Improved electronic keyboard

This invention relates to a keyboard. It relates more particularly to an electronic keyboard used to control the transmission of information. Such keyboards are used, for example, to apply data to a computer, to control a printer or to control information being displayed on a video terminal.

Background of the Invention

Conventional electronic keyboards usually comprise a base which supports a matrix board that defines the keyboard's key positions. Each position includes a pair of switch contacts, a spring-biased plunger and a key cap for depressing the plunger which thereupon allows the spring contacts to come together. This completes an electrical circuit to initiate a selected function, e.g. the printing of a character associated with the depressed key. Thus, the manufacture of the keyboard as a whole requires the hand assembly of a large number of small parts which is time consuming and expensive. Also, there is ample opportunity for misassembly of those parts. Furthermore, electrical connections have to be made between the switch contacts at the different key positions and a printed circuit board, further adding to the time required to assemble keyboards of this general type.

There do exist membrane keyboards or touch pads which are used in some calculators and in the control panels for some appliances such as radar ovens. See, for example, U.S. Patents 3,773,998; 3,978,297; 3,982,081 and 4,028,509. However, those prior apparatus are not entirely suitable a3 full keyboards for use with a computer, printer, 3isplay terminal, or the like. First of all, the "keys" on most of those pads do not move to any appreciable extent. Therefore, they do not provide any feedback to the operator which is desirable if the operator is to "type" accurately at a reasonably high rate of speed. Also the switches incorporated into those prior membrane keyboards at the different key positions are generally not reliable or durable enough for this application and the electrical signals they initiate are not always consistent and uniform.

Those prior pads which do have movable keys tend to require relatively complicated spring structures associated with the keys. Often the keys do not have the right feel as far as the operator is concerned and rapid operator fatigue results.

Also in the usual full keyboard, the key positions are arranged in columns and rows with the rows further away from the front of the keyboard being located at progressively higher levels or elevations like the keys of a conventional typewriter. It has been the convention to regard the second key row or level above the space bar as the so-called home row over which the fingertips are usually returned after reaching for keys in the other rows.

To enable the operator's fingertips to properly contact the keys in the different rows, the tops of the key caps in the different rows have different shapes or profiles. For example, in a typical keyboard, the tops of the key caps in the home row may be more or less horizontal. On the other hand, the tops of the key caps in the topmost row are angled downwardly, the angle being such as to more or less match the angle of the operator's fingertips when he reaches for those keys. Conversely, the key caps in the lowest or front row of the keyboard may be angled upwardly to account for the fact that the operator's fingers have to reach back and down in order to properly depress those keys. This means that several differently sculptured key caps must be manufactured for each keyboard. Not only are there attendant die costs, but also these caps must be separately inventoried and they must be installed in the correct rows of the keyboard, adding to the overall cost of keyboards of this general type.

Also, because the keys are different as aforesaid, each key is dedicated to a particular row or rows of the keyboard. Therefore, it is not possible to change the format of the keyboard by rearranging the keys, e.g. from a telephone format to a calculator format.

Conventional electronic keyboards have other drawbacks as well. Some are excessively noisy in that they emit a clacking sound when the operator rapidly depresses the keys one after the other in the manner of a competent typist. Some prior keyboards of this type do not satisfy the height standard recently agreed upon by European countries which requires that the height of the keys in the home row be no more than 30 mm. from the surface upon which the keyboard rests.

Summary of the Invention

It is the object of the present invention to provide an improved electronic keyboard for general use. Briefly, our keyboard may be a stand-alone item for applying information to a nearby video terminal or directly to a computer. Alternatively, it may be incorporated into the apparatus it is controlling, a so-called intelligent terminal, for example.

The keyboard comprises a base whose floor is formed as an upwardly rearwardly-extending ramp that determines the elevations of the various rows of keys on the keyboard. The ramp may have a uniform slope so that each row of keys is located at a different height or level or more preferably its slope may change so that more than one row of keys is located at the same height or level.

Positioned on that floor are upper and lower flexible printed circuits printed with two arrays of registering switch contacts as well as the required connections between those contacts and a set of terminal strips. A dielectric sheet placed between the two layers is formed with openings at the location of each pair of upper and lower switch contacts thereby forming a switch. By pressing down on the circuit at the location of a switch, the upper switch contact is pushed through the registering sheet opening so as to engage the lower contact and close the switch. Upon removal of pressure, the switch opens. In accordance with the usual keyboard format, the switch positions are arranged in rows, e.g. five rows, there being, say, up to twenty switch positions in a typical row.

