Abstract:
An inductive angular sensor is disclosed as including a first part and a second part which are swivellably movable relative to each other, in which the first part includes a primary coil energizable to generate a voltage and two secondary coils each on a side of the primary coil for sensing the voltage generated by the primary coil, and a channel runs through the primary and secondary coils, and the second part includes a rotor mounted with two wires, such that during relative swivelling movement between the first and second parts, the wires reciprocate in the channel, and when the angle of rotation between the first and second parts is within a pre-determined range about a zero position, the wires are out of said primary coil. A sensing device is also disclosed as including an angular sensor and a zero position detector, in which the angular sensor includes a first part and a second part which are swivellably movable relative to each other, and the zero position detector has a logic level output when the angle of rotation between the first and second parts is within a pre-determined range about a pre-defined zero position.

Description:
[0001]     This invention relates to an angular sensor and, in particular, such a sensor for contactless determination of a rotary angle, and a safety mechanism for use in conjunction with an angular sensor.  
       BACKGROUND OF THE INVENTION  
       [0002]     There has been a constant need for position sensors for use in such commercial applications as electrical scooters, wheelchairs and joysticks, to name just a few. Existing sensors include contact type potentiometer sensors, which are known to be wanting in reliability.  
         [0003]     It is thus an object of the present invention to provide an inductive angular sensor in which the aforesaid shortcomings are mitigated.  
         [0004]     It is a further object of the present invention to provide an inductive angular sensor which is both reliable and of a relatively low cost.  
         [0005]     It is a yet further object of the present invention to provide an angular sensor with a built-in safety mechanism.  
       SUMMARY OF THE INVENTION  
       [0006]     According to a first aspect of the present invention, there is provided an inductive angular sensor including a first part and a second part which are swivellably movable relative to each other, wherein said first part includes a primary coil energizable to generate a voltage and two secondary coils each on a side of said primary coil and adapted to sense the voltage generated by said primary coil, wherein a channel runs through said primary coil and said two secondary coils, wherein said second part includes a body member mounted with at least one wire member, wherein during relative swivelling movement between said first and second parts, said at least one metallic wire member reciprocates in said channel, and wherein when the angle of rotation between said first and second parts is within a pre-determined range about a pre-defined zero position, said at least one metallic wire member is out of said primary coil.  
         [0007]     According to a second aspect of the present invention, there is provided a sensing device including an angular sensor and a zero position detector, wherein said angular sensor includes a first part and a second part which are swivellably movable relative to each other, and wherein said zero position detector is adapted to have a logic level output when the angle of rotation between said first and second parts is within a pre-determined range about a pre-defined zero position. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     Preferred embodiments of the present invention will now be described, by way of examples only, with reference to the accompanying drawings, in which:  
         [0009]      FIG. 1  is a transverse sectional view of an inductive angular sensor according to a first preferred embodiment of the present invention;  
         [0010]      FIG. 2  is a circuit diagram of the sensor shown in  FIG. 1 ;  
         [0011]      FIG. 3A  is a schematic circuit diagram of a safety mechanism according to the present invention as used in conjunction with an inductive angular sensor;  
         [0012]      FIG. 3B  is an alternative switch arrangement for use in the safety mechanism shown in  FIG. 3A ;  
         [0013]      FIG. 4A  shows a front view of a position detecting mechanism of an inductive angular sensor according to a further preferred embodiment of the present invention;  
         [0014]      FIG. 4B  is a side view of the position detecting mechanism shown in  FIG. 4A ;  
         [0015]      FIG. 4C  is a partial schematic circuit diagram of the position detecting mechanism shown in  FIG. 4A ;  
         [0016]      FIG. 4D  shows a front view of an alternative arrangement of a position detecting mechanism of an inductive angular sensor according to a yet further preferred embodiment of the present invention; and  
         [0017]      FIG. 4E  is a side view of the position detecting mechanism shown in  FIG. 4D . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]     An inductive angular sensor according to a first preferred embodiment of the present invention is shown in  FIG. 1 , and generally designated as  100 . A spindle  102 , which is attached to a device (not shown) the angle of which is to be measured, is fixedly secured with a rotor  104 . The rotor  104  supports two arcuate metal wires  106   a,    106   b,  each on one side thereof, for simultaneous swivelling movement about the longitudinal axis of the spindle  102 . It should be understood that the invention may also work with a rotor with only one arcuate wire, e.g. in which the lower ends of the wires  106   a,    106   b  are joined with each other.  
         [0019]     The metal wires  106   a,    106   b  should preferably be made of a metal of a high magnetic permeability and low permanence, e.g. soft iron or silicon iron. With a high magnetic permeability, a high magnetic flux will be generated by only a small relative movement, thus enhancing the sensitivity of the sensor. Permanence is also called coercivity. A permanent magnet has a high permanence as magnetism is retained effectively, whereas a soft iron has a low permanence.  
