GB2115565A

GB2115565A - Automatic pen-sensor

Info

Publication number: GB2115565A
Application number: GB08235087A
Authority: GB
Inventors: David C Tribolet; David L Paulsen
Original assignee: Hewlett Packard Co
Current assignee: HP Inc
Priority date: 1982-02-25
Filing date: 1982-12-09
Publication date: 1983-09-07
Also published as: DE3306261A1; GB2115565B; DE3306261C2; JPH0263080B2; JPS58155999A

Abstract

A bi-directional pen changer mechanism not requiring the use of mechanical or optical switches to determine pen locations, is made up of two pen stables (11, 31) for holding pens when not in use, and a pen holder (14) movable between the two pen stables for snatching a pen from or inserting a pen into either pen stable. Four physically distinct stops to the motion of the pen holder at each pen stable relate to: (1) having a pen in both the pen holder and the pen stable; (2) having no pen in either the pen stable or the pen holder; (3) having a pen in the pen stable but no pen in the pen holder; (4) having a pen in the pen holder but no pen in the pen stable. These four stops correspond to four stall points of a D.C. motor (35) used to drive the pen holder. <IMAGE>

Description

SPECIFICATION Automatic pen-sensor This invention is concerned with improvements in or relating to automatic pen-sensors.

In recent years, with the development of microand mini-computers, the expense of associated computer peripherals has often outweighed the expense of the central processing unit (CPU) itself. This has been especially true with electronic drafting devices. As a result, there has been a number of efforts in this latter area to reduce costs, the particular philosophy being to reduce the number of electromechanical parts required and to rely on as many passive elements as possible. This philosophy has been particularly predominant in the development of pen-holding and pen-changing devices, but has not seen concerted application in the area of pen-sensing devices.

Generally, in multi-pen plotters, it is important for the plotter to sense the location of all the pens in the device in order to avoid trying to select a pen which does not exist, to avoid writing without a pen, or to eliminate pen-to-pen collisions. The customary solutions to the pen sensing problem have been to use mechanical switches or optical detectors, both of which have serious deficiencies. In the case of mechanical switches, each sensor requires a switch, wire, soldering, adjustment, and considerable involvement in assembly. Furthermore, the switches themselves are prone to have reliability problems. Optical sensors, too, require considerable assembly time, wire soldering and adjustment; and the cost of photodetectors is not insignificant.Additionally, paper dust and other foreign particles are known to build-up on the surfaces of the photodetectors, causing interference with their operation. Both of these solutions to the sensing problem are known to be expensive to implement since they require a significant amount of hardware in addition to that required to snatch or hold a pen.

The present invention provides a device for identifying pen locations in a plotter, the device comprising first stable means for holding a pen at a first fixed location when said pen is not in use; second stable means spaced apart from said first stable means for holding a pen at a second fixed location when said pen is not in use; pen holder means located between said first and second stable means for holding a pen during plotting, for snatching a pen from either of said first and second stable means, and for inserting a pen into either of said first and second stable means; drive means for moving said pen holder means into close proximity to either of said first and second stable means; said pen holder means and said first stable means together providing a total of four possible combinations of pen locations, said pen holder means and said first stable means coacting when moved into said close proximity to provide a first set of four separate stop points of said drive means, each stop point corresponding to a particular combination of said four possible combinations of pen locations of said pen holder means and said first stable means; said pen holder means and said second stable means together having a total of four possible combinations of pen locations, said pen holder means and said second stable means coacting when moved into said close proximity to provide a second set of four separate stop points of said drive means, each stop of said second set corresponding to a particular combination of said four possible combinations of pen locations of said pen holder means and said second stable means; position means for determining the relative positions of said pen holder means as said pen holder means encountered two successive stop points in coacting with said first stable means and as said pen holder means encounters two successive stop points in coacting with said second stable means; and logic means for executing an algorithm to deduce initial pen locations from said relative position determined by said position means.

According to a preferred embodiment of the invention, a bi-directional pen changer mechanism is disclosed which does not require the use of additional mechanical switches or optical detectors to determine pen locations. The device is made up of two pen stables, one at each end of a pen carriage bar, for holding pens when not in use, and a pen holder located between the two pen stables which holds a pen during plotting. The pen holder is mounted on the pen carriage bar and is configured with two independent clamp arms, one for engaging each pen stable, making a symmetric device. Each pen stable has a fixed body and a single clamp arm for holding a pen firmly against the fixed body.

