Stylus printer impact energy control

In a magnetically operated matrix printer a circuit makes a decision when a magnet is actuated. The decision is whether or not the relevant magnet has already been actuated during the printing of the previous column of the matrix character being printed. When it has not been actuated, it is actuated with a larger quantity of energy (longer pulse). Thus the operation of the printer is in "resonance" with the mechanical movements of the magnet armature.

The invention relates to a stylus printer, comprising a number of printing 
styli which are arranged one underneath the other, each stylus being 
movable by an electromagnet so as to print a dot on a record carrier, the 
arrangement being such that a character to be printed can be built up in 
columns by selective actuation of the magnets in combination with a 
relative movement of the record carrier with respect to the printing 
styli, a magnet being actuated by one energy pulse or by a series of 
energy pulses, depending on the shape of the character to be printed. 
During the printing of a matrix character, a printing head in which the 
printing styli are arranged in a row one underneath the other, is 
intermittently or continuously moved from one matrix column to the next 
matrix column. The character to be printed is then built up in columns. 
The printing styli are selectively actuated for this purpose. For example, 
for the printing of the character "A", the upper one of, for example, 
seven printing styli, being arranged one underneath the other, is actuated 
only once, the second stylus being actuated twice with a short interval, 
the third and the fourth stylus being each time actuated twice with a long 
interval, the fifth stylus being actuated five times in succession, and 
the sixth and the seventh stylus being moved only twice with one long 
interval by the associated magnet. Consequently, for the character "A" the 
magnets of the fifth printing stylus are energized by a series of pulses, 
whilst the other magnets are controlled by only single pulses. For other 
letters or digits, there are other combinations of pulse series and single 
pulses. 
The repetition frequency at which the magnets are to be actuated 
constitutes a restrictive parameter for high printing speeds. For example, 
it is difficult to keep the masses to be moved small enough and to adhere 
at the same time to the conditions for an efficient electromechanical 
energy conversion. Therefore, matrix printers of this kind operate with 
short strokes and substantial development of heat in the coils. However, 
this is a drawback for the application of this printing principle. 
It has already been attempted to eliminate these drawbacks by operating the 
printing magnets so that the actuation pulses and the movement are 
adjusted to resonance in the case of a continuous pulse series, i.e., it 
is attempted to attune the actuation in the time of the magnets for the 
printing of characters to the mechanical movements of the magnet systems. 
However, in practice this effect cannot be utilized, or only when a poor 
printing quality is accepted, because the actuation pulse series is 
discontinuous, depending on the character matrix. 
The invention has for its object to attune the actuation and the mechanical 
properties of the magnets of a stylus printer to each other so that 
resonant operation is possible in the case of a continuous and 
approximately equidistant pulse series. To this end, the stylus printer in 
accordance with the invention is characterized in that for the selective 
actuation of the magnets there is provided a control circuit which is 
adapted to determine whether a magnet to be actuated has already been 
actuated during the printing of the directly preceding column, and to 
supply a magnet where this is the case with a pulse containing a quantity 
of energy which is smaller than that applied to a magnet where this is not 
the case. 
It is to be noted that from German Patent specification no. 1,181,241 it is 
known that for typewriters or automatic printing devices comprising type 
levers it must be determined, prior to the printing of a complete 
character, whether the type lever to be operated is struck for the first 
time or repeatedly. However, this introduces a delay in order to force the 
type arm back to the starting position in the case of repeated striking. 
However, in this case the energy supply cannot be influenced, so that no 
effect whatsoever can be exerted on the printing image of the character to 
be printed. 
However, in the stylus printer in accordance with the invention an 
advantage is obtained in that for the same stroke of the styli operation 
at a higher speed or, for the same speed, operation with a longer stroke 
can be realised. It is also achieved that the mean quantity of electrical 
energy to be applied is smaller, because, due to the supply of the larger 
quantity of energy at the first pulse, the subsequent pulses are exactly 
in resonance with the mechanical movements of the stylus and hence require 
substantially less energy than in the known method.

