Keyboard Musical Instrument Equipped With Small Simple Economical Key Touch Generator

This invention relates to a keyboard musical instrument and, more particularly, to a keyboard musical instrument equipped with a key touch generator for exerting load variable like that of an acoustic piano.

Manufacturers presently offer various kinds of keyboard musical instruments such as an acoustic piano and an electronic keyboard to musicians, and these keyboard musical instruments have different key touches.

The electronic keyboard has a plurality of turnable keys urged to respective rest positions by means of spring members, and sensors monitor the keys to see whether or not a player depresses them. When a musician depresses a key, the key is moved from the rest position toward the end position against the resilient force of the spring member, and the associated key sensor produces a key position signal representative of the downward motion of the key. The key position signal is supplied to a digital signal processor, and a music data code is formed on the basis of the key position signal. The music data code is supplied from the digital signal processor to a tone generator, and the tone generator tailors an audio signal. The audio signal is supplied to a speaker system, and the speaker system produces an electronic sound from the audio signal. The resilient force is simply exerted on the key moved between the rest position and the end position, and the player feels the load constant.

The acoustic piano also has a keyboard consisting of black keys and white keys, and the black/white keys are linked with key action mechanisms for driving hammers. When a players depresses a black/white key, the depressed key actuates the associated key action mechanism. The key action mechanism rotates the hammer toward a set of strings, and the hammer suddenly escapes from the key action mechanism on the way toward the set of strings. The hammer starts a free rotation, and strikes the set of strings. The player firstly feels the key heavy, and notices the key suddenly become light at the escape of the hammer. Thus, the key touch of the acoustic piano is quite different from that of the electronic keyboard.

When the musician usually playing the acoustic piano fingers on the keys of the electronic keyboard, he feels the key touch unusual, and may look back the key touch of the acoustic piano with nostalgia. For this reason, various key touch generators have been proposed.

Japanese Patent Publication of Unexamined Application No. 4-204697 discloses a key touch generator comprising a memory storing a series of load data, a key sensor monitoring a key movable between a rest position and an end position and a solenoid-operated key actuator exerting the load on the key. The key touch generator disclosed in the Japanese Patent Publication of Unexamined Application is hereinbelow referred to as "first prior art key touch generator". The series of load data is representative of load variable with a current key position on the way from the rest position to the end position, and the variation of the load data is matched with the variation of the resistance against the finger of a player. The solenoid-operated key actuator generates the electromagnetic force, and the magnitude of the electromagnetic force is variable with the magnitude of a driving current signal. The series of load data is sequentially read out from the memory in response to the current key position, and the magnitude of the driving current signal is varied in dependence on the load data. For this reason, the solenoid-operated actuator exerts the variable load on the depressed key, and the player feels the variation of the resistance like the piano key touch.

Japanese Patent Publication of Unexamined Application No. 7-111631 discloses another key touch generator similar to that of Japanese Patent Publication of Unexamined Application No. 4-204697. The key touch generator disclosed therein is hereinbelow referred to as "second prior art key touch generator". Although the first prior art key touch generator determines the load to be exerted on the depressed key on the basis of the current key position, the second prior art key touch generator determines the magnitude of the load to be exerted on the depressed key on the basis of two physical quantities such as the key position, the key velocity, the acceleration of the depressed key and the force actually exerted on the depressed key. The magnitude of the driving current signal is also varied with the two physical quantities, and the solenoid-operated actuator causes the player to feel the resistance against the key motion like the key touch of an acoustic piano.

Japanese Patent Publication of Unexamined Application No. 7-99475 discloses the third prior art key touch generator. The third prior art key touch generator is implemented by an induction type electromagnetic repulsion generator. A magnetic field generator is attached to one of a key and a key supporting member, and a conductive member is attached to the other of the key and the key supporting member. When the key is depressed, repulsion is electromagnetically generated therebetween, and the player feels the repulsion as the resistance against the key motion.

The solenoid operated actuator unit incorporated in the first prior art key touch generator unidirectionally exerts the electromagnetic force on the plunger and, accordingly, the depressed key. However, the key touch of the acoustic piano is hardly reproduced by the unidirectional solenoid operated actuator. For this reason, the first prior art key touch generator merely reproduces a key touch rather close to an acoustic piano than an electronic keyboard.