A spring strip covers each row of switches formed by the printed circuit. Each such strip comprises a lengthwise series of cantilevered spring members, there usually being one member for each switch. Superimposed on each row of spring strips is a key guide strip. Each guide strip defines a lengthwise series of key guides, there usually being one such guide for each switch. Means are provided for anchoring the key guide strips to the base through the spring stripes and printed circuit to maintain the proper relative positions of all of those components.

A key is positioned in each key guide. Each key is composed of a key cap accessible at the top of the keyboard and an integral plunger which is slidably received in a key guide and engages the free end of an underlying spring member. Normally, the key cap is supported at an elevated position by its engaged spring member. However, each key can be depressed so as to flex its spring member downwardly to the underlying printed circuit to close the associated switch thereon. In the present keyboard, force is not transmitted directly from the key caps to the switches in the printed circuits, but rather indirectly through the spring strips. As will be described in detail later, these strips are designed to assure that a substantially constant flexing or switch closing force is applied to the printed circuit even though the depressing forces applied to the key caps may vary. Resultantly, the electrical signals initiated by the keyboard are consistent and reliable. Also, this construction is found to provide the desired operator feedback from the keys to enable the operator to type correctly at a maximum rate of speed without suffering undue fatigue.

Because of the ramped construction of the keyboard base, all of the keys in our keyboard have exactly the same shape so that they can be formed in a single mold. That is, the tops of the key caps on all of the keys have exactly the same contour or angle. Thus, by properly selecting the ramp angle under each row of key guide strips, the key caps in those strips can be tilted to the optimum angle for that particular row. Moreover, any key can be used at any location on the keyboard. Accordingly, the character format of the keyboard can be changed at will simply by moving the keys around.

The forming of the keyboard using a flexible printed circuit and sets of spring strips, key guide strips and keys to define the key positions at the different rows or levels of the keyboard results in a drastic reduction in the number of separate parts required to make the keyboard, as compared with prior comparable electronic keyboards of this general type. This not only means a considerable savings in manufacturing cost; it also means that the keyboards themselves can be assembled very quickly and correctly by the average production worker.

With all of these advantages, then, our keyboard should find wide application in connection with the transferring, printing, computing or displaying of graphic information or data.

Brief Description of the Drawings

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description, taken in connection with the accompanying drawings, in which:

• FIG. 1 is perspective view of an electronic keyboard embodying the principles of this invention shown in conjunction with a video terminal;
• FIG. 2 is an exploded perspective view showing the major components of the FIG. 1 keyboard in greater detail;
• FIG. 3 is a side elevational view on a larger scale with parts broken away of the FIG. 1 keyboard;
• FIG. 4 is a fragmentary front elevational view with parts broken away on a still larger scale illustrating the operation of the FIG. 1 keyboard;
• FIGS. 5A and 5B are side elevational and top plan views respectively of a typical spring strip incorporated into the FIG. 1 terminal; FIGS. 5C and 5D are similar views of another spring strip embodiment;
• FIGS. 6A to 6C are end elevational, front elevational and top plan views respectively of a typical key guide strip incorporated into the FIG. 1 terminal;
• FIGS. 7A and 7B are top and bottom perspective views respectively of the keys utilized in the FIG. 1 terminal; and
• FIGS. 8A and 8B are sectional and top plan views with parts broken away respectively illustrating the construction of the switches in the F_IG. 1 terminal.

Description of the Preferred Embodiment

Referring to FIG. 1 of the drawings, a keyboard made in accordance with this invention is indicated generally at 10. Keyboard 10 is shown in conjunction with a conventional video terminal 12 positioned on an adjustable base 13. It should be understood, however, that the keyboard can also be used to provide a direct input to a computer or to control a printer or be incorporated directly into other electronic apparatus such as an "intelligent" terminal. Also the keyboard 10 may have its own microprocessor.

The illustrated keyboard is connected electrically to terminal 12 by way of base 13 by a cable 14 extending from the terminal and terminated by a plug 14a which plugs into a receptacle in the base. Both the keyboard and terminal are usually connected electrically to a remote computer (not shown). The cable 14 is secured in a cable trough 15 (FIG. 3) in the underside of the base which extends the entire width of the base so that the cable can be brought out from either side of the keyboard.

