Impact Transducer Switch

Abstract

An impact transducer switch includes a manually operable key, an energy storage spring, and a piezoelectric element. Upon actuation of the key, means is provided for moving said spring through a first range of movement where energy is stored in said spring, and for thereafter effecting release of said spring at a predetermined point to cause release of said energy and impact of said piezoelectric element to cause an electrical signal to be generated by said piezoelectric element. In one form, an end of the energy storage spring impacts the piezoelectric element, while in another form, the spring transfers the energy to an impact means which in turn causes the impact.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a switching device, and more particularly to an impact transducer switching device adapted for use in a keyboard.

The prior art discloses a variety of switching units adapted for use as data entry devices. In one common form of use, these switching devices are used as actuating elements for a keyboard. The keyboard generally comprises a plurality of individual keys coupled to a switching unit which upon actuation of the key causes an electrical or other signal to be generated and encoded into a group of discrete signals having a unique combination signifying the designation of the actuated key. A typical and common use of such a keyboard is as an input device in the data processing system.

These prior art devices require an external electrical power source. In many forms, the electrical power source is coupled to a load through a plurality of normally open electrical contacts, and actuation of the key effects a contact and closure, connecting the power source to the load, thereby generating an output signal. In these types of devices the moving electrical contacts incur an attendant deterioration due to arcing, erosion and normally occuring atmospheric contaminants. It is one object of the present invention to eliminate the requirement of an external electrical power source, and also to eliminate moving electrical contacts.

Another disadvantage of prior art devices is that the output from the key actuated element is of a continuous rather than of a pulse type nature and generally has a low voltage or current level. The low signal level generally causes the keyboard to require amplifying means to raise the signal strength to a level sufficient to assure operation by and of the remainder of the data processing system. Hence, it is another object of the present invention to provide a data entry device having a pulse output rather than a continuous type output, and a substantially high signal level which is capable in itself of initiating a following action by the data processing system.

Another disadvantage of prior art devices is the absence of true overcenter action, and the ability of the key to be teased. True overcenter action and the inability to be teased are important, since the feel of the key should approach that of a high quality typewriter, allowing the keyboard operator to have a true feel of the actuation of the key and the concurrent generation of an electrical signal. Hence it is another object of the invention to provide a data entry device having true overcenter action and inability to be teased.

STATEMENT OF THE INVENTION

According to a salient feature of the present invention, an impact transducer switch comprises: manually operable key means; actuating means movable by said key means; an energy storage spring movable between first and second positions by said actuating means, and operable to store energy during a first portion of said movement and to release said stored energy during a second portion of said movement; a piezoelectric element for generating an electrical signal in response to impact thereof; impact means for transferring said stored energy upon release thereof by impact with said piezoelectric element; and holding means for maintaining said impact means spaced apart from said piezoelectric element during said first portion of said spring movement, and responsive to said actuating means for releasing said impact means after a predetermined movement of said actuating means.

DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will further become apparent upon description of the various features and aspects of my invention, in conjunction with the accompanying drawing, in which like reference numerals identify like components, and in which:

FIG. 1 is a schematic drawing in perspective view showing an assembled switch embodying the principles of the invention;

FIG. 2 is a schematic drawing showing another embodiment of the invention.

FIGS. 3 and 4 are schematic drawings depicting another embodiment; and

FIG. 5 depicts alternative impact means which may be used with the switch shown in FIGS. 3 and 4.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings and in particular to FIG. 1, there is shown a keyboard having a keyboard surface 10 and keyboard body or panel 12 which may be an insulating or metallic but preferably nonmagnetic material. The panel 12 has a plurality of slots 14, one at each key position, each slot acting as a plunger guide for the actuator. The actuator may include a keystem 18 which is mechanically affixed to a key cap 16, and which is guided by the body walls 13 and 15 of the keyboard panel 12. A return spring 20 is disposed about the reduced top portion 21 of plunger or keystem 18, and is interposed between the lower surface 17 of key cap 16 and the upper surface 10 of panel 12. It should be appreciated that the body walls 13 and 15 may be variously dimensioned. For example, in FIG. 1 body wall 15 is substantially longer than the body wall 13. In this form, the guide means may be effectively utilized for restraining movement of the plunger stem in a vertical movement along the path of travel depicted by the multidirectional arrows 28.