To snatch a pen from a pen stable, the empty pen holder is moved into contact with the stable causing the pen holder clamp arm to engage the pen stable clamp arm, pushing it aside as the pen holder clamp arm takes control of the pen. The pen holder then is moved clear of the pen stable and standard plotting routines can be followed.

Upon completion of the plotting routines, the pen holder re-inserts the pen in the pen stable by the reverse procedure. In this reverse procedure, however, the pen holder clamp arm is moved aside by the pen stable clamp arm which then clasps the pen, and the pen holder is again moved clear of the pen stable. The symmetry of the pen holder makes it possible to snatch or re-insert a pen from either side. Also, the pen holder clamp arms are configured such that the pen tip is always at the same location relative to the clamp arms when the pen holder is holding a pen, regardless of the side from which the pen is snatched.

Information as to pen locations is provided through an initialization scheme before plotting Foutines are begun. In a preferred embodiment of the invention, the pen holder and each pen stable are arranged to coact in a manner to provide four separate and distinct stops during their contact, the four stops corresponding to the four possible configurations available on each side; i.e., initially having (1) a pen in both the pen holder and the pen stable; (2) no pen in either the pen holder or pen stable; (3) a pen in the pen stable but no pen in the pen holder; and (4) a pen in the pen holder but no pen in the pen stable. These four stops correspond directly to stall points of a D.C. motor used to drive the pen holder.

On start up, the pen holder is moved first to a pen stable on one side of the pen carriage bar until it hits a stop and the D.C. motor stalls. The pen holder is then backed off and moved into contact again with the same pen stable until the D.C. motor stalls a second time. The pen holder is then moved to the opposite end of the pen carriage bar until the D.C. motor stalls, thereby determining the position of a first stall point at the other pen stable. The pen holder is then backed off and moved into contact again with this other pen stable, thereby determining the relative position of a second stall point. The information as to the relative positions of these four stall points obtained through this initialization procedure, together with an appropriate algorithm, is sufficient for the plotter control system to uniquely determine the initial location of all pens in the system.

There now foliows a detailed description which is to be read with reference to the accompanying drawings of a device according to the invention; it is to be clearly understood that this device has been selected for description to illustrate the invention by way of example and not by way of limitation.

In the accompanying drawings:- Figures 1 to 8 illustrate, in schematic plan views, a sequence of stages of operation of a device according to the present invention; Figures 9 to 13 illustrate, in perspective view, stages of the movement of elements of the device of Figures 1 to 8 whilst the device is operating; Figures 14 to 17 illustrate, more precisely, the geometry of the elements of the device shown in the preceding Figures; Figure 18 is a schematic diagram illustrating the relative positions of stopping locations in the operation of a device according to the present invention; Figure 1 9 is a chart showing possible pen configurations with a device according to the present invention; and Figure 20 is a flow chart of the sequence of operations controlled by logic means of a device according to the invention.

Figure 1 shows a pen stable 11 having a concave portion formed by a side 10 and a side 20 for cradling a pen 12 in a well defined position.

Also shown is a single clamp arm 13 hinged about a vertical axis Z on the pen stable 11, the clamp arm 13 having a clamp arm end portion 23 in the shape of a truncated barb. The clamp arm 13 is typically equipped with a rubber band or spring (not shown) for holding the clamp arm 13 firmly in contact with the pen 12, in order that the pen 12 is held in place in the concave portion of pen stable 11 formed by the sides 10 and 20.

Also shown in Figure 1 is a pen holder 14 for snatching the pen 12 from the pen stable 11 and for holding the pen 12 during plotting. The pen holder 14 is symmetrical in a plane P perpendicuiar to its direction of motion, and is equipped with two clamp arms 16 and 17 located opposite each other (i.e., on opposite sides of the plane P) in order to snatch a pen from either side.

The clamp arms 16 and 17 have barb-shaped end portions 26 and 27, respectively.