The second prior art key touch generator is equipped with a bi-directional solenoid operated actuator unit. The plunger is bi-directionally controlled with a pair of solenoid coils, and the key touch is much closer to that of the acoustic piano. However, a standard keyboard musical instrument has eighty-eight keys, and eighty-eight bi-directional solenoid operated actuator units are required for the eighty-eight keys. A pair of solenoid coils is incorporated in each bi-directional solenoid operated actuator unit, and the eighty-eight bi-directional solenoid operated actuator units occupy large space. For this reason, the second prior art key touch generator makes the keyboard musical instrument large, heavy and costly.

The third prior art key touch generator encounters a problem in that the induction type electromagnetic repulsion generator can not promptly respond to the control data, and hardly reproduces the key touch like the acoustic piano.

It is therefore an important object of the present invention to provide a keyboard musical instrument a key touch generator of which is light, compact and economical and precisely reproduces a key touch of an acoustic piano.

To accomplish the object, the present invention proposes to offer a resistance against a motion of a movable member through friction produced by a braking unit.

In accordance with one aspect of the present invention, there is provided a keyboard musical instrument for generating a sound, comprising: a movable member supported by a stationary member, and manipulated by a player for specifying an attribute of the sound; a sound generating system responsive to a motion of the movable member so as to produce the sound with the attribute; and a touch generating system including a braking unit having a first member fixed to the movable member, a second member stationary with respect to the stationary member and an actuator pressing the first member and the second member to each other so as to produce a friction therebetween, and a controller causing the actuator to vary the friction so as to offer a resistance against the motion of the movable member.

The movable member may be a key or a pedal.

In accordance with another aspect of the present invention, there is provided a resistance generator provided for a mechanism having a first member movable with respect to a second member, comprising: a third member fixed to said first member; a fourth member stationary with respect to said second member; a sensor monitoring said first member, and producing a piece of status information representative of current status of said first member; an actuator responsive to an instruction representative of a force for pressing said third member and said fourth member to each other so as to vary a friction therebetween; and a controller responsive to said piece of status information so as to change said force represented by said instruction.

The resistance generator may be used in a keyboard musical instrument.

The features and advantages of the keyboard musical instrument according to the present invention will be more clearly understood from the following description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic side view showing an electronic keyboard instrument according to the present invention;

FIG. 2 is a partially-cut-away plan view showing a keyboard incorporated in the electronic keyboard instrument;

FIG. 3 is a fragmentary perspective view showing a key assembled with an electromagnetic disk braking unit incorporated in the electronic keyboard instrument;

FIG. 4 is a block diagram showing the circuit arrangement of a controller incorporated in the key touch generator;

FIG. 5 is a perspective view showing a key sensor incorporated in another electronic keyboard instrument according to the present invention;

FIG. 6 is a block diagram showing the controller connected to the key sensor;

FIG. 7 is a perspective view showing the structure of the keyboard musical instrument;

FIG. 8 is a cross sectional view showing a dial accompanied with the electromagnetic braking unit according to the present invention;

FIG. 9 is a schematic perspective view showing an organ according to the present invention;

FIG. 10 is a fragmentary view showing an electromagnetic actuator incorporated in the organ;

FIG. 11 is a cross sectional view showing the electromagnetic actuator;

FIG. 12 is a schematic view showing a disc braking system according to the present invention; and

FIG. 13 is a perspective view showing an electromagnetic braking unit incorporated in the disc braking system.

Referring first to FIG. 1 of the drawings, an electronic keyboard instrument embodying the present invention largely comprises a keyboard 1 exposed to an open area of a case, an electronic sound generating system 3 and a key touch generator 4. In the following description, term "front" is indicative of a position closer to a player fingering on the keyboard than "rear" position. Term "lateral" means a direction perpendicular to the line drawn between a front position and a rear position.

The keyboard 1 includes a bracket member 1a, a plurality of black keys 1b and a plurality of white keys 1c arranged in a similar manner to the keyboard of an acoustic piano as shown in FIG. 2. The bracket member 1a is shared between the black/white keys 1b/1c, and turnably supports the black/white keys 1b/1c. Each of the black/white keys 1b/1c turns between a rest position and an end position. The bracket member 1a is bolted to a frame 2a of the case. Although the black keys 1a are different in length from the white keys 1b, the black/white keys 1b/1c are similarly assembled with electromagnetic braking units 4a of the key touch generator 4, and description is made on one of the white keys 1b with reference to FIG. 3.