Affixed to the lower portion of the keystem 18 is a permanent magnet 22. Disposed adjacent the left side of the keystem 18 is an energy storage flexure spring 24, the upper portion of which may be relatively fixed at a permanent location such as the block 25 by securing means such as the screw 26. As the keystem 18 and top portion 21 are moved in a downward direction by manual depression of the key cap 16, the permanent magnet 22 is operative to attract the flexure spring 24 to the right. As the energy storage flexure spring is moved between its initial at rest or first position toward the right side, energy is stored in the spring due to the attraction by the magnet 22. The force of attraction between magnet 22 and flexure spring 24 is of a predetermined value, and at a predetermined position during the downward path of travel of keystem 18, the force of attraction between magnet 22 and flexure spring 24 is exceeded by the energy stored in the flexure spring 24. The flexure spring 24, which travels along an arcuate path depicted by the multidirection arrows 30, is operative to store energy therein during the first portion of its movement between the initial at rest or first position and the point to the right of the at rest position at which the snap action of the spring, due to energy stored therein, creates a force which exceeds the attractive force between the magnet 22 and flexure spring 24. When the energy stored in the spring exceeds this attractive force, the spring is released from the attractive force and the energy stored in the spring is effective to cause the flexure spring to snap toward the left, whereupon the lower or impact portion 31 of the flexure spring impacts a piezoelectric element 32 located at a second position to the left of the lower portion 31 of flexure spring 24. Piezoelectric element 32 is operable to generate an electrical signal over connected conductors 34 and 36 in response to impact by impact portion 31 of flexure spring 24. The electrical signal so generated is coupled over output conductors 38 and 40 to an encoding device (not depicted herein) and thus represents an electrical signal generated in response to depression of the key cap 16. Thus it can be seen that a relatively small amount of slowly applied mechanical energy is gathered until a predetermined level is reached, at which time the energy is temporarily stored in the flexure spring 24, and there is provided a control means for releasing the energy stored therein in a relatively short time so that the power can be obtained in the form of a single high-level mechanical impact upon a piezoelectric element exhibiting the ability to convert energy from a mechanical to an electrical form.

Piezoelectric element 32 may be a crystal, quartz, ceramic, or other element having the property of being able to convert mechanical energy to electrical energy. By way of example, one relatively inexpensive but efficient element which was utilized was a common crystal phonograph cartridge. A main advantage of such an element lies in the ability to provide a relatively high signal level output. By way of example, commonly used piezoelectric elements can easily produce outputs of 100 volts amplitude, upon impact by a device such as the impact portion 31 of the flexure spring 24. By providing a substantially high output level, a printed encoding matrix such as a capacitive type encoding matrix can be utilized to provide the requisite encoding to encode the signal generated at each key station into the required digital output code which is to be utilized by the remainder of the data processing system coupled to the data entry device.

FIG. 2 shows another embodiment of the invention. As shown therein, the keyboard may have a keyboard surface 10 and keyboard body or panel 52. Panel 52 has a slot at each key position, each slot having guide walls 54 and 56 serving as a plunger guide for the actuator. The actuator may include a keystem having an upper portion 50 secured to the key cap 16 and guided by guide walls 54 and 56 for longitudinal movement, and a reduced lower portion 51. A return spring 58 may be coupled at one end 44 to the body or panel 52 of the keyboard, and may be disposed to lie in a horizontal or lateral plane so that the left hand portion of return spring 58 abuts but is not necessarily connected to the lower portion of the upper keystem part 50. Key cap 16, and keystem portions 50 and 51 may be an integral unit. Lower keystem portion 51 is disposed to move vertically or longitudinally at its lower end through a bore in magnetic retentive means or permanent magnet 60, which magnet is permanently affixed to the keyboard by conventional means (not shown). There is no relative movement between magnet 60 and panel 52.