The keyboard 10 includes a housing 18 which supports a multiplicity of keys 22 and a space bar 24 arranged in a more or less standard typewriter keyboard format having five rows of keys at various elevations with the space bar being in the front row. It will be appreciated, however, that the keyboard can have other key formats. For example, a block of the keys 22, say, at one side of the keyboard, can be organized in a calculator or telephone type arrangement.

As is the case with most keyboards of this general type, keyboard 10 includes certain keys 22 which are so-called character keys and other keys which execute control functions, the RETURN key 22R and SHIFT key 22S being examples of the latter type. There are also certain keys which are able to perform both functions. By depressing one or another of the keys on the keyboard,- one can read data into the computer with which the keyboard and terminal are associated or retrieve data from that computer for display on the terminal 12.

Turning now to FIGS. 2 and 3, housing 18 comprises a generally rectangular shell-like lower section or base 18a molded of a suitable impact-resistant plastic material. All of the components of the keyboard including the keys 22 are mounted on that base and a shell-like upper section or cover 18b is positioned on base 18a covering those portions thereof not occupied by keys 22 or space bar 24. Thus all of the components of the terminal except the keys are protectively enclosed within housing 18.

The base 18a is formed with a ramped floor 27 which extends from the front of the base upwardly rearwardly toward the rear thereof, leaving a relatively wide channel or trough 32 at the rear of the base. This space 32 may be utilized to contain various electrical components associated with the keyboard such as resistors, rheostats, printed circuit boards, electrical connectors, etc., some of which are shown at 33 in FIGS. 2 and 3.

Positioned on floor 27 is a rigid plate 28. This plate is divided into a plurality of lengthwise segments 28a, 28b and 28c which are oriented at different angles relative to the horizontal plane. Plate segment 28a which spans the first two rows of keys in the keyboard is more or less horizontal, segment 28b supporting the third row of keys is angled up relatively sharply relative to segment 28a and segment 28c containing the top two rows of keys is oriented at a still larger angle with respect to the horizontal plane. Also as best seen in FIG. 2, the plate 28 is formed with a rectangular array of small vertical holes 36 arranged in columns and rows over all three segments 28a, 28b and 28c. A similar array of dimples 37 are present in the surface of floor 27. Normally, plate 28 is secured to floor 27 by suitable means such as screws 41 (FIG. 2). Alternatively, it may be keyed to the base.

Positioned on base 18a, or more particularly, on the plate 28 thereof, is a key position switch-forming printed circuit assembly indicated generally at 42. As shown in FIG. 2, assembly 42 comprises a flexible printed circuit 44 which is folded over on itself about its longitudinal center line so that one longitudinal section 44a of the circuit lies directly above the other longitudinal section 44b thereof. Printed on the surface of section 44a and facing section 44b is a rectangular array of conductive switch contacts 46. Also formed on section 44a are a multiplicity of electrical paths 48 leading from each contact 46 to one or another of the terminals 52 printed on tabs 44c extending from a rear edge of printed circuit 44. Connectors (not shown) electrically connect these terminals to the keyboard cable 14 positioned in cable trough 15 in the underside of the base.

Circuit section 44b carries a similar array of switch contacts 54 printed on the surface thereof facing contacts 46. However, they also are connected to one or another of the terminals 52 by conductive paths 56 printed onto circuit section 44b. Alternatively, of course, the two circuit sections 44a and 44b could be formed separately.

As shown in FIG. 2, the printed circuit assembly 42 also includes an electrically insulating plastic sheet 58 which is more or less the same size and shape as the printed circuit 44. Sheet 58 may be folded about its longitudinal axis and positioned so that its lower section or leaf 58a is positioned between printed circuit sections 44a and 44b as shown in FIG. 2. The other half or section 58b of that sheet is folded over on top of circuit section 44a. Sheet section 58a is formed with a rectangular array of openings 62, the openings being positioned so that they are in register with the switch contacts 46 and 54 on the folded-over printed circuit sections 44a and 44b. The sheet layer or section 58a functions as an insulating spacer between the circuit sections 44a and 44b except at those locations between the switch contacts 46 and 54. Thus each pair of registering contacts 46 and 54 and the opening 62 between them function as a switch shown generally at 63 in the printed circuit assembly 42. The other half 58b of sheet 58 which overlies circuit section 44a protects that section from abrasion and improves the operation of the switches as will be discussed later.

