Abstract:
A sensing apparatus for detecting a translation of a body relative to a surface, the apparatus comprising: a rolling component for contact, in use, with the surface, the rolling component being retained by, and able, in use, to rotate independently of the body; one or more indicator means associated with the rolling component and rotatable therewith; and one or more transducers for producing one or more signals in response to a rotation of the indicator means relative to the one or more transducers wherein, in use, the rolling component rolls upon the surface in response to a relative translation of the body to the surface, thereby causing the positional orientation of the indicator means to change with respect to the transducers.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is the U.S. National Stage filing under 35 U.S.C. § 371 of International Application No. PCT/GB02/04817 filed Oct. 24, 2002 and published on May 1, 2003 as Publication No. WO 03/036560, which claims priority to UK Application No. 0125529.8, filed Oct. 24, 2001. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to a sensing apparatus and, in particular, a sensing apparatus for detecting the translation of a body relative to a surface.  
         [0003]     Prior known sensors have either detected movement per se or specific movement in one or more directions. Such sensors have been incorporated in hand-held devices.  
         [0004]     Well known hand-held input devices which allow the user of such devices to interact with computer generated environments include touch screens, track balls, mice, joysticks, gloves, digitising tablets with styli and light pens interacting on electronic write boards. A number of these are designed principally to be “easy to use” and so have a degree of accuracy which allows them only to be of use in the directional control or pointing of a cursor. Many of these cannot be used in a natural writing position and so cannot easily generate information related to written characters or shapes which can be captured and further analysed.  
         [0005]     Those devices which can be held in a natural writing position, such as light pens or digitising tablets, can only be used to a generate information by using two distinct parts, whether the parts are tethered or wireless, and therefore they are expensive, cumbersome and impractical to use as portable devices, i.e. when the user is traveling.  
         [0006]     Accordingly, it is an aim of the present invention to provide a sensing apparatus, which can be used in a hand-held input device such as a stylus or pen, which can be used in a natural writing position to generate information relating to written characters or shapes.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     According to the present invention, there is provided a sensing apparatus for detecting a translation of a body relative to a surface, the apparatus comprising: a rolling component for contact, in use, with the surface, the rolling component being retained by and able, in use, to rotate independently of, the body; one or more indicator means associated with the rolling component and rotatable therewith; and one or more transducers for producing one or more signals in response to a rotation of the indicator means relative to the one or more transducers; wherein, in use, the rolling component rolls upon the surface in response to a relative translation of the body to the surface, thereby causing the position or orientation of the indicator means to change with respect to the transducers.  
         [0008]     The indicator means may be a permanent or temporary magnetic field in the rolling component and the magnetic field maybe anisotropic or inhomogeneous.  
         [0009]     The indicator means may be generated by means external to the rolling component but could be changed by the characteristics of the surface of the rolling component. For example, the indicator means may be a coating on the surface of the rolling component, the coating being activated by an activation source. The coating may be phosphorescent, thermochromic, or thermal. The activation means may be a light source, a heat source or a magnetic field generator. The activation source may be pulsed.  
         [0010]     Alternatively, or additionally, the indicator means may include markings on the surface of the rolling component.  
         [0011]     The indicator means may be based on a transient field, which could be induced in part of the rolling component, and which decays over time. This may be magnetic field or decaying charge.  
         [0012]     The one or more transducers may include magnetic field sensors, charge sensors or optical sensors for generating a signal in response to the relative rotation of the indicator means to the transducers. The signal produced by the transducers may be proportional to the sensed property or may be bistable about a threshold value.  
         [0013]     The surface of the rolling component may include a surface coating of magnetisable material and there may be means for magnetising the surface coating and erasing means for removing the magnetisation after the transducers have produced the relevant signal. The erasing devices may be permanently switched on.  
         [0014]     There may be a predefined pattern of magnetisation of the surface of the rolling component such as an array of dipoles on or in the surface of the rolling component. Alternatively, the rolling component itself may include one or more dipoles.  
         [0015]     The rolling component is preferably formed from tungsten carbide.  
         [0016]     The apparatus may include means for detecting temporary breaks in the movement of the rolling component when it is lifted from the surface, which means may be a pressure sensor.  
