IE 131 Solutions for Problems due Feb 24 (Chs 5 and 6)
5.1 A fleet of forklift trucks has an average travel distance per delivery of 600 ft loaded and an
average empty travel distance of 500 ft. The fleet must make a total of 55 deliveries/hr. Load and
unload times are each 0.4 min and the speed of the vehicles is 400 ft/min. The traffic factor for the
system is 0.93. Availability is 1.0 and worker efficiency is assumed to be 100%. Determine (a)
ideal cycle time per delivery, (b) the resulting average number of deliveries per hour that a forklift
truck can make, and (c) how many trucks are required to accomplish the specified number of
deliveries per hour.
Solution
: (a)
T
c
= 0.4 + 600/400 + 0.4 + 500/400 = 3.55 min/delivery
(b) Ideally,
R
dv
= 60/3.55 = 16.9 deliveries/hr
With traffic factor,
R
dv
= 16.9(0.93) = 15.72 deliveries/hr
(c) Number of trucks
n
c
= 55/15.72 = 3.5 rounded up to 4 forklift trucks
5.7 An AGVS has three load/unload stations (numbered 1, 2, and 3) that form the corners of an
equilateral triangle whose sides are each 1000 m long. The hourly rate of loads carried between
stations is as follows: 20 loads from station 1 to station 2, 20 loads from station 2 to station 3, and
15 loads from station 3 to station 1. The FromTo chart requires that the vehicles always move in
one direction around the triangle (from 1 to 2 to 3 to 1 . . . ), so the traffic factor is assumed to be
1.0. Vehicle speed is 60 m/min. A total of 1.0 min is required for handling time per delivery (0.5
min for loading and 0.5 min for unloading). The AGVs must be scheduled as efficiently as
possible, but the delivery requirements make it impossible to avoid some empty traveling by the
vehicles. Assume that availability is 100%. Determine (a) average delivery cycle time of a vehicle
and (b) how many vehicles are needed to meet the hourly delivery schedule.
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 Spring '08
 Groover
 Cycle Time, Shift work, Forklift truck

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