Design and Analysis of Globoidal Cam Index Drive

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Volume 2 ssue pp 16-16 June21 www.ijsret.

1 Volume 2 ssue pp June21 SSN 22 2 Design and Analysis of Globoidal Cam ndex Drive Suresh Sanap 1, Ketan Jagtap 2 and Keshav Nandurkar 1-2 Government Polytechnic, Nashik E Mail: sanapsd@gmail.com 1 and ketanjagtap@gmail.com 2 K.K.W.. E. E. & R Nashik E Mail: keshav16@gmail.com ABSTRACT n Globoidal cam mechanism, index motion is smooth and they are specially designed to minimise vibrations. A globoidal cam with cylindrical rollers radially mounted at its turret is one of the mechanisms employed for angular indexing motion control. As operating speed is high, there should be finite and low value of jerk. Present paper focuses the different motion curves. After studying the two different cases regarding the same input values of input parameters, peak output torque and jerk are determined. The results were discussed after comparing with the graphs obtained from the centesimal scales. Finally appropriate motion curves are suggested for the given applications. Keywords - Cam ndexer, Globoidal Cam, Modified Constant Velocity Curve, Modified Sine Curve, Modified Trapezoid curve, Surface based modelling 1. NTRODUCTON Compare to other cam-follower mechanisms, the structure of globoidal cam follower mechanisms are relatively compact. These mechanisms also have some special features such as: high loading capacity, low noise, low vibration, and high reliability. Hence globoidal cams have widely been used in various automatic equipments in industry. Typical usages of globoidal cam mechanisms are in machine tools, automatic assembly lines, paper processing machines, packing machines, and many other automated manufacturing devices. n selecting a globoidal cam-turret device for a specific application, generally the parameters for its index time and Fig. 1 Cam ndexer for intermittent action inertial moments of work pieces with its table loaded at the output shaft must first be specified. Then, the required total output torque containing the inertia torque, the friction torque, and the work torque can be calculated. To meet the total required output torque, the cam shaft torque at the demanded rotational speed should be estimated based on the number of dwells of a complete circle at the output shaft, index period, dimensional parameters, and the selected or synthesized turret motion. n addition, to ensure a proper design for such a cam-turret mechanism, the cam profile has to be determined so that its pressure angles, surface curvatures, contact stresses, and load life can be characterized. As a result, a motor and its reducer with an appropriate rotational speed and torque can be decided to satisfy the total required output torque of a globoidal cam-turret device. For driving the output shaft and satisfying the required output torque, the needed globoidal cam shaft torque is transmitted to its turret through the direct contact between the cam

2 Volume 2 ssue pp June21 SSN 22 2 and its engaged cylindrical rollers. During an indexing period, it is clear that the cylindrical rollers mounted at the turret must bear the input torque and the contact stress with the cam. Fig. 1 shows schematic diagram of Cam ndexer for intermittent action. Ching Huan Tseng et al. (1) investigated new concept of introducing pairs of rollers instead of single roller in adjacent cam ribs. They claimed increased accuracy and stability, reduced contact stresses and improvement in preload. n their patent they claimed improved arrangement and geometry design of globoidal cam index mechanism. Fu Yang Ming et al. (2) designed the contour surface of the globoidal cam with the aid of computer. He wrote a program in Visual BASC Language. The program adopts the form of personcomputer dialogue. He also prepared optimum mathematical model of the cam with minimum volume. He also discussed the problem of pressure angle of the globoidal cam mechanism in detail and put forward a new concept of equivalent pressure angle. Jie Shing Lo et al. (21) studied bearing contact of roller gear cams which is useful to understand contact nature, and contact stresses of the roller gear cam, which are considered as design indices for performance consideration and especially for lubrication of cam. Vu-Thinh Nguyen et al. (2) described synthesis method of designing flexible cam profiles by using smoothing spline curves. He presented a very flexible cam profile synthesis method that uses smoothing spline curves. The proposed method can control the displacement, velocity and acceleration of a cam profile simultaneously. nherent characteristics of the smoothing spline curve guarantee the smoothness of the designed cam profile. The numerical results for the simulated dynamic response histograms of the high speed operating GC system are in good agreement with the experimentally measured by Huang et al. (2). Tuong et al. (2) described a co mputer-aided design for design of the concave globoidal cam with cylindrical rollers and swinging follower. Four models with different modeling methods were made from the same input data. The input data was angular input and output displacements of the cam and the follower and some other geometrical parameters of the globoidal cam mechanism. Tuong et al. (2) proposed some important tasks which are necessary in the modeling procedure of globoidal cams. These tasks are modeling and virtual animation of the globoidal cam mechanism for checking interference between components of the system. The correlation between the dynamic response of a globoidal cam (GC) system and the motor driving speed is investigated numerically and experimentally investigated J H Kuang et al. (21). 2. METHODOLOGY AND DEVELOPMENT There are applications in which the motion of a mechanism is dictated by a special function it has to perform or by the motion of an associated mechanism. f cam is used to move a drill forward at a constant feed rate the shape of the cam must be designed with the regard to geometry of the follower and transmission to provide a constant velocity. Those sections of such cam which are governed purely by dynamic considerations (accelerations and deceleration) require the selection of suitable law. There are applications which are the majority requiring simply moving a mass of mechanism from one position to another in a certain time. f the speed of operation is very slow it matters little which motion law is chosen. However, for high speeds efficient performance is essential to select a dynamically suitable cam motion law. 2.1 Motion Laws (Motion Curves) The output motion is a normalized function of the input rotation. Mathematical expressions to produce suitable follower motions are known as cam laws. There are well-known laws used for cam motions, all of which has virtues and vices. The problem is to decide which law is best suited for a particular application, or which law can be used as a standard for a wide variety of applications in different machines without departing vary from ideal. n the design of a globoidal cam-turret mechanism, the desired turret motion of its roller-follower must be well defined. Motion curves for index drives provide

