previous stroke, hook on right side engages the pallet and

hook on left side disengages pallet. (Compare Fig. 11(h) & Fig.13)

Fig. 12: Double Rod Cylinder with Hook Arrangement Fig. 13: Arrangement of Cylinder Below the Layout




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In the similar way, another location of the layout in which pallets moving in opposite direction can be controlled

by one double acting cylinder (consider the doted arrows of Fig. 13).

IV. EXPERIMENTAL VERIFICATION

The cylinder selections made depend upon force requirement for worst situation. For example, consider the Fig.

11(d) in which maximum force is required to displace the 6 pallets. But the layout needs the force absorption system to

absorb the energy where minimum amount of energy required. For example, consider Fig. 11(b) and Fig. 11(f), where

energy requirement is only for two pallets. Otherwise uneven movement malfunction the operation i.e. component may

fall down from the pallet which is not desirable. Further, in order to accomplish better repeatability, cylinder has to reach

its extreme end position before it starts the next stroke. In other words cylinder has to complete its stroke. Bulky

cylinders sometimes cause problems in the alignment and positioning of the cylinder during assembly. This is very

important because incomplete stroke of the cylinder hinders the further sequencing of the cylinder.

V. RESULTS AND DISCUSSIONS

1. The space and assembly constraints can be overcome by using the rod fixing concept of the cylinder. This type of

cylinder consumes 30 to 40% times less space than the conventional cylinder because in this case the fluid enters

the cylinder through the rod and body moves instead of rod [6].

2. Absorbers have to be designed in order to absorb excess energy which can be accomplished by assembling to all

the corners of the layout.

3. Precise motion of the cylinder is essential in order to ensure timely supply of pallets for production and at the

same time guide the pallets properly. This can be enabled by providing appropriate guide and rail combination.

4. The layout is integrated to VTL which reduces the door opening and closing time and other repetitive jobs [7].

Production rate is inversely proportional to the cycle Tc time. This leads to increase in the production [4].

R c = ��

��

pc/hr (2)

Tc = Max{Tm, Ts} + Tr (3)

Where Tm = machine time, Ts = worker service time and Tr = repositioning time of pallet

VI. CONCLUSIONS

It is clear from the above discussions that the circulation of pallets both for loading and unloading in different

directions i.e. 6 directions in this case can be controlled by 4 cylinders instead of 6 cylinders. Reduction in the number

of cylinders automatically reduces the control valves required to build the hydraulic circuit, and position sensors.

Reduction in the number of cylinders minimizes the assembly constraints; space constrains and makes the co-ordination

motion of the cylinder simple. Further it results in simplifying hydraulic, electrical circuit which in turn reduces signal

overlapping and enables smooth operation.

VII. REFERENCES

[1] William W. Luggen, computer numerical control: a first look primer Cengage Learning, 1st Edition, 1996.

[2] S. Sandeep & K. R. Prakash, (2013), Automation of loading and unloading to CNC turning center, International

Journal on Mechanical Engineering and Robotics, Volume 1, Issue-2, pp.8-12.

[3] C. H. Patel, G. C. Mohan Kumar, Vishwas Puttige, (2012), Low cost automation for CNC machining center,

International Journal of Mechanical Engineering and Technology, Volume-3, Issue-2, pp. 806-817.

[4] M P Groover, automation, production system and CIM PGI, New Delhi, 3rd

Edition, 2013.

[5] Misumi India, factory automation components,

(http://in.misumi-ec.com/asia/CategorySearchView/103_26000000_26010000_26011300.html).

[6] Anthony Esposito, fluid power with applications Prentice Hall of India, Delhi, 6th

edition, 2007.

[7] Rohan Kulkarni, S. Shivkumar and Rroopa K Rao, (2011), Productivity improvement on CNC lathe by

automatic loading and unloading of throttle valve component, International Journal of Scientific & Engineering

Research, Volume 2, Issue -12, pp. 1-7.