Drawing apparatus

A drawing apparatus which allows a user to select various writing sensations without experiencing an unnatural operational feeling. This drawing apparatus comprises operating device designed to be movable within predetermined space; detection device which detects a moving position of the operating device within the space; display device which displays an image according to a locus of the operating device based on a detection output of the detection device; and driving device which imparts a reaction force to the operating device in motion. As the operating device is moved along an imaginary surface in the space, the image according to the locus of the operating device is displayed, the detection device detects a moving speed and/or velocity or an output of a pressure sensor corresponding to each position of the operating device in the space, and the driving device imparts the reaction force according to a detection result from the detection device to the operating device.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a drawing apparatus as a terminal device
 for inputting an image on the display screen of a display apparatus or the
 like of a computer.
 2. Description of Related Art
 There are known drawing apparatuses which are designed to detect
 characters, a figure or the like, drawn on a tablet as an imaginary paper
 using a pen-like input device, and to display what has been input on a
 display.
 FIGS. 1A and 1B are schematic diagrams showing a conventional drawing
 apparatus. As shown in FIG. 1A, the drawing apparatus has an input pen 101
 comprised of a coordinate indicator, and a plate-like tablet 102 comprised
 of a digitizer. As the input pen 101 is moved and slid on the tablet 102,
 the coordinates of the moving pen 101 are detected and are supplied to an
 unillustrated computer or the like so that the locus of the moving pen 101
 is displayed on the display screen of a monitor or the like to draw
 whatever has been input.
 The thickness (width) of the locus can be changed by drawing software which
 runs on the computer, so that a user can make drawing while properly
 selecting the thickness of the locus as needed.
 Even though the thickness of the locus is selected from various types
 available, the sliding resistance of the input pen 101 with its core 103
 slid on the tablet 102 does not vary and the touch or the writing
 sensation the user feel through his hand does not change. This gives the
 user awkward feelings in the drawing operation.
 When one actually writes characters on paper with a writing brush or the
 like, he can write them while adjusting the thickness of a line by
 controlling the stroking pressure. With the use of the conventional input
 pen as shown in FIG. 1B, however, when the core 103 made of metal or the
 like is pressed against the tablet 102, the stroking pressure is detected
 by taking the deformation of a pressure sensor 104 as a change in electric
 capacitance. Since the deformation of the pressure sensor 104 is so subtle
 that there hardly is a stroke of the input pen to the tablet 102.
 Further, the deformation characteristic of the input pen with respect to
 the level of the stroking pressure is fixed. Therefore, the user cannot
 sense a non-linear deformation characteristic of each writing brush with
 respect to the level of the stroking pressure, which the user feels
 through his hand when actually using various kinds of writing brushes, or
 the brush strength or the like which varies from one brush to another.
 Thus, the writing sensation does not change, which still gives the user
 awkward feeling in the drawing operation.
 OBJECTS AND SUMMARY OF THE INVENTION
 Accordingly, it is a primary objective of the present invention to provide
 a drawing apparatus which allows a user to select various writing
 sensations without experiencing an unnatural operational feeling.
 According to the first aspect of this invention, a drawing apparatus
 comprises operating device designed to be movable within predetermined
 space; detection device which detects a moving position of the operating
 device within the space; display device which displays an image according
 to a locus of the operating device based on a detection output of the
 detection device; and driving device which imparts a reaction force to the
 operating device in motion, whereby as the operating device is moved along
 a virtual surface in the space, the image according to the locus of the
 operating device is displayed, the detection device detects a moving speed
 and/or velocity or an output of a pressure sensor corresponding to each
 position of the operating device in the space, and the driving device
 imparts the reaction force according to a detection result from the
 detection device to the operating device.
 According to the second aspect of this invention, the drawing apparatus
 with the first aspect further comprises setting device which sets the
 virtual surface in the space; and as the operating device is moved along
 the virtual surface set by the setting device, the detection device
 detects the moving speed and/or velocity or the output of the pressure
 sensor corresponding to each position of the operating device in the
 space, and the driving device imparts the reaction force according to the
 detection result from the detection device to the operating device.
 According to the third aspect of this invention, in the drawing apparatus
 with the second aspect, the virtual surface set by the setting device
 consists of an arbitrary surface including a plane.
