GB1604578A - Method and apparatus for sensing the position of a printing element - Google Patents

Abstract

A printing element consists of a daisywheel (10) in which the types are held at the ends of a number of radially extending spokes (38) so that they form a circular arrangement. The rotary position of the daisywheel (10) is scanned directly and optically by a number of light sources (56, 58) which are directed onto the spokes (38) and through the gaps onto a number of light detectors. The different types of the daisywheel (10), which forms the rotor of a rotary stepping motor, are maintained in the printing position in accordance with the feedback made available by the light detector. <IMAGE>

Description

(54) METHOD AND APPARATUS FOR SENSING THE POSITION OF A PRINTING ELEMENT (71) We, EXXON RESEARCH AND ENGINEERING COMPANY, a Corporation duly organised and existing under the laws of the State of Delaware, United States of America, of Linden, New Jersey, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state- ment: This invention relates to a method and apparatus for sensing the position of a printing element, more especially of printing elements of the type utilized in serial impact printers.

The printing elements of serial impact printers comprise a plurality of characters which are sequentially moved to the printing position on a copy medium. The printing element is forced and deflected into contact with a marking or inking medium which in turn contacts the copy medium by appropriate means such as a solenoid-actuated hammer.

One particularly popular printing element comprises a daisy-like array of character elements which are supported at the end of a plurality of radially extending beams.

Such a daisy-like printing element is disclosed in copending application No.

21580/78 Serial no 1601728. The particular printing element as disclosed therein additionally includes integral rotor elements which are located in the hub which forms the movable magnetic structure or rotor of a rotary stepper motor.

When serial impact printers are capable of operating in an automatic, high speed mode, it becomes particularly important to continually monitor the position of the character element and provide appropriate feedback to assure that the print wheel comes to rest at exactly the right position after approaching that position at high speed. Heretofore, this feedback has been accomplished by means coupled to the drive shaft associated with the daisy printing element but not the daisy printing element itself. Accordingly, the possibility of feedback error with respect to the exact position of the daisy printing element exists if there is any misalignment between the daisy printing element and the source of feedback despite the complexity of the system.

Moreover, the use of the printing element disclosed in the aforesaid copending application No. 21580/78 Serial No. 1601728 eliminates the drive shaft and the possibility of utilizing feedback coupled to that drive shaft.

U.S. patent 3,651,916 - Becchi discloses a daisy printing element in combination with an optical sensor which so-to-speak indirectly senses the beams or petals of the daisylike array by means of a light source and a detector located on opposite sides of, and directly sensing, the hub or shaft associated with the beams. The daisy printing element is continuously rotated (i.e., does not come to rest) and the signal generated by the sensor controls the carriage and hammer of the printer and not the position of the printing element. The drive of the printing element is not therefore controlled in response to the direct sensing of the beams or petals.

It is an object of this invention to provide improved accuracy in sensing the position of a printing element in a printer.

In accordance with the present invention there is provided printing apparatus capable of positioning a printing element; which apparatus has a printing element forming a daisy-like character wheel including a hub, a plurality of beams extending radially outwardly from the hub and character elements supported at the radial outer extremities of the beams in a substantially circular array; and which apparatus also has feedback means for sensing the position of the printing element, and means for rotatably driving and stopping the printing element in response to the sensed position, the feedback means comprising means adjacent said radially extending beams for directly sensing the position of the beams.

In a preferred embodiment, the means for directly sensing comprises optical sensor means; which means preferably include light emitting means located on one side of the printing element for directing light between and at the beams and light detecting means located on the opposite side of the printing elements for detecting the light. The light emitting means may comprise a first plurality of light sources having substantially equal spaces and a first plurality of light detectors juxtaposed to said first plurality of light sources and having substantially equal spaces therebetween.In addition, an equally spaced second plurality of light sources and an equally spaced second plurality of light detectors may be utilized where the space between the first plurality and the second plurality differs from the spaces between the light emitting sources and the light detectors within said first plurality and said second plurality.

The preferred embodiment may also include means for adjusting the light emitting means and the light detecting means on an arcuate path substantially concentric with the character element.

In the preferred embodiment of the invention, a means for rotatably driving the printing element may comprise a rotary stepper motor where the printing element comprises the rotor thereof including a plurality of arcuately arranged rotor elements located on the hub. Additional drive means move the rotary stepper motor and the character element relative to the copy medium. Hammer means strike the character elements of the printing element to force the character elements against the copy medium.

Brief Description of the Drawings Figure 1 is a top view of a printing apparatus representing a preferred embodiment of the invention; Figure 2 is an exploded view of the printing element sensing mechanism; Figure 3 is an elevational view of the system shown in Figure 1 from the side of the platen; Figure 4 is an enlarged fragmentary sectional view of the sensor shown in Figure 2; Figure 5 is an enlarged fragmentary sectional view showing the printing element and a portion of the sensor shown in Figure 2; Figure 6 is a partial sectional view showing the adjustable mounting for the sensor of Figure 2; Figure 7 is a sectional view taken along line 7-7 of Figure 6; and Figure 8 is a block diagram of a feedback loop for controlling the printing element.

