Touch Response Sensor for an Electronic Musical Instrument

This invention relates to a touch response sensor of a keyboard type electronic musical instrument to perform touch control upon depression of keys and more particularly, to an after-control sensor for the electronic musical instrument capable of varying the volume or the like of musical tones to be produced in response to intentional change of key depressing pressure after normal depression of the keys. Generally, the feelings of a performer can be expressed in musical tones through the key depressing operation of the organ by controlling the volume, pitch, tone-color or the like in response to the performer's finger touch in the attack and sustain states of the tones, which is called "touch control". More specifically, the volume, pitch, tone-color or the like of the tones being played may be changed responsive to a conscious variation of the key depressing pressure after a normal or initial depression of the keys to be played, which is called "after-control". For achieving such touch control there is needed a device for detecting the key depressing pressure upon depression of the keys, which device is required to have an insensible region with regard to the increase of the key depressing pressure. This insensible region means a range where the touch control is not effective under a normal depressing pressure so that the touch control is not executed in ordinary key depressing operation but is effected only upon a conscious increase of the key depressing pressure for performing the positive touch control. The device is also required to detect the key depressing pressure sensitively in response to the key touching operation by the performer's fingers once the touch control is conducted by the conscious increase in the key touching pressure.

Heretofore, as shown in FIG. 1, the prior art touch control sensor of the electronic musical instrument has an electrically conductive cylindrical rubber member 2 fixed to a predetermined position of the lower surface of a key 1, and stationary contact members 4 and 5 spaced in parallel with each other and fixed onto a base plate 3 and having contact pieces 4a and 5a, respectively of suitable configurations such as a substantial triangular shape and located at the position opposite to the rubber member 2. Upon depression of the key the conductive member 2 come into contact with the contact pieces 4a and 5a of the contact members 4 and 5 to electrically connect the contact pieces 4a with 5a. When the key depressing force is weak, the rubber member 2 is not so deformed in shape, as designated by a solid line in FIG. 2, and, accordingly, the area where the rubber member 2 is in contact with the contact pieces 4a and 5a is small. If the key depressing force is strong, the rubber member 2 is flattened as shown by two-dotted broken line in FIG. 2, and therefore the contacting area of the member 2 with the contact pieces 4a and 5a increases.

Thus, the contacting area of the rubber member 2 with the contact pieces 4a and 5a of the members 4 and 5 is varied in response to the strength of the key depression, resulting in variation of the resistance value therebetween in response to the key depression. If the contacting area increases, the resistance value decreases. The key depressing pressure is thus detected based on the variation of the resistance.

However, the aforementioned sensor is inconvenient for the after-control purpose because the cylindrical conductive rubber member is not distorted in exact proportion to the key depressing force when the key is further deeply depressed for the after-control since it becomes more easily deformable, if once distorted, due to its specific characteristics owing to its cylindrical shape. In addition, since the maximum contacting area of the rubber member of the after-control sensor is obtained in a state wherein the cylindrical rubber member is collapsed to almost half from its original configuration, the sensor cannot detect a stronger key depressing force. Another disadvantage exists in the complicated molding of the cylindrical conductive rubber members.

It is, therefore, an object of this invention to provide a touch response sensor for an electronic musical instrument of a remarkably compact construction capable of directly disposing the sensor onto a printed substrate.

It is another object of the invention to provide a touch response sensor for an electronic musical instrument capable of detecting the key depressing pressure sensitively in response to the key touching operation by a performer's fingers once the touch control is conducted.

It is another object of the invention to provide a touch response sensor for an electronic musical instrument in which the variation in resistance between contact pieces upon further depression of keys after the normal depression of the keys is obtained by adopting the substantially inverted V-shaped conductive or resistant resilient member as an area variable contacting member.

It is another object of the invention to provide a touch response sensor for an electronic musical instrument capable of providing an easy after-control by forming the contacting area of the respective stationary contact pieces with the substantially inverted V-shaped conductive or resistant resilient member in such a manner that the contacting area increases toward the center of the member so as to expand the expression of musical tones with the touch response of the keys being depressed.

