US 3655019 A
An electrostatic device utilizing the "Johnson-Rahbek" effect. At least first and second drums are rotated at constant but substantially different speeds. An electrically conductive band contacts a portion of the peripheries of the drums; the peripheries of the drums are coated with semi-conductor material. One end of the band is connected to a tensioning device, and the other end is connected to a utilization device (like a print hammer). By energizing the first drum and then energizing the second drum while simultaneously deenergizing the first drum, a controlled acceleration of the band is obtained. Several drums and several bands (to operate several utilization devices) may be used. Selective energization of the bands to be driven is obtainable.
Description (OCR text may contain errors)
United States Patent Trzaska  Apr. 11, 1972  ELECTROSTATIC DEVICE WITH Primary Examiner-Allan D. Herrmann CONTROLLABLE ACCELERATION Attorney-Louis A. Kline, Albert L. Sessler, Jr. and Elmer Wa o  Inventor: Theodore T. Trzaska, Dayton, Ohio rg  Assignee: The National Cash Register Company ABSTRACT  Filed: Nov. 23, 1970 An electrostatic device utilizing the Johnson-Rahbek" effect. 21 A l N 91 956 At least first and second drums are rotated at constant but 1 PP substantially different speeds. An electrically conductive band contacts a portion of the peripheries of the drums; the  U.S. Cl ..192/48.9, 192/80, 192/84E peripheries of the drums are coated with semi-conductor P- F164! F 164 27/12 material. One end of the band is connected to a tensioning Field of Search t 34 E device, and the other end is connected to a utilization device (like a print hammer). By energizing the first drum and then  References cued energizing the second drum while simultaneously deenergizing UNITED STATES PATENTS the first drum, a controlled acceleration of the band is obtamed. Several drums and several bands (to operate several 2,350,907 1953 Foster E utilization devices) may be used. Selective energization of the 2,350,908 9/1953 Foster bands to be driven is obtainable. 2,916,920 12/1959 Planer et al ..l92/80 X 5 Claims, 4 Drawing Figures ENERGIZING BAND/ LOAD DISPLACEMENT PATENTEDAPR 1 1 1912 ENERGIZING MEANS FIG.4
DRUM C CONTROL l ENERGIZING MEANS 331 42 K TOBDRUM To DRUM INVENTOR THEODORE T. TRZAS KA HIS ATTOR NEYS BACKGROUND OF THE INVENTION This invention relates to an electrostatic, actuator or clutch utilizing the Johnson-Rahbek effect and having a controllable acceleration.
Electrostatic clutches or devices utilize electro-adhesion; i. e., a mutual attraction between a semi-conductor (which is usually placed on the periphery of a rotating drum) and a conductor (which is usually an electrically conducting band wrapped around a portion of the drum).
Some typical examples of electrostatic actuators or devices are found in the following U.S. Pats.
No. 2,568,824, which issued on Sept. 25, 1951, on the application of Knud Rahbek;
No. 2,897,424, which issued on July 28, 1959, on the application of Robert W. Waring;
Bo. 3,132,267, which issued on May 5, 1964, on the application of Roland M. Schaffert; and
No. 3,493,157, which issued on Feb. 3, 1970, on the application of Donald L. Burdorf et al.
One of the problems inherent in electrostatic devices of the prior art is that there is generally some slippage between the semi-conductor material (on a drum usually) and the conducting band when the devices are energized. As a result of the slippage, the acceleration of the band by the drum is not accurately controlled.
The electrostatic device of the present invention provides for a more controlled and accurate acceleration. By utilizing at least first and second drums, which are operated at substantially different speeds, it is possible for the drums and their associated electrically conducting band to operate within more ideal loads. For example, when the band is to be accelerated positively, the first drum is rotated at a lower constant velocity than the second drum. The first drum is energized to transfer its motion to the band, and then the second drum is energized" while the first drum is simultaneously deenergized. Because the first drum is rotating at a lower velocity, the first drum and the band coact within a more ideal friction range to get the band accelerated from a rest position. After the bandis accelerated from its rest position, the second drum is energized to further accelerate the band to the desired terminal velocity with a minimum of slippage, thereby providing a more accurately controlled acceleration. While this invention is generally described as employing positive acceleration, it should be apparent that this technique can be used in devices which utilize negative acceleration as in electrostatic braking devices.
