This document summarizes a paper that proposes a new layout design for part storage systems on vertical turret lathes. The design aims to increase storage capacity and reduce costs by decreasing the number of required hardware components like cylinders. The proposed layout uses shapes like T, L, and O to circulate pallets through multiple directions using double rod cylinders connected by hooks and torsion springs. An L-shaped layout is analyzed in detail, showing how pallets can be shifted in 6 directions to continuously supply new parts for machining while removing finished parts. The new design is expected to improve production rates by reducing cycle times associated with part loading and unloading.

1. 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 L2
, AJITH KUMAR G3
, PRAKASH K R4
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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2. Proceedings of the 2nd
International Conference on Current Trends in Engineering and Management ICCTEM -2014
17 – 19, July 2014, Mysore, Karnataka, India
240
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.

3. Proceedings of the 2nd
International Conference on Current Trends in Engineering and Management ICCTEM -2014
17 – 19, July 2014, Mysore, Karnataka, India
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

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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
17 – 19, July 2014, Mysore, Karnataka, India
242
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
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
International Conference on Current Trends in Engineering and Management ICCTEM -2014
19, July 2014, Mysore, Karnataka, India
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
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

5. Proceedings of the 2nd
International Conference on Current Trends in Engineering and Management ICCTEM -2014
17 – 19, July 2014, Mysore, Karnataka, India
243
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

6. Proceedings of the 2nd
International Conference on Current Trends in Engineering and Management ICCTEM -2014
17 – 19, July 2014, Mysore, Karnataka, India
244
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 =
૟૙
ࢀࢉ
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.