         [0017]     There may be only one axis of rotation sensed.  
         [0018]     The invention also includes an implement including a sensing apparatus as defined above, wherein the sensing apparatus is located in a tip of the implement and is used to track the motion of the tip over the surface.  
         [0019]     The invention also includes an implement including a sensing apparatus as defined above, wherein the rolling component is located in a sensing point of the implement and is used to sense and track the motion of a surface in relation to the sensing point.  
         [0020]     In either of the above the tip may be fed with ink which is then deposited onto the surface as the rolling component moves along the surface. In this case, the implement becomes a writing implement with incorporated sensors.  
         [0021]     In the current preferred example, the method for detecting the position of a spherical object detects the magnetic field associated with the spherical object. To deduce information about the movement of the rolling object, it is necessary to ensure that the sensors are sampled frequently enough so that the rolling object cannot complete one or numbers of whole revolutions between sensor samples.  
         [0022]     This technique can be applied to rolling objects which have freedom to rotate about any axis without restriction and can also be applied to articulated joints which have a restricted range of motion. Multiple sensors are required for detection of motion in more than one axis—at least one sensor per degree of freedom.  
         [0023]     The position of the rolling object is detected through measuring the magnetic field at a number of positions around it. This is can be achieved by using an anisotropic magneto resistive (AMR) sensor or other sensor which detects magnetic field strength. This has the advantage over techniques which detect the rate of change of magnetic field in that the position rather than the motion of the spherical object can be detected and this functionality allows this technique to be applied to many applications. The ball does not need to be moving for its position to be determined. Also rotation speeds and accelerations are directly available by processing the signals from the sensors.  
         [0024]     This technique can be used in conjunction with rolling objects which have one of the following permanent magnetic fields:  
         [0025]     Simple magnetic dipole. This has the advantage of being the simplest and cheapest magnetic field to apply to a spherical object. Additionally the magnetic field strength for a given size of spherical object will be the highest for this form of magnetisation.  
         [0026]     Curved magnetic dipole. This has the advantage of eliminating axial degeneracy associated with a simple dipole. This means that the case where the spherical object can rotate about the magnetic axis, and so eliminate any change in magnetic field measured by the sensors, is eliminated.  
         [0027]     Multiple magnetic domains—quadrupole and multiple pole. Whilst creating a spherical object with 4 or multiple poles is more complicated than creating a single dipole (straight or curved) this magnetic field pattern has the advantage of providing finer resolution of position of a spherical object.  
         [0028]     The preferred sensor arrangement incorporates a majorly or wholly spherical magnetised body—e.g. the former could be a ball and socket articulating joint, the latter a free ball.  
         [0029]     In the latter case, for the ball to be able to rotate, it is necessary that it is held within a bearing that allows it to rotate freely. The ball can then respond to any applied rotational disturbance. The bearing may additionally require some form of static or hydrodynamic fluid lubrication to aid smooth and/or reliable operation.  
         [0030]     For example, a sphere where the centre of mass is not in the physical centre of the ball can operate as a tilt sensor. Alternatively the ball could be pressed against a surface and rotate and the bearing is moved relative to that surface as in a rollerball pen or a 1 or 2 dimensional translation encoder.  
         [0031]     If the ball housing is also sprung within its housing, position and motion in the third dimension (z) can be detected.  
         [0032]     To achieve the required accuracy in this analogue system, the relative position of the sensors and ball to be fixed and well controlled to find the orientation of the ball requires.  
         [0033]     Accurate machining of the ball housing can be used to fix this, but since in many cases the housing can actually wear during use, it would be advantageous to separate the ball and its housing from the sensor assembly. This will allow easy replacement of worn parts.  
         [0034]     Once the system comprises two parts—the ball in its housing as one and the sensor assembly as the other, there is a requirement for accurate positioning of these two components relative to each other. Using the principles of kinematic theory of constraint, it is only necessary to constrain the bearing for the ball in three of its six degrees of freedom—those of translation, but in practice, given its geometry all six of its degrees of freedom end up constrained in operation.  
