Background of the Invention
1. Field of the Invention
[0001] This invention relates in general to a serial printer which includes a rotatable
print wheel. More particularly, this invention relates to a serial impact printer
which serrates a check or other document with a protected amount field. Still more
particularly, this invention relates to a serial print wheel engine for use as the
protect amount print station of a check writer.
2. Description of the Prior Art
[0002] Serial printers which include a print element in the shape of a disk or cup are known
in the art. In general, such printers can be divided into two types. In the first
type, the print element is constantly rotating and printing takes place on the fly.
In the second type, the print element stops and starts and printing takes place while
the print element is stationary.
[0003] An example of a serial printer with a constantly rotating print element can be found
in U. S. Pat. No. 3,461,235 (Wilcox). Examples of a serial printer with a print element
that stops before printing occurs can be found in U. S. Pat. Nos. 3,707,214 (Panzo)
and 4,037,707 (Ku).
[0004] Serial print elements where the print element is in the shape of a cup are also known.
For example, U. S. Pat. No. 3,640,369 (Rolph) shows a print element with a cup-shaped
shell having integrally formed characters on the outer surface of the shell.
[0005] In U. S. Pat. No. 4,037,707 (Ku), the sides of a cup shaped print element are formed
by a plurality of fingers, each of which has a number of characters. A hammer is located
in the center of the cup. Printing is accomplished by rotating the cup so that the
desired finger is located between a hammer and the paper. The hammer is then fired
to print the desired character.
[0006] In the cited prior art references, the hammer utilized to depress the characters
against the paper provides sufficient pressure to accomplish normal printing. However,
the hammer pressure is insufficient to enable the print characters to serrate the
paper in the manner required to produce a protected amount field on a check or other
document.
Objects of the Present Invention
[0007] It is the general object of the present invention to provide an improved serial printer.
[0008] It is another object of the present invention to provide a serial printer which produces
high quality printing of a serrated protected amount field on a check or other document.
[0009] It is still another object of the present invention to provide a serial printer for
printing serrated characters on a document wherein the print force is precisely controlled.
[0010] It is yet another object of the present invention to provide a serial printer which
generates a low level of accoustical noise when operating.
[0011] It is a further object of the present invention to provide a low cost, high reliability
serial printer which requires little maintenance.
[0012] The foregoing and other objects, features and advantages of the invention will be
apparent from the following description of the preferred embodiment of the invention,
as illustrated in the accompanying drawings.
Summary of the Invention
[0013] The foregoing and other objects and advantages are achieved by providing a print
wheel including a wheel-like circular member, the hub of which is rotated by a motor
to position the desired print character in a print position. In the preferred embodiment,
each print character is mounted on the first end of a finger-like element, the second
end of each finger-like element mounted in the top of the circular member's perimeter.
[0014] Positioned within the circular member, behind the print position, is an anvil against
which the back of the print character is pressured by an impact mechanism during a
print operation. The impact mechanism is positioned outboard of the circular member.
It includes a d.c. motor which turns a threaded shaft either clockwise or counterclockwise.
The threaded shaft is coupled to a threaded hole bored in the end of a hammer. The
head of the hammer is positioned in front of the print position. The hammer passes
through a guide which prevents the hammer from rotating as the d.c. motor rotates.
The document and an inked ribbon are fed in between the hammer's head and the print
wheel and are repositioned after each character is printed.
[0015] When the d.c. motor is turned counterclockwise, the threaded shaft moves the hammer
toward the anvil so that the hammer's head pushes the selected character against the
anvil at a precisely controlled force. The selected character image is thus printed
and serrated on the document. The d.c. motor is then rotated clockwise to restore
the impact mechanism to its original position. Next, the print wheel is rotated to
position the next selected character to be printed into position in front of the anvil.
Brief Description of the Drawings
[0016]
FIG. 1 shows a top view of the preferred embodiment of the present invention.
FIG. 2 is a side view of the print wheel and anvil shown in FIG. 1.
Description of the Preferred Embodiment
[0017] An overall view of the major elements of the printer is shown in FIG. 1. The printer
includes a print wheel 10, an anvil 12, and an impact mechanism 14. A document 16
or other recording medium is positioned between the print wheel 10 and impact mechanism
14. Print wheel 10 is rotated by a motor 18. A frame 20 supports anvil 12. An inked
ribbon 22 is positioned between print wheel 10 and document 16.