Still referring to FIG. 2, locating holes 64 are provided at several places, e.g. the four corners, in the folded-over printed circuit 44. Similar locating holes 64 are formed at the four corners of the folded-over sheet 58 with the openings at the corresponding corners being in register. When the printed circuit assembly 42 is positioned properly on base 18a, locating pins 66 projecting up from the four corners of the ramped plate 28 project through the locating holes so as to maintain the alignment of printed circuit 44 and sheet 58. Resultantly, the switch contacts 46 and 54 and the openings 62 of each switch 63 are all in proper register.

Also formed in circuit 44 and sheet 58 are rectangular arrays of small holes 67 arranged in columns and rows corresponding to the array of holes 36 in plate 28. When the assembly 42 is positioned on the plate as aforesaid, the holes 36 and 67 are all in register.

Still referring to FIG. 2, positioned on the printed circuit assembly 42 is a layer of spring strips 72. In the illustrated keyboard having five rows of keys, there are five rows of such spring strips. Each spring strip comprises a plurality of more or less identical sections 72a, each such section containing a cantilevered spring 74. The spring strips 72 may be of various lengths depending upon the format of the keyboard 10. For example, the spring strip shown at the right hand end of the first row of strips is seven sections long and contains seven springs 74, while the strip 72 at the left hand end of that same row is three sections long. In general, the strips 72 are arranged so that there is a spring 74 for each active key position on the keyboard.

Referring now to FIGS. 5A and 5B, the spring strips 72 are identical except for their length, i.e. the number of sections 72a and springs 74 in the strip. In FIG. 5B, the various sections 72a are shown bounded by vertical dotted lines L. Each strip is formed from a single piece of spring steel by a conventional etching process or by a stamping process using a progressive die. Thus, the strips can be made in a limited number of fixed lengths. Alternatively, the strip can be formed as a continuous roll with the needed strip lengths being drawn from the roll.

Each spring section 72a includes a pair of spaced parallel side rails 76 with the right hand ends of the rails being formed with tabs 76a which project toward one another. Each cantilevered spring 74 in each section 72a comprises a pair of legs 74a whose right hand ends are joined to the tabs 76a in that strip section. The spring legs 74a are angled toward one another and their opposite ends are connected by a bridging portion 74b. Each bridging portion 74b has a nose 78 which projects from its leading or upper edge. Furthermore, that nose is upwardly curved or dimpled as best seen in FIG. 5A. The lower edge of the spring bridging portion 74b is formed with a small depending tail 82 at the root of the spring legs 74a. Tail 82 is hook-shaped, extending downwardly toward the right and then curving back on itself. A dimple 84 is formed at the end of each tail 82 at the underside thereof.

As best seen in FIG. 5B, the legs of the springs 74 are shaped so that when the free end of each spring is depressed, that end fits between the legs of the adjacent spring so that all of the springs operate independently. Also as shown there, a small hole 86 is punched through each strip tab 76a. When the strips 72 are arrayed end to end to form a layer of five rows as depicted in FIG. 2 and are properly juxtaposed to the base floor 28, their holes 86 are in register with holes 36 formed in the base. As such, they are also in register with the holes 62 formed in the printed circuit assembly 42.

Referring now to FIGS. 2, 3 and 6A to 6C, positioned above the layer of spring strips 72 is a layer of key guide strips 92. Since there are five rows of spring strips in the illustrated keyboard, there are usually five rows of key guide strips. The strips 92 are molded plastic parts and they are substantially identical except as to their length. Each strip is composed of a plurality of more or less identical sections 92a, the division between those sections being shown by the vertical dotted lines L in FIGS. 6B and 6C. The lengths of the various strips 92 in each row of the strip layer depicted in FIG. 2 depend upon the format of the keyboard 10 and whether or not the keyboard has any empty key positions. For example, because of the presence of the space bar 24, the key guide strip 92 at the left end of the front row of the layer shown in FIG. 2 comprises three sections 92a. On the other hand, the strip section 92 at the opposite end of that same row is eight sections long. The remaining rows in the layer of key guide strips can be composed of single strips 92 extending the entire length of that row or a plurality of shorter strips laid end to end. Generally, as with the spring strips, the guide strips are made in a limited number of different lengths to save manufacturing and inventory costs.

