It has been noted that a significant problem, amongst others, for visually impaired people is travelling, especially walking, in a straight line. Whilst a variety of apparatus ranging from a simple walking cane to sophisticated electronic devices is available to help guide the visually impaired this apparatus is mainly concerned with alerting a user to the presence of obstacles and does not help with travelling in a straight line.

The present invention has been made in consideration of this problem.

According to a first aspect of the present invention there is provided guide apparatus comprising a sensing means operative to sense the direction of travel of the apparatus, input means operative to enable a user to select a direction and an output means operative to provide a signal to a user if the direction of travel of the device deviates from the selected direction by a predetermined amount wherein the means for sensing direction of travel is operative to sense the direction of travel of the apparatus irrespective of the orientation of the apparatus or means for sensing in three dimensional space.

By alerting a user when it deviates from a selected direction the apparatus helps the user to travel in the selected direction.

The sensing means may comprise a means for detecting the earth's magnetic field, such as an electronic compass. In one embodiment the sensing means comprises three magnetic, field detectors operative to detect magnetic field in respective mutually substantially orthogonal directions. Each detector preferably produces an output which depends upon the strength of detected magnetic field. The sensing means preferably further comprises a processing means operative to determine the direction of travel and/or orientation of the detectors with respect to a detected magnetic field. Each detector may comprise a Hall Effect device. Each Hall Effect device may be comprised in a single "multi-axis"Hall Effect chip.

Alternatively or additionally the sensing means may comprise an inertial sensor, for example one or more gyroscopes and/or a positional sensing receiver operative to receive location and/or direction of travel information from an external source, for example a satellite navigation system such as the Global Positioning System (GPS).

The input means may take any suitable form. Preferably it comprises a user operable control, such as an electrical switch, and the apparatus is arranged so that when the control is operated the direction with which a part of the-apparatus is aligned is selected, so that the current direction of travel of the apparatus is selected.

The output means is preferably operative to produce a tactile output and preferably comprises one or more actuators. The actuators may cause a part of the apparatus to protrude and/or vibrate. Preferably the output means is operative to provide at least two different signals, one being to alert a user that they are deviating to the right of the selected direction, and the other that they are deviating to the left of the selected direction. The output means may indicate the degree of deviation from the selected direction, conveniently by varying the intensity of the signal indicating the direction of deviation. The amplitude and/or frequency of the signal could be varied. The signal could comprise an oscillating signal.

The apparatus preferably comprises a housing, housing the sensing means. The input means and means to provide a tactile output are preferably mounted on the outside of the housing. The housing is preferably sized and shaped so that it may be comfortably held in the hand. In one embodiment the housing forms part of a walking cane or white stick.

According to a second aspect of the present invention there is provided guide apparatus comprising a sensing means operative to sense the direction of travel of the apparatus, an input means operative to enable a user to select a direction and a tactile output means operative to provide a tactile signal to a user if the direction of travel of the device deviates from the selected direction by a predetermined amount.

In order that the invention may be more clearly understood an embodiment thereof will now be described by way of example with reference to the accompanying drawings of which : Figure 1 is a perspective view of apparatus according to the invention; Figure 2 is a schematic circuit diagram of the apparatus of Figure 1; Figure 3 is a perspective view of the magnetic sensor arrangement of the apparatus of Figure 1 ; and Figure 4 is an exploded view of one of the rods of the sensor of Figure 3.

Referring to the drawings the apparatus takes the form of a white stick or blind cane having a handle 1 and a shaft 2. Mounted on the handle are an on-off switch 3, a direction selecting switch 4 and left and right piezoelectric actuators 5,6.

The handle 1 houses electronic circuitry including a magnetic field sensor 7, and an associated power supply (not shown).

The magnetic field sensor comprises three pairs of ferrite rods 8. Each pair are fastened together end to end with a Hall Effect chip 9 disposed between the two rods.

The long axes of the three pairs of rods 8 extend in three mutually substantially orthogonal directions which shall be referred to as the X, Y and Z directions.

The magnetic sensor 7 is operative to measure the earth's magnetic field in three substantially orthogonal directions. Each pair of ferrite rods 8, which incidentally could be formed from any other suitable material of high magnetic permeability, serves to concentrate the magnetic field present onto its associated Hall Effect chip 9 which produces a Hall voltage the magnitude of which depends upon the intensity of the <BR> <BR> incident field. Each Hall Effect chip is of course provided with a drive current.

However, as the use of the Hall effect chips is well known the arrangements for this, or for determining the Hall voltage, will not be described in further detail.

The output from each Hall Effect chip 9 is conducted to a respective amplifier 10 and the amplified output is conducted to a multiplexer and analog to digital converter 11.

The resultant digital signals are conducted to a microprocessor 12. The microprocessor is operatively connected to the direction selector switch 4 and to the piezoelectric actuators 5, 6.

The microprocessor 12 is operative to compute changes in the orientation of the magnetic field sensor 7 with respect to the earth's magnetic field, and hence changes in the orientation of the white stick with respect to the earth's magnetic field. This is achieved by comparison of the output of each of two pairs of the Hall Effect chips 9, for example the X and Y and X and Z chips.

The X, Y and Z directions define three orthogonal planes, the X, Y plane, the X, Z plane and the Y, Z plane. By comparing the output of any two of the Hall Effect devices it is possible by simple geometry to calculate the angle between the direction of a measured magnetic field and one of the axes lying within a plane, in that plane. By repeating this process for two of the defined planes it is possible to calculate the direction of detected magnetic field in three dimensions with respect to the detector arrangement.

Although only two pairs of ferrite rods and associated Hall Effect chips disposed at right angles to each other arel sufficiem lo aetermine the direction of travel along the ground they would need to be held parallel to the ground in order to accurately do this.

Provision of a third pair of ferrite rods and associated Hall Effect chip extending at right angles to the other two pairs of rods enables the microprocessor 12 to compensate for tilting of the other two pairs of rods relative to the ground.

In use a user selects a direction in which they wish to travel by pointing the stick in that direction and pressing the select direction switch 4. Then, as the user and stick move the microprocessor 12 determines, via the magnetic field sensor 7, the direction of travel of the stick. If the direction of travel deviates from the selected direction the microprocessor causes either the left 5 or right 6 piezoelectric actuator to vibrate in order to alert a user holding the handle 1 of the stick so that they have deviated from the selected direction, and the direction in which they have deviated.

The user is thus prompted to correct their course and will know when this has been sufficiently corrected as the actuator will stop vibrating.

The microprocessor may vary the frequency of vibration of the actuators 5,6 depending upon the extent to which the selected direction has been deviated from.

The above embodiment is described by way of example only. Many variations are possible without departing from the invention.