         [0035]     Structures are required in the sensor assembly together with complementary structures in the ball housing that allow the ball housing to be pushed into position and locked.  
         [0036]     Taking structures with rotational symmetry as an example, in two planes, say the x and y, three points of contact constrain that plane. Mating datum surfaces on the third plane complete the constraint. A mechanism is required to push the datum faces together and maintain their relative position. One example of this is a bayonet cap fitting.  
         [0037]     Products which would incorporate the sensing apparatus of the present invention would range in functionality from text, or graphics, or velocity profile input. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0038]     Examples of the present invention will now be described with reference to the accompanying drawings, in which:  
         [0039]      FIG. 1  is a schematic side view of one example of the present invention;  
         [0040]      FIG. 2  is a plan view of the first example;  
         [0041]      FIG. 3  is a schematic side view of a second example of the present invention;  
         [0042]      FIG. 4  is a plan view of the second example;  
         [0043]      FIG. 5  is a schematic side view of a third example of the present invention;  
         [0044]      FIG. 6  is a plan view of the third example;  
         [0045]      FIG. 7  is a schematic side view of a fourth example of the present invention;  
         [0046]      FIG. 8  is a plan view of the fourth example;  
         [0047]      FIG. 9  is a schematic side view of a fifth example of the present invention;  
         [0048]      FIG. 10  is a plan view of the fifth example;  
         [0049]      FIG. 11  is a schematic side view of a sixth example of the present invention;  
         [0050]      FIG. 12  is a plan view of the sixth example;  
         [0051]      FIG. 13  is a schematic side view of a seventh example of the present invention;  
         [0052]      FIG. 14  is a plan view of the seventh example;  
         [0053]      FIG. 15  is a schematic side view of an eighth example of the present invention;  
         [0054]      FIG. 16  is a plan view of the eighth example;  
         [0055]      FIGS. 17A  to F show a ninth example of the present invention;  
         [0056]      FIG. 18  is a plan view of the ninth example;  
         [0057]      FIG. 19  is a schematic side view of a tenth example of the present invention;  
         [0058]      FIG. 20  is a plan view of the tenth example;  
         [0059]      FIG. 21  is a schematic cross section through a pen tip;  
         [0060]      FIG. 22  is a schematic perspective view of a pen tip;  
         [0061]      FIG. 23  is a schematic longitudinal cross sectional view of a sensing implement using the present invention;  
         [0062]      FIG. 24  is a schematic longitudinal cross sectional view through the tip of the implement  FIG. 23 ;  
         [0063]      FIG. 25  is a graph showing an example of output voltages obtained experimentally from the implement of  FIG. 23 ;  
         [0064]      FIG. 26  is a graph showing the sensed line against the line vector drawn by the implement based on the sensor signals; and  
         [0065]      FIGS. 27A and 27B  are schematic perspective views of a refill and tip shroud for use in an implement such as that in  FIG. 23 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0066]     In  FIG. 1 , the sensing apparatus  10  comprises a spherical ball  11  which is magnetised with a dipole  12 . The ball is typically 700-1000 μm in diameter. The ball is retained in a housing (not shown) of typical wall thickness of 100 μm in which three magnetic field sensors  13  are mounted. The sensors  13  are approximately 200 μm from the surface of the ball  11 . In use, the ball  11  is placed in contact with surface  14  such that, as the body is moved relative to the surface, the ball  11  rotates relative to the magnetic field sensors  13 . In this way, the orientation of the dipole changes, thereby altering the magnetic field around the ball. This alteration is then detected by the sensors  13 . The sensors  13  convert the detected field change into continuously variable output signals  15 .  
         [0067]     The magnetic field sensors  13  are, in this example, thin film transducers. In this example three sensors are preferred to determine the motion of the ball  11 . In the description of the remaining Figures, the same reference numerals have been used in respect of like features.  
         [0068]     The second example shown in  FIGS. 3 and 4  shows a different form of magnetic field on ball  11 . In this case, the ball  11  is inhomogeneously magnetised and this is indicated by magnetic field lines  16  which are, of course, only a schematic representation of the magnetic field which could be of any suitable form. In this example, as ball  11  rotates with respect to sensors  13 , the change in magnetic field is detected by sensors  13 .  
