Stapleton, Jeff T.
| 1. | A solenoidbased linear driver which can be employed for precision bidirectional movement comprising: a) a solenoid having a coil and an armature disposed in said armature for powered longitudinal movement in a first direction, said armature providing an actuating movement of the driver; b) bias means for applying a force urging said armature in a second direction opposite said first direction; c) motion sensor means for sensing a linear position of said armature and for outputting a positional signal reflecting said linear position; d) driver circuit means for outputting a variable current to said coil of said solenoid as a function of a control signal at an input thereof; and, e) control logic means for inputting said positional signal and a desired position request and for outputting control signals to said driver circuit means to move said armature to said desired position. |
| 2. | The solenoidbased linear driver of claim 1 wherein: said bias means comprises a spring connected to said armature. |
| 3. | The solenoidbased linear driver of claim 2 wherein: said spring is directly connected to said armature. |
| 4. | The solenoidbased linear driver of claim 2 wherein: said spring is connected to said armature through a linkage. |
| 5. | The solenoidbased linear driver of claim 1 wherein: said motion sensor means comprises a blocking blade moving in combination with said armature between a light source and a light detector separated from said light source by a space and having a sensing surface upon which a beam of light from said light source impinges and wherein the level of a signal output therefrom is a function of the amount of light not blocked by said blocking blade and impinging on said sensing surface. |
| 6. | A solenoidbased linear driver for precision bi¬ directional up and down movement of a pen holder in a pen plotter to raise and lower the pen holder and a pen held thereby comprising: a) a solenoid having a coil and an armature disposed in said armature for powered longitudinal movement in a first direction; b) linkage means connecting said armature to the pen holder for raising and lowering the pen holder in combination with longitudinal movement of said armature; c) bias means for applying a force urging said armature in a second direction opposite said first direction; d) motion sensor means for sensing a linear position of the pen holder and for outputting a positional signal reflecting said linear position; e) driver circuit means for outputting a variable current to said coil of said solenoid as a function of a control signal at an input thereof; and, f) control logic means for inputting said positional signal and a desired position request and for outputting control signals to said driver circuit means to move the pen holder to said desired position. |
| 7. | The solenoidbased linear pen holder driver of claim 6 wherein: said bias means comprises a spring connected to said armature. |
| 8. | The solenoidbased linear pen holder driver of claim 7 wherein: said spring is connected to said armature through a linkage. |
| 9. | The solenoidbased linear pen holder driver of claim 6 wherein: said motion sensor means comprises a blocking blade moving in combination with the pen holder between a light source and a light detector separated from said light source by a space and having a sensing surface upon which a beam of light from said light source impinges and wherein the level of a signal output therefrom is a function of the amount of light not blocked by said blocking blade and impinging on said sensing surface. |
| 10. | Solenoidbased pen raising apparatus for raising and lowering a pen of a pen plotter comprising: a) pen holder means for holding a pen mounted for vertical up and down motion in combination with a pen held thereby; b) a solenoid having a coil and an armature disposed in said armature for powered longitudinal movement in a first direction; c) first linkage means connecting said armature to said pen holder means for raising and lowering said pen holder means in combmation with longitudinal movement of said armature; d) a spring; e) second linkage means connected to said spring for applying a force urging said armature in a second direction opposite said first direction; f) motion sensor means for sensing a linear position of said pen holder means and for outputting a positional signal reflecting said linear position; g) driver circuit means for outputting a variable current to said coil of said solenoid as a function of a control signal at an input thereof; and, h) control logic means for inputting said positional signal and a desired position request and for outputting control signals to said driver circuit means to move said pen holder means to said desired position. |
| 11. | The solenoidbased pen raising apparatus of claim 10 wherein: said motion sensor means comprises a blocking blade moving in combination with said pen holder means between a light source and a light detector separated from said light source by a space and having a sensing surface upon which a beam of light from said light source impinges and wherein the level of a signal output therefrom is a function of the amount of light not blocked by said blocking blade and impinging on said sensing surface. |
SOLENOID FOR PRECISION MOTION
Background of the Invention:
The present invention relates to electrically-powered, linear motion-producing devices and, more particularly, to a solenoid-based linear driver which can be employed for precision bi-directional movement comprising, a solenoid having a coil and an armature disposed in the armature for powered longitudinal movement in a first direction, the armature providing an actuating movement of the driver; bias means for applying a force urging the armature in a second direction opposite the first direction; motion sensor means for sensing a linear position of the armature and. for outputting a positional signal reflecting the linear position; driver circuit means for outputting a variable current to the coil of the solenoid as a function of a control signal at an input thereof; and, control logic means for inputting the positional signal and a desired position request and for outputting control signals to the driver circuit means to move the armature to the desired position. There are many applications for electrically-powered, linear actuators. Where precision linear motion is required, as in the pen raising and lowering apparatus of a pen plotter, the prior art has been limited to the use of devices such as the DC motor 10 of Figure 1. By varying the polarity and level of current flow into the motor 10 through the wires 12, the actuator 14 driven thereby can be moved bi-directionally left and right as the figure is viewed in a precision manner. Thus, the force versus travel curve for the motor 10 and actuator 14 is as appears in Figure 2; that is, the amount of force on the actuator is independent on the amount of travel thereof. The principle problem with DC motors like that of Figure 1 is the cost thereof. Being a true motor, the cost of manufacture is relatively high as compared with other types of linear actuators
which are known in the art, but have performance characteristics which are not acceptable for the particular uses.