The white key has a disc portion 1d, a lever portion 1e projecting from the disc portion 1d, a touch surface portion 1f connected to the upper edge of the lever portion 1e, a stopper portion 1g brought into contact with a key end felt member 1h attached to the bracket member 1a at the end position, a lower projection 1i, a shutter portion 1j rearwardly projecting from the disc portion 1d and a boss portion 1k laterally projecting from the disc portion 1d.

A coil spring 1m is inserted between the bracket member 1a and the lower projection 1i, and the white key 1c is urged toward the rest position. The rear surface of the touch surface portion 1f is brought into contact with a key rest felt member 1n attached to the case 2 at the rest position, and the front surface of the touch surface portion 1f is depressed by a player.

The shutter portion 1j has a sectoral configuration, and the curved rear edge 1o is smaller in radius of curvature than the disc portion 1d. In other words, when a point is upwardly moved along the curved rear edge 1o, the horizontal distance between the point and a corresponding point on the disc portion 1d is increased. The shutter portion 1j cooperates with a key sensor 4b so as to generate a key position signal KP1 indicative of a current position of the white key 1c on the trajectory between the rest position and the end position.

The boss portion 1k has a hole 1p, and provides an axis 1q of rotation to the white key 1c. When a player depresses the touch surface portion 1f, the white key 1c turns around the axis 1q of rotation.

The white key 1c is formed of synthetic resin except for the disc portion 1d. The disc portion 1d is formed of magnetic substance, and is assembled with the lever portion 1e. Otherwise, the white key 1c is formed of synthetic resin, and the magnetic disc portion 1d is attached to one side surface of the lever portion 1e.

The electronic sound generating system 3 includes the key sensors 4b for producing the key position signals KP1, a digital signal processing unit 3a accompanied with an analog-to-digital converter, a tone generator 3b and speakers 3c. The electronic sound generating system 3 is similar to that of the prior art electronic keyboard instrument. Namely, when a player depresses one of the black/white keys 1b/1c, the key position signal KP1 is supplied to the digital signal processing unit 3a, and a music data code is formed on the basis of the key position signal KP1. The music data code is supplied from the digital signal processing unit 3a to a tone generator 3b, and the tone generator 3b tailors an audio signal. The audio signal is supplied to the speakers 3c, and the speakers 3c produce an electronic sound from the audio signal.

The key touch generator 4 includes the electromagnetic braking units 4a respectively associated with the black/white keys 1b/1c, the key sensors 4b also associated with the black/white keys 1b/1c and a controller 4c. The key sensors 4b are attached to a sensor sheet 1aa at intervals, and are implemented by photo-interrupters accompanied with a current-to-voltage converter. The electromagnetic braking unit 4a is detailed with reference to FIG. 3.

The electromagnetic braking unit 4a includes the disc portion 1d of the magnetic substance, a protective sheet 4d and an electromagnetic actuator 4e, and a stator yoke 4f, a bobbin 4g and a coil 4h form in combination the electromagnetic actuator 4e. The coil 4h is wound on the bobbin 4g, and the coil 4h and the bobbin 4g as a whole constitute a solenoid coil. The protective sheet 4d prevents the bobbin 4g and the coil 4h wound thereon from the rotation of the disc portion 1d, and allows the white key 1c to smoothly turn. For this reason, the protective sheet 4d is as large in diameter as the bobbin 4g or slightly smaller than the bobbin 4g.

The protective sheet 4d and the bobbin 4g are shaped into ring configurations, and the stator yoke 4f and a pin member 4i define a ring-shaped hollow space. The boss portion 1k is inserted into the hollow space 4j of the protective sheet 4d and the hollow space 4k of the bobbin 4g, and the pin member 4i is inserted into the hole 1p. As a result, the bobbin 4g and the protective sheet 4d are accommodated in the ring-shaped hollow space, and the ring-shaped hollow space is closed by means of the disc portion 1d. When the electromagnetic braking unit 4a is assembled with the white key 1c, the center axis of the pin member 4i is aligned with the axis 1q of rotation, and the white key 1c turns around the pin member 4i.

