Method of adjusting the impact energy of a letter key or type element of a printing machine and typewriter, printer or the like printing machine using that method

The method for determining impact energy of a type element of the printing machine includes providing at least two different-length flight paths for the type elements by changing a distance between a resting position of the hammer and a place of impact of the type elements by at least one known amount; measuring at least two different hammer flight times corresponding to the at least two different-length flight paths of the type elements differing by the at least one known amount, each of the different hammer flight times being equal to a difference between a time of impact of one of the type elements and a time of onset of current flow in the hammer electromagnet; forming a difference between two different hammer flight times; dividing the known amount by which the two flight paths associated with the two different hammer flight times differ by the difference determined for the two hammer flight times to obtain a speed of the type element at impact and thus the impact energy of the type element. By comparing the actual value of the hammer flight time differences with a set value for the flight time differences the impact energy of a type element can be electronically controlled by controlling current flow in the hammer electromagnet.

BACKGROUND OF THE INVENTION 
The present invention relates to a method of adjusting and/or correcting 
the impact energy of a letter key or type element of a typewriter, printer 
or the like printing machine, and also to the typewriter, printer and/or 
other printing machine which uses that method. 
A printing machine is known, in which a type element or letter key is 
pressed against a substrate by a hammer accelerated by a hammer 
electromagnet. The hammer flight time determines the magnitude of the 
impact energy and the duration of current flow in the hammer electromagnet 
is adjusted according to that. 
It is important that the impact of the letter key or the type element on 
the substrate, e.g. a paper guided around a typewriter roll, occurs with a 
definite predetermined impact energy, so that a uniform type character 
with sufficiently strong impression results, while avoiding damage to the 
substrate. 
The impact energy of the key or type element is proportional to the square 
of the speed at the moment of impact. The impact speed of the type element 
and/or the hammer is produced because the hammer electromagnet accelerates 
the hammer with a certain current level flow through the electromagnet for 
a predetermined current flow duration. After this acceleration stage, a 
motion stage occurs without acceleration, in which the hammer up to the 
time of impact moves toward the type element and/or the substrate with a 
uniform speed. Since the geometric relationships and dimensions, i.e. 
especially the path of the hammer to impact, remain the same, the free 
flight time is directly proportional to the free flight speed and produces 
accordingly a certain impact energy. 
Conventionally the free flight speed of the hammer is measured in 
production of the typewriter or printer with different measuring methods 
and is stored in the data memory of the central data processing unit of 
the typewriter or printer, so that, when a certain type element or letter 
key is activated, an appropriate current flow duration results, which 
leads to the desired impact energy. 
Determination of a certain current flow duration in advance for the hammer 
electromagnet for a certain type element has not previously taken into 
account variations in the impact conditions due to manufacturing 
conditions and changes with increasing operating time. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method of adjusting 
the impact energy of a letter key or type element of a printing machine to 
compensate for manufacturing tolerances and operational variations by 
adjusting the actual free flight speed of a letter key or type element 
during operation and/or when first put into service. 
It is also an object of the present invention to guarantee that, during 
operation of the typewriter or printing machine, the actual impact energy 
of a letter key or type element is controlled so that the striking of the 
letter key or type element is adjustable and occurs with a desired impact 
energy independent of manufacturing tolerances or operational variations. 
According to the invention, the method for determining the impact energy of 
a letter key or type element includes determining a time of impact of the 
hammer and/or a type element or letter key on the substrate being printed 
and/or on the typewriter roll guiding the substrate by a sensing means 
including a sensor and a processor means including a memory connected with 
the sensing means, determining a time of onset of current flow in the 
hammer electromagnet for the flight path associated with the impact 
detected by the sensing means, determining the hammer flight time for the 
corresponding flight path as the difference of the time of onset of 
current in the electromagnet and the time of impact determined by the 
sensing means, and repeating the determination of hammerflight time for at 
least one other different-length flight path. 
The flight time of at least one of the letter keys or type elements and its 
impact energy is controlled by changing the current flow in the hammer 
electromagnet according to an actual value of a difference between the 
flight times for two different-length flight paths and a set value. 
Since the free flight speed and thus the speed at impact is just the 
quotient of a flight path difference and a time difference between the 
flight durations for the different flight paths, then from the flight time 
difference, when, the flight path length difference is known, the flight 
speed at impact can be determined by division and thus the impact energy 
can be thus be derived from that. 