Referring especially to FIGS. 6A to 6C, each key guide strip 92 is a channel-shaped part having a top wall 94a and a pair of spaced-apart depending side walls 94b. Projecting up from the center of the wall 94a in each strip section is a generally cylindrical neck 96. A passage 98 extends down through neck 96 to the underside of the strip, which-passage has a cross section which is in the shape of an X or a cross as best seen in FIG. 6C. Formed in diagonally opposite corners of the strip wall 94a in each section 92a are a pair of small rectangular openings 102. Formed in the remaining two corners of the wall 94a in each section 92a are a pair of resilient tongues 104. These tongues extend in from the opposite walls 94b of the strip parallel to one another on opposite sides of the neck 96 in that section, terminating more or less at the longitudinal center line of the strip.

A pair of posts 108 extend down from the lower edge of strip walls 94b in each strip section at points just to the right of the neck 96 in that section. As will be seen later, these posts are used to anchor the components of the keyboard to the base 18a..Accordingly, they are dimensioned so that they can project through the openings 86 in spring strips 72 and through the openings 67 in circuit assembly 42, as well as through the openings 36 in plate 28 as best seen in FIG. 4. Thus, since each strip 92 contains at least two strip sections 92a, each strip has at least four posts 108.

To facilitate aligning the strips 92 end to end, the end edges of their walls 94a and 94b may be shaped or stepped so that the opposing ends of adjacent strips interfit or interlock with one another. Thus, as shown in FIG. 6B, the left hand end of the strip front wall 94b may have a small foot 94c which extends out toward the left, while the right hand end of that same wall may have a small notch 94d. It is apparent then that the foot 94c can project into the notch 94d of a strip positioned in the same row to the left of the illustrated strip, while the notch 94d will receive the foot 94c of a strip positioned to the right. In a similar fashion, as best seen in FIG. 6C, the opposite ends of the top wall 94a ir each strip may be stepped so as to mate with correspondingly stepped strips positioned at either end of the illustrated strip 92.

Turning now to FIGS. 7A and 7B, each key 22 comprises a unitary part molded of a suitable impact-resistant plastic material. It comprises a shell-like key cap 110 having a contoured or sculptured upper surface 110a and a shaped skirt 110b. Projecting down from the inside of the key cap is a plunger 112 whose cross section is in the shape of an X or a cross. The plunger is dimensioned so that it can be slidably received in the openings 98 of the key guide strips 92.

Extending down from the lower edges of the key cap skirt 110b at more or less diametrically opposite locations on the key are a pair of elongated key retainers or clips 114. These are resilient members whose lower ends are terminated by pronounced barbs 114a which project out laterally somewhat beyond the key cap skirt. Also extending down from the lower edge of the skirt 110b on opposite sides of the plunger 112 are a pair of short posts 116 whose function will be described later.

It is important to note that, unlike the keys in most prior keyboards of this general type, the keys 22 may be identical. That is, the curvature and profile and orientation of the key cap top surface 110a can be the same for all keys, as can the shape of the key cap skirts 110b. Of course, the key caps may have unique shapes such as the RETURN key 22R shown in FIG. 1 or even non-standard shapes. Therefore, all the keys can be made from the same mold. It is even possible to mold all the keys at once in a single mold after which the individual keys can be separated.

As a direct result of the aforesaid construction and design of the various keyboard components, those components can be assembled to the terminal base 18a very quickly and easily. First, the flexible printed circuit 44 is folded over and interleaved with the folded-over spacer sheet 58 as shown in FIG. 2 and that assembly is positioned on the plate 28 using the locating holes and pins 64 and 66 described above. This automatically aligns the holes 67 in the printed circuit assembly 42 with the holes 36 in the plate. With this, the locations of the five rows of key positions in the keyboard are determined.

Next, the key guide strips and spring strips are assembled to the base starting with, say, the top or rear row of keys. Assume, for example, that the top row comprises a single key guide strip 92 and a single spring strip 72 both of which extend the entire length of that row. The spring strip 72 is positioned at the underside of the key guide strip with the guide strip foot 94c and springs 74 facing leftward as shown in FIG. 2. The posts 108 projecting down from the key guide strip are then inserted through the holes 86 in the spring strip. This automatically positions the spring strip so that nose 78 at the end of each spring 74 in the strip is centered directly below the plunger passage 98 in a key guide section 92a as shown in FIG. 4.