The disc portion 1d has a side surface 4m, and the side surface 4m provides large friction as will be described hereinlater. The stator yoke 4f has a pair of edge portions 4n, and the edge portions 4n are engaged with grooves formed in the bracket member 1a (see FIG. 1).

The black/white key 1b/1c is assembled with the electromagnetic braking unit 4a as follows.

The edge portions 4n are inserted into the grooves of the bracket member 1a, and the stator yoke 4f is assembled with the bracket member 1a.

On the other hand, the boss portion 1k is inserted into the hollow space 4j of the protective sheet 4d and the hollow space 4k of the bobbin 4g. Subsequently, the pin member 4i is inserted into the hole 1p. As a result, the bobbin 4g, the coil 4h and the protective sheet 4d are accommodated in the ring-shaped hollow space defined between the stator yoke 4f and the disc portion 1d, and the bobbin 4g and the coil 4h become stationary with respect to the stator yoke 4f. The shutter portion 1j is inserted into the gap formed in the key sensor 4b.

Subsequently, the coil spring 1m is inserted between the lower projection 1j and the bracket member 1a, and the coil spring 1m urges the black/white key 1b/1c in the counter clockwise direction.

When the black/white key 1b/1c is assembled with the electromagnetic braking unit 4a, the side surface 4m is opposed to the side surface 4o of the stator yoke 4f, and extremely narrow gap takes place between the periphery 4p of the stator yoke 4f and the side surface 4m of the disc portion 1d. The black/white key 1b/1c is laterally movable over the narrow gap. However, the lateral movement is so little that a player does not notice it.

Finally, the bracket member 1a is bolted to the frame 2a, and the black/white keys 1b/1c assembled with the electromagnetic braking units 4a are installed in the case 2.

The black/white key 1b/1c is turnable between the rest position defined by the key rest felt member 1n and the end position defined by the key end felt member 1h, and the coil spring 1m urges the black/white key 1b/1c toward the rest position. When a player depresses the black/white key 1b/1c against the resilient force of the coil spring 1m, the black/white key 1b/1c turns in the clockwise direction, and the key end felt member 1h stops the black/white key 1b/1c at the end position. If the player removes the force from the black/white key 1b/1c, the coil spring 1m urges the black/white key 1b/1c toward the rest position, and the black/white key 1b/1c is recovered to the rest position.

The electromagnetic braking unit 4a offers the resistance against the key motion as follows. When the coil 4h is energized, the coil generates magnetic field looped around the cross section of the bobbin 4a, and the stator yoke 4f is magnetized. The disc portion 1d is attracted to the stator yoke 4f, and the side surface 4m is brought into contact with the periphery 4p of the stator yoke 4f. The friction between the side surface 4m and the periphery 4p offers the resistance against the key motion, and the friction and, accordingly, the resistance are variable with the electromagnetic force in the lateral direction. When the side surface 4m is attracted to the periphery 4p, the black/white key 1b/1c is slightly moved in the lateral direction. However, the lateral movement is so little that the player can not notice it. The player recognizes the resistance as a key touch, and the controller 4c varies the friction and, accordingly, the resistance.

While the black/white key 1b/1c is turning between the rest position and the end position, the shutter portion 1j intersects the light beam produced by the key sensor 4b, and the intersectant area is varied depending upon the current key position on the trajectory between the rest position and the end position. As described hereinbefore, the key sensor 4b is implemented by a photo-interrupter, and the amount of current produced therein is variable with the amount of light incident thereon. For this reason, the key sensor 4b converts the current key position to the amount of current and, accordingly, the output potential level, and the output potential is supplied through the analog-to-digital converter to the digital signal processing unit 3a and the controller 4c as the key position signal KP1. Thus, the key position signal KP1 is representative of the current key position. The digital signal processing unit 3a determines a key-on timing and a key-off timing, and calculates a key velocity so as to produce music data codes. Though not shown in the drawings, a player selects one of timbres by manipulating a switch array on a board, and the electronic sound generating system 3 imparts the selected timbre to the electronic sound.

