Ribbon feed mechanism

A ribbon feed mechanism for printing machines has a motor coupled to a ribbon drive mechanism for feeding a ribbon in response to energization of the motor. A control mechanism is coupled to the ribbon drive mechanism and responsive to the ribbon drive mechanism during ribbon feeding for limiting the amount of ribbon feed to predetermined feed increments.

BACKGROUND OF THE INVENTION 
The present invention relates to a ribbon feed mechanism for printing 
machines and more particularly relates to a control mechanism for 
incrementally feeding a print ribbon in a ribbon cassette. 
A known ribbon feed mechanism has a motor coupled to a ribbon drive 
mechanism by a slip clutch for advancing a print ribbon from a supply 
spool to a take-up spool. A control mechanism including a stepping magnet 
is connected to the print ribbon for limiting the amount of ribbon feed to 
predetermined feed increments. This ribbon feed mechanism is disclosed in 
U.S. Pat. No. 3,481,446 issued on Dec. 2, 1969 and invented by Gisbert 
Burkhardt et al. 
A disadvantage of this ribbon feed mechanism is having a stepping magnet 
and having a means for selectively energizing the stepping magnet in 
addition to the motor for advancing the ribbon results in excessive 
manufacturing costs. 
A known linespacing mechanism has a D.C. motor coupled to a drive member 
which includes a cam profile having a cam surface and an abutment. The 
linespacing mechanism has a cam follower for following the cam surface to 
provide a power source for actuating linespacing increments. The cam 
follower also contacts the abutment for stopping the drive mechanism. This 
linespacing mechanism is disclosed in U.S. Pat. No. 4,365,904 issued on 
Dec. 28, 1982 and invented by Hans W. Mueller et al. 
A disadvantage of this linespacing mechanism is having the cam follower 
provide the power source for actuating the linespacing requires additional 
linkage compared to the present invention which results in excessive 
manufacturing costs. 
SUMMARY OF THE INVENTION 
A ribbon feed mechanism for printing machines has a D.C. motor coupled to a 
wheel for incrementally rotating the wheel. A drive shaft is rigidly 
connected to the wheel for rotation therewith. The drive shaft engages a 
drive member in a ribbon cartridge for feeding a print ribbon mounted in 
the cartridge in response to energization of the stepper motor. A toothed 
shaped cam profile is formed in the wheel. A control mechanism includes a 
cam follower mounted on a pivotable arm actuated by the cam profile in 
response to rotation of the wheel for limiting the amount of rotation of 
the wheel to limit the amount of ribbon feed to predetermined feed 
increments. 
Accordingly an object of this invention is to provide a low manufacturing 
cost and an efficient ribbon feed mechanism by combining an economical 
control mechanism and a D.C. motor for limiting the amount of ribbon feed 
to predetermined feed increments. 
Other objects, features and advantages of the invention will become more 
apparent from the following description, including appended claims and 
accompanying drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a ribbon feed mechanism 10 for printing machines 
consists of a power source 12 coupled to a drive means 14 for feeding a 
print ribbon 16 carried in ribbon cartridge 18 (FIG. 4). A control means 
20 is coupled to the drive means 14 for limiting the amount of ribbon feed 
to predetermined feed increments. 
The power source 12 includes a D.C. motor 22 and a pinion gear 24 mounted 
on a shaft 26 of the D.C. motor 22. 
The drive means 14 includes a wheel 28 which has gear teeth 30 integrally 
formed around a periphery thereof. The gear teeth 30 are in mesh with the 
pinion gear 24 for coupling the drive means 14 to the power source 12. A 
drive shaft 32 is supported on a frame 34 for rotation relative thereto. 
The wheel 28 is rigidly assembled to the drive shaft 32 for rotation 
therewith. When the ribbon cartridge 18 is inserted into the printing 
machine, the drive shaft 32 engages a drive member 36 in the ribbon 
cartridge 18 (FIG. 4) for feeding the print ribbon 16. A cam profile 38 is 
integrally formed in a face 40 of the wheel 28. The cam profile 38 
includes an outwardly projecting tooth 42 (FIG. 2), which has a first 
working cam surface 44 and a second working surface 46. The cam profile 38 
also includes an inwardly projecting tooth 48, which has a non-working 
surface 50 and an abutment 52. The cam profile 38 forms a circular path 
made up of a plurality of the teeth 42 and 48 and arranged parallel to and 
with a smaller diameter than the gear teeth 30 of the wheel 28. 