Some of the advantages of the electrostatic device of this invention are as follows. The device has:
a. Increased load acceleration capability from a given band without increasing band width dimensions, thereby improving the stacking factor when several bands are to be operated in parallel from the drums.
b. Controlled acceleration to any desired terminal velocity.
c. More predictable operation, as each band-drum clutch combination is operated in an initially lower slip velocity region.
d. Less strain on the band and the utilization device connected to the band through the controlled acceleration of the band.
SUMMARY OF THE INVENTION This invention relates to an electrostatic device which utilizes the Johnson-Rahbek effect. The device includes at least first and second drums, which are rotated at constant but substantially different velocities. The drums are coated with a semi-conductor material, and an electrically conducting band contacts a portion of the peripheries of the drums. One end of the band is connected to a tensioning device, and the other end is connected to a utilization device. By energizing the first ously deenergizing the first drum, a controlled acceleration of the band is obtained. Several drums and several bands (to operate in parallel on the drums) may be used. Both positive and negative accelerations of the band may be utilized, depending upon the particular application of the device of this invention. Selective energization of the bands to be driven is also obtainable.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a general perspective view of an electrostatic device embodying the principles of this invention. Several drums with semi-conductor material on their peripheries are shown with an electrically conducting band engaging portions of the peripheries of the drums. The output of the device, for example, may be used to actuate a print hammer.
FIG. 2 is an energization diagram showing the sequence of energizing the various drums used.
FIG. 3 is a diagram showing the displacement of the band with respect to time as each of the drums is energized.
FIG. 4 is a perspective view similar to FIG. 1, showing a portion of a second embodiment, which permits selective energization of the bands operating from a common set of drums.
DETAILED DESCRIPTION OF THE INVENTION FIG. I is a general perspective view of the electrostatic device of this invention, which is designated generally as 10. The device 10 includes at least two drums, A, B, and C, which are supported on shafts for rotation by conventional drive means shown only diagrammatically as 12, 14, and 16, respectively. Each of the drums A, B, and C has a conventional semiconductor coating 18 on its periphery, as is done with devices utilizing the Johnson-Rahbek effect. Various examples of coatings are disclosed in the U.S. patents cited earlier in this application. Each of the drums is rotated at a constant velocity but at substantially different speeds. As an example, the drums A, B, and C may be respectively rotated at 100, 200, and 300 revolutions per minute. While the drums are shown as having equal diameters, they could naturally be of different diameters if the specific requirements of a particular situation dictated it.
As is typical with electrostatic devices, an electrically conducting band is wrapped around a portion of the periphery of the drum; however, in the device 10 (FIG. 1) an electrically conducting band 20 engages the peripheries of the drums A, B, and C, as shown.
One end of the band 20 is connected to an electrically grounded tensioning device (like a spring 22), and the remaining end is connected to a utilization device, which, for illustrative purposes, is shown as a print hammer lever 24. The band 20 is wrapped around a portion of the periphery of the drum A, and around portions of the peripheries of the drums B and C. While the drums A, B, and C are shown as rotating on axes in spaced parallel relationship, which axes lie in a common plane, they need not lie in the same plane. The amount of surface contact desired between the band 20 and the particular drum helps determine the location of the drums relative to one another. In addition, the width of the band, the diameters of the drums, the type of semi-conductor material used, and the speeds of the drums are all factors to be considered in the design for a specific application. Because these particular design considerations may be conventional, they are not reviewed herein in detail.