Detailed Description of a Preferred Embodiment A portion of a printer or typewriter as shown in Figure 1 includes a print wheel 10 mounted on a carriage 12 which is adapted to move in a direction parallel with the axis of a platen (not shown) so as to position the print wheel 10 at various positions along a print receiving medium. As the carriage 12 is moved, the print wheel 10 is rotated by a rotary stepper motor 14 mounted the carriage 12.

The motor 14 comprises a rotor integrally formed with the printing element or wheel 10 and a stator comprising a first excited portion 16 and a second unexcited portion 18. The excited portion 16 includes winding 20 associated with various poles or phases of the stepper motor 14. Additional details of the rotary stepper motor and the wheel 10 are disclosed in copending application No.

21580/78, Serial No 1601728.

As also shown in Figure 1, the carriage 12 for the print wheel 10 is coupled to and driven by a passive slider (not shown) of a high performance linear stepper motor including a stator having an active portion 22 and a passive portion 24 so as to define a stator-to-stator air gap 26. The active portion 22 of the stator is energized by windings 28 located at each of the pole positions 30 which extend along the length of the stator.

Further details concerning the high performance linear stepper motor may be found in copending application No. 23098/ 78, Serial No. 1604268, or our U.S. Patent No. 4,149,808.

The carriage 12 is supported on the stator of the linear stepper motor by means of roller bearings 32 and other bearings disclosed in the aforesaid application No.

23098/78, Serial No. 1604268.

Referring to Figures 3 to 5, the printing element or print wheel 10 referred to with respect to Figure 1 comprises a hub 36 which supports a plurality of radially extending, flexible beams 38 which are terminated at the radial outer extremities thereof by character elements which are mounted on character slugs 40. Rotor elements 42 are inserted in the hub 36 so as to be integrally formed with the print wheel 10. The character slugs 40 are impacted by a hammer (not shown) so as to flex or deform the beams and drive the character elements into contact with an ink ribbon which in turn contacts the copy medium supported by the platen.

In accordance with this invention, the position of the print wheel 10 is sensed and determined by directly and optically sensing the beams 38 and the spaces therebetween.

More particularly, optical sensor means 44 is provided as shown in Figure 1 and Figure 4 for sensing the variation in light as the relatively opaque beams 38 and the intermediate transparent spaces or openings rotate.

As best shown in Figure 4, the sensor means 44 comprises a bracket 46 through which the beams 38 and the character slugs 40 of the print wheel 10 pass as the print wheel 10 rotates. One side 48 of the bracket 46 carries a light emitting means 50 and the other side of the bracket 46 carries light detector means 54. As best shown in Figures 2 and 5, the light emitting means may, in order to increase reliability, comprise a first plurality of light sources 56 such as light emitting diodes and a first plurality of light detecting means such as a photo diode, one of which 54 is only partially shown in Figure 2. The equal spaces between the first plurality of light sources and the first plurality of light detectors substantially corresponds with the equal spaces between pairs of beams 38, i.e., space between every other pair of beams 38.As also shown in Figures 2 and 5, the light emitting means further comprises a second plurality of light sources 58 and a second plurality of light detectors not shown. The space between the first plurality 56 and the second plurality 58 differs from the spacing between the light sources and detectors within the first plurality 56 and the second plurality 58 so as to generate signals providing information as to the direction or rotation of the print wheel 10. The sensor 44 includes an additional light source 86 and a detector 88 for sensing coded openings 59 carried by the print wheel 10 as described in copending application No. 23094/78. Serial No. 1604577.

By sensing the position of the print wheel 10 directly from the beams 38 and the openings therebetween, the position of the character elements mounted on the slugs 40 may be assured. Moreover, the mechanism for sensing the position of the character elements is greatly simplified.

Advantageously, the sensor 44 is mounted for adjustment such that the light emitting means 50 (i.e., the pluralities 56 and 58 of light sources) and the light detecting means (i.e., the first and second plurality of light detectors) may be moved along an arcuate path substantially concentric with the character element. In this connection, the bracket 44 as shown in Figures 2 and 4-6 is attached to a support 60 which is in turn slidably mounted on a member 62 including a track 64. The member 60 as shown in Figure 6 includes a slot 66 formed by portions 68 and 70 which is adapted to receive the track 64 and a spring member 72 as shown in Figures 2 and 6. The spring 72 forces the track outwardly against the wall of the portion 70 which is arcuately formed so as to conform with the track 64 and define the arcuate path of adjustment.