The key position signal KP is supplied to the controller 4c so as to vary the resistance against the key motion. FIG. 4 illustrates the arrangement of the controller 4c. The controller 4c includes a touch selector 4r for selecting one of key touches, a memory 4s storing a plurality of key touch tables and a driving circuit for supplying driving signals DR1 to the electromagnetic actuators 4e. The controller varies the electromagnetic force by changing the magnitude of the driving signal DR1 so as to change the friction and the resistance as follows.

There are many kinds of keyboard musical instrument such as an acoustic piano, a harpsichord, a celesta, an electronic keyboard instrument and so on, and they are different in key touch. The plurality of key touch tables are corresponding to the key touches of those kinds of keyboard musical instrument. If a player selects the piano key touch, the touch selector 4r supplies a selecting signal SEL representative of the piano key touch, and the key touch table for the piano becomes accessible.

Each of the key touch tables stores a series of load data representative of the resistance to be offered to the associated black/white key 1b/1c. The series of load data represents not only the variation of resistance from the rest position to the end position but also the variation of resistance from the end position to the rest position. When the manufacturer prepares the series of load data, the resilient force of the coil spring 1m is taken into account.

The resistance is variable with the current key position, and the series of load data is sequentially read out from the memory 4s in response to the key position signal KP1. Thus, the memory 4s supplies a load data signal DS1 representative of the load data to the driving circuit 4t.

The driving circuit 4t is responsive to the load data signal DS1 so as to change the magnitude of the driving signal DR1. The electromagnetic force is proportionally changed together with the magnitude of the driving signal DR1, and the friction and the resistance are varied together with the electromagnetic force. Thus, the controller 4c regulates the friction and the resistance to a certain value appropriate for the current key position by changing the magnitude of the driving signal DR1.

Assuming now that the player depresses one of the black/white keys 1b/1c, the black/white key 1b/1c turns around the axis 1q of rotation in the clockwise direction along the trajectory. The key sensor 4b monitors the depressed black/white key 1b/1c, and reports the current key position to the memory 4s. The series of load data is read out from the memory 4s in response to the key position signal KP1, and the driving circuit 4t regulates the driving signal DR1 to the magnitude corresponding to the load data. The coil 4h is energized with the driving signal DR1, and the electromagnetic force is generated in the lateral direction. The side surface 4m is attracted to the stator yoke 4f, and the friction takes place therebetween.

The read-out load data is varied depending upon the current key position, and, accordingly, the driving circuit 4t varies the magnitude of the driving signal DR1 accordingly. As a result, the electromagnetic actuator 4e varies the electromagnetic force along the trajectory of the black/white key 1b/1c, and the electromagnetic braking unit 4a changes the resistance against the key motion like the key touch of the selected keyboard musical instrument. The player feels the key touch identical with the key touch of the selected keyboard musical instrument.

The player releases the black/white key 1b/1c at the end position. The black/white key 1b/1c returns to the rest position. The key sensor 4b informs the memory 4s of the current key position on the way from the end position to the rest position. The memory 4s supplies the load data to the driving circuit 4t in response to the current key position, and the driving circuit 4t varies the magnitude of the driving signal DR1 along the trajectory. The electromagnetic actuator 4e changes the friction and the resistance, and the player feels the key touch like that of the selected keyboard musical instrument.

In this instance, the black/white key 1b/1c serves as the movable member, and the first member and the second member are implemented by the side surface 4m and the periphery 4p, respectively.

As will be appreciated from the foregoing description, only one electromagnetic actuator 4e offers the resistance against the key motion not only from the rest position to the end position but also from the end position to the rest position, and the electromagnetic braking unit is light, compact and economical. Moreover, the electromagnetic actuator promptly changes the electromagnetic force and the friction so as to exactly offer the selected key touch.

Another keyboard musical instrument embodying the present invention is similar to the first embodiment except for a servo-controller 10. Description is focused on the servo-controller 10 with reference to FIGS. 5 and 6, and the other components are labeled with the same references designating corresponding components of the first embodiment without detailed description.