         [0069]     The magnetic field strength at the surface of the ball  11  is typically of the order of 1 to 100 Gauss, depending upon the material from which the ball  11  is formed.  
         [0070]     A third example of the present invention is shown in  FIGS. 5 and 6  in which the ball  11  is provided with anisotropic or inhomogeneous magnetic permeability. The ball may or may not be intrinsically magnetised. An array of permanent or switchable electromagnets  18  are spaced around the ball  11  to control the strength of the magnetic field applied to the ball  11 . In this arrangement, the electromagnets are arranged in a plane substantially parallel to the surface  14  and substantially at the midpoint of the ball  11 .  
         [0071]      FIGS. 7 and 8  show a fourth example in which the ball  11  is provided with a surface coating  19  of a magnetisable material such as ferric oxide e.g. as in a magnetic tape. A write head  20 , located, as can be seen from  FIG. 8 , over the centre of the ball  11  in plan view, imposes a magnetised region  22  on the surface layer  19 . This magnetised region is detected by the sensors as the ball  11  rotates. The region is erased when exposed to the erase field provided by erase heads  21 . In this example, the erase heads  21  are permanently on but they could be controlled such that they are activated only when required. The rotational speed of the ball  11  would determine the read head signal strength and the direction of rotation is given by the correlation between the sensor signals.  
         [0072]     The fifth example shown in  FIGS. 9 and 10  shows a centrally located write head  20 , as in the fourth example, and is provided with an equatorial erase head  21 . In this example, the write head  20  is pulsed to produce binary patterns of surface magnetism  23 . In this example, the output signal  15  from the sensors  13  will also be pulsed.  
         [0073]     In  FIGS. 11 and 12 , the ball  11  in the sixth example is provided with a predefined pattern of magnetisation in the surface coating  19  such that the surface comprises an array of individual dipoles. The sensors  13  are able to detect the movement of the predefined pattern of dipoles as the ball  11  is rotated. An optional central “reference” sensor  24  could also be provided to enhance the accuracy of the readings.  
         [0074]     The seventh example shown in  FIGS. 13 and 14  has a ball  11  on which a surface activatable coating  25  is provided. The coating may be phosphorescent, thermochromic or thermal and is activated by an activation source  26  which may be a heat or a light source. The sensors  27  may be either heat or light sensors depending upon the activation source. The activation source is typically mounted in a solid or hollow tube  28  and provides a localised area of activation  29  on the surface of the ball  11  which can be detected by the sensors. The activation decays at a known rate and this can be used in determining the direction and speed of rotation of the ball  11 .  
         [0075]     The eighth example shown in  FIGS. 15 and 16  is identical to that of the seventh example but in this arrangement, the activation source is pulsed to provide a differently shaped activation region on the surface of the ball  11 .  
         [0076]     The ninth example shown in  FIGS. 17A  to F and  FIG. 18  comprises optical sensors  30  for the detection of a pattern on the surface of ball  11 . Different forms of patterns as shown in  FIG. 17B  to F and could be, respectively, random, tessellated, line patterns or micro coded.  
         [0077]      FIGS. 19 and 20  show the tenth example of the present invention in which ink  31  is supplied to the ball  11  and can be deposited on the surface  14  in a manner well known from previous writing implements. However, in this example, an activation source  32  is provided to alter the properties of the ink for example, using heat, light or magnetic field to alter the ink temperature, phosphorescence or magnetic alignment of particles in the ink. The sensors  33 , which are of whatever form necessary to detect the specific activation, detect the change in the activation field as the ball rotates due to the decay in the activation.  
         [0078]     In particular, the ink may contain magnetisable particles which are locally oriented by the activation source  32  as the ink is drawn out on to the ball  11 . The detection, in this case, would be by a magnetic sensor. The magnetic alignment will be lost when the ink is passed to the surface  14 . Although not shown, it is envisaged that the thickness of the ink film could be detected to provide an indication of the rotation of the ball  11  and this can be done capacitively, based upon the ink permeability, or optically, based upon the ink optical density.  