Then the key guide strip with the spring strip impaled thereon is positioned against the plate 28 so that its posts 108 are in register with the holes 67 in the printed circuit assembly and the holes 36 in the plate. The key guide strip is then pressed down toward the base so that the spring strip and circuit assembly are sandwiched between the key guide strip and the base as best seen in FIG. 4. With the guide strip held in that position, the free ends of the posts projecting through the underside of the plate are upset or heatstaked to the underside of the plate as shown at 108a in FIGS. 3 and 4. This permanently anchors that top key guide strip and associated spring strip as well as the uppermost lengthwise segment of the circuit assembly 42 to the plate.

The assembler follows the same procedures to mount the other rows of key guide strips and spring strips to the plate. If a particular row is composed of more than one spring strip or more than one key guide strip, those strips are attached to the plate one at a time and in end-to-end relationship so that all of the active key positions in that row of the keyboard are filled. After all of the key guide strips are anchored to the plate, all of the key positions in the keyboard are apparent from the raised necks 96 of those units. The plate 28 can now be mounted to the base 18a and secured there by screws 41 (FIG. 2). The dimples 37 in the base floor accommodate the post ends 108a. Electrical connections are then made between terminals 52 and cord 14. The only thing that remains is to mount the keys 22 to the key guide strips. This is accomplished simply by positioning a key 22 bearing the particular character at the desired position on the keyboard and inserting its plunger 112 into the neck passage 98 such that the depending key retainers 114 are located opposite the openings 102 in the key guide strip. To facilitate properly orienting the key, the front wall of the key skirt 110b has a distinctively broad face as compared with the other skirt walls as shown in FIG. 3. Once the key is in the passage 98, it is simply depressed. This causes the key retainers 114 to project through the openings 102 so that their barbs 114a engage under the edges of those openings as best seen in FIG. 4.

Thus the retainers permit the key to be moved vertically between a depressed position wherein the lower edge of the key cap 110 almost touches the top of the key guide strip to a normal or elevated position wherein the retainer barbs 114a engage against the underside of the key guide strip top wall 94a all as shown in FIG. 4. The tight sliding fit between the X-shaped key guide passages 98 and key plungers 112 minimizes lateral play of the keys and aids in reducing rotational play of the keys. The retainers 114 prevent the keys from falling out of the keyboard during shipping and handling of the keyboard. Yet each key 22 can be removed if need be simply by squeezing its two retainers together until their barbs 114a clear the opening 102 edges. The retainers are accessible from the top of the keyboard. To facilitate key removal, a tool which squeezes the retainers together may be used.

Usually there is one spring 74 and one flexible circuit switch 63 associated with each key 22. However, in some cases, it may be desirable that a single key, e.g. a control function key, actuate two or more switches 63. Such a key is located at the left hand end of the front row of the keyboard in FIG. 1. That particular key 22S overlies two key strip guide sections 92a as well as two springs 74.

Also, while the space bar 24 is essentially a single key, because it is used with great frequency, it is desirable that it control two switches 63 in the flexible circuit assembly 42. These switches are connected in parallel so that those switches are in essence redundant. Therefore, in the event that there is an open circuit or failure of one switch 63, the space bar will still operate. In the illustrated keyboard shown in FIG. 2, the space bar 24 has plungers 112 projecting down from its opposite ends. These slidably engage in the key guide strip sections 92a directly below the opposite ends of the space bar.

It should also be mentioned at this point that, as best seen in FIG. 4, the spring 74 flexed by the depressed key 22 in each key guide strip section 92a is actually anchored to the key guide strip section 92a to the right of the depressed key position. Therefore, as shown in that figure, the key guide strip sections 92a at the right hand ends of the keyboard rows simply serve to anchor the right hand ends of the spring strips. They do not define active key positions and, in fact, those sections do not even support keys. Rather, they may be covered over by the right hand end of the keyboard housing cover 18b. The same is true of the last guide section 92a under the left end of the space bar 24 in FIG. 2. By the same token, there are no springs 74 anchored under the key guide strip sections at the extreme left end of each row of the keyboard. This offset arrangement of the springs permits the replacement of one double key such as key 22S with two single keys 22 at the same location.