3 Volume 2 ssue pp June21 SSN 22 2 superior velocity, acceleration and input characteristics. The acceleration and input characteristics greatly affect the accuracy and life of index drives. mprovement of these characteristics is necessary for high-speed and high-accuracy index drives. Three motion curves considered for the study which are as per industry standards are, Modified Constant Velocity (MCV) Modified Trapezoid (MT) Modified Sine (MS) n case of globoidal cam, the relationship between input and output motion is expressed by two rotary motions. Modified Constant Velocity Curve (MCV) The constant velocity curve has a straight line displacement at a constant slope. t also has the smallest cam for a given rise and provides a long stroke action. The cycloidal curve or parabolic curves have been utilized depending on the cam speed, mass of the follower, and work performed by the machine. To obtain a lower peak figure of velocity, the peak of the velocity curve should be flattened. This is to provide the constant velocity period with acceleration of zero. Modified Sine Curve (MSC) The modified sine curve is a combination of quarter sine wave curves. n terms of its torsional action, the change from positive to negative torque occurs in over 4 percent of the travel time. This attribute makes this curve attractive as a choice in moving large masses such as indexing intermittent turrets. ts lower torque and power demand make the modified sine curve one of the best choices of curves. Modified Trapezoid Curve (MTC) A trapezoidal acceleration curve is composed of a parabolic motion combined with the cycloidal curve. This combination reduces the maximum acceleration at the expense of somewhat higher jerk values. The modified trapezoidal curve is popular in industry. However, it has one objectionable characteristic: the torque goes from positive maximum to negative maximum in 2 percent of the travel time. f dynamic Sr. No TABLE NPUT DATA FOR TWO DFFERENT CASES Symbol Unit Application Type Cam ndex Period Weight of the dial plate, Diameter of dial plate Total Wt. of work station Radius of work circle No. of stations - - Case Start Stop Case Start Stop degree 2 2 Wd kg 4 22 D m. 1.2 Ws kg 2 Rs m.4. S ndex time sec forces represent a significant part of the load on the cam, this sudden release of energy may be detrimental to the cam-follower system performance and limit the operating speeds. Much better torque characteristics can be obtained with the modified sine curve. With indexing motion, unlike constant speed motion, the moving parts have to be accelerated from rest to a maximum velocity and decelerated to rest again once every indexing cycle. To accelerate the mass a torque is exerted by the mechanism to overcome the inertia of the load. This torque is the function of the indexing speed, the cam motion law and the mass and size of the indexed parts. nertia torque is as determined for the given input parameters. For comparison applications where cam index period and number of stations are same are selected. Table shows the values of input parameters for Case and Case.

4 Volume 2 ssue pp June21 SSN RESULTS AND DSCUSSON Globoidal cam indexing mechanism produces controlled output acceleration /deceleration because its output shaft is at all times tightly connected to its input shaft, making the output rotation a strict function of the input rotation, determined by the shape of the cam profile. The cams are designed to have the required index time, dwell time and number of stations, and to meet the requirements of static and dynamic loading, rigidity and accuracy. As part of dynamic loading the torque imposed on the output shaft during the index period and the jerk developed during start-stop indexing are selected as the performance parameters. The results for three motion curves for two different applications are presented in Table. Motion Curve/ paramete r nertia Kg-m² Angular Accelerati on ε - rad/sec² Peak Output Torque T Nm Radius of gyration K nput Torque T i/p - Nm nput Power P i/p - hp Maximum Jerk m/ TABLE RESULTS FOR THREE MOTON CURVES Modified Sine (MS) Modified Trapezoid (MT) Modified Constant Velocity (MCV) Dat a From the above Table it can be seen that for the same input parameters the values of peak output torque and jerk are minimum for MT curve for both applications. Time period 1 is assumed for both the data in which index angle is 2 degree for input motion and degree for output motion. From the centesimal scales prepared for Modified Sine, Modified Trapezoid, Modified Constant Velocity motion curves graph of cam angle and jerk values are obtained. The graphs obtained are shown in Fig 2. Fig. 2 Non Dimensional Time Vs Jerk MSC MTC MCV ndex drives utilize the dual-dwell curves to perform the cycle of the dwell-index-dwell. The MT, MS and MCV curves are the most commonly used motion curves at present. MT has lowest peak acceleration and is known to be