One such device is the common solenoid. Solenoids are cheap and reliable for their intended purpose ~ which is typically to exert a high opening or closing force in one direction. Thus, they uniquely suited to open the water valves in washing machines, open door latches, and the like. Being a uni¬ directional device, they are unsuited for bi-directional uses more suited to the DC motor of Figure 1. The force versus travel curve for a solenoid is as appears in Figure 3. As can be seen, the curve is completely non-linear. Thus, it is commonly accepted in the art that a solenoid cannot be employed for precision bi-directional movement.
Wherefore, it is an object of the present invention to provide a solenoid-based linear driver which can be employed for precision bi-directional movement.
It is another object of the present invention to provide a solenoid-based linear driver which can be employed in a pen plotter to drive the pen up and down mechanism thereof. Other objects and benefits of the invention will become apparent from the detailed description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.
Summary:
The foregoing objects have been achieved by the solenoid- based linear driver for precision bi-directional up and down movement of a pen holder in a pen plotter to raise and lower the pen holder and a pen held thereby of the present invention comprising, a solenoid having a coil and an armature disposed in the armature for powered longitudinal movement in a first direction; linkage means connecting the armature to the pen holder for raising and lowering the pen holder in combination with longitudinal movement of the armature; bias means for applying a force urging the armature in a second direction opposite the first direction; motion sensor means for sensing a
linear position of the pen holder and for outputting a positional signal reflecting the linear position; driver circuit means for outputting a variable current to the coil of the solenoid as a function of a control signal at an input thereof; and, control logic means for inputting the positional signal and a desired position request and for outputting control signals to the driver circuit means to move the pen holder to the desired position.
In the preferred embodiment, the bias means comprises a spring connected to the armature. The spring can be connected to the armature through a linkage or directly.
Also in the preferred embodiment, the motion sensor means comprises a blocking blade moving in combination with the pen holder between a light source and a light detector separated from the light source by a space and having a sensing surface upon which a beam of light from the light source impinges and wherein the level of a signal output therefrom is a function of the amount of light not blocked by the blocking blade and impinging on the sensing surface.
Description of the Drawings:
Figure 1 is a simplified drawing of a prior art linear DC motor.
Figure 2 is a graph of force versus travel for a motor as in Figure 1. Figure 3 is a graph of force versus travel for a common solenoid.
Figure 4 is a partial functional block diagram drawing of apparatus according to the present invention in a generalized embodiment thereof. Figure 5 is a partial functional block diagram drawing of apparatus according to the present invention in an embodiment thereof specifically for accomplishing pen raising and lowering in a pen plotter.
Description of the Preferred Embodiment:
A solenoid-based linear driver according to the present invention in a generalized embodiment which can be employed for precision bi-directional movement is shown in Figure 4 where it is generally indicated as 16. As those skilled in the art will quickly recognize and appreciate, the objects of the present invention are accomplished by incorporating a common solenoid 18 into a closed control loop 20.
The coil 22 of the solenoid 18 is connected to a driver circuit 24 providing a variable current into the coil 22 as a function of a control signal from the control logic 26. Being a uni-directional device, as current is applied to the coil 22 the electro-magnetic force created thereby will attempt to pull the armature 28 into the coil 22 so as to minimize the path that the electro-magnetic force has to travel. To accomplish the objects of the present invention, a spring 30 is connected to the armature 28 to pull the armature 28 in the opposite direction. As an actuator, therefore, the armature 28 can now be caused to move bi-directionally by controlling the net force of the coil 22 and the spring 30 on the armature 28.
The necessary control is accomplished by including data of the curve of Figure 3 for the particular solenoid 18 and spring 30 within the control logic 26 and by providing a positional feedback signal to the control logic 26. The positional feedback signal is provided by a motion sensor 32. In a preferred and tested embodiment, the motion sensor 32 comprises an optical sensor 34 of the type well known in the art having a light source 36 and a light detector 38 separated from the light source by a space and having a sensing surface 40 upon which a beam of light impinges and wherein the level of signal output at 42 is a function of the amount of light impinging on the sensing surface 40. There is a light-blocking blade 44 mounted on the armature 28 and disposed in the space between the light source 36 and light detector 38. Thus, as the armature 28 moves in and out of the coil 22, the blade 44 covers more or less of the sensing surface 40 and the signal output at 42 (which is input to the
control logic 26) directly reflects the position of the armature 28. Thus, when a desired position is input at 46 to the control logic 26, the control logic 26 has sufficient static and dynamic information to move the armature 28 in either direction with great precision.
Turning now to Figure 5, the present invention is shown therein as incorporated into a pen plotter to raise and lower the pen holding mechanism thereof. The pen holding mechanism 48 comprises a vertically-sliding pen holder 50 which holds the pen 52. The pen holder 50 is spring-biased to the pen-lowered or down position by spring 30' and also has the blade 44 of the motion sensor 32 incorporated therein. The solenoid 18 is mounted at a distance and connected to raise the pen holder 50 to the pen-raised or up position through a linkage 54. The balance of the electrical connections for the control loop 20 are as in the prior embodiment. While the mechanical connections are slightly different, those skilled in the art will readily appreciate that the two embodiments, in fact, work substantially in the same way. In a tested embodiment of the present invention, the performance was so good as to have it incorporated into the final design of a soon to be commercial pen plotter from the assignee of this application.
Wherefore, having thus described the present invention, what is claimed is:
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