Print Hammer Impact Detection
Original Publication Date: 1990-Jan-01
Included in the Prior Art Database: 2005-Mar-14
Print forms equivalent thickness and the time of impact are determined during printing on any forms thickness by analysis of the output of a piezoelectric platen during hammer impact; the data are used to adjust hammer firing energy and time.
Print Hammer Impact Detection
equivalent thickness and the time of impact
are determined during printing on any forms thickness by analysis of
the output of a piezoelectric platen during hammer impact; the data
are used to adjust hammer firing energy and time.
A circuit for
determining equivalent forms thickness and time
of impact is shown in Figs. 1-3, and an impact waveform and signal
timing diagram is in Fig. 4. In Fig. 1, the output signal from an
impact-sensitive platen transducer 1, as polyvinylidenediflouride, is
applied to differential 2, whose output serves as inputs to low level
(LLDET) 3, high level detector (HLDET) 4 and buffer 5. The LLDET and
HLDET circuits produce logic outputs. The LLDET signal indicates the
beginning of presumed impact period, and it may sense false 'impacts'
by very low-level pressure signals from transducer due to the print
band running in proximity to the HLDET 4 determines whether a valid
hammer occurred by requiring the signal from amplifier 2 to a
predetermined amplitude criteria.
amplifier 5 and its attendant circuits extend
dynamic amplitude range of the overall circuit by small signals
unattenuated to the differentiation 6 and 7 while reducing its gain
to large signals. is key to using a single power supply and very
low-cost for the circuit while keeping the time of impact a constant
relative to the peak of input signal.
differentiator circuit at 6 and 7 produces a voltage the
detector 8 which returns to its reference level a time (5 seconds)
after the transducer 1 signal is a slope of zero at the time of
maximum impact energy (by this is flight time).
In Fig. 2, a
valid impact is detected at gate 11 in the of
ZSDET and, if LLDET is present with the gate at flip flop 13, the
high level gate trigger HLGATE turned on until the cycle end. When
trigger 13 is not impact and contact time (CTTM) end outputs are
blocked. impact filter (IFIL) single shot 14 is supplied with signals
from HLGATE 13 and ZSDET 8 (Fig. 1) and, if 14 can time out, zero
slope detection must last at 10 seconds and a valid impact (HLDET) is
occurring. False along the slope of the input waveform with
multiple-part forms not exceed 5 seconds and thus are ignored by the
Low level end
(LLEND) trigger 18 is set on by LLDET 3 HLGATE
13. So that invalid force signals will not contact time outputs,
LLEND cannot turn on if HLGATE is not present. The output from LLEND
18, through OR 20 Fig. 3, is applied to low level filter single shot
23; this requires that LLDET be continuously present gate 21 for 10
seconds in order for LLFIL to time out. 23 must operate in holdover
mode while searching for a LLDET signal. If the later is present at
time-out, a cycle is started. Since CTTM starts late, is must
equally late so LLFIL 23 operates from the trailing edge of LLDET if
a valid has been detected. Once a valid LLDET ends, L...