Adjustment is accomplished by means of a screw 74 as best shown in Figures 2 and 7 which threadedly engages a sleeve 76 which is carried by and secured to the support member 60. By fixing the head position of the screw 74 by means of a pin 78 as best shown in Figures 2 and 7, the sleeve or nut 76 is forced to rise or descend as the screw 74 is turned thereby raising or lowering the support member 60 along the defined arcuate path as well as the bracket 44. An additional screw 80 and an associated nut 82 are utilized to lock the bracket 44 in place.

In this connection, a slot 84 as best shown in Figures 2 and 6 is provided in the support member 60. With the screw 80 and the nut 82 loose, the support member 60 may slide relative to the screw 80 and the nut 82 thereby permitting adjustment of the bracket 44.

Figure 8 discloses a block diagram of a feedback sensor system utilizing the output of the sensor 44. As shown, a position determining circuit 90 utilizes the output from the sensor 44 to generate a signal representing the position of the print wheel.

The output from the positioning determining circuit 90 is then applied to motor drive circuitry 92. The motor drive is utilized to energize the winding 20 as shown in Figure 1 of the stator 94 which is magnetically coupled to the rotor 96 integrally formed with the print wheel 10 so as to control the stopping position of the print wheel 10. Of course, the beams of the print wheel which are integrally formed with the rotor 96 are directly and optically coupled to the sensor 44 as described in the foregoing. Details concerning the position determining circuit 90 and the motor drive circuit 92 may be found in copending application No. 23096/ 78. Serial No. 1600837.

The frequently used used handle or flag 100 shown in Figure 3 which extends radially outwardly from the hub 36 includes a plurality of openings 102 having spaces therebetween which are substantially identical to the circumferential width of the beams 38. This allows the feedback control of the printing element 10 even when the handle 100 is in the vicinity of the sensor 44.

In other words, the motor is capable of stopping at a plurality of positions with the handle generally in the printing position. Of course, the handle can be eliminated with beams 38 substituted in order to fill the area of the handle 100 so as not to interfere with the feedback.

Although details of a particular preferred embodiment of the invention have been shown and described, it will be understood that various modifications may be made without departing from the scope of the invention as set forth in the appended

Claims (12)

claims. WHAT WE CLAIM IS:

1. Printing apparatus capable of positioning a printing element, which apparatus has a printing element comprising a character wheel having a hub, a plurality of beams extending radially outwardly from the hub and character elements supported by the radial outer extremity of the beams in a substantially circular array; and which apparatus also has feedback means for sensing the position of the said printing element and means for rotatably driving and stopping the printing element in response to the sensed position, the feedback means comprising means adjacent said radially extending beams for directly sensing the position of said beams.

2. Apparatus as claimed in claim 1, wherein said means for directly sensing comprises optical sensor means.

3. Apparatus as claimed in claim 2, wherein said optical sensor means comprises light emitting means located on one side of said printing element for directing light between and at said beams and light detecting means located on the opposite side of said printing element for detecting said light.

4. Apparatus as claimed in claim 3, wherein said light emitting means comprises a first plurality of light sources having spaces therebetween susbtantially equal to the spaces between said beams of said optical sensor means and said light detecting means comprises a first plurality of light detectors having spaces therebetween substantially equal to the spaces between said light sources.

5. Apparatus as claimed in claim 4, wherein said light emitting means comprises a second plurality of said light sources and a second plurality of said light detectors, the spaces between said light sources of said second plurality and said light detectors of said second plurality being equal to the spaces between said light sources of said first plurality and said light detectors of said first plurality, the distance between said first plurality and said second plurality differing from said spaces.

6. Apparatus as claimed in claim 3, including adjustable means for moving said light emitting means and said light detecting means in an arcuate path substantially concentric with said printing element.

7. Apparatus as claimed in any preceding claim, wherein said means for rotatably driving said printing element comprises a rotary stepper motor and said printing element comprises the rotor of said stepper motor including a plurality of arcuately arranged rotor elements located in said hub.

8. Apparatus as claimed in claim 7, further comprising means for linearfy moving said rotary stepper motor and said printing element relative to said copy medium.

9. Apparatus as claimed in claim 7 or claim 8, wherein said character element comprises a handle portion extending radially outwardly between a pair of said beams, said handle portion including a plurality of openings having circumferential spacing substantially corresponding to the spaces between said beams.

10. A method of operating a printing element comprising a character wheel including a hub, a plurality of beams extending radially outwardly from the hub, and character elements supported at the radial outer extremities of said beams, said method comprising: directing light at said beams as said character wheel rotates; sensing the variation in light as said beams pass therethrough for determining the position of said character wheel; and stopping the character wheel in response to the determined position of said character wheel.

11. A method as claimed in claim 10, wherein said character wheel further comprises a handle portion extending radially outwardly between a pair of said beams, said handle portion incuding a plurality of openings therein, said method comprising the step of directing light through said windows; and sensing the variation in light as said beams pass through said windows for determining the position of said character wheel.

12. Printing apparatus as claimed in claim 1 and substantially as herein described with reference to the accompanying drawings.