It is another object of the invention to provide a touch response sensor for an electronic musical instrument capable of varying the volume, pitch, tone-color or the like by variations of voltage value by means of resistance value in response to the key depressing pressure with substantially inverted V-shap resilient member together with contact pieces.

Other objects and features of the invention will become apparent from the description made hereinbelow with reference to the accompanying drawings.

FIG. 1 is a perspective view of the essential part of the conventional touch response sensor for an electronic musical instrument;

FIG. 2 is a side view of the conventional touch response sensor shown in FIG. 1 for explaining the operation thereof;

FIG. 3 is an exploded perspective fragmentary view of one embodiment of the touch response sensor for an electronic musical instrument according to this invention;

FIG. 4 is a side view of the sensor shown in FIG. 3 for explaining the operation thereof;

FIG. 5 is a perspective view showing another example of substantially inverted V-shape conductive resilient member used in touch response sensor according to the invention;

FIGS. 6(a) to 6(c) are plan views of other examples of stationary contact pieces used in the touch response sensor of the invention;

FIG. 7 is an exploded perspective view showing another embodiment of the touch response sensor according to the invention;

FIG. 8 is a sectional view of the sensor shown in FIG. 7 for describing the operation thereof;

FIG. 9 is a perspective view of another example of the substantially inverted V-shape resistant resilient member used in the touch response sensor of the invention;

FIG. 10 is an enlarged sectional view showing another embodiment of the sensor according to the invention;

FIG. 11 is a plan view of another example of the stationary contact pieces of the sensor shown in FIG. 10;

FIG. 12 is an enlarged sectional view showing another embodiment of the sensor of this invention;

FIG. 13 is a plan view of another example of the stationary contact pieces of the sensor shown in FIG. 12;

FIG. 14 is an enlarged fragmentary exploded perspective view of another embodiment of the sensor of this invention; and

FIG. 15 is a side view of the sensor shown in FIG. 14 for describing the operation thereof.

Referring first to FIG. 3, which shows one preferred embodiment of the touch response sensor for an electronic musical instrument according to the present invention, a projection 1b is downwardly extending from a predetermined position of the lower surface 1a of a key 1. Stationary contact pieces 6 and 7 of a substantially rectangular shape are arranged in parallel and spaced away from each other at a position opposite to the projection 1b of the key 1 on a base plate 3, and are electrically connected respectively to the electric circuit (not shown) of the electronic musical instrument. The aforesaid contact pieces 6 and 7 are formed or attached on the base plate 3 by printing or other suitable means. Stopper or engaging members 8 and 9 are fixedly secured on the contact pieces 6 and 7 across the ends 6a, 6b and 7a, 7b of the contact pieces 6 and 7, respectively. The aforementioned stopper members 8 and 9 are made of insulating material so as to electrically insulate the stationary contact pieces 6 and 7 from each other. The touch response sensor of this invention comprises an electrically resistant resilient or elastic member 10 of a substantially inverted V-shape in section, which member 10 has an upper inside valley portion 10c, a top portion 10d projecting upwardly and facing the projection 1b of the ky key 1, and downwardly flaring, forked leg portions 10a and 10b. The leg portions 10a and 10b of the resilient member 10 are so arranged that the span between the lower ends 10a' and 10b' thereof is substantially equal to the interval between the stopper members 8 and 9. The resilient member 10 thus formed and arranged is made of, for example, electrically conductive rubber, which contains carbon as a resistant material so that a desired resistance value is determined by changing the carbon content therein.

The resilient member 10 thus shaped is placed between the stopper members 8 and 9 on the stationary contact pieces 6 and 7 in such a manner that both the lower ends 10a' and 10b' of the respective legs 10a and 10b are in abutting engagement with the stopper members 8 and 9 at the respective ends 6a, 6b and 7a, 7b of the contact pieces 6 and 7, as seen in FIG. 4.

In the state wherein the resilient member 10 is thus arranged, the top portion 10d of the resilient member 10 is located beneath the projection 1b of the key 1.

