Pointing stick device

1. Field of Invention

The present invention relates to a method and apparatus of pointing stick device, and more particularly to a method and apparatus of pointing stick device using in compact electronics devices with reduced cost.

2. Description of Related Arts

A pointing stick device is first used in laptop computer for controlling the movement and position of the cursor. Most of pointing stick devices is also known as isometric joysticks because they are operated by sensing applied forces through two or more pairs of resistive strain gauges. Generally a pointing stick device includes a cantilever, and two pairs of strain gauges coupled with the cantilever. When the cantilever is exerted with force and generates deformation, the strain gauges will sense it and generate electronic signal. Then this signal can be used to control other devices such as a cursor.

The advantage of a pointing stick device is it can be operated by one finger, and this finger doesn't need to be moved away from the pointing stick. But in order to sense the force exerted by the finger which is normally very weak, the pointing stick device needs to be very sensitive. For this reason, the tolerance of the components is very low. For example, the current available products highly depend on accurate voltage sources cooperating with resistors as power resource and reference voltage. The current source is conveniently provided by many integrated chips such as micro controller unit (MCU), and is programmable. Doesn't like current source, voltage source needs extra separate to provide particular voltage level, and the voltage level is not adjustable. The precision is anther important issue. For acceptable performance, the precision of the sensors (strain gauges) is requested to be less than 2˜3% which is expensive. This increases the cost, part count, and device space.

Device space is always highly considered in compact electronic equipment. The more external components are used, the more space is taken. Current products are using more than 30 external components which have a large edge to reduce. Another issue of compact electronic equipment is radio frequency noise. As the dimension of the circuit is getting smaller and smaller, electric magnetic interference, such as cell phone signal, is much easier to be introduced. The effect is magnificent especially for sensitive devices. The common solution is using different kinds of filters. But it is obvious that using filters will increase the cost, and make the system more complex. Besides these considerations, there is always an attempt for the device to perform faster and more accurate. Therefore, both the circuit and the operation process are necessary to be improved for a better performance.

A main object of the present invention is to provide a pointing stick device circuit which reduces the cost.

Another object of the present invention is to provide a pointing stick device circuit with reduced discrete components.

Another object of the present invention is to lower the requirement of the quality and precision of the components used in the pointing stick device.

Another object of the present invention is to provide a pointing stick device reducing the radio frequency disturbing.

Another object of the present invention is to provide a method of pointing stick device to improve the performance.

Accordingly, in order to accomplish the above objects, the present invention provides a pointing stick device circuit, comprising:

a signal source element which comprises a plurality of strain gauges for sensing forces exerted onto the pointing stick and generating voltage signals;

a voltage approaching element providing an incremental voltage for comparing with the voltage signal generated by the signal source, wherein the voltage approaching element further comprises a first approaching unit and a second approaching unit; and

a signal process element counting the time for the incremental voltage to approach the level of the voltage signals and calculating the forces exerted onto the pointing stick.

Moreover, the present invention also provides a method of a pointing stick device for sensing the force exerted whereon, comprising the steps of:

(a) resetting a circuit of said pointing stick device;

(b) sampling a signal source from said circuit;

(c) increasing an incremental voltage via a first approaching unit to a predetermined voltage level;

(d) linearly increasing said incremental voltage via a second approaching unit at a predetermined linear incremental rate;

(e) comparing said voltage signal of said sampled signal source with said incremental voltage from said second approaching unit; and

(f) determining a time for said incremental voltage in responsive to said incremental rate thereof for calculating said force exerted onto said pointing stick device.

These and other objectives, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.

FIG. 1 is a circuit diagram of the pointing stick device according to the present invention.

FIG. 2 is a flow chart of the method of a pointing stick device for sensing the exerted force.

FIG. 3 is a circuit diagram of an alternative embodiment of the present invention.

FIG. 4 is a circuit diagram of another alternative embodiment of the present invention.

FIG. 5 is a schematic diagram of the integrated circuit.

Referring to FIG. 1 of the drawings according to the present invention, a pointing stick device comprises a signal source element 100 , a voltage approaching element 200 , and a signal process element 300 . The signal source element 100 comprises three sensors sensing the forces exerted on the x, y, and z axes respectively. As in FIG. 1 , the strain gauges R 1 and R 2 are coupled in serial for sensing the x axis, the strain gauges R 3 and R 4 are couple in serial for sensing the y axis. The R 1 , R 2 , and the R 3 , R 4 are coupled in parallel and then are connected with the resistor R 5 in serial for sensing the z axis. These voltage division circuits can tell the change of the resistance of the strain gauges which is caused by force exerted on the pointing stick device. The change of the voltage signals is generally in milli-volt level. The three signals are input into an analog multiplexer 110 . The analog multiplexer 110 can select one signal once to pass through for further processing. The output of the analog multiplexer 110 is controlled by a switch SW 1 to be connected with the next element.

