Appeal No. 96-3744 Page 8
Application No. 08/173,764
that control the passage of pressured oil from an accumulator
96 to the three rams 24 - 28. Three ram position sensors 100,
102, 104 are also provided, each sensing the height of a
corresponding one of the rams, and with each position sensor
being coupled to the control circuit 86. Thus, a feedback
circuit is provided to enable close control of the position of
each ram. Each of the rams has a fluid outlet connected
through a corresponding valve 110, 112, 114 which leads to a
reservoir 106 that stores hydraulic fluid. A pump 108 pumps
fluid from the reservoir to the accumulator 96 to maintain a
high pressure in the accumulator, so that pressured hydraulic
fluid is always available. Each of the outlet valves 110, 112,
114 is electrically energized from the control circuit 86.
Trumbull '256 teaches that each of the inlet valves 90-94
is constructed so that it remains closed when no current is
applied to it, and so that it can be opened only upon the
application of current. On the other hand, each outlet valve
such as 110 is constructed so that it remains open when no
current is applied to
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