Also depicted in FIG. 2 is an energy storage flexure spring 48 having an upper portion 61 permanently in contact with the lower portion of the return spring 58 which is in turn in contact with the keystem portions 50 and 51. The lower portion 62 of the energy storage flexure spring 48 has an impact member 63, and is not permanently secured to any part of the actuating mechanism, but it lies in a substantially horizontal plane so that it is in very close proximity to the lower surface of permanent magnet 60. Hence, the magnet 60 is operable to attract the lower portion 62 when the actuating mechanism is at rest. Also shown in FIG. 2 is a piezoelectric element 64 which lies in a horizontal plane, and is disposed at a fixed second position. Output terminals 66 and 68 are secured to opposed surfaces of the piezoelectric element, and are coupled to output conductors 70 and 72 at the other end thereof.

In operation, the embodiment of FIG. 2 utilizes the same general principles as the embodiment of FIG. 1. Thus, prior to manual depression of key cap 16, the magnet 60 is operative to attract the lower portion 62 of energy storage flexure spring 48. Upon depression of key cap 16, the attractive force still restricts movement of portion 62, but the upper portion 61 is flexed downward, and this flexure enables energy to be stored in energy storage flexure spring 48 and in return spring 58 during a predetermined path of travel of the actuating mechanism. Magnet 60 holds lower portion 62 of the spring as the keystem portions 50 and 51 are moved downward upon depression of the key cap. As the lower keystem portion 51 contacts the lower portion 62 of the spring, it applies a downward force thereto, and when this force in cooperation with the energy stored in spring 48 exceeds the attractive force between magnet 60 and spring portion 62, then the stored energy is released, and the lower portion 62 of spring 48 is operative to rapidly move downwardly and cause impact member 63 of spring 48 to strike the upper part of piezoelectric element 64, effecting generation of an electrical signal in response to the impact.

With both of the FIG. 1 and FIG. 2 embodiments, the impact of an impact portion of the flexure spring and piezoelectric element causes respective springs 24 and 48 to exhibit damped oscillatory movements, so that after the impact, movement of the spring is so restricted that there is but a single impact with the piezoelectric element. This is so because the impact absorbs a large part of the energy stored in each spring. With respect to FIG. 1, flexure spring 24 returns to its initial at rest position without the aid of the actuating mechanism, while in the FIG. 2 arrangement, removal of the downward manual force on key cap 16 causes return spring 58 to urge flexure spring 48 upward to the initial at reset position.

Referring now to FIGS. 3 and 4, and in particular to FIG. 3, there is shown another form which the invention may take. The keyboard may include a keyboard surface 10 and keyboard top panel 80 having a slot of each key position, each slot having upper guide walls 82 and 84. The housing for each key or switch may also include side plates 86 and 88 having respective guide walls 90 and 92 along the interior portions thereof. The actuator assembly for the switch includes an upper keystem 94, affixed to key cap 16 at one end thereof, and guided vertically by guide walls 82 and 84, and also includes a lower keystem 96, affixed to upper keystem 94. Lower keystem 96 is guided vertically by guide walls 90 and 92, and 96 has a recessed cavity 98 at the lower portion thereof which accommodates the upper end of energy storage compression spring 100. Spring 100 may, in a preferred form, be affixed to the top wall 102 of cavity 98 by conventional means.

Also shown in FIGS. 3 and 4 is a lower actuator assembly which includes a plunger 104 guided vertically by guide walls 90 and 92, and having a recessed cavity 106 at the top portion thereof. Cavity 106 accommodates the lower end of energy storage compression spring 100 which in a preferred form need not be affixed to plunger 104. The lower portion of plunger 104 has formed therein a recessed cavity 108 which serves as a guide and pressure point for the stem portion 110 of impact means 112. Cavity 108 is shown in FIG. 4 where the plunger 104 has been raised above its at rest position to depict said cavity. A magnetically attractable member 114 is securely fastened to stem 110 and is retained in the initial at rest position shown in FIGS. 3 and 4 by a permanent magnet 116. Magnet 116, which contains a bore through the center thereof allowing for vertical movement of stem 110, is permanently fastened to side plates 86 and 88.