The control means 20 includes an arm 54 pivotably mounted on a post 56 
between two rubber washers 58 and 60 (FIG. 1). A cam follower 62 is 
rigidly attached to a free end 64 of the arm 54. The cam follower 62 is 
seated in the cam profile 38 at an inoperative or rest position 66 (FIG. 
2). A spring 68 connected between the arm 54 and a rigid spring anchor 70 
biases the arm 54 clockwise about the post 56. The cam follower 62 is 
biased in the rest position 66 by the spring 68. A disc 72 (FIG. 1) is 
mounted on a hub 74 integrally formed with the wheel 28 by a c-ring 76. A 
finger 78 is integrally formed from the arm 54 to abut against the disc 72 
for holding the cam follower 62 seated in the cam profile 38. 
A ribbon feed operation will now be described. When a single printing 
operation is actuated in the printing machine, the D.C. motor 22 is 
energized for a sufficient length of time (38 milliseconds) to rotate the 
pinion gear 24 clockwise a slightly greater amount than that needed to 
feed the print ribbon 16 a full predetermined increment. The pinion gear 
24 rotates the wheel 28 counterclockwise about its axis 80. The wheel 28 
rotates the drive shaft 32 counterclockwise about the axis 80. The drive 
shaft 32 will rotate the drive member 36, when the ribbon cartridge 18 is 
inserted into the printer, which will feed the print ribbon 16. The amount 
of the print ribbon 16 fed is controlled by the combination of the cam 
follower 62 and the cam profile 38. 
Referring now to FIGS. 2 and 3, when the wheel 28 is rotated 
counterclockwise by the pinion gear 24, the cam follower 62 rides along 
the cam surface 44 to locate the cam follower 62 in alignment with the 
abutment 52. The D.C. motor 22 continues to rotate the wheel 28 until the 
wheel 28 is stopped by the abutment 52 contacting the cam follower 62 
(FIG. 3). When the cam follower 62 is seated against the abutment 52, the 
abutment 52 forms a locking angle relative to a path of the cam follower 
62 when pivoted about the post 56. The locking angle of the abutment 52 
prevents the cam follower 62 from moving out of the path of the abutment 
52 whether the D.C. motor 22 remains energized or is deenergized after 
completion of the counterclockwise rotation of the wheel 28. 
To allow the cam follower 62 to return to the rest position 66, the D.C. 
motor 22 is energized by a short pulse of reverse polarity to rotate the 
pinion gear 24 counterclockwise a slight amount. The pinion gear 24 
rotates the wheel 28 clockwise a slight amount (about 8.degree.). The 
clockwise rotation of the wheel 28, opposite of the ribbon feeding 
direction, removes the locking angle of the abutment 52 from the path of 
the cam follower 62. Only a low tensioned spring 68 is needed to move the 
cam follower 62 from the abutment 52, along a passageway 82 formed between 
the abutment 52 and the second working surface 46, to the rest position 
66. It is desirable to have the spring 68 low tensioned to allow the 
rotational velocity of the wheel 28 to move the abutment 52 against the 
cam follower 62 instead of the cam follower 62 returning to the rest 
position 66 for each ribbon feed increment. A higher tensioned spring 
would require a higher rotational velocity of the wheel 28 which would 
result in an undesirable noise caused by the abutment 52 contacting the 
cam following 62. The low tensioned spring 68 also minimizes noise caused 
by the cam follower 62 returning to the rest position 66 after each ribbon 
feed increment. 
When the cam follower 62 enters the passageway 82, the second working 
surface 46 contacts the cam follower 62 to prevent further clockwise 
rotation of the wheel 28 as the D.C. motor 22 stops rotating in the 
reverse direction. 
After completing one ribbon feed increment and actuating another printing 
operation, the D.C. motor 22 will rotate the wheel 28 in the 
counterclockwise direction 38.degree.. The first 8.degree. of the 
38.degree. will take up any loss motion caused by the reverse direction of 
the previous feed increment and the next 30.degree. will rotate the wheel 
28 for feeding the ribbon a full feed increment. 
The rubber washers 58 and 60 and an integral rubber hub (not shown) formed 
therebetween minimize a noise caused by the abutment 52 contacting the cam 
follower 62, which tends to vibrate the arm 54. 
It can now be understood that limiting the amount of ribbon feed to 
predetermined feed increments by the cam follower 62 being responsive to 
the cam profile 38 provides an economical control means 20. It can now 
also be understood that the combination of the economical control means 20 
and the D.C. motor 22 provides a low manufacturing cost and efficient 
ribbon feed mechanism.