 According to the fourth aspect of this invention, any of the drawing
 apparatuses described above further comprises noise generation device; and
 as the operating device is moved along the virtual surface in the space,
 the detection device detects the moving speed and/or velocity or the
 output of the pressure sensor corresponding to each position of the
 operating device in the space, and the driving device imparts the reaction
 force according to the detection result from the detection device and a
 driving force according to a signal, generated by the noise generation
 device, to the operating device.
 With the above structures, when a user moves the operating device along the
 virtual surface, the reaction force is generated by the driving device to
 permit the user to feel through his hand the force corresponding to the
 stroking pressure of a brush on the virtual surface, the writing friction,
 the dead weight of the brush, the roughness of the writing surface, etc.
 The user can therefore select various writing sensations without
 experiencing an awkward feeling in operating the drawing apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 A preferred embodiment of the present invention will now be described with
 reference to the accompanying drawings.
 FIG. 2 is a schematic block diagram of a drawing apparatus according to one
 embodiment of this invention. Referring to this figure, an input/output
 (I/O) interface unit 1 has an unillustrated operation grip. When a user
 moves the operation grip along an imaginary input surface, individual
 rotary encoders, which are coupled to the operation grip and provided in
 association with three axes crossing one another at right angles, detect
 the amount of movement of the operation grip in terms of the amounts of
 rotation of the individual coupling portions associated with the three
 axial directions and send detection signals to an I/O processing section 2
 comprising a sensor processor 2A and a motor driver 2B.
 The I/O interface unit 1 has setting device for permitting the user to
 select an imaginary input surface along the desired direction in the space
 that is defined by the three axes. For example, such an imaginary input
 surface may be set by previously designating the spatial coordinates of
 three points which constitute a plane, or selecting the desired one from a
 plurality of imaginary input surfaces that have already been set.
 Information on the setting is sent to the I/O processing section 2.
 The I/O processing section 2 converts the amounts of rotation of the
 individual rotary encoders, provided in association with the three
 perpendicular axes, to the amounts of movement of coordinates on the set
 imaginary input surface to properly compute the amounts of movement of the
 coordinates of the operation grip on the imaginary input surface in
 accordance with the amounts of rotation of the individual rotary encoders.
 Based on signals from the rotary encoders and the information on the
 setting of the imaginary input surface, both supplied from the I/O
 interface unit 1, motor control voltages for the amounts of rotation of
 the individual coupling portions are generated to drive motors (not
 shown), provided in association with the rotary encoders, at predetermined
 timings. As a result, a predetermined reaction force is applied to allow
 the operation grip of the I/O interface unit 1 to be movable on the set
 imaginary input surface. In addition, signals corresponding to the line
 thickness, the type of an imaginary pen, the roughness of the surface of
 imaginary paper and so forth, which have been selected by the user through
 control CG (Computer Graphics) software 7 are supplied to the operation
 grip in motion via a personal computer 4 and an interface board section 3.
 Based on those signals, motor control voltages are also generated to apply
 the corresponding reaction force to the operation grip.
 The I/O processing section 2 supplies the signals, sent from the individual
 rotary encoders of the I/O interface unit 1, to the interface board
 section 3 comprising an A/D coverter 3A, a counter 3B, a PPI 3C, and a D/A
 converter 3D, one by one. As the operation grip moves, the interface board
 section 3 sequentially computes the moved distance and the moving
 direction of the operation grip on the imaginary input surface, i.e., the
 coordinates of the moved position of the operation grip based on the
 supplied signals, and sends digital signals, acquired by executing
 predetermined signal processing, to the personal computer 4.
 Based on the supplied digital signals and in accordance with the control CG
 software 7, the aforementioned setting of the imaginary input surface and
 the level of the reaction force applied to the operation grip, the
 personal computer 4 displays a position indicator 6 corresponding to the
 imaginary input surface on the display screen of a monitor 5, and controls
 the display of the locus of the position indicator 6 in accordance with
 the movement of the operation grip on the imaginary input surface.
 The structures of the individual sections of the I/O interface unit 1 will
 be discussed below.
 FIG. 3 presents a schematic outline structural diagram of the I/O interface
 unit 1. In this diagram, reference numeral "29" denotes setting device for
 setting an imaginary input surface. In the illustrated example, an
 imaginary input surface 30 is set as a plane along the X and Y axes in the
 spatial coordinates (X, Y, Z) in the aforementioned manner.
 FIGS. 4 and 5 are detailed diagrams of an operation grip 8 of the I/O
 interface unit 1. As shown in FIG. 4, the I/O interface unit 1 has the
 operation grip 8 of nearly a rod shape, for example, which is coupled to a
 fixed section 10 via a wire 9 and a plurality of elastic members 11 to be
 supported like a cantilever.