The lower portion of the key assembly includes a bottom plate 120, and lower plates 122 and 124, which are adhered to bottom plate 120, and which support and are fastened to side plates 86 and 88 respectively. Adhered to bottom plate 120 is an impact absorbing means 126 which may be of a material such as rubber. Affixed to the top of absorbing means 126 is a piezoelectric element 128 which has a first output lead over conductors 130 and 132 connected through terminal 134 and a second output lead (not shown) connected to terminal 136.

In operation, the Impact or switch is shown in the initial or at rest position of FIG. 3, with actuating members 96 and 104 spaced apart. As the key cap 16 is manually depressed, upper and lower keystems 94 and 96 move downward and energy is stored in compression spring 100 as it is compressed. Impact means 112, stem 110 and plunger 104 are retained in the depicted initial position due to the attractive force between magnet 116 and magnetically attractable member 114. As keystem 96 contacts plunger 104 after a predetermined movement of the upper keystem assembly, the energy stored in compression spring 100 exerts a downward force that approaches the attractive force between permanent magnet 116 and magnetically attractable member 114. Upon a slight further downward depression of key cap 16, plunger 104 is moved downward and member 114 is stripped from magnet 116. The energy stored in spring 100 forces plunger 104, stem 110 and impact means 112 downward and impact means 112 impacts the top surface of piezoelectric element 128 causing generation of an electrical signal. The tip of impact means 112, which may be of a resilient material will rapidly rebound from piezoelectric element 128, and member 114 will be attracted to and retained by magnet 116.

Spring 100 also acts as a return spring to return the upper actuator assembly and key cap 16 to the initial at rest position. While the rebounding impact means 112 and stem 110 force plunger 104 upward to the initial at rest position.

Another advantage of my invention may be shown by reference to FIG. 5. As depicted therein, the impact means may take one of several shapes. When a wide and relatively flat impact means 140 is used, the top surface of piezoelectric element 128 will be impacted over a relatively wide area, and a relatively low amplitude but wide pulse is generated. When a relatively narrow impact means 142 is used, the top surface of piezoelectric element 128 is impacted over a relatively small area and a large amplitude and relatively narrow pulse is generated. This is so because the shape of the impact member determines the area of deformation of element 128, and the area and depth of deformation determine the output signal shape. A small and sharp impact member causes a larger, deeper deformation over a small area and a resultant high amplitude narrow pulse, while a broad impact member causes a small but wide deformation pattern and a lower amplitude wide pulse output pulse. Hence the shape of impact means can be used to control the amplitude and width of the electrical output signal produced by the switch.

While only certain features and advantages of my invention have been fully described and illustrated, it should be obvious that other modifications and alternations may be made therein.

Claims

What I claim as my invention and what I desire to secure by Letters Patent is:

1. An impact transducer switch comprising: manually operable key means; an upper housing having first and second vertical guide walls; actuator means having an upper portion connected to said key means, and including a first recessed cavity at the lower portion thereof, and a lower portion separated from said upper portion and having a second recessed cavity at the upper portion thereof; an energy storage compression spring having a first end contained within said first cavity and a second end contained within said second cavity; a lower housing; a piezoelectric element mounted within said lower housing, for generating an electrical signal upon impact thereof; a permanent magnet secured to said upper housing; and impact means, communicating with said lower portion of said actuator means, and normally retained by said permanent magnet during a first portion of movement of said actuator means, said first portion of movement compressing said spring to store energy therein, and being further operable to overcome the attractive force of said magnet and impact said piezoelectric element after a predetermined movement of said actuator means.

2. The invention defined in claim 1 wherein said impact means has a shape adapted to define the amplitude and pulse width of said electrical signal.

3. An impact transducer switch comprising: manually operable key means; an energy storage flexure spring having first and second end portions; a piezoelectric element spaced apart from said second spring end portion, for generating an electrical signal upon impact thereof; a permanent magnet for normally attracting and retaining said second end portion of said spring; actuator means, movable by said key means, for deflecting said first spring end portion to store energy in said spring and for thereafter effecting release of said second spring end portion to cause said impact, said first end portion of said spring being in contact with said actuator means; and a return spring having a first fixed end and a second end in contact with said first end spring portion and said actuator means.