Referring now to FIG. 4, in any given row on the keyboard, the plunger 112 of each key is located directly over the nose 78 of a spring 74 in the same row. Moreover, the tail dimple 84 on each spring is located directly above a printed circuit switch 63 in that row. When a particular key 22 is in its raised position as shown in FIG. 4, the corresponding spring 74 is in its raised unflexed position with its tail 82 spaced slightly from the top of the flexible printed circuit assembly 42 at the associated switch 63. Accordingly, the two contacts 46 and 54 of that switch are spaced from one another because of the presence of the spacer sheet section 58a in the assembly. Therefore, that switch 63 remains open. Each spring 74 is sufficiently stiff and resilient to support quite easily the full weight of the associated key 22. Therefore, that key is normally maintained in its raised position shown in FIG. 4 so that the corresponding switch 63 in the printed circuit assembly is normally open.

On the other hand, when a key 22 is depressed as indicated by the arrow A in FIG. 4, the associated spring 74 is flexed downwardly. This causes its tail 82 or more particularly its dimple 84 to depress the top of the printed circuit assembly 42 at the associated switch 63 so that the contact 46 of that switch is pressed against contact.54, thereby closing that switch..

Thus, as the various keys 22 in the keyboard 10 are depressed and released, various switches 63 in the printed circuit assembly 42 are opened and closed correspondingly. This switching action in the keyboard initiates control signals for the associated terminal 12 (FIG. 1) and for the computer to which the keyboard is connected in a manner similar to other conventional electronic keyboards.

It is important to note that each spring 74 is constructed so that its tail 82 which engages the circuit assembly 42 is offset along the same row from the spring nose 78 which is engaged by the associated key 22. Accordingly, when the key is depressed, it does not apply any force directly to the circuit assembly; it simply flexes the spring downwardly. It is the flexed spring which applies the downward force to the circuit assembly. In this, each cantilevered spring 74 functions more or less as a lever so that a moderate amount of downward force on the free end of the spring results in the application of a larger force by the tail 84 to the associated printed circuit switch 63 located closer to the spring fulcrum. This enables the operator to depress the key using a moderate amount of finger pressure, yet assuredly close the associated switch. We should mention in this connection that the sheet layer 58b contacted by each spring when a key is struck helps to distribute the impact force over the appropriate switch 63 area of the upper circuit section 44b. This further assures that good electrical contact is made between each pair of switch contacts 46 and 54.

By the same token, as the printed circuit is flexed when each key is depressed, there is minimum shock force transmitted back to the operator's finger. Consequently, the operator can use the keyboard for a prolonged period without suffering undue fatigue. Moreover, because of the illustrated offset key and spring construction, the force which presses each switch contact 46 against contact 54 at each switch position 63 can be controlled to a great extent by properly selecting the dimensions and stiffness of spring 74. Furthermore, the forces exerted by the springs at all switches 63 of assembly 42 will remain more or less the same even though the depressing forces on the keys 22 may vary. This assures that the momentary electrical connections made by the keyboard and the resultant initiated electrical signals are consistent and reliable even though operators having different "touches" use the keyboard. This arrangement also enables the keyboard to provide a proper amount of mechanical feedback to the operator when the keys are depressed so that the unit has the desired "feel" as far as the operator is concerned. In addition, the offset key and spring arrangement enables the entire keyboard to be housed in a very low profile package.

FIGS. 5C and 5D illustrate another spring strip embodiment 72' which has the same advantages as strip 72. This strip is composed of a series of springs 74'. In this version, the springs have longer noses 78'. Also their tails are substituted for by transverse channels 82' formed at the junctions of the spring legs and which project down below the general planes of the springs 74'. A dimple 84' is formed at the underside of each such channel. The strip functions in more or less the same way as strip 72.

Turning now to FIGS. 4, 6C and 7B, when each key 22 is depressed, its short posts 116 engage the free ends of the tongues 104 formed in the top wall of the guide strip supporting that key. Since those tongues are flexible and resilient, they function as shock absorbers which absorb the impact of the depressed key. Thus these elements also contribute to the operator feedback provided by the keyboard. In addition, they minimize the vibration produced by the keyboard when in use.

Referring now to FIGS. 8A and 8B, the flexible printed circuit assembly 42 specifically illustrated is specially designed to provide consistent and reliable electrical connections at all of the switches 63 defined thereby. To meet this objective, the circuit assembly 42 is formed quite differently from flexible touch pads, membrane-type touch panels and other such flexible switches already known in the art of which we are aware.