         [0020]     A primary magnetic coil  108   a  and two secondary magnetic coils  108   b,    108   c  are arranged as a Linear Voltage Differential Transformer, in which the primary coil  108   a  is positioned between the two secondary coils  108   b,    108   c.  An arcuate channel  110 , which is of essentially the same radius of curvature as the iron wires  106   a,    106   b,  runs through the three magnetic coils  108   a,    108   b,    108   c.  As the spindle  102  swivels about its longitudinal axis, the iron wires  106   a,    106   b  will swivel, thus reciprocate, within the channel  110 , and thus within and relative to the coils  108   a,    108   b,    108   c.  In the “zero position”, as shown in  FIG. 1 , the centre line S-S of the primary coil  108   a  is aligned with the centre line T-T of the rotor  104 . However, as the rotor  104  rotates relative to the coils  108   a,    108   b,    108   c,  the angle of rotation (i.e. the angle between the lines S-S and T-T) will vary. It should also noted that when in the “zero position” as shown in  FIG. 1 , or when the angle of rotation is within a narrow range about this zero position, the wires  106   a,    106   b  are positioned within the two secondary coils  108   b,    108   c,  but out of the primary coil  108   a.    
         [0021]     As the primary coil  108   a,  also called “exciting coil”, is energized by a sinusoidal oscillator, to be discussed below, the secondary coils  108   b,    108   c,  also called “detecting coils”, act as detectors. The primary coil  108   a,  so energized, will generate magnetic fluxes which are detected by the secondary coils  108   b,    108   c.  When the spindle  102  swivels, which will bring about simultaneous swivelling movement of the rotor  104  and the wires  106   a,    106   b  carried by it, the fluxes coupled to the secondary coils  108   b,    108   c  will increase or decrease, in which the outputs from the secondary coils  108   b,    108   c  will be proportional to the angle of rotation of the wires  106   a,    106   b  (and thus the rotor  104 ) relative to the coils  108   a,    108   b,    108   c.    
         [0022]     Referring now to  FIG. 2 , a sinusoidal oscillator  112  energizes the primary coil  108   a  to generate corresponding sinusoidal magnetic fluxes, which are detected by the secondary coils  108   b,    108   c.  The signals from the secondary coils  108   b,    108   c  are respectively amplified by an amplifier  114 ,  116 . Signals from the coil  108   b  will generate a positive voltage, through rectification by a diode  118 , whereas signals from the coil  108   c  will generate a negative voltage, through rectification by a diode  120 . The two voltages will then be summed up, by resistors  122 ,  124  and an amplifier  126 , as V out , which is proportion to the angle of rotation of the wires  106   a,    106   b  (and thus the rotor  104 ) relative to the stationary coils  108   a,    108   b,    108   c.  A resistor  130  is also provided between the resistor  122  and the output of the amplifier  126 .  
         [0023]     It can be seen that the use of two iron wires in a rotary voltage detector transformer simplifies the construction of the sensor. It is found in practice that, as compared with conventional arrangement, it is easier to assemble the wires  106   a,    106   b  in the sensor. In addition, the use of operational amplifiers eliminates the necessity of using a phase detector circuit, as in the conventional design.  
         [0024]     In devices such as electrical wheelchairs for disabled persons, it is important that any defects in the circuitry will not affect the zero position output. According to a further preferred embodiment of this invention, an inductive angular sensor with a safety mechanism is provided. It should be understood that a safety mechanism according to the present invention may be incorporated in various types of contactless potentiometers or rotary sensors, including, but not limited to, inductive angular sensors and optical sensors, although it will henceforth be explained in the context of an inductive angular sensor. As shown in  FIG. 3A , the output signals from the detecting coils are inputted to an Angular Sensor Electronics  150 , e.g. the inductive angular sensor  100  discussed above, where such are processed to produce an output which is proportional to the angular position of the rotor  104  relative to the coils  108   a,    108   b,    108   c.    
         [0025]     The coil signals are also fed into a Zero Position Detector  152 . When the wires  106   a,    106   b  are in the centre position, i.e. as shown in  FIG. 1 , the differential signals will be or very close to zero. The circuit of the Zero Position Detector  152  is designed to have a logic level output when the wires  106   a,    106   b  are within a small angle, called the “dead zone”, around the centre position. The Angular Sensor Electronics  150  may be designed to output linear signals only when the dead zone angle is exceeded.  
         [0026]     The output from the Zero Position Detector  152  is used for controlling a switch  154 , so that at the zero dead zone, the switch  154  is at position B. The output (now shown at  162 ) would be connected to the centre of a fixed resistor  156 , and divided substantially equally for output by two resistor terminals  158 ,  160  respectively. On the other hand, when the sensor  100  rotates outside of the dead zone, the switch  154  will be switched to position A, in which case its position can be controlled by the Angular Sensor Electronics  150 . Thus, if either of the Angular Sensor Electronics  150  or the Zero Position Detector  152  is defective, the output will still be safe at the mid position. Since the chance of both the Angular Sensor Electronics  150  and the Zero Position Detector  152  failing at the same time is small, the control is very safe and reliable.  