[0018] The document 16 and ribbon 22 are incrementally advanced in the direction shown between
each print operation. For clarity and ease of illustration, the support and drive
mechanisms for the ribbon 22 and document 16 are not shown. Both can be constructed
from conventional drive mechanisms which are well known in the prior art.
[0019] Motor 18 selectively rotates the print wheel 10 whereby a selected print finger 24
can be positioned between anvil 12 and ribbon 22. The rotational motion of print wheel
10 stops before the impact mechanism 14 presses the ribbon 22 and document 16 against
the finger 24, which is in turn pressed against the anvil 12 to print a character.
In the preferred embodiment, neither the impact mechanism 14 or print wheel 10 moves
across the document 16. Instead, means (not shown) reposition the document 16 prior
to printing each character.
[0020] In the preferred embodiment, print wheel 10 has sixteen fingers designated 24-1 to
24-16. For clarity of illustration, not all of the fingers 24-1 to 24-16 are shown.
Each of the fingers 24-1 to 24-16 has either one of the character digits 0-9 or a
special character(s), the set of sixteen fingers 24-1 to 24-16 thus including all
characters necessary to print a protected field on document 16. In the preferred embodiment,
the characters on the fingers 24-1 to 24-16 are formed from raised line patterns.
As a result, when a character is printed on the document 16, the character's line-like
pattern serrates the document 16, thus providing one character of the protected amount
field.
[0021] Details of how the print wheel 10 is constructed are shown in FIG. 2. Print wheel
10 is mounted on shaft 26 which is connected to motor 18. Print wheel 10 includes
a wheel-like circular member 28, the hub 30 of which is connected to shaft 26 by setscrew
32. Each finger 24-1 to 24-16 is mounted in a corresponding slot in the perimeter
of the circular member 28 by a semi-flexible steel bar 34. A print character element
36 is mounted on the unconnected end of each steel bar 34. A steel print character
38 is attached to the outer surface of each print character element 36.
[0022] In the preferred embodiment, a conventional stepper motor is used for motor 18. The
circuitry for driving the stepper motor to position the desired finger 24 in front
of anvil 12 is not shown herein since such circuitry could be conventional commercially
available circuitry.
[0023] Referring again to FIG. 1, the operation of the impact mechanism 14 will now be explained.
In the preferred embodiment, the impact mechanism 14 is driven by a conventional d.c.
motor 40, such as that manufactured by Indiana General. Alternately, a conventional
rotary-type solenoid such as that manufactured by Ledex can be used instead of d.c.
motor 40. In the preferred embodiment, the d.c. motor 40 is characterized as rotating
in either direction in response to supplied control signals. The circuitry for controlling
the d.c. motor will be described below.
[0024] The shaft 42 of d.c. motor 40 is connected to threaded shaft 44 which thereby rotates
the same number of degrees and in the same direction as the d.c. motor 40. The threaded
end of shaft 44 is engaged with corresponding female threads machined in the end of
hammer 50. Alternately, the hammer 50 may be molded with the threaded hole included,
thus eliminating the need to machine the threaded hole.
[0025] In the preferred embodiment, the hammer 50 is of a semicylindrical shape and is fabricated
from steel or another suitable material. The hammer 50 is slidably mounted in an aperture
in guide 52.
[0026] In the preferred embodiment, the outer cylindrical surface of hammer 50 has two flat
sections running along its longitudinal axis. Corresponding flat sections are also
provided in the aperture in guide 52. The purpose of the flat sections is to insure
that the hammer 50 does not rotate as it is moved toward or away from the print wheel
10. As an alternative, the cylindrical shape of the hammer 50 may instead be square
or hexagonal with the aperture in guide 52 being similarly shaped, the object again
being to prevent the hammer 50 from rotating.
[0027] In the preferred embodiment, the guide 52 is made of a material such as plastic which
provides a low friction surface for the outer surface of the hammer 50 to slide against.