The servo-controller 10 includes a resilient member 10a fixed to the bracket member 1a under each of the black/white keys 1b/1c, a strain gauge unit 10b attached to the upper surface of the resilient member 10a and a servo-amplifier 10c. When a player depresses the black/white key 1b/1c, the black/white key 1b/1c is downwardly moved, and deforms the resilient member 10a. The strain gauge unit 10b generates a servo-control signal KP2 representative of a current key position, and the servo-control signal KP2 is supplied to a servo-amplifier 10c.

The servo-amplifier 10c is connected between the memory 4s and the driving circuit 4t, and compares the current key position estimated from the load data and the current key position represented by the servo-control signal KP2. If the current key position estimated from the load data is matched with the current key position represented by the servo-control signal KP2, the servo-amplifier 10c supplies the data signal DS1 without a correction to the driving circuit 4t. However, if the current key position estimated from the load data is different from the current key position represented by the servo-control signal KP2, the servo-amplifier 10c corrects the load data, and supplies a corrected data signal CDS1 representative of the corrected load data to the driving circuit 4t. Thus, the servo-controller 10 enhances the reliability of the load data, and causes the electromagnetic braking unit 4a to offer the resistance exactly matched with the resistance against the key motion of a selected keyboard musical instrument.

FIG. 7 illustrates the keyboard musical instrument implementing the second embodiment. A pipe 11 is bent twice so as to have an upper lateral bar 11a and a lower lateral bar 11b. The electromagnetic braking units 4a are accommodated in an inner space of the upper lateral bar 11a, and the black/white keys 1b/1c project from the upper lateral bar 11a. A pair of pedals 12a/12b is turnably supported by the lower lateral bar 11b, and the electromagnetic braking units 4a are provided for the pedals 12a/12b, respectively. The electromagnetic braking units for the pedals 12a/12b are connected to a controller (not shown), and the controller varies the magnitude of driving signals so as to offer a pedal touch like that of a selected keyboard musical instrument.

Turning to FIG. 8 of the drawings, a dial 21 embodying the present invention is assembled with a touch generating system 22, and a spiral spring 23 urges the dial 21 to rotate in one direction. The dial 21 may be incorporated in a keyboard musical instrument so that a player changes an attribute of sound such as, for example, the volume of the sound or the timbre. However, the dial 21 is not limited to a part of the keyboard musical instrument. The dial 21 may be incorporated in any kind of apparatus such as, for example, a car, a computer system, an industrial machinary, home applications and so on.

The dial 21 has an umbrella-like portion 21a and a knob 21b integral with the umbrella-like portion 21a. An operator pinches the knob 21b, and rotates the dial 21 in the other direction.

The touch generating system 22 includes an electronic braking unit 22a, an encoder 22b and a controlling circuit 22c. The encoder 22b monitors the dial 21, and determines a current angular position of the dial 21. The encoder produces a detecting signal AP1 representative of the current angular position of the dial 21, and supplies it to the controlling circuit 22c. The controlling circuit 22c determines a resistance to be offered to the operator on the basis of the current angular position, and varies the magnitude of a driving signal DR2. The driving signal DR2 is supplied to the electromagnetic braking unit 22a, and the electromagnetic braking unit 22a offers the resistance against the rotation of the dial 21.

The electromagnetic braking unit 22a includes a disc-shaped rotor 22d formed of magnetic substance, a stator yoke 22e fixed to a stationary member 24, a solenoid coil 22f accommodated in the stator yoke 22e and connected to the controlling circuit 22c and a shaft 22g integral with the disc-shaped rotor 22d and fixed to the disk at one end 22h. The shaft 22g passes through the stator yoke 22e and the encoder 22b, and is fixed to the spiral spring 23 at the other end thereof. The spiral spring 23 urges the shaft 22g and, accordingly, the dial 21 in one direction, and the operator rotates the dial 21 in the opposite direction against the resilient force of the spiral spring 23.

The periphery 22i is slightly spaced from the stator yoke 22d, and the dial 21 is smoothly rotated. When the solenoid coil 22f is energized with the driving signal DR2, the stator yoke 22e is magnetized, and the disc-shaped rotor 22d is attracted to the stator yoke 22e. Sliding friction takes place between the periphery 22i and the stator yoke 22e. When the disc-shaped rotor 22d is attracted to the stator yoke 22e, the dial 21 is slightly moved; however, the gap between the periphery 22i and the stator yoke 22e is so narrow that the operator does not notice it.