 The materials and shapes of the wire 9 and the elastic members 11 are so
 selected as to provide a relatively small stiffness, which permits the
 user to easily bend the operation grip 8, as shown in FIG. 5. The fixed
 section 10 is secured to one end of a stick 12.
 As shown in FIG. 3, the other end of the stick 12 is secured to a coupling
 block 13 which is attached to an associated coupling base 14 to be
 rotatable around a center axis A in FIG. 3.
 Attached to the rotational axis of the coupling block 13 is a rotary
 encoder 16 which consecutively detects the amount of rotation of the
 coupling block 13 that rotates around the axis A with respect to the
 coupling base 14, and sends the detection result to the I/O processing
 section 2 (not shown). The coupling block 13 is designed to be rotatable
 around the axis A by a motor 15 attached to the coupling base 14.
 The coupling base 14 is secured to one end of a stick 17, which is formed
 along the axis A, while the other end of the stick 17 is secured to a
 coupling block 18. The coupling block 18 is attached to an associated
 coupling base 19 to be rotatable around a center axis B in FIG. 3.
 Attached to the rotational axis of the coupling block 18 is a rotary
 encoder 20 which consecutively detects the amount of rotation of the
 coupling block 18 that rotates around the axis B with respect to the
 coupling base 19, and sends the detection result to the unillustrated I/O
 processing section 2. The coupling block 18 is designed to be rotatable
 around the axis B by a motor 21 attached to the coupling base 19.
 The coupling block 19 is attached to a secured base 22 to be rotatable
 around a center axis C in FIG. 3. Attached to the rotational axis of the
 coupling base 19 is a rotary encoder 23 which consecutively detects the
 amount of rotation of the coupling base 19 that rotates around the axis C
 with respect to the base 22, and sends the detection result to the
 unillustrated I/O processing section 2. The coupling base 19 is designed
 to be rotatable around the axis C by a motor 24 attached to the base 22.
 The motors 15, 21 and 24, like ultrasonic motors, have holding torques to
 hold the associated coupling blocks 13 and 18 and coupling base 19 not to
 rotate around the respective axes in the initial state. Therefore, the
 operation grip 8 does not move and can keep the current position unless
 force is externally applied. With electromagnetic motors in use as an
 alternative, the operation grip 8 can be set free in the initial state.
 The motors 15, 21 and 24, connected to the I/O processing section 2 (not
 shown), are driven by the motor control voltage output from the I/O
 processing section 2 in accordance with the amounts of rotation of the
 associated coupling blocks 13 and 18 and coupling base 19 over a
 predetermined time, which are detected by the associated rotary encoders.
 As a result, a reaction force is applied to the operation grip 8 in
 motion.
 According to the thus structured drawing apparatus embodying this
 invention, as the user moves the I/O interface unit 1 on an imaginary
 input surface, as desired, using the operation grip 8, the coupling blocks
 13 and 18 and the coupling base 19 rotate around their respective axes.
 The rotary encoders 16, 20 and 23 provided in association with the axes in
 turn successively detect the amounts of rotation of the coupling blocks
 and base 13, 18 and 19 and send the detection results to the I/O
 processing section 2. In accordance with the detection results and
 information on the coordinates on the imaginary input surface that have
 been set previously by the I/O interface unit 1, the I/O processing
 section 2 drive the motors 15, 21 and 24 to impart the reaction force to
 the hand of the user manipulating the operation grip 8 whenever necessary.
 In addition, the I/O processing section 2 moves the position indicator 6
 on the imaginary input surface, which is displayed on the display screen
 of the monitor 5, via the interface board section 3 and the personal
 computer 4 in accordance with the locus of the operation grip 8, and
 controls the display of the locus of the operation grip 8 based on the
 line thickness, the type of the imaginary pen, the roughness of the
 surface of imaginary paper and so forth, set by the control CG software 7,
 the setting of the imaginary input surface and the level of the reaction
 force applied to the operation grip 8.
 A description will now be given of the reaction force that is applied by
 each motor to the operation grip which moves along the imaginary input
 surface. The reaction force that is imparted to the operation grip in
 motion is expressed as follows.