In Figure 2, the pen holder 14 is moved toward the pen stable 11 , the barb-shaped end portion 26 of the clamp arm 16 moving the clamp arm 13 aside in order to snatch the pen 12 from the stable. A rubber band orspring (not shown) is typically used to provide a restoring force on the clamp arm 1 6 to maintain the clamp arm 1 6 near its home position illustrated in Figure 1. Figure 3 shows the full depth of penetration of the pen holder 14 as the barb-shaped end portion 26 hits a stop 33 provided by a shoulder of the clamp arm 13. Figure 4 shows the nominal position of the pen 12 centered in a concave portion 1 5 of the pen holder 14 after the snatch.

Figures 5 to 8 show the process of re-insertion of the pen 12 into the pen stable 11. In this process, the pen holder 14 is again moved toward the pen stable 11. The clamp arm 13 is configured to have a normal position, when not holding a pen, such that the clamp arm 13 moves inside the clamp arm 16, forcing it to one side, as the pen holder 14 closes with the pen stable 11 (see Figure 6). The pen holder 14 continues to close with the pen stable 11 until the pen 12 hits the side 20 of the concave portion of the pen stable 11, thus providing a well defined stop to the motion of the pen holder 14 (see Figure 7).

Once inside the clamp arm 16, the clamp arm 13 takes control of the pen 1 2 and the pen holder 14 then moves clear of, or retracts from, the pen stable 11, as shown in Figure 8.

Figures 9 to 1 3 show a perspective view of this same process. In Figure 9, the pen holder 14 is shown mounted on a carriage bar 19 and is being moved toward the pen stable 11 , typically by a belt 39 driven by a motor 34 having an optical shaft encoder 37. The clamp arms 1 6 and 1 7 are hinged about a horizontal axis via extension arms 28 and 29, respectively. As illustrated in Figure 10, the clamp arm 13 is moved aside as the pen holder 14 snatches the pen and subsequently moves away.

In the reverse procedure shown in Figures 11 to 13, the pen 12 is re-inserted into the pen stable 11. As the pen holder 14, holding the pen 12, approaches the pen stable 11, the clamp arm 13 pushes the clamp arm 1 6 aside, causing the extension arm 28 to rotate about its hinge. The clamp arm 13 then clasps the pen 12, thereby holding the pen 12 in firm contact with the pen stable 11. Just as the snatch and re-insertion procedure was performed from one side with the pen stable 11, the symmetry of the pen holder 14 permits operation from the other side as well. To take advantage of this symmetry, a second pen stable 31 and pen 22, opposite the pen stable 11, is typically provided so that a two-pen system is available as illustrated in Figures 9 to 13, the pen holder alternately using one pen and then the other.

In order to eliminate the usual requirement for switches or optical detectors to locate pen positions, an initialization scheme is typically used in a preferred embodiment of the invention to locate all pens that may be in the system before any plotting routines are begun. As illustrated by Figures 14 to 18, this scheme relies on the geometry and interactions of the pen stables with the pen holder 14. The pen holder is configured to coact with each pen stable in a manner to provide four separate and distinct stops, each stop corresponding to a stall point of the D.C. motor 35 which is used to drive the pen holder 14. The stop closest to the center of the pen carriage 1 9 occurs when both the pen stable 11 and the pen holder 14 contain a pen.This occurrence is illustrated in Figure 14 where the barb-shaped end portion 26 is shown colliding with the truncated portion of the clamp arm end portion 23; Similarly, the stop which is next closest to the center of the pen carriage bar 19 occurs when neither the pen stable 11 nor the pen holder 14 contains a pen, as illustrated in Figure 1 5. This stop is further from the centre of the pen carriage bar 1 9 than the stop shown in Figure 14 due to the fact that the clamp arm 13 describes an arc about its axis of rotation which is not in alignment with the barbshaped end portion 26. Hence, the pen holder 14 travels further before the clamp arm end portion 23 and the barb-shaped end portion 26 collide.

Although this difference in distance is typically small (1 mm), the optical shaft encoder 37 is typically chosen to have a resolution of approximately 0.025 mm or better in order to meet plotting demands. Hence, resolution is usually not a problem in distinguishing these two stops. The stop shown in Figure 1 6 is located even further from the center of the pen carriage bar 1 9 and corresponds to the situation described in Figure 3, i.e., initially having a pen in the pen stable 11 and no pen in the pen holder 14. As described earlier, the stop occurs as the barbshaped end portion 26 collides with the stop 33 of the clamp arm 13.The stop furthermost from the center of the pen carriage bar 1 9 is shown in Figure 17, which corresponds to initially having a pen in the pen holder 14 and inserting it into an empty pen stable 11, as described earlier in the discussion of Figure 7. The relative positions of these stops, for both the left and right sides, is shown diagramatically in Figure 18, and the various possible pen configurations is shown in Figure 19.