In FIG. 4, which shows a state wherein the key 1 is not depressed as designated by solid lines, the projection 1b of the key 1 is spaced with a predetermined gap from the top portion 10d of the resilient member 10. In this state, the resilient member 10 is maintained in the shape shown in FIG. 4 by the resilient force of the legs 10a and 10b thereof, and is in contact with the stationary contact pieces 6 and 7 at only the ends 10a' and 10b' of the respective legs 10a and 10b thereof. The contact is made in such a small area that it is substantially a line contact. Since the resilient member 10 is made of the resistant material as described above, the stationary contact pieces 6 and 7 are thus in contact with the resilient member 10 with extremely high resistance.

Upon depression of the key 1, the resistant resilient member 10 is accordingly depressed at the top portion 10d thereof by the projection 1b of the key 1. The legs 10a and 10b are bent downwardly under the depressing pressure of the key 1 so that the inner wall surfaces 10a" and 10b" of the respective legs 10a and 10b partly come into contact with the contact pieces 6 and 7 as designated by two-dotted broken lines in FIG. 4. Then, the area where the inner surfaces 10a" and 10b" of the legs 10a and 10b are in contact with the contact pieces 6 and 7 increases responsive to the increase of the key depressing pressure. Therefore, the resistance value between the contact pieces 6 and 7 decreases as the aforedescribed contacting area increases.

Inasmuch as the resistant resilient member 10 is formed substantially in the inverted V-shape in section, the deeper the resilient member 10 is depressed by the depression of the key 1, the smaller becomes a falling rate D, which is a length or distance in mm of the resilient member 10 fallen downwardly relative to change .DELTA.P of the key depressing pressure P. Even if, therefore, the key 1 is depressed with a considerable force, the entire surfaces of the stationary contact pieces 6 and 7 will not contact with the inner wall surfaces 10a" and 10b" of the legs 10a and 10b. More specifically, even though the key 1 is further depressed after the initial depression of the key 1, the change of the resistance between the stationary contact pieces 6 and 7 will not become saturated. Thus, "further variations" of the resistance change between the contact pieces 6 and 7 can be obtained by the further depression of the key after the initial and normal depression of the key.

It will be understood that the touch response can be detected in response to the key depression on the basis of the change of the resistance value between the stationary contact pieces 6 and 7 and also that the "further variations" of the resistance value between the contact pieces 6 and 7 can be attained thereby.

It is to be noted that if the conductive resilient member 10 is so treated that the resistance is provided only on the inner surfaces 10a" and 10b" of both the leg portions 10a and 10b thereof to use a surface current only, irregularity in the resistance values caused by the respective production lot can be reduced.

FIG. 5 shows another example of the resistant resilient member 10 used for the touch response sensor of this invention, Two pieces of leaf springs 11 and 12 are bent as illustrated in FIG. 5, and the top inside portions of the bent springs 11 and 12 are fixedly secured to each other in such a manner that leg portions 11a and 12a thereof are flared so as to form substantially an inverted V-shape similar to the previously described resilient member 10. Then, the surfaces of the inner walls 11a" and 12a" facing each other of the legs 11a and 12a are surface-treated so as to have a predetermined resistance value.

It will therefore be understood that the resilient member 13 of this example will also perform the same functions as those of the resilient member 10 of the previous example.

In FIGS. 6(a) through 6(c), which show various other examples of the stationary contact pieces used for the touch response sensor of this invention, the contacting areas where the respective contact pieces 15, 15', 16, 16' and 17, 17' contact with the resilient member increase as the resilient member approaches the respective central portions of the contact pieces 15, 15'; 16, 16' and 17, 17'.

