Your team has been assigned the task of designing a catapult capable
of delivering a specific projectile to a prescribed target. You
will be loaned a generic catapult and a projectile for this project.
This is a simulated medieval catapult that you are to position
on the floor and use to launch the projectile at a target on the
floor at least 3 meters, but no more than 5 meters, away. The distance
measurement is to be made from the front edge of the catapult base
to the center of the target. You are not allowed to modify the
catapult in any way other than varying the built-in parameters
and the number of rubber bands. Also, you are to use the projectiles
and rubber bands provided with the catapult. You will be allowed
to specify the distance to the center of the target, but once specified,
your projectile is to land within ? 17.5 cm (measured in the direction
of the launch) of that distance.
Based on the catapult settings that you determine best, you are
to conduct a catapult capability study to determine if your catapult
is in statistical control, and if it operates within the specifications
of ? 17.5 cm. To do this, you are to collect at least twenty-five
subgroups of three measurements each to ascertain the capability
of the catapult:
1. Plot these 25 points sequentially on a control chart.
· Is the process in control?
· Are all data points associated with common causes, or are some
associated with special causes?
· • If there are special cause data points outside the
process control limits, and if you decide to recommend process
improvement actions, should you address these causes prior to
using the other control chart data to adjust the process, or
should you use the other data to adjust the process before addressing
the special causes?
2. Calculate Cp, Cpk and St. Then give a description of what they
mean with respect to future improvement of the catapult to meet
the designated need.
Since you probably have never designed a catapult, the following
will be a useful guide:
Play with the catapult for a while to learn its capabilities.
Examine the catapult and determine the variables (control factors)
that can be adjusted to change the distance the projectile will
be thrown. A sketch of the catapult indicating the variables
will be very helpful. Determine what the noise factors are that
have an impact on the distance, but that are not under your control.
Gather some data and brainstorm as a team to determine which
three control factors are most important in making a projectile
land on target (distance and accuracy). Fix all other variable
factors at whatever positions you think best, but for each of
the three most important control factors select two levels and
run a half-factorial Design Of Experiments to determine which
of the two levels of each factor results in an optimization of
the performance index.