5 Volume 2 ssue pp June21 SSN 22 2 suitable for high-speed applications. The MS has a reasonable and also, the lowest provides the advantage of the lowest input shaft rotational irregularity. This curve is estimated as the best compromise, and % of cams for index mechanisms utilize this curve. Though the MCV has the lowest and is known to be suitable for low speed and heavy load applications, it is also often used for applications requiring the constant velocity period. Generally the higher increases the pressure angle of cam, and the cam size should be increased to obtain the desired torque. The higher reduces the curvature radius of the cam and might cause an undercut. The represents the input shaft torque and the lower figure of this allows a drive motor with a smaller rated output. Considering all these factors, the most suitable motion curve should be selected. This is a real example but its modeling procedures can be applied for other situations when the angular input/output are known. For the two different inputs from the customers the values obtained from calculations of various components are analyzed. The result of this study is very useful in terms of modeling and manufacturing globoidal cam. With the modified trapezoid curve the torque goes from positive maximum to negative maximum in 2 % of travel time, the sudden release of energy is detrimental to the cam follower system performance. This limits the operating speed for MT curve. Comparatively MS curve exhibits better performance for different combinations of application parameters. For the same input power requirement and output torque may be little bit higher (the same electric motor may be required) but performance and life of the system is better. For the Application studied input power required is.2 hp with MS curve and.2 hp with MT curve and for Application input power.4 hp and.42 hp respectively which indicates that the motor of. hp is required. n such situations MS curve should be preferred. From the result Table 2 it is clear that Results for MT and MS curve are closer, it is clear that there is a choice between these curves. The MCV is suitable for very low speed and heavy load applications and where operation demands uniform velocity. 4. CONCLUSON Considering the problems faced by the manufacturers of indexing mechanism in deciding the appropriate cam motion laws, three motion curves MS, MT and MCV are selected for the study. The input data is from real life applications. From the result and analysis of motion curves, it is observed that for high loads and high speeds modified trapezoid is suitable, for low load and high speed modified sine is the best choice and for high load conditions and low speeds modified constant velocity is preferable. For other combinations modified sine gives better results. From the numerical analysis values of torque and jerk are minimum and input power required is also low, for the applications chosen for the study the modified trapezoid motion curve seems to be suitable. As values are so closer modified sine curve is better choice for both the applications. ACKNOWLEDGEMENT The authors are grateful to Orbital Systems Pvt. Ltd., Nashik (MS), ndia for providing the experimental facility. Also thankful to the support of Prof. D. R. Nandanwar, Principal of Government Polytechnic Nashik (MS), ndia. REFERENCES [1] Ching-Huan Tseng and Wei-Han Wang, ndexing Mechanisms Using Pairs of radially Disposed Rollers Engaged between Adjacent Cam Ribs, U.S. Patent, No.666, 1. [2] FU Yan Ming, Analysis and Design of the Globoidal ndexing Cam Mechanism, Journal of Shanghai University, Vol. 4, No. 1 Mar. 2, pp 4-. [] Jie-Shing Lo, Ching-Haun Tseng, Chung- Biau Tsay, A Study on the bearing contact

6 Volume 2 ssue pp June21 SSN 22 2 of roller gear cams, Computer Methods in Applied Mechanics and Engineering, Vol. 1, No., 21, pp [4] Vu-Thinh Nguyen, Do-Joong Kim, Flexible Cam Profile Synthesis method using smoothing spline curves, Mechanism and Machine Theory, Vol.42, 2, pp. 2-. [] Kuang-Yuh Huang, Pei-Chuan Lin and Sheng-Fu Tsai, Magnetic Torque Compensating Methods for Cam ndexing Devices, EEE Transaction of Magnetics, Vol.4, No., March 2, pp [6] Nguyen Van Tuong, and Premysl Pokorny, Modeling Concave Globoidal Cam with Swinging Roller Follower: A Case Study, Journal of World Academy of Science, Vol.2, 2, pp [] Nguyen Van Tuong, and Premysl Pokorny, Virtual Animation For Checking nterference of Globoidal Cam, Machine Manufacturers Science Journal, Oct 2, pp [] Jao-Hwa Kuang, Chao-Ming Hsu, Chin-Che Hu, Dynamic Behavior of Globoidal Cam Systems with Torque Compensation Mechanisms, Mechanism and Machine Theory, Vol.4, 21, pp

Cam makes a higher kinematic pair with follower. Cam mechanisms are widely used because with them, different types of motion can be possible.

CAM MECHANISMS Cam makes a higher kinematic pair with follower. Cam mechanisms are widely used because with them, different types of motion can be possible. Cams can provide unusual and irregular motions