[0028] The operation of the printer will now be described in detail. The motor 18 is rotated
to position the print finger 24 corresponding to the character selected to be printed
in front of anvil 12. Either before, after or during the respositioning of print wheel
10, the ribbon 22 and document 16 are advanced to position the area of the document
16 to be printed on in front of the selected print finger 24.
[0029] Next, a first polarity d. c. current is applied to d. c. motor 40 causing it to rotate
in a counterclockwise direction, thereby causing hammer 50 to be moved toward anvil
12. The level of the first polarity current is chosen to result in a specific amount
of torque being generated by the d. c motor 40. As a result, the amount of force the
hammer 50 exerts against the selected print character element 36 is precisely controlled.
The time duration of the first polarity current is chosen to assure that the hammer
50 will move a sufficient distance so that it bottoms out pressing the selected print
character element 36 against anvil 12 with the motor 40 in a stalled condition, thereby
causing the selected print character 38 to print and serrate the document 16 with
the selected character. After the first polarity current has been applied for the
chosen time duration, an opposite polarity current is applied to d. c. motor 40 causing
it to rotate in a clockwise direction, thereby causing hammer 50 to be restored to
its original position. The time duration that the opposite polarity current is applied
is the same as that for the first polarity current, so that on the return stroke the
hammer 50 bottoms out against return stop 56.
[0030] Thereafter, the ribbon 22, document 16, and (if necessary) the print wheel 10 are
repositioned and the same operation is repeated to print the next selected character
on the document 16. Of course, the above-described sequence is performed quite rapidly
so that printing speed typically in the range of 3-10 cps may be achieved.
[0031] The print force is determined by the torque that motor 40 applies to threaded shaft
44. Those skilled in the art will appreciate that the torque of d. c. motor 40 is
proportional to its current and that the motor 40 torque can be controlled in two
ways, namely by directly controlling the current through the motor 40 with a constant
current controller 54 or indirectly by controlling the voltage applied to the motor
40. In the preferred embodiment, the torque necessary to achieve the desired print
force is precisely controlled by controlling the current through d. c. motor 40. The
design of the current control circuitry 54 necessary to achieve a motor torque which
produces the desired print force is not shown herein, but will be obvious to those
of ordinary skill in the art.
[0032] Those skilled in the art will appreciate that a character to be printed having a
large surface area (i.e., an "8") requires a relatively larger print force to achieve
optimum serration than a character having less surface area (i.e., a "1"). By utilizing
a current controller 54 to control the motor 40 current, the optimum print force may
be obtained for each character printed by varying the torque generated by motor 40.
[0033] In the preferred embodiment, a standard microprocessor (not shown) receives inputs
from a keyboard (not shown) used by the operator to select the character to be printed.
In response to the selection of a character, the microprocessor determines whether
the character selected has a relatively large, medium or small amount of surface area.
Based on this determination, the microprocessor provides logic signals to the current
controller 54 indicating which of three print force levels is to be utilized to print
the selected character. In response to these logic signals, the current controller
54 changes the current through the motor 40 to one of three levels, the largest current
level corresponding to selected characters having the largest surface area.
[0034] Various designs of the microprocessor and current controller 54 will be obvious to
those skilled in the art. What is important is the fact that the motor 40 current
can be precisely controlled to achieve the optimum print force.
[0035] In the preferred embodiment, the first polarity current is applied to the d. c. motor
40 for approximately 30 milliseconds and immediately thereafter the opposite polarity
current is applied for 30 milliseconds. Nominally, the time duration of each of the
first or opposite polarity currents causes d. c. motor 40 to rotate counterclockwise
or clockwise by approximately 180 degrees, respectively. However, in actual operation,
during the forward thrust, the motor 40 rotates counterclockwise until it stalls with
the selected print character element 36 forced against the anvil 12. Similarly, on
the return stroke, the motor 40 rotates clockwise until it stalls with the hammer
50 against the return stop 56. Typically, such stalling occurs when the motor 40 has
rotated counterclockwise or clockwise by a few degrees more or less than the nominal
180 degrees.
[0036] The number of degrees the motor 40 rotates is dependent on the thread helix angle
of shaft 44 and the distance the hammer 50 must travel before it bottoms out with
the selected print character element 36 against the anvil 12. In the preferred embodiment,
a nominal 180 degree rotation of motor 40 was chosen since the motor 40 has two sets
of brushes. Thus, by rotating the motor 40 180 degrees each set of brushes gets equal
wear.