The deeper the key 1 is depressed so that the resilient member 10 is downwardly depressed, the smaller becomes the falling rate D of the member 10 with respect to the change .DELTA.P of the key depressing pressure P, and, accordingly, the increasing rate .DELTA.S of the contacting areas of the inner wall surfaces 10a" and 10b" of the respective legs 10a and 10b with the stationary contact pieces 6 and 7 becomes smaller with the result that the resistance between the stationary contact pieces 6 and 7 does not linearly vary with the key depressing pressure. Simultaneously, since the changing rate of the resistance value therebetween becomes small, the after-control sometimes becomes difficult in the previously described touch response sensor. However, by forming the stationary contact pieces of the sensor in the manner of the present example, i.e. such that the contacting areas of the respective contact pieces 15, 15'; 16, 16' and 17, 17' with the resilient member 10 increase as the member 10 approaches the central portions of the respective contact pieces 15, 15'; 16, 16' and 17, 17' as designated in FIGS. 6(a) through 6(c), even if the falling rate D of the resilient member 10 is small, the contacting area of the contact pieces 15, 15'; 16, 16' and 17, 17' with the resilient member 10 can be increased in proportion to the increase of the key depressing pressure. It will therefore be understood that a richer musical expression depending upon the key depressing pressure can be achieved than in the case wherein the contact pieces 6 and 7 are formed in a rectangular shape as shown in FIG. 3.

It will also be understood that the change of the resistance value to be detected through the combination of the resilient member and the contact pieces may be provided as desired, i.e., lineary or nonlinearly, with respect to the key depressing pressure by suitably forming the contacting area of the contact pieces.

FIG. 7 shows another embodiment of the touch response sensor of this invention, wherein the same component parts as those shown in FIG. 3 are denoted by the same reference characters and description thereof is omitted. In this embodiment, stationary contact pieces 6 and 7 are longitudinally arranged in series with a predetermined space therebetween at a position opposite to the projection 1b of the key 1 on the base plate 3. Stopper or engaging members 8 and 9 are fixedly secured to the intermediates of the stationary contact pieces 6 and 7 crossing these contact pieces 6 and 7. The touch response sensor of this embodiment comprises a resilient or elastic member 20 of a substantially inverted V-shape, which member 20 has a upper inside valley portion 20c, a top portion 20d projecting upwardly and facing the projection 1b of the key 1, and forked leg portions 20a and 20b of a downwardly flaring form. The leg portions 20a and 20b of the resilient member 20 are so arranged that the span between the lower ends 20a" and 20b" thereof is substantially equal to the interval between the engaging members 8 and 9. The resilient member 20 thus formed and arranged is made of, for example, ordinary rubber.

A resistant portion 21 is formed on the inner wall surfaces 20a' and 20b' of the respective leg portions 20a and 20b of the resilient member 20. This resistant portion 21 is, for example, made of silicon rubber containing carbon or silver so as to form a predetermined resistance value. It is to be noted that the contents of the carbon or silver in the silicon rubber is a matter of design and therefore will not be described any further. It should be appreciated that other resistant materials may also be employed instead of the aforementioned material. The resistant resilient member 20 is thus formed. It is to be noted that the resilient member 20 and resistant portion 2 may, for example, be made integrally of conductive rubber having a predetermined resistance value.

The resilient member 20 thus shaped is placed on the stationary contact pieces 6 and 7 in such a manner that the lower ends 20a" and 20b" of the legs 20a and 20b are respectively in abutting engagement with the respective stopper member 8 and 9 so that the end portions of the inner resistant surfaces 21a and 21b thereof are brought into a close contact with the respective stationary contact pieces 6 and 7, as seen in FIG. 8.

In the state wherein the resilient member 20 is thus arranged, the top portion 20d of the resilient member 20 is located beneath the projection 1b of the key 1. It is to be noted that the lower ends 20a" and 20b" of the respective legs 20a and 20b of the resilient member 20 may preferably be adhered or bonded to the stopper members 8 and 9, respectively so as to completely retain the aforementioned configuration.

In FIG. 8 which shows the state wherein the key 1 is not depressed as designated by solid lines, the resilient member 20 is in contact with the stationary contact pieces 6 and 7 at the resistant portion 21. The contacting area is so small that it is substantially a linear contact. Accordingly, the stationary contact pieces 6 and 7 are thus connected by the resilient member 20 with an extremely high resistance, i.e., with the entire resistance value of the resistant portion 21 of the resilient member 20.