The controlling circuit 22c includes a touch selector 22j manipulative by an operator, a memory 22k storing a plurality of touch tables and a driving circuit 22m. The touch selector 22j, the memory 22k and the driving circuit 22m are basically corresponding to those of the first/second embodiment. The plurality of touch tables represent different load pattern to be exerted to the dial 21, and an operator selects one of the touch tables through the touch selector 22j. The load pattern stored in one of the touch tables causes the electromagnetic braking unit 22a to intermittently offer a resistance against the rotation of the dial 21. The operator feels the dial 21 to click.

A plurality of grooves 22n are formed in the shaft 22g, and the encoder 22b counts the grooves passing in front of itself. The encoder 22b determines the current angular position on the basis of the number of grooves and which direction the dial 21 is rotated. The encoder 22b reports the current angular position to the memory 22k.

The memory 22k is responsive to the detecting signal AP1 so as to sequentially supply load data from the selected touch table to the driving circuit 22m, and the driving circuit 22m changes the magnitude of the driving signal DR2 on the basis of the load data. The solenoid coil 22f generates the electromagnetic force in proportional to the magnitude of the driving signal DR2, and the electromagnetic braking unit 22a offers the resistance against the rotation of the dial 21. If the operator selects the touch table for the click, the electromagnetic braking unit 22d intermittently increases the resistance during the rotation of the dial 21.

FIGS. 9, 10 and 11 illustrate an organ embodying the present invention. The organ has a keyboard 31 implemented by stops 31a, and the stops 31a are slidable with respect to an enclosure 32. The stops 31a have a rectangular cross section, and are connected to an action so as to selectively open and close air passages 34 to pipes 35. When a player pushes the stop 31a into the enclosure 32, the stop 31a closes the associated air passage 34. On the other hand, when the stop 31a is pulled out, the stop 31a opens the air passage 34 so as to allow the pipe 35 to sound. Thus, the stop 31a is reciprocally moved by the player.

A touch generating system 36 is provided for the stops 31a, and includes electromagnetic braking units 36a respectively provided under the stops 31a, sensors 36b monitoring the stops 31a so as to provide detecting signals DT1 each representative of a current position of the associated stop 31a and a controlling circuit 31 for varying driving signals DR3.

The electromagnetic braking unit 36a includes a pair of stator yokes 36b, a solenoid coil 36e and a braking plate 36f of magnetic substance. As shown in FIGS. 10 and 11, the solenoid coil 36e has a hollow space, and the pair of stator yokes 36d are inserted into the hollow space in such a manner as to be partially overlapped with each other. The stator yokes 36d have respective braking surfaces 36g closer to the braking plate 36f than the solenoid coil 36e. The braking plate 36f is attached to the lower surface of the stop 31a, and is slightly spaced from the braking surfaces 36g.

When the solenoid coil 36e is energized, the braking plate 36f is attracted to the stator yokes 36d, and friction takes place therebetween so as to offer a resistance against the sliding motion of the stop 31a. Although the stop 31a is downwardly moved together with the braking plate 36f, the movement is so little that the player does not notice it.

The controlling circuit 36c includes a touch selector 36h for specifying a load pattern, a memory 36i storing a plurality of touch tables representative of different load patterns and a driving circuit 36j for varying the magnitude of the driving signal DR3 on the basis of the load data. While a player is pushing the stop 31a into the enclosure 32, the load pattern stored in one of the touch tables may cause the electromagnetic braking unit 36a to increase the resistance against the sliding motion. Another load pattern may cause the electromagnetic braking unit 36a to stepwise change the resistance against the sliding motion of the stop 31a.

The load data representative of the load pattern are sequentially read out form the selected touch table to the driving circuit 36j, and the driving circuit 36j varies the magnitude of the driving signal DR3. The solenoid coil 36e changes the electromagnetic force in proportional to the magnitude of the driving signal DR3, and, accordingly, the stator yokes 36d and the braking plate 36f vary the friction therebetween. Thus, the electromagnetic braking unit 36a offers the resistance varied along the stroke of the stop 31a.