EQU Fct1=Fp+Fv+Fa+Fn
 where Fct1 indicates the torque generated by each motor, Fp is the force
 corresponding to imaginary stroking pressure applied to the imaginary
 input surface (imaginary stroking pressure), Fv is the force corresponding
 to friction according to the relative speed of the imaginary pen and
 imaginary paper during drawing (the slidability of the imaginary pen on
 the imaginary paper), Fa is the force corresponding to the acceleration of
 the imaginary pen used in drawing (which includes the dead weight of the
 imaginary pen), and Fn is the force corresponding to the state of contact
 of the imaginary pen on the imaginary paper (imaginary roughness).
 Fct1 is the sum of Fp, Fv, Fa and Fn, and the I/O processing section 2
 supplies motor control voltages to the individual motors 15, 21 and 24 so
 that those motors are driven with forces corresponding to the individual
 components of the force in the directions of three axes (A, B and C) shown
 in FIG. 2, thereby applying the reaction force to the operation grip 8.
 The force Fp corresponding to the imaginary stroking pressure to be applied
 to the imaginary input surface will be discussed next.
 In drawing a line on actual paper using a writing brush or the like, for
 example, the thickness or the like of a character or line to be written
 can be determined by the perpendicular movement of the writing brush
 against the surface of the paper. That is, the thickness or the like of a
 character or line to be written becomes thicker as the brush is pressed
 against the paper harder, and it becomes thinner as the contact of the
 brush on the paper gets softer.
 In this embodiment, the I/O processing section 2 or the interface board
 section 3 sequentially computes the position of the distal end of the
 operation grip 8 on the imaginary input surface using the coordinate
 system of the imaginary input surface or the individual rotary encoders.
 The line width is set in accordance with the computed positional
 coordinates and data on the line thickness selected by the control CG
 software 7 or data on the type of the imaginary pen.
 FIGS. 6A and 6B exemplarily show the position of the distal end of the
 operation grip 8 with respect to an imaginary input surface. FIG. 6A shows
 the case where the operation grip 8 is not in contact with the imaginary
 input surface, and FIG. 6B shows the case where the operation grip 8 is in
 contact with the imaginary input surface. In FIGS. 6A and 6B, the
 coordinates on an imaginary input surface are shown as those of a X-Y
 plane in the spatial coordinates (X, Y, Z), and the position of the distal
 end of the operation grip 8 on the imaginary input surface is indicated by
 the displacement of the Z axis.
 As apparent from those diagrams, the I/O processing section 2 successively
 computes a change in the distance, .DELTA.z, between the imaginary input
 surface and the operation grip 8. When the computed result becomes equal
 to or smaller than a given value, the I/O processing section 2 can
 determine that the operation grip 8 is in contact with the imaginary input
 surface, and sends data on the line width according to the computed result
 to the interface board section 3 and generates, for each motor, a control
 voltage whose level accords to the computed result.
 The data sent to the interface board section 3 is put through predetermined
 arithmetic operations and the resultant data is supplied to the personal
 computer 4. Accordingly, the thickness of the locus of the moving position
 indicator 6 on the monitor 5 is adjusted under the control of the control
 CG software 7.
 Further, the individual motors are driven with the respective control
 voltages supplied thereto to control the operation grip 8 so that the
 reaction force is applied to the operation grip 8 along the Z axis in
 FIGS. 6A and 6B.
 FIGS. 7A through 7C exemplarily show the force Fp corresponding to the
 reaction force which is successively generated as the user moves the
 operation grip 8 along the imaginary input surface while adjusting the
 stroking pressure, and shows an example of the locus which is drawn on the
 monitor 5 in this case.
 The force Fv corresponding to the friction according to the relative speed
 of the imaginary pen to the imaginary paper during drawing will now be
 discussed.
 In the case of drawing a line on actual paper using a felt pen or the like,
 for example, the friction of the felt pen varies between when the felt pen
 is moved slowly and when it is moved quickly. More specifically, the
 friction becomes relatively large when the felt pen is moved slowly, but
 it becomes relatively small when the pen is moved quickly. The friction
 which varies according to the stroking of the pen differs depending on the
 type of the pen selected and the condition or quality of paper in use.
 In this embodiment, the I/O processing section 2 or the interface board
 section 3 sequentially computes the speed of the operation grip 8 moving
 along the set imaginary input surface and the positional coordinates
 representing the state of contact of the operation grip 8 to the imaginary
 input surface using the coordinate system of the imaginary input surface
 or the individual rotary encoders, based on data on the line thickness,
 the type of the imaginary pen, the roughness of the surface of the
 imaginary paper, etc. selected by the control CG software 7. Then, a
 control voltage for each motor whose level accords to the computed result
 is generated.