The transmittal of force to the stationary band of an electrostatic device utilizing the Johnson-Rahbek effect is generally accomplished by applying a voltage between the band and the semi-conductor on the rotating drum. In the present invention, each of the drums A, B, and C (FIG. 1) has its own slip ring 26, 28, and 30, respectively, by which the coating 18 on the corresponding drum is energized. An energizing means 32 is used to sequentially energize the drums A, B, and C.
The energizing means 32 (FIG. 1) utilizes conventional drum and then energizing the second drum while simultaneelectronic circuitry to energize the drums A, B, and C as follows. The spring 22 provides the normal tension and electrical ground potential on the band 20, which is normally in slipping engagement with the drums. When the device is to be actuated, the first drum A is energized by placing an electrical potential on its coating 18 via a conductor 34 from the energizing means 32 and the slip ring 26, causing the band to be attracted to the drum A. Because the drum A rotates clockwise (as viewed in FIG. 1), the motion of the drum A will be imparted to the band. The timing chart showing the energization of the drums A, B, and C is shown in FIG. 2, and the band displacement is shown in FIG. 3. The point 36 on FIG. 3 represents the start of the energization of the drum A. After a fixed time interval, the drum B will be energized via a conductor 38 from energizing means 32 and the slip ring 28, causing the band 20 to be attracted to the drum B. Because the drum B rotates counter-clockwise, the motion of the drum B will be imparted to the band 20 to add to the velocity of the band imparted by the drum A. When the drum B is energized, the drum A is simultaneously deenergized, as shown by the timing chart in FIG. 2. The point 40 on FIG. 3 represents the start of the energization of the drum B and the deenergization of the drum A. After a fixed time interval, the drum C will be energized via a conductor 42 from the energizing means 32 and the slip ring 30, causing the band 20 to be attracted to the drum C. Because the drum C rotates clockwise, the motion of the drum C will be imparted to the band 20 to add to the velocity of the band imparted by the drums B and A. When the drum C is energized, the drum B is simultaneously deenergized, as shown by the timing chart in FIG. 2. The point 44 on FIG. 3 represents the start of the energization of the drum C and the deenergization of the drum B. After a fixed time interval, the band 20 will be accelerated to the desired terminal velocity (i. e., the peripheral velocity of the drum C), represented by the point 46 on FIG. 3, and the drum C will be deenergized. In the embodiment shown, the fixed time interval of energization of each of the drums A, B, and C was 1 millisecond; however, the actual time interval selected is, of course, dependent upon the particular application of the device 10 and the design factors relating to band width, speed and diameter of the drums, and
the semi-conductor material 18 used on the drums.
Through the sequential energization of the drums A, B, and C, with each of the successive drums operating at a higher peripheral velocity, the band 20 may be accelerated more smoothly and be controlled more accurately than can be done through using one drum alone to obtain a desired terminal velocity of the band. The process just described is somewhat analogous to the shifting of gears in an automobile to accelerate it to a desired terminal velocity. While the device 10 has been described as accelerating the band 20 to a positive terminal velocity, the device 10 may also be used to decelerate the band and thereby use the device as an electrostatic brake.
When the device 10 is used to decelerate or brake a moving body, the first drum to be energized is the one whose speed is highest relative to the other two drums when three drums are used. For example, the drum which is closest to the end of the band which is to be decelerated would have a peripheral velocity which is in the same direction as the moving band, but the actual velocity of the periphery of the drum contacting the band would be less than the velocity of the moving band, thereby decelerating the moving band when the drum is energized. The remaining drums would successively further brake the band toward zero velocity.
In the embodiment shown in FIG. 1, several bands like 20 may be operated from the same drums A, B, and C. When so operated, the bands like 48 (shown only in dashed outline) may be placed parallel to the band 20. From FIG. 1, it is apparent that the two bands on the drums would be accelerated simultaneously.