Upon depression of the key 1, the inner surfaces 21a and 21b of the resistant portion 21 are partly brought into contact with the contact pieces 6 and 7 as designated by two-dotted broken lines in FIG. 8. Then, the contacting area of the inner surfaces 21a and 21b with the contact pieces 6 and 7 increases in response to the increase of the key depressure. Therefore, the length or distance of connection of the stationary contact pieces 6 and 7 by the resistant portion 21 of the resilient member 20 becomes shorter with the result that the resistant value between the contact pieces 6 and 7 will decrease. More specifically, the resistance between the contact pieces 6 and 7 will vary in response to the key depressing pressure.

It is to be noted that even if the key 1 is depressed with a considerable strength or force, the entire surfaces of the contact pieces 6 and 7 will not contact with the inner surfaces 21a and 21b of the resistant portion 21 of the resilient member 20. More specifically, even though the key 1 is further depressed after the depression of the key 1, the change of the resistance between the contact pieces 6 and 7 will not become saturated. Thus, the "further variations" of the resistance change between the contact pieces 6 and 7 can be obtained by the further depression of the key after the initial depression of the key.

FIG. 9 shows another example of the resistant resilient member used for the touch response sensor of this invention, wherein the same component parts as those shown in FIG. 5 are denoted by the same reference characters and description thereof is omitted. The surfaces of the inner walls 11a" and 12a" facing each other of the respective legs 11a and 12a are surface-treated so as to provide a predetermined resistance value to a resistant portion 24 of a resilient member 25.

It will therefore be understood that the resilient member 25 of this example will also perform the same functions as those of the resilient member 20 shown in FIGS. 7 and 8.

It should be understood from the foregoing description that since the touch response sensor of this invention is thus constructed, it is extremely compact and light, and it can be directly arranged on a printed substrate with easy assembling. It should also be understood that since the sensor of this invention is simple in construction, it becomes less expensive. It should also be appreciated that even if the key is further depressed after the depression of the key being played, the resistance change will not be saturated and the "further variations" of the resistance value between the contact pieces may be obtained thereby.

In FIG. 10, which shows another embodiment of the touch response sensor of this invention, wherein the same component parts as those shown in FIG. 3 are designated by the same reference characters and description thereof is omitted, a plurality of stationary contact pieces 30a through 30e of substantially rectangular shape are arranged in parallel with a predetermined space therebetween on a base plate 3 under the key 1. The contact pieces 30a through 30e are formed or attached to the base plate 3 by printing or other means.

As shown in FIG. 11, which shows one example of the arrangement of the stationary contact pieces, the respective contact pieces 30a through 30e are connected through resistors R.sub.1 through R.sub.4 connected in series to terminals 31a and 31b. The resistors R.sub.1 through R.sub.4 may be those obtainable in the market or may be formed between the respective stationary contact pieces 30a through 30e by means of deposition or the like.

The touch response sensor of this embodiment comprises an electrically conductive resilient or elastic member 32 of a substantially inverted V-shape, while member 32 has two leg portions 31a and 32b formed such that one leg portion 32a is asymmetrically longer than the other leg portion 32b as shown in FIG. 10. The resilient member 32 thus shaped is placed between the stopper members 8 and 9 fixedly secured onto the base plate 3 in such a manner that the respective contact pieces 30a through 30e are all located under the longer leg 32a and facing the inner surface 32a' of the leg 32a with a predetermined space and that the side and bottom ends 32e and 32f of the short leg 32b of the member 32 are fixedly secured or adhered to the stopper member 8 and base plate 3, respectively, and also that the side end 32d of the long leg 32a of the member 32 is in slidable contact with the side wall 9a of the stopper member 9 and the bottom end 32a" of the long leg 32a the member 32 is spaced with a predetermined gap d from the contact piece 30a.

The resilient member 32 also has a top portion 32c projecting upwardly and facing the projection 1b of the key 1 with a predetermined space.

In the state wherein the resilient member 3 is thus arranged and the key 1 is not depressed as designated by solid lines in FIG. 10, the resilient member 32 is maintained in shape by means of the resilient force acting on the leg portion 32b thereof and is not in contact at the inner surface 32a' thereof with any of the contact piece 30a through 30e. Therefore, the respective contact pieces 30a through 30e are not connected by the conductive resilient member 32 with the result that the resistance R of the resistors R.sub.1 through R.sub.4 between the terminals 31a and 31b is at a maximum value, i.e. the sum of the respective resistances (R.sub.1 + R.sub.2 + R.sub.3 + R.sub.4) of the resistors R.sub.1 through R.sub.4.