         [0079]      FIGS. 21 and 22  shows schematic arrangements of tips which could be used in a writing implement using the sensor arrangement shown in  FIGS. 19 and 20 .  
         [0080]     In particular,  FIGS. 21 and 22  show a refill tip  40  which includes a refill cartridge  41  for the supply of ink, a brass tip insert  42 , through which the ink can flow to tip  43 . Transducers  44  are provided at spaced intervals around the circumference of the refill and are shaped so that they fit within the tip casing  45  of a writing implement.  
         [0081]      FIGS. 23 and 24  shows an implement  50  that converts hand writing into typed text that appears within an application on a host processor. The rollerball  51  is housed within a standard rollerball ink refills  53  which is held accurately, as shown in  FIGS. 27   a  and  27   b,  with respect to the sensors  52  located within the pen body. The sensors  52  are mounted on a carrier  66 , encapsulated in epoxy (Ciba Geigy 2019) and encased in a plastic protective conical shroud  54 .  
         [0082]     A rollerball  51  is made of Ruballoy, a standard alloy of tungsten carbide (containing 72% WC, 20% Co, 5% Cr). It is typically of 1.0 mm diameter. The rollerball is magnetised before assembly with a uniform dipole by exposure to a saturating linear magnetic field produced by an electromagnet coil.  
         [0083]     A rollerball housing  53   a  at one end of the refill  53  is brass, a standard pen tip material that is non-magnetic. There is a small amount of free space  65  between the rollerball  51  and housing  53   a  to allow ink  63  to flow and the rollerball to roll.  
         [0084]     The rollerball housing  53   a  encapsulates the rollerball to just beyond its equator in order for the rollerball to be captive within the housing.  
         [0085]     The sensors  52  are Anisotropic MagnetoResistive (AMR) sensors used in a bridge configuration. The magnetic field strength can be detected by applying a voltage to the bridge containing a number of these AMR sensors and measuring the voltage offset generated.  
         [0086]     In this example, three sensors are used. They are arranged with rotational symmetry about the longitudinal axis of the pen at an angle of 45° to this axis with the active face of the sensor being directed towards the centre of the rollerball.  
         [0087]     The sensors  52  are electrically connected to a PCB  67  via connectors  57  using conductors  55  that lead from the sensor positions through the carrier  66  into the main pen body  56 . The small voltage differences developed across the sensor are sent via the electrical conductors  55  to operational amplifiers  58  which amplify the signals.  
         [0088]     The amplified signals are sent to an analogue to digital converter  59 . A microprocessor  60  then processes and compresses the sensor signals. A radio-frequency transmitter module  61  (for example a BlueTooth module) sends the signals via an antenna  62  to an equivalent antenna and receiver module on a host processor (a personal computer or PDA for example)  
         [0089]     The vector reconstruction algorithm can be described simply in the following sequence. 
        Sensor data from the three sensors is acquired by the microprocessor.     The data from each sensor is normalized with respect to the sensors local maximum and minimum values by the microprocessor.     This data is transmitted to the host processor.     The sensor data from the three sensors is used to calculate the magnetic dipole orientation in the magnetized rollerball by the host processor. This gives a measurement of the dipole orientation.     The rotational axis of the rotating magnetized sphere is calculated using a sequence of dipole orientations by the host processor. This gives a measurement of the dipole rotation.     The vector translation of the rollerball along a plane is calculated by the host processor.        
 
         [0096]      FIGS. 27A and 27B  show the example of a mechanism by which the alignment of the sensors located on the inside of the shroud  54  and the rollerball  51 .  
         [0097]     The refill  53  is provided with a guide groove  70 , and a corresponding groove directly opposite on the other side of the refill, into which a guide pin  71 , located on the inner surface of the shroud  54 , is fitted. The grooves  70  are provided with a substantially straight section  72  and a hook portion  73 . When the guide pin  71  has reached the end of the straight portion  72 , relative rotation of the shroud  54  and the refill  53  causes the guide pin  71  to travel into the hook portion  73 . A projection  74  creates a narrowed section  75  through which the guide pin  71  is urged, thereby locking the refill with the shroud.