In a preferred embodiment of the invention, the initialization scheme begins much as described in the sequence of Figures 9 to 13, the control system 40 typically having no information as to initial pen locations or the location of the pen holder 1 4. As shown in the flow chart in Figure 21, the pen holder is first moved to the left hand pen stable, which is pen stable 11, until saturation occurs, i.e., until the pen holder hits a stop and the D.C. motor 35 stalls, thus, initializing the system and establishing an initial position, Y1, for the pen holder 14, as measured by the optical shaft encoder 37. The pen holder 14 is then backed off and moved into contact again with pen stable 11, the new stall position being recorded by the control system 40 as Y2.The pen holder 14 is then moved to saturation on the right hand side at the second pen stable 31, and a new stall position Y3 is recorded by the control system 40.

As before, the pen holder is backed off and then moved into contact again with the pen stable 31 until saturation occurs. Thus, a new stall point Y4 is determined. As can be seen from Figure 20, information as to the relative positions of Y1, Y2, Y3, and Y4 is sufficient to determine uniquely the initial pen configuration. Typically, the plotter control system 40 includes a ROM 41 as illustrated in Figure 9, for implementing various plotting routines. Hence, with minor firmware changes in the ROM, the simple logic depicted in Figure 20 can be easily implemented to provide the initialization scheme.

The configuration of the various clamp arms can vary widely and still provide four separate stops, and many different distance measuring systems are available other than an optical shaft encoder. Also, a number of different algorithms could be developed. For example, instead of using only the relative positions of Y3 and Y4 at the pen stable 31, the actual distances to these right hand stall points from Y1 and Y2 would yield information directly as to whether a pen is located on the right hand side or not. Also, in some implementations it may be advantageous to alter the logic sequence. For instance, if the control system determines from its initial inquiry on the left hand side that a pen is located in the pen holder but not in the pen stable, then it may be advantageous to insert the pen into the pen stable 11 before proceeding with the inquiry on the right hand side. Furthermore, the concept of the invention is usable in a system having pens on only one side of the pen holder, say in a pen magazine arrangement. In such a system, however, something such as a fixed stop would be required to provide an origin for measuring distances. Also, it should be apparent that the concept of the invention is not restricted to an initialization scheme, but is equally applicable to determining pen locations during plotting. For example, should a pen be removed from a pen stable during a plotting routine for some reason, the control system would sense the absence when it attempted to snatch the absent pen because the D.C. motor would saturate at a stop which was not at the proper location.

Claims

1. A device for identifying pen locations in a plotter, the device comprising: first stable means for holding a pen at a first fixed location when said pen is not in use; second stable means spaced apart from said first stable means for holding a pen at a second fixed location when said pen is not in use; pen holder means located between said first and second stable means for holding a pen during plotting, for snatching a pen from either of said first and second stable means, and for inserting a pen into either of said first and second stable means:: drive means for moving said pen holder means into close proximity to either of said first and second stable means; said pen holder means and said first stable means together providing a total of four possible combinations of pen locations, said pen holder means and said first stable means coacting when moved into said close proximity to provide a first set of four separate stop points of said drive means, each stop point corresponding to a particular combination of said four possible combinations of pen locations of said pen holder means and said first stable means;; said pen holder means and said second stable means together having a total of four possible combinations of pen locations, said pen holder means and said second stable means coacting when moved into said close proximity to provide a second set of four separate stop points of said drive means, each stop point of said second set corresponding to a particular combination of said four possible combinations of pen locations of said pen holder means and said second stable means; position means for determining the relative positions of said pen holder means as said pen holder means encounters two successive stop points in coacting with said first stable means and as said pen holder means encounters two successive stop points in coacting with said second stable means; and logic means for executing an algorithm to deduce initial pen locations from said relative positions determined by said position means.

2. A device for identifying pen locations in a plotter, substantially as hereinbefore described with reference to the accompanying drawings.