Upon depression of the key 1, the conductive resilient member 32 is accordingly depressed at the top portion 32c thereof by the projection 1b of the key 1. The leg 32b of the resilient member 32 is then bent downwardly in response to the depressing pressure of the key 1. When the depressing pressure of the key 1 is weak, the leg 32b of the member 32 is bent slightly in such a manner that the side end 32d thereof slides downwardly along the side wall 9a of the stopper member 9 so that the bottom end 32a" thereof is brought into contact with the contact pieces 30a and 30b. Accordingly, the resistance R.sub.1 between the contact pieces 30a and 30b is short-circuited by the resilient member 32 and the resistance R between the terminals 31a and 31b consequently becomes the sum of the resistances (R.sub.2 + R.sub.3 + R.sub.4) of the resistors R.sub.2 through R.sub.4.

Upon further depression of the key 1, the leg 32a is bent to a greater degree than the leg 32b as shown by two-dotted broken lines in FIG. 10, because the leg 32a is longer than the leg 32b. Asuming that the inner surface 32d of the member 32 is brought into contact, for example, with the contact pieces 30a through 30c through the further bent leg 32a, the resistors R.sub.1 and R.sub.2 between the contact pieces 30a and 30c are short-circuited. Therefore, the resistance R between the terminals 31a and 31b becomes the sum of the resistances (R.sub.3 + R.sub.4) of the resistors R.sub.3 and R.sub.4, thereby being reduced further.

Upon further stronger depression of the key 1, the inner surface 32a' of the leg 32a of the member 32 contacts with all the contact pieces 30a through 30e with the result that all the resistors R.sub.1 through R.sub.4 between the terminals 31a and 31b are short-circuited. Accordingly, the resistance R between the terminals 31a and 31b becomes zero.

Upon release of the depressed key 1, the resilient member 32 is returned to the original position or state in the respective legs 32a and 32b due to the resilient force acting thereon. Consequently, the inner surface 32a' of the leg 32a of the member 32 are separated upwardly from all the contact pieces 30a through 30e. Accordingly, the resistance R between the terminal 31a and 31b becomes the original sum value (R.sub.1 + R.sub.2 + R.sub.3 + R.sub.4).

Thus, the touch response sensor of this embodiment can detect the variations of the resistance value responsive to the key depression. Therefore, assuming that the terminals 31a and 31b are, for example, connected to a known charging and discharging circuit (not shown), the volume, pitch, tone-color etc. of the musical tones can be varied in response to the depression of the key.

FIG. 12 shows another embodiment of the touch response sensor of this invention, wherein the same component parts as those shown in FIGS. 3 and 10 are designated by the same reference characters and description thereof is omitted. The touch response sensor of this embodiment comprises an electrically conductive resilient member 33 formed symmetrically in a substantially inverted V-shape in section.

It will be understood that the inner surfaces 33a' and 33b' of both legs 33a and 33b of the member 33 are covered with silicon rubber and carbon so as to form an electrically conductive surface. The resilient member 33 is located and arranged in the same manner as the resilient member 10 shown in FIG. 3 except that both ends 33d and 33e of the legs 33a and 33b are engaged tightly within the recesses 34a and 35a of respective stopper members 34 and 35 fixedly secured onto the base plate 3.

A pair of common contact portions 36a and 36b of common contact piece 36 of a substantially rectangular shape are arranged in the vicinities of the stopper members 34 and 35, respectively on the base plate 3 so as to face the inner surfaces 33a" and 33b" of the resilient member 33, and a plurality of stationary contact pieces 37a through 37d and 38a through 38d of a substantially rectangular shape are arranged between the contact portions 36a and 36b on the base plate 3.