To permit selective acceleration of a plurality of bands being operated from a common plurality of drums, the device 50 shown in FIG. 4 may be used. The device 50 is substantially the same as the device 10 shown in FIG. 1 except that means are shown for selectively energizing the bands to be accelerated. Elements in FIG. 4 which are identical to those shown in FIG. I bear the same reference characters, and a portion of the device 50 is omitted to simplify the drawing, as this omitted portion is identical to FIG. 1.
In referring to FIG. 4, the electrically conducting bands 20 and 48 have one of their ends connected to springs 22, which are supported by a support 52, made of electrically insulating material so as to isolate one band from the other. When the device 50 is used in a printer application, for example, a control circuit 54 would be used to select the particular band to be energized, thereby actuating a particular print hammer lever, like 24 in FIG. 1. The control circuit may be conventional and, in effect, merely grounds the particular band selected to be energized over its output conductors 56 and 58 connected to the bands 20 and 48, respectively. If, for example, the band 48 is to be energized, the control circuit 54 grounds the band 48 over the conductor 58 and simultaneously actuates the energizing means 32 over the conductor 60. The energizing means 32 then sequentially energizes the drums A, B, and C, as previously described in relation to FIGS. 2 and 3. Upon completion, the grounded conductor, like 58, is opened by the control circuit 54, the next band selected for energization is grounded, and the energizing process described is repeated.
What is claimed is 1. An electrostatic device utilizing the Johnson-Rahbek" effect comprising:
at least first and second drums having axes of rotation in spaced, parallel relationship, and having peripheries coated with semi-conductor material;
first and second drive means for rotating said first and second drums respectively at a constant rotational velocity;
said first and second drums being dimensioned so as to produce substantially different peripheral speeds in cooperation with said first and second drive means respectively; at least one electrically conducting band being wrapped around a portion of the periphery of the first drum and around a portion of the periphery of the second drum so as to contact the semi-conductor material thereon; said band having first and second ends with the first end being connected to a tensioning device and the second end being connected to a utilization device; and energizing means to energize the first drum to attract the band thereto to impart the motion of the first drum to the band, and to simultaneously deenergize the first drum and energize the second drum to attract the band thereto to impart the motion of the second drum to the band, the motion imparted to the band by the first and second drums being cumulative and in the same direction. 2. The electrostatic device as claimed in claim 1 in which the second drum is rotated in a direction opposite to the direction of the first drum, and in which the second drum is rotated at a higher speed than the first drum.
3. The electrostatic device as claimed in claim 1 further including a third drum having its periphery coated with semiconductor material and third drive means for rotating said third drum at a constant rotational velocity;
said first, second, and third drums being identical in size and having their axes of rotation lying in a common plane;
said second drum being rotated in a direction which is opposite to the direction of said first and third drums; and said second drum being rotated at a substantially higher speed than said first drum, and said third drum being rotated at a substantially higher speed than said second drum;
said band also being wrapped around a portion of the periphery of the third drum;
said energizing means being adapted to energize the third drum after the second drum is energized and to simultaneouslyrdeenergize the second drum upon the energization of the third drum.
4. The electrostatic device as claimed in claim 3 further comprising at least a second electrically conducting band being wrapped around portions of said first, second, and third drums to operate in a manner identical to that of said firstnamed band.
5. An electrostatic device utilizing the Johnson-Rahbek effect comprising:
a plurality of drums having axes of rotation in spaced, parallel relationship with one another and having peripheries coated with semi-conductor material;
drive means for rotating each of said drums at aconstant rotational velocity,
said drums being so dimensioned as to produce substantially different peripheral speeds in cooperation with said drive means, with said drums being arranged in a sequence so that the first drum in the sequence has a first peripheral speed and each succeeding drum in the sequence has a substantially higher peripheral speed than the preceding drum;
a plurality of electrically conducting bands being wrapped around a portion of each of the peripheries of said drums so as to contact the semi-conductor material thereon, each said band having a first end and a second end,
means for connecting said first ends to a tensioning device and for insulating said bands from one another; each said second end being connected to a utilization device;
control means for selecting the band to be energized; and energizing means to energize the first drum to attract the