[0037] Those skilled in the art will appreciate that variations in the speed of d. c. motor
40, the throw length of the hammer 50 and the thread coarseness of shaft 44 will necessitate
changes in the time duration of the first and opposite currents. Those skilled in
the art will further appreciate that the directions of rotation of motor 40 and the
thread directions of shaft 44 and the hole in hammer 50 may be reversed without changing
the direction of movement of the hammer 50 toward and away from the anvil 12.
[0038] Although the preferred embodiment of the impact mechanism is only capable of varying
the level of print force in response to the character selected to be printed, those
skilled in the art will appreciate that modifications may be made to additionally
vary the print force depending on the number of plys in the document 16. For example,
a switch may be added to enable the operator to select the number of plies in the
document 16 to be printed. In response to a selected switch setting, the voltage level
or current to the d. c. motor 40 can further be varied so that the torque generated
by motor 40 is increased when the switch is set to a position corresponding to an
increased number of document 16 plies.
[0039] As another alternative, the previously discussed microprocessor may additionally
be responsive to a detector which detects the number of plies in the document 16.
Based on the character to be printed and the number of plies in the document 16, the
microprocessor would signal the current controller 54 to change the motor 40 current
to generate a torque which will produce an optimum force to print and serrate the
document 16 for each selected character.
[0040] Having shown and described the preferred embodiment of the present invention, we
state that the subject matter which we regard as being our invention is particularly
pointed out and distinctly claimed in the following claims. Those skilled in the art
to which the present invention pertains will appreciate that equivalents or modifications
of, or substitutions for, parts of the specifically described embodiment of the invention
may be made without departing from the scope of the invention as set forth in what
is claimed.
1. A printer operative to selected one from among a plurality of print character elements
(36,38), to position said selected print character element (36,38) adjacent to a document
(16) between a hammer (50) and an anvil (12), to advance the hammer (50) towards the
selected print character element (36,38) to urge the selected print character element
(36,38) against the anvil (12), and thereafter to withdraw the hammer (50) to allow
retraction of the selected print character element (36,38) from the anvil; said printer
being characterised by said hammer (50) being operative to urge said selected print
character element (36,38) against said anvil (12) with a controlled force whose magnitude
depends upon which one out of said plurality of print character elements (36,38) is
the selected print character element (36,38).
2. A printer according to Claim 1 further characterised in that said hammer (50) is
operative to vary said controlled force dependently upon the number of plies in the
document (16).
3. A printer according to Claim 2 further characterised by comprising switch selection
means selectably operable to provide output indicative of the number of plies in the
document.
4. A printer according to Claim 2 further characterised by comprising a detector operative
to detect the number of plies in the document (16) and to provide output indicative
thereof.
5. A printer according to any of the preceding Claims further characterised by comprising;
an electric motor (40) coupled to advance said hammer (50) towards said anvil (12)
and to stall when said hammer (50) fully engages said anvil (12); and a current controller
(54) coupled to provide a controlled electric current to said motor (40); where said
current controller (54) is operable in response to a control signal (LOGIC SIGNALS
FOR SELECTING PRINT FORCE) indicative of which one out of said plurality of print
character elements (36,38) is the selected print character element (36,38) to control
the magnitude of said controlled electric current.
6. A printer according to Claim 5 wherein said current controller (54) is operative
to select one of three force levels dependently upon whether said selected print character
element (36,38) carried a print character (38) of large, medium or small area, said
print force increasing with increase in said area.
7. A printer according to Claim 5 or Claim 6 when dependent upon Claim 2, 3 or 4 wherein
said control signal (LOGIC SIGNALS FOR SELECTING PRINT FORCE) includes further indication
to said current controller (54) being operable in response to said further indication
to vary said magnitude of said controlled current.
8. A printer according to Claim 7 when dependent upon Claim 4 wherein said output
of said detector is coupled to provide said further indication of the numberf of plies
in the document (16).
9. A printer according to Claim 7 when dependent upon Claim 3 wherein said output
of said switch selection means is coupled to provide said further indication of the
number of plies in the document (16).