Geneva Mechanism based Automatic paper punching machine B tech Mechanical final year project

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Project Objective

To reduce the time consumed in ?conventional punching machine for job setting, marking, punching operation is more.

To reduce the Labor cost and maintenance cost.

In this project we are designing and fabricating the prototype of Auto roll punching machine using Geneva mechanism.

The major components involved in this project are dc motor, cam arrangement, chain drive, Geneva mechanism and punching tool. In this project we are using two rollers for moving the sheet during operation. A dc motor is connected with cam. The cam has a pin which rotates the Geneva wheel. The Geneva wheel is attached to the chain drive. The other end of the chain drive is connected to the rollers which roll the metal sheet and the punching operation is done by the punch tool. It is suitable for making mass production of the sheet metal punching.

DESIGN

Design of Geneva mechanism

• Geneva wheel radius (b) = 75 mm
• of slots in Geneva wheel (n) = 4
• Drive pin diameter (p) = 8 mm
• Allowed clearance (t) = 2 mm
• Centre distance (c) = = ?= 106 mm
• Drive crank radius (a) = = = 75 mm
• Slot center length (s) = (a + b) – c = (75 + 75) ? 106 = 44 mm
• Width of slot (w) = p + t = 8 + 2 = 10 mm
• Angle between two slots (?) = 2 x 180/n = 2 x 180/4 = 90?
• Angle at the entrance of the pin into the slot (?) = 45?
• Stop arc radius (y) = a ? (p x 1.5) = 75 ? (8 x 1.5) = 63 mm
• Thickness of Geneva wheel (h) = 6 mm
• Stop disc radius (z) = y ? t = 63 ? 2 = 61 mm
• Thickness of crank drive (i) = 9mm
• Height of pin = h + t = 6 + 2 = 8mm
• Distance of drive pin from the center of the disc (a) = 75 mm
• Number of revolutions per minute (N) = 51 rpm
• Total cycle time (Tc) = 1/N = 1/51 = 0.0196 min
• Available service time per cycle (Ts) = (180 + ?)/360 x N = (180 + 90)/360 x 51 = 0.014 min
• Dwell time or processing time

(Td) = (180 – ?)/360 x N = (180 – 90)/360 x 51 = 4.901 x 10-3 min

?Design of roller chain drive

• Pitch of chain (p) = 3.17 mm
• of teeth on smaller sprocket Z1 = 18 teeth
• of teeth on larger sprocket Z2 = 28 teeth
• Diameter of smaller sprocket d1 = 70 mm
• Diameter of larger sprocket d2 = 130 mm
• of links in roller chains = 49 links
• Center distance between two sprocket wheels = 410 mm

Motor calculations

• Current (I) = 1.5 Amps
• Voltage (V) = 12 V
• The consumed electric power of the motor (Pin) = I x V = 1.5 x 12 = 18 W
• The output mechanical power of the motor (Pout) = T x ?out Watts
• The speed of the motor (N) = 51 x 20 = 1020 rpm
• The actual Torque of the motor
  • (Tin) = Eb x Ia x 60 / 2 x ? x N
  • 55 x 1.5 x 60 / 2 x 3.14 x 1020
  • 1341 N-m

• Angular speed (?out) = 2 x ? x rpm / 60 = 2 x 3.14 x 1020 / 60 = 106.8 rad/sec
• Pout = 0.3141 x 106.8 = 14.3 W
• Efficiency of motor = Pout / Pin = 14.3 / 18 = 794 x 100 = 79.4%
• Input angular speed (?in) = 2 x ? x rpm / 60 = 2 x 3.14 x 51 / 60 = 5.34 rad/sec
• Fundamental equation for Gear pair = Tout / Tin = ?out / ?in = Tout / 0.1341 = 106.8 / 5.34
• Tout = 6.282 N-m

?Puncher specifications

• Punching diameter = 5.5 mm
• Punching distance = 80 mm
• Punching Capacity = 22 sheets

Power required to punch

• Power required to punch (p) = 2?NT/60 W
• Torque input to the cam drive (Tin) = 6.22 N-m
• The output torque of cam drive (T) = Tin (?2 cos? ? 1)= 6.22 (?2 cos0 ? 1) = 2.57 N-m (At maximum acceleration ? = 0)
• Power required to punch = 2 x ? x N x T / 60 = 2 x 3.14 x 51 x 2.57 / 60 = 72 W

Punching done on papers

• Hole diameter (d) = 5.5 mm
• Thickness of the paper (t) = 0.5 mm
• Ultimate shear stress of a carbonless paper
  • ( )= 500 KPa
• Area under shear stress A = ? x d x t mm2