As shown in FIG. 13, which shows another example of the arrangement of the contact pieces used for the sensor of this embodiment, the common contact piece 36 is formed in substantially U-shape. The contact pieces 37a through 37d and 38a through 38d are arranged with predetermined spaces therebetween in such a manner that their arrangement is asymmetrical with respect to the center 33f of the resilient member 33, i.e., the contact pieces 37a through 37d are remoter from the center 33f of the resilient member 33 by a distance r than their respective counterpart contact pieces 38a through 38d, as shown in FIGS. 12 and 13.

Upon depression of the key 1, the conductive resilient member 33 is accordingly depressed, in which case each of the contact pieces 37a through 37d is brought into contact with the electrically conductive inner surface 33a' of the resilient member 33 earlier than each correspondingly located one of the contact pieces 38a through 38d being contacted by the surface 33b'. More specifically, the inner surfaces 33a' and 33b' will alternately and sequentially contact with the contact pieces 37a through 37d and 38a through 38d in the order of 37d, 38d, 37c, 38c . . . 37a, 38a.

As shown in FIG. 13, resistors R.sub.1 through R.sub.8 are connected in series with each other at respective connecting points a through i between terminals 39a and 39b, and the contact portion 36a of the common contact piece 36 is also connected to the connecting point a. The contact pieces 37a through 37d and 38a through 38d are respectively connected alternately to the connecting points b through i in the order of 37d, 38d, 37d, 38c . . . , 37a, 38a, as shown in FIG. 13.

In the state wherein the resilient member 33 is thus arranged and the key 1 is not depressed as designated by solid lines in FIG. 12, only the cottom ends 33a" and 33b" of the member 33 are in contact with the contact portions 36a and 36b of the common contact piece 36 but other contact pieces 37a through 37d and 38a through 38d are not in contact with the inner surfaces 33a' and 33b', respectively of the member 33 at all. Consequently, the resistance R of the resistors R.sub.1 through R.sub.8 between the terminals 39a and 39b is at a maximum, i.e. the sum of the respective resistances (R.sub.1 + R.sub.2 + . . . , +R.sub.8) of the resistors R.sub.1 through R.sub.8.

Upon depression of the key 1, both the legs 33a and 33b of the resilient member 33 are symmetrically bent downwardly in response to the depressing pressure of the key 1 as designated by two-dotted broken lines in FIG. 12, so that the inner surfaces 33a' and 33b' of the member 33 are successively and alternately brought into contact with the contact pieces 37a through 38d in the order of 37d, 38d, 37c, 38c, . . . 37a, 38a as previously described. Therefore, the resistors R.sub.1 through R.sub.8 are in turn short-circuited therebetween with the result that the resistance R of the resistors R.sub.1 through R.sub.8 between the terminals 39a and 39b is thus reduced.

When the depressed key 1 is released, the legs 33a and 33b of the resilient member 33 move upwardly and are returned to the original position due to the resilient force acting thereon with the result that they are separated from the contact pieces 37a through 38d. Consequently, the resistance R of the resistors R.sub.1 through R.sub.8 between the terminals 39a and 39b becomes the original sum value (R.sub.1 + R.sub.2 + , . . . + R.sub.8).

Thus, the touch response sensor of this embodiment can also detect the V variations of the resistance value responsive to the key depressing pressure.

In FIG. 14, which shows another embodiment of the touch response sensor of this invention, wherein the same component parts as those shown in FIGS. 3 and 10 are designated by the same reference characters and description thereof is omitted, stationary contact pieces 6 and 7 of a substantially rectangular shape are provided in parallel with a predetermined space on the base plate 3 under the key 1.

An electrically resistant piece 45 of a substantially rectangular shape is provided between the contact pieces 6 and 7 on the base plate 3 so as to engage between the pieces 6 and 7. This resilient pieces 45 may be formed on the base plate 3 by deposition or other suitable method.

The resistant piece 45 is, for example, formed of silicon rubber containing carbon or silver so as to provide a predetermined resistance value. It is to be noted that the content of the carbon or silver in the carbon or silver group material is a matter of design and will not be therefore described any further. It should be appreciated that other resistant materials may also be employed instead of the aforementioned material.