As is known, the printing points required for the reproduction of the 
character in maxtrix printing are chosen from the total number of possible 
matrix points. In this embodiment, the character to be printed is built up 
of n columns, in that the magnets M1 to Mn of the associated printing 
styli N1 to Nn are separately actuated one after the other or in a 
sequence. For each column of the matrix print the corresponding pulse 
combination is applied (in a known manner not shown) to the input I of a 
first register A1. This register comprises outputs 11 to 1n which are 
connected to a second register A2 which receives, after the printing of a 
column, the contents of the first register A1, said register A2 having 
corresponding outputs 21 to 2n. The first register A1, moreover, is 
connected to two clock generators T1 and T2 so that both clock generators 
T1 and T2 are switched on as soon as one or more outputs 11 to 1n are 
actuated in the register A1. The clock generators T1 and T2 supply pulses 
having the same pulse repetition frequency, be it that they have a 
different pulse duration. The first clock generator T1 supplies pulses 
which are longer than those supplied by the second clock generator T2. 
Their ratio with respect to each other can be chosen at random and is 
determined by the pulse repetition frequency and by the geometrical and 
magnetic properties of the magnets. 
The outputs of the registers A1 and A2 and the two clock generators T1 and 
T2 are followed by logic networks V1 to Vn, each of which is associated 
with a switching circuit of one of the printing magnets M1 to Mn. These 
logic networks V1 to Vn consist of the delta connection of each time two 
AND-gates U1i and U2i and one OR-gate Oi (i=1 to n). Each of the AND-gates 
comprises three inputs which, as is clearly shown in the drawing, are 
connected to the outputs of the registers A1 and A2 and to the outputs of 
the two clock generators T1 and T2. While the outputs 11 to 1n and 21 to 
2n of the two registers A1 and A2 respectively, are each time connected to 
both associated AND-gates, each AND-gate is each time connected to only 
one of the two clock generators T1 and T2. Moreover, the outputs of the 
second register A2 are connected directly to the one AND-gate U2i to U2n 
and in inverted form to the input of the other AND-gate U11 to U1n. 
Each logic network V1 to Vn has associated with it a transistor Tr1 to Trn, 
the emitter of which is connected to a voltage +U2, the collector being 
connected, via resistors, to a switching circuit of one of the magnets M1 
to Mn. These switching circuits comprise switching transistors TM1 to TMn, 
which are capable of connecting the magnets M1 to Mn to a voltage U1 which 
is chosen so that it is sufficient to actuate the magnets. 
When it is assumed that printing of characters takes place in accordance 
with a matrix of seven rows R1 to R7 and five columns C1 to C5 (see FIG. 
2), seven magnets M1 to M7 are required. If, for example, the letter "E" 
is to be printed on the record carrier P, the input I of the first 
register A1 for the printing of the first column C1 receives a pulse 
combination which actuates all seven outputs 11 to 17 of the first 
register A1. Simultaneously, the clock generators T1 and T2 are switched 
on. Via the connection lines between the outputs 11 to 17 and the inputs 
of the corresponding AND-gates U11 to U17 and U21 to U27, these two 
AND-gates are each time prepared. Because the outputs 21 to 27 of the 
second register A2 are not actuated, the inputs of the AND-gates U21 to 
U27 connected to these outputs are not prepared; however, the 
corresponding inputs of the AND-gates U11 to U17 are prepared by the 
inversion. 
Because the two clock generators T1 and T2 have the same pulse repetition 
frequency, pulses are simultaneously applied to the various AND-gates via 
the corresponding lines. However, only the AND-gates U11 to U17 which are 
connected to the first clock generator T1, supplying the longer pulses, 
are conductive for the duration of this pulse and switch, via the 
subsequent OR-gate O1 to O7, the transistors Tr1 to Tr7 and hence the 
magnets M1 to M7. Thus, for the printing of the first column C1 all 
magnets are actuated and the first column of the letter "E" is printed. 
For the sake of simplicity, the drawing shows only the first, the second 
and the last magnet with the corresponding circuits. 
After termination of the pulse supplied by the first clock generator T1, 
the state prevailing on the outputs 11 to 17 of the first register A1 is 
transferred to the second register A2, so that instead of the outputs 11 
to 17 the outputs 21 to 27 are actuated. When the combination of the 
second column C2 to be printed appears via the input I of the first 
register A1 (in this example, the first, the fourth and the seventh matrix 
point of the seven possible matrix points would be concerned), the outputs 
11, 14 and 17 are actuated in the register A1. 
At the same time, the clock generators T1 and T2 are actuated again. 
The situation then arising for the outputs 11, 14 and 17 differs from that 
for the outputs 12, 13, 15 and 16. For the outputs 11, 14 and 17, the 
outputs 21, 24 and 27 of the second register A2 are at the same time also 
actuated, so that the AND-gates U21, U24 and U27 switch due to the 
inversion, while the AND-gates U11, U14 and U17 are blocked. Thus, via the 
associated OR-gates O1, O4 and O7, the subsequent transistors Tr1, Tr4 and 
Tr7 are switched by the second clock generator T2 which supplies the 
shorter pulse. As has already been described, the magnets M1, M4 and M7 
are thus energised. 
The outputs 12, 13, 15 and 16 of the first register A1 are not actuated, 
but the corresponding outputs 22, 23, 25 and 26 of the second register A2 
are actuated. Thus, the inputs of the AND-gates U22, U23, U25 and U27 
which are connected to the outputs 22, 23, 25 and 27 of the register A2 
are prepared, but the inputs of the AND-gates U12, U13, U15 and U16 
connected thereto are not prepared. (Because the outputs 12, 13, 15 and 16 
of the first register A1 and hence those of the AND-gates U12, U13, U15 
and U17 connected thereto are not actuated, the two AND-gates for the 
outputs 22, 23, 25 and 26 of the second register A2 remain inactive. The 
printing magnets M2, M3, M5 and M6 connected to these combination circuits 
are not energised. For the printing of the character "E", the same 
switching situation will prevail for the following columns C3 to C5, so 
that for all further matrix points each time only the short pulses 
supplied by the second clock generator T2 become effective. 
It will be obvious from the foregoing description that a switching 
transistor Tri is connected to the second clock generator T2, supplying 
the short pulses, by the logic network Vi only if a voltage is present on 
the relevant output 1i of the first register A1 as well as on the relevant 
output 2i of the second register A2. However, if the output 1i of the 
first register A1 is actuated, but the associated output 2i of the second 
register A2 is not actuated, the associated switching transistor Tri is 
connected to the first clock generator T1 supplying the longer pulses. 
Connection of the transistor Tri to one of the clock generators T1 or T2, 
however, is not effected when only the associated output 2i of the second 
register A2 is actuated, but not the associated output 1i of the first 
register A1. 
The circuit shown in the drawing is merely a diagrammatic example. The same 
effect can also be readily obtained by another switching device. For 
example, in that it is checked whether or not a given period of time has 
expired between two actuation pulses and that the actuation time is 
increased or reduced in dependence thereof. The supplied voltage U1 or the 
coil current can also be varied instead of the influencing of the 
actuation time of the magnets. Combinations of these variants are also 
possible.