Different free flight paths can be obtained, according to one embodiment of 
the invention, by measuring successive impact of different type elements 
or letter keys of different thickness. If, e.g., one type element of a 
type wheel with a greater thickness than another type element is struck by 
the same hammer, thus the free flight path of the hammer is shortened. The 
path differences in the path of the hammer can be directly related to 
thickness differences of the type elements struck in succession. 
In another embodiment of the invention different length free flight paths 
for the same letter key or type element are obtained by insertion of a 
strip of material of thickness between the strip of material and the 
substrate in the vicinity of the impact. Therefore one and the same type 
element or letter key directly strikes the substrate or the typewriter 
roll one time and immediately after that impacts with the material strip 
intervening. Consequently, different flight times result, so that the free 
flight speed can be obtained from the flight time difference and the 
flight path difference which is equal to the thickness of the material 
strip. 
Because of the features of the inventive method all variables, which are 
relevant to the acceleration region of the hammer, are not considered and 
only the free flight speed is taken into consideration and determined. 
A microphone, for example, can be used as sensor for detection of the 
occurrence of the hammer impact on the typewriter substrate and/or the 
typewriter roll. This microphone converts the sound of the impact into an 
electrical signal which is received by a processor means which determines 
the impact time. 
To be sure that a running adjustment of the impact energy in cases of 
variation of the impact energy from a predetermined set value occurs 
properly, the microphone can be attached rigidly to the typewriter or 
printer, and an adjustment is performed by comparison with stored set 
value flight time difference for two known type elements during the 
typewriter operation and by current flow duration in the hammer 
electromagnet performed according to that comparison.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A hammer electromagnet 1, which is formed as a substantially cylindrical 
electromagnet, is shown in FIGS. 1 and 2. A hammer 2 longitudinally 
slidable in the hammer electromagnet 1 is positioned to be accelerated in 
the direction of a typewriter roll 3. A sensing means 4, e.g. including a 
microphone, is provided on the other side of the typewriter roll 3 from 
that of the hammer electromagnet 1. This sensing means 4 detects the 
impact of the type element 6 on the typewriter roll 3. 
A processor means 9 is connected to sensing means 4 to receive signals from 
the sensing means 4 and to store a time of impact of the type element 6 
determined from the signals received from the sensing means 4. The 
processor means 9 is also connected to and controls the current flow in 
the hammer electromagnet 1. 
In the embodiment shown in FIG. 1, a strip of material 5 of thickness S can 
be put between a type element 6 receiving the impact of the hammer and the 
typewriter roll 3 so as to shorten the free flight of the hammer 2 and to 
allow the determination of the flight time difference between the impact 
times of the type element 6 with and without the intervening strip of 
material 5. 
In the method according to FIG. 1 as shown diagrammatically in FIG. 3 the 
hammer 2 drives the type element 6 to impact on the typewriter roll 3. The 
flight time t.sub.I between onset of current in the electromagnet and 
impact of the type element 6 on the substrate consists of an acceleration 
time t.sub.1 plus a free flight time t.sub.2 during which its speed is 
constant. The flight time is measured as the difference between the impact 
time of the type element 6 and the time current flow in the electromagnet 
and is stored in the memory of processor means 9. Then the strip of 
material 5 is interposed between the typewriter element 6 in the vicinity 
of the place of impact and the typewriter roll 3. The flight time t.sub.II 
is measured again as the difference between the time current flows in the 
electromagnet and the time of impact and is also stored in the memory of 
the processor means 9. The free flight time t.sub.3 and thus the flight 
time t.sub.II differs from the previously measured values without the 
strip of material 5 present, because the strip of material 5 changes the 
free flight time, however the type element speed will be the same. Then 
the speed of the type element 6 can be determined since it equals the 
thickness S of the strip of material 5 divided by the difference of the 
flight times t.sub.I -t.sub.II stored in the processor means 9. 
In the embodiment according to FIG. 2, a flight time difference is 
attained, because type elements 7 and with different thicknesses S1 and/or 
S2 impact one after the other. Just as in the embodiment according to FIG. 
1 the flight time difference the known thickness difference S1-S2 allows 
one to determine the free flight speed and thus provides information on 
the determination of the impact energy. 
While the invention has been illustrated and described as embodied in a 
method of adjusting the impact energy of a letter key or type element and 
typewriter, printer and the like printing machine using that method, it is 
not intended to be limited to the details shown, since various 
modifications and structural changes may be made without departing in any 
way from the spirit of the present invention. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention. 
What is claimed is new and desired to be protected by Letters Patent is set 
forth in the appended claims.