The conductive resilient member 32 is, for example, made of ordinary rubber, and an electrically conductive portion 46 is formed on the inner surface 32a' of one leg 32a of the member 32. This conductive portion 46 is, for example, made of electrically conductive rubber and is integrally formed with the resilient member 32. It is to be noted that the conductive portion 46 is not formed separately from the member 32 but is integrally formed with the resilient member 32 with the conductive rubber material. The end 46a of the conductive portion 46 is constructed to have substantially the same area as that of the contact piece 6 and the length of the inclined portion 46b of the portion 46 is constructed to be longer than the length of the resistant piece 45, i.e., the distance between the contact pieces 6 and 7.

The contact pieces 6 and 7 and the resistant piece 45 are arranged under the leg 32a of the resilient member 32 in such a manner that the end 46a of the conductive portion 46 is in close contact with the contact piece 6 and the inclined portion 46b of the portion 46 is spaced from the resistant piece 45 and the contact piece 7. The resilient member 32 is so arranged that it is retained at the side ends 32d and 32e of the respective legs 32a and 32b between the stopper members 8 and 9 and held at the bottom end 32f of thee leg 32b on the base plate 3.

In the state wherein the resilient member 32 is thus arranged and the key 1 is not depressed as designated by solid lines in FIG. 15, which shows the operational state of the touch response sensor shown in FIG. 14, the resilient member 32 is maintained in configuration due to the resilient force acting on the legs 32a and 32b thereof as shown and the inclined portion 46b of the conductive portion 46 is separated from the resistant piece 45. Accordingly, the resistance between the contact pieces 6 and 7 becomes the sum of resistance value of the resistant piece 45 and therefore is at maximum.

Upon depression of the key 1, the conductive resilient member 32 is thus depressed at the top portion 32c thereof by the projection 1b of the key 1. Accordingly, the legs 32a and 32b of the resilient member 32 are then bent downwardly in response to the depressing pressure of the key 1. The inclined portion 46b of the conductive portion 46 is gradually brought into contact with the resistant piece 45 from the contact piece 6 side as the leg 32a of the member 32 is bent downwardly with the result that it will short-circuit the resistant piece 45 by the amount contact by the inclined portion 46b of the portion 46. Consequently, the resistance between the contact pieces 6 and 7 decreases to that degree.

Upon further strong depression of the key 1, the leg 32a is further downwardly bent so that the inclined portion 46b of the conductive portion 46 will further short-circuit the resistant piece 45 with the result that the resistance between the contact pieces 6 and 7 is further reduced.

Upon release of the depressed key 1, the resilient member 32 is returned to the original position or state in the respective legs 32a and 32b due to the resilient force acting thereon. Consequently, the inclined portion 46b of the conductive portion 46 is separated upwardly from the resistant piece 45 and the contact piece 7. Accordingly, the resistance value between the contact pieces 6 and 7 is reset to the original resistance value, i.e., the total resistance value of the resistant piece 45.

It should be understood from the foregoing description that if the contact pieces 6 and 7 are, for example, connected via lines (not shown) to a known voltage-controlled variable-frequency oscillator circuit, voltage-controlled variable filter circuit, voltage-controlled variable gain amplifier circuit (not shown), or the like, the volume, pitch, tone-color etc. of the musical tones can be varied in response to the voltage change caused by the resistance variations upon depression of the key.

It should also be understood that according to the touch response sensor of this invention, a very small sensor such as having width equal to that of one key can be easily formed and that since this sensor can be directly provided on the circuit substrate it is very advantageous in designing a compact circuit. It should also be understood that as the contacting resistance between the contact pieces and the conductive resilient member can be ignored by increasing the resistance value of the resistant piece formed between the contact pieces on the base plate, it can reduce irregularities of the operation among the respective keys of the instrument. It should be appreciated that the asymmetrical construction of the legs of the resilient member or the asymmetrical arrangement of the contact pieces located under the member enables provision of a large number of contact points so as to enhance the sensitivity of the key touching operation. It should also be noted that the sensor of this invention is simple in construction and suited for mass production and, accordingly, the cost of manufacture can be considerably reduced.