 As the individual motors are driven with the respective control voltages
 supplied thereto, the operation grip 8 is so controlled as to receive the
 reaction force with respect to the moving direction and with the level
 according to the moving speed.
 When the I/O processing section 2 determines that the distal end (reference
 position) of the operation grip 8 in motion is in contact with the
 imaginary input surface, the aforementioned reaction force is applied to
 the operation grip 8. When it is determined that the operation grip 8 is
 positioned apart from the imaginary input surface, the force Fv
 corresponding to the reaction force becomes zero. The coefficient value of
 the force Fv changes in accordance with the level of the aforementioned
 force Fp corresponding to the stroking pressure of the operation grip 8 in
 motion.
 The force Fa corresponding to the acceleration of the imaginary pen to be
 used in drawing will now be described.
 In the case of drawing a character on paper, for example, the weight of a
 writing implement the user feels varies between a fountain pen and a
 pencil due to the difference in their masses.
 In this embodiment, the dead weight of the imaginary pen in use can be
 adjusted by applying the force Fa corresponding to the acceleration to the
 operation grip 8.
 Based on data on the type of the imaginary pen, the mass of the imaginary
 pen, etc. selected by the control CG software 7, the I/O processing
 section 2 or the interface board section 3 regulates the control voltages
 to be supplied to the respective motors in such a way that the force Fa is
 applied to the distal end of the operation grip 8 in a predetermined
 direction. The motors are driven with those control voltages so that the
 force Fa always in one direction is applied to the operation grip 8.
 Therefore, the user manipulates the operation grip 8 while receiving the
 force Fa corresponding to the dead weight of the imaginary pen.
 The force Fn corresponding to the state of contact of the imaginary pen to
 the imaginary input surface (imaginary roughness) will now be described.
 In the case of drawing a character on actual paper using a pencil, for
 example, depending on the hardness of the lead of the pencil and the
 surface roughness of the paper, the user may feel the state of contact of
 the point (lead) of the pencil to the surface of the paper as rough
 through the hand holding the pencil. This is because as the hardness of
 the lead of a pencil increases or the surface roughness of paper
 increases, such rough feeling is obtained through a hand as vibration at a
 specific frequency component.
 In this embodiment, the I/O processing section 2 is provided with a
 roughness signal generator 25 shown in FIG. 8. The output signal of the
 roughness signal generator 25 is added to the control voltages generated
 for the individual motors to cause the motors to generate the components
 of the force Fn corresponding to the rough feeling. The force Fn obtained
 by combining those components of the force is applied to the moving
 operation grip 8 to impart the rough feeling.
 FIG. 9 shows an example of the structure of the roughness signal generator
 25. As illustrated, the roughness signal generator 25 is designed such
 that the power-spectrum density v.s. frequency characteristic of white
 noise generated by, a white noise generator 26, is adjusted by a DSP
 (Digital Signal Processor) 27, and is enabled or disabled by a switch 28.
 As a result, signals in individual modes, as shown in FIG. 10, are added
 to the control voltage for each motor as needed.
 The modes of the DSP 27 are acquired through coefficient control in
 association with the surface of the imaginary paper and the type of the
 imaginary pen, which are controlled by the control CG software 7. The
 modes of the DSP 27 to be switched are not limited to those illustrated in
 FIG. 10, but may be changed in accordance with the moving speed of the
 operation grip 8.
 When the I/O processing section 2 determines that the distal end (reference
 position) of the operation grip 8 is positioned apart from the imaginary
 input surface, as in the aforementioned case of the force Fv, the I/O
 processing section 2 sets the switch 28 off so that the user does not feel
 the roughness.
 Instead of acquiring the force from acceleration, the force may be detected
 directly by device of a strain gauge provided at the stick 7.
 With the above structures, when a user moves the operating device along an
 imaginary surface, the reaction force is generated by the driving device
 to permit the user to feel through his hand the force corresponding the
 stroking pressure of a brush on the imaginary surface, the writing
 friction, the dead weight of the brush, the roughness of the writing
 surface, etc. The user can therefore select various writing sensations
 without experiencing an awkward feeling in operating the drawing
 apparatus.
 The present invention has been described above with reference to the
 preferred embodiment thereof. It should be understood that various
 modifications and variations can be made by those skilled in the art and
 that all such modifications and variations are included in the scope of
 the appended claims.