         [0027]     The switch  154  shown in  FIG. 3A  is a mechanical single pole double throw relay. In practice, although a mechanical relay is a relatively simple arrangement, such is of a limited life time. The switch may alternatively be constructed of electro-magnetically controlled reed switches. Reed switches may be used in applications where a higher voltage and a low contact resistance are required. While reed switches are more reliable than mechanical relays, it is believed that electronic switches offer the highest reliability.  
         [0028]     A construction of an electronic switch which may be used in the present application, in place of the switch  154 , is shown in  FIG. 3B . As shown in  FIG. 3B , control signals from the Zero Position Detector  152  are used for controlling electronic switches SW 1  and SW 2 . SW 1  should “make” when SW 2  “breaks”, and vice versa. To achieve this result, a logic Inverter  170  is connected with and upstream of SW 2 . The switches SW 1  and SW 2  can be constructed of simple transistors or FETs. With common design practice, it is possible to use just one or two transistors or FETs for each switch, and reliability can be ensured.  
         [0029]     A further safety arrangement, in particular an infrared centre position detector, is shown in  FIGS. 4A  to  4 C. Two infrared light emitting diodes (IR LEDs)  202   a,    202   b  are arranged one above the other on a first side of the rotor  204 , and two phototransistors  206   a,    206   b  are arranged, again one above the other, on a second side of the rotor  204 . In the absence of any intervening obstacles, the phototransistor  206   a  can detect infrared transmission from the IR LED  202   a,  and the phototransistor  206   b  can detect infrared transmission from the IR LED  202   b.  As shown in  FIG. 4C , the signals from the phototransistors  206   a,    206   b  are fed to the Zero Position Detector  152  (discussed above), whose output is used for controlling the switch  154 , or the electronic switch shown in  FIG. 3B , as discussed above.  
         [0030]     The rotor  204  is in the shape of a sector and has an arcuate hollow slot  210  and a cut-out portion  212 . When the rotor  204  is in the position as shown in  FIG. 4A , or within the small dead zone angle α, infrared transmission between the IR LED  202   a  and the phototransistor  206   a,  and between the IR LED  202   b  and the phototransistor  206   b  will be blocked by the rotor  204 , thus signalling a centre position.  
         [0031]     When the rotor  204  rotates clockwise, i.e. in the direction indicated by the arrow P, while infrared transmission between the IR LED  202   a  and the phototransistor  206   a  will still be blocked, the cut-out portion  212  will allow infrared transmission emitted by the IR LED  202   b  to be detected by the phototransistor  206   b.  On the other hand, when the rotor  204  rotates anti-clockwise, i.e. in the direction indicated by the arrow Q, infrared transmission between the IR LED  202   b  and the phototransistor  206   b  will be blocked, whereas the hollow slot  210  will allow infrared transmission emitted by the IR LED  202   a  to be detected by the phototransistor  206   a.    
         [0032]     By way of such an arrangement, it is not only possible to determine the angular position of the rotor  204 , and thus a shaft  220  to which it is secured, but also possible to detect whether the rotation is in the clockwise or the anti-clockwise direction. Such an arrangement can thus differentiate between a forward or a rearward motion, which may be important in the safe operation of an electrical wheelchair.  
         [0033]     As an alternative to the arrangement shown in  FIGS. 4A and 4B , and as shown in  FIGS. 4D and 4E , two infrared light emitting diodes (IR LEDs)  252   a,    252   b  are arranged next to each other on a first side of a rotor  254 , and two phototransistors  256   a,    256   b  are arranged, again next to each other, on a second side of the rotor  254 . In the absence of any intervening obstacles, the phototransistor  256   a  can detect infrared transmission from the IR LED  252   a,  and the phototransistor  256   b  can detect infrared transmission from the IR LED  252   b.  As in the arrangement shown in  FIG. 4C , the signals from the phototransistors  256   a,    256   b  are fed to the Zero Position Detector  152  (discussed above), whose output is used for controlling the switch  154 , as discussed above.  
         [0034]     When the rotor  254  is within the small dead zone angle, infrared transmission between the IR LED  252   a  and the phototransistor  256   a,  and between the IR LED  252   b  and the phototransistor  256   b  will be blocked by the rotor  254 , thus signalling a centre position.  
         [0035]     When the rotor  254  rotates clockwise, i.e. in the direction indicated by the arrow G, while infrared transmission between the IR LED  252   b  and the phototransistor  256   b  will still be blocked, infrared transmission emitted by the IR LED  252   a  can be detected by the phototransistor  256   a.  On the other hand, when the rotor  254  rotates anti-clockwise, i.e. in the direction indicated by the arrow H, infrared transmission between the IR LED  252   a  and the phototransistor  256   a  will be blocked, whereas infrared transmission emitted by the IR LED  252   b  can be detected by the phototransistor  256   b.    
         [0036]     It should be understood that the above only illustrates examples whereby the present invention may be carried out, and that various modifications and/or alterations may be made thereto without departing from the spirit of the invention.  
         [0037]     It should also be understood that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any appropriate sub-combinations.