FIGS. 12 and 13 illustrate a disc brake system embodying the present invention. The disc brake system is provided for a shaft member 41, and another shaft member 42 transfers a torque through a transmission unit 43 to the shaft member so as to rotate the shaft member 41 around a center axis 41a thereof.

The disc brake system comprises a disc-shaped rotor 44a fixed to the shaft member 41, a brake caliper 44b connected to a stationary frame 45 by means of a pair of U-letter shaped springs 45a, a sensor 44c for producing a detecting signal DT2 representative of a current angular position of the disc-shaped rotor 44a, a controlling circuit 44d producing a driving signal DR4 and a solenoid coil 44e attached to the brake caliper 44b. When the solenoid coil 44e is energized with the driving signal DR4, the brake caliper 44b pinches the disc-shaped rotor 44a, and offers a resistance against the rotation of the shaft member 41. The U-letter shaped springs 45a are connected to each other by means of a pair of rigid members 45b, and the U-letter shaped springs 45a are resiliently deformed when the brake caliper 44b pinches the disc-shaped rotor 44a.

The brake caliper 44b includes a supporting portion 44f for supporting the solenoid coil 44e, a stationary arm 44g fixed to the supporting portion 44f and a movable arm 44h turnably connected to the supporting portion 44f. The movable arm 44h turns around a pin member 44ha. The stationary arm 44g and the movable arm 44h have respective friction surfaces 44i and 44j, and the friction surfaces 44i/44j are pressed against the both surfaces of the disc-shaped rotor 44a. Though not shown in the drawings, a spring member urges the movable arm in the counter clockwise direction, and a gap takes place between the stationary arm 44g and the movable arm 44h.

The disc-shaped rotor 44a passes through the gap between the stationary arm 44g and the movable arm 44h. When the solenoid coil 44e is energized, the stationary arm 44g is magnetized, and the movable arm 44h is attracted to the stationary arm 44g. Thus, the brake caliper 44b pinches the disc-shaped rotor 44a between the stationary arm 44g and the movable arm 44h, and offers the resistance against the rotation of the disc-shaped rotor 44a. The braking force is proportional to the electromagnetic force generated by the solenoid coil 44e and the stationary arm 44g.

The controlling circuit 44d includes a touch selector 44m for specifying a load pattern, a memory 44n storing a plurality of touch tables representative of different load patterns, a servo-amplifier 44o for correcting the load to be exerted to the disc-shaped rotor 44a and a driving circuit 44p for varying the magnitude of the driving signal DR4 on the basis of the load data. A load sensor 44q is attached to the U-letter shaped spring 45a, and produces a detecting signal representative of the load from the deformation of the U-letter shaped spring 45a. The detecting signal DT3 is supplied to the servo-amplifier 44o. In this instance, the load sensor 44q is implemented by a strain gauge unit.

The load pattern stored in one of the touch tables causes the braking force or the resistance against the rotation of the disc-shaped rotor 44a to be linearly increased, and another load pattern causes the braking force to be quadratically increased.

When a user specifies one of the load patterns through the touch selector 44m, a series of load data representative of the selected load pattern is sequentially read out from the memory 44m in response to the detecting signal DT2, and the servo-amplifier 44o compares the load data with the actual load represented by the detecting signal DT3. If the load data is appropriate, the load data is transferred to the driving circuit 44p. However, if the load data is different from the actual load, the servo-amplifier 44o corrects the load data, and the corrected load data is supplied to the driving circuit 44p.

The driving circuit 44p varies the magnitude of the driving signal DR4. The solenoid coil 44e changes the electromagnetic force in proportional to the magnitude of the driving signal DR4, and, accordingly, the brake caliper 44h changes the braking force.

As will be appreciated from the foregoing description, a single actuator causes a movable member and a stationary member to offer a resistance against a bi-directional motion of an object, and the resistance generator is light, compact and economical.

Although particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present invention.

For example, each of the key touch tables may be divided into a plurality of sub-tables for storing different load data. The plurality of sub-tables may be assigned to the respective black/white keys 1b/1c or key groups.

The series of load data may be read out from the memory in response to a detecting signal representative of a velocity, an acceleration, a force or a combination thereof.

The actuator may be implemented by a mechanical actuator such as a pneumatic actuator or a hydraulic actuator.