In the present arrangement, the upper section 44a of the flexible printed circuit 44 comprises a sheet substrate 120 of a suitable electrically-insulating flexible plastic material such as Mylar polyester. Affixed to the underside of that substrate 120 is a thin layer 122 of a conductive metal such as copper plated all over with solder. At the location of each switch 63 in the printed circuit assembly is a very thin conductive silver (carbon) contact disk which is plated onto the underside of the coated copper layer 122. This disk constitutes the switch contact 46 discussed above. Substantially the entire area of section 44a is covered by the copper layer 122 except along selected narrow etched paths 126 which extend over the surface of the substrate 120 and which serve to electrically isolate the contacts 46 from each other. The topology of those etched paths 126 is such as to establish separate electrical paths 48 from each plated contact 46 at each switch 63 to another contact or to an electrical terminal 52 on the printed circuit tabs 44c (FIG. 2), while maintaining the area of the copper layer 122 on the substrate 120 at a maximum.

The bottom section 44b of the flexible printed circuit 44 comprises a Mylar substrate 132 to which is adhered a thin layer 134 of a conductive metal such as copper coated all over with solder. Plated onto the coated copper layer 134 at each switch 63 is a small silver (carbon) contact disk of a relatively inert electrically-conductive metal such as silver. Each such disk constitutes a switch contact 54 which is located directly opposite the contact 46 of that switch 63. Also the copper layer 134 is etched away from the substrate to define a multiplicity of narrow paths 138 extending over the surface of the copper layer. These paths are also arranged so as to electrically isolate the contacts 54 at each switch position and to establish electrical paths 56 from each such contact to another contact or to one or more terminals 52 on the printed circuit tabs 44c.

Actually as described above, the printed circuit sections 44a and 44b comprise a single folded-over flexible printed circuit so that the substrates 120 and 132 are formed as a single sheet and the paths 126 and 138 are etched at the same time on that sheet. Thus the contact areas 46 are applied to one-half of the resultant flexible circuit, while the contact areas 54 are applied to the other half so that, when the flexible circuit is folded in half and interleaved with the sheet 58, the two sets of contacts 46, 54 are in register with the openings 62 in the spacer sheet 58a as noted above.

When the printed circuit assembly 42 is sandwiched between the key guide strips 92 and the base 18a, the contact areas at each switch position 63 are more or less isolated and therefore protected from dirt and corrosion that might degrade the electrical connections between the contacts when the associated key 22 is depressed. However, there is still no air cushion effect at the switches 63 because the air is vented from those switch positions through paths 126 and 136 on the printed circuit sections when the keys 22 are depressed.

Also, it is important to note that the flexible circuit section 44a, which is flexed when the keys are depressed to establish electrical contacts at the various switch position 63, carries copper plating 122 over substantially its entire area. This is in sharp contrast to other flexible circuits which have copper conductors only along narrow paths from one point to another on the substrate. This means that the stiffness and resilience of circuit section 44a is determined by the copper layer 122 which layer is insensitive to changes in temperature, humidity and the like, rather than by the plastic substrate 120 which is affected greatly by such atmospheric variations.

Moreover, the copper layers 122 and 134 maintain the shape of the printed circuit so that the positions of the switch contacts 46 and 54 can be located precisely on the circuit. The thickness of the spacer sheet 58a can also be controlled quite accurately as can the heights of the raised silver contacts 54 at each switch position 63. Resultantly, the present printed circuit assembly 42 has very uniform electrical and mechanical characteristics at all of its switch positions. In other words, when a selected amount of downward force is applied to the top of the assembly at a particular switch position 63, a consistent and reliable electrical connection is made between the contacts 46 and 54 at that position. Resultantly, the keys of the keyboard 10 initiate uniform electrical signals.

While we have shown in detail one specific flexible circuit construction, it should be understood that a conventional printed circuit construction may be employed, e.g. a Mylar substrate carrying printed circuit paths and contact areas of conductive silver.

In summary then, the electronic keyboard described herein is a great improvement over prior comparable keyboards in that it is composed of a relatively small number of different parts which are quickly and easily assembled without requiring any wiring steps at all to be performed at the different key locations on the keyboard. Also, since identical keys can be used at all key positions, the format of the keyboard can be changed as needed to suit different applications. The keyboard establishes very consistent reliable electrical contacts at its different switch positions and it emits a minimum amount of noise when in use. Furthermore, the keyboard as a whole is relatively rugged and compact and meets the height standards set by the industry.