Referring to FIG. 1 , in a preferred embodiment of the present invention, the output of the multiplexer is connected with a sampling capacitor C 1 . The other electrode of the sampling capacitor C 1 is connected with ground. So when one voltage signal is selected to pass through the multiplexer and the switch SW 1 is closed, the voltage signal will charge the sampling capacitor C 1 until the voltage level is the same as the voltage signal. Then the signal is sampled by the sampling capacitor C 1 . The electrode of the sampling capacitor C 1 is also connected with ground through a switch SW 2 . When the switch SW 2 is closed, the sampling capacitor C 1 will be discharged.

The voltage approaching element 200 includes a first approaching unit 210 , a second approaching unit 220 , and a voltage division circuit 230 . Referring to FIG. 1 , in a preferred embodiment, the first and second approaching units are charged by two current sources to approach to the voltage level of the signal. It is worth to mention, since the two current sources are used respectively, referring to FIG. 5 , in a real circuit, they can be shared through one analog multiplexer. It is because the current source is programmable to provide different value. In this manner, some elements are saved.

The first approaching unit comprises a first approaching capacitor C 2 . One electrode of the first approaching capacitor C 2 is connected with the ground through a switch SW 6 . The other electrode of the first approaching capacitor C 2 is connected with a first current source through a switch SW 4 . When the switch SW 4 is closed in a predetermined period of time, the capacitor will be charge to a predetermine voltage level. This voltage level is close but lower than the voltage level of the signals. This electrode is also connected with ground through a switch SW 7 for discharging when the switch SW 7 is closed.

The second approaching unit comprises a second approaching capacitor C 3 . One electrode of the second approaching capacitor C 3 is connected with the ground. The other electrode of the second approaching capacitor C 3 is connected with a second current source through a switch SW 3 . When the switch SW 3 is closed, the second approaching capacitor C 3 is being charged, and the voltage of the capacitor is lift linearly with a predetermined rate.

The voltage division circuit comprises three resistors R 8 , R 9 , and R 10 , and a reference voltage. The three resistors are connected in one junction and then further connected with one electrode of the first approaching capacitor. Resistor R 9 is also connected with the reference voltage. The resistor R 10 is also connected with ground. The resistor R 8 is also connected with one electrode of the second approaching capacitor C 3 . The voltage division circuit is arranged in such a manner that when the switch SW 5 is closed and switch SW 6 is open, the voltage division circuit will lift the voltage of the first approaching capacitor C 3 close to the signal sample in the sampling capacitor C 1 and slightly lower. When both of the switches SW 5 and SW 6 are open, the voltage of the second approaching capacitor C 3 is added to the first approaching capacitor C 2 as the voltage output of the voltage approaching element 200 , and this voltage will be increased linearly as well as the second approaching capacitor C 3 .

The signal process element 300 comprises a comparator 310 , a logic gate 320 , and a counter 330 . Referring to FIG. 1 , in the preferred embodiment of the present invention, the voltage output of the sampling capacitor C 1 is connected with the non-inverting input (V+) of the comparator; the voltage output of the voltage approaching element 200 is connected with the inverting input (V−) of the comparator. The logic gate is an AND gate. One input of the logic gate is connected with the output of the comparator; the other input of the logic gate is connected with a control signal. The output of the logic gate is connected with the counter. When the output of the comparator is high, and the control signal is high at the same time, the output of the logic gate is high. The counter can count the time during the output of the logic gate is high.

FIG. 3 is a circuit diagram of an alternative embodiment of the present invention. In this embodiment, a referent voltage is connected with the non-inverting input (V+) of the comparator. The output of the analog multiplexer is directly coupled with the output of the voltage approaching element. The signal voltage is added with the voltage output of the voltage approaching element and input into the inverting input (V−) of the comparator. In this way, the counter counts the time for the sum of the voltage output of the signal source element and the voltage approaching element to approach the referent voltage. The value of the voltage signal can still be calculated. The force exerted on the pointing stick device can be known.

In this present invention, the current source can be replaced by a voltage source coupled with a resistor. FIG. 4 is a circuit diagram of an alternative embodiment of the present invention. In this embodiment, the first current source is replaced by a voltage source coupled with a resistor. The second current source is also replaced by a voltage source coupled with a resistor. In this embodiment, the present invention can also use voltage source and resistor to provide charging current, but this circuit needs more extra components, and the tolerance of some components is much smaller.

Referring to FIG. 2 , the pointing stick device is working in this process:

At first the device is set in idle state. The current sources and the voltage sources are disconnected. The switches SW 3 and SW 4 are open; the switches SW 1 , SW 2 , SW 5 , SW 6 and SW 7 are closed to discharge the capacitors. The counter is reset. The control signal is set to low. Connect the voltage source with the signal source element 100 . The sensors (strain gauges) are sensing the forces and transform into voltage signals. These signals include signals of x, y, and z axes respectively. The analog multiplexer 110 then selects one signal to pass through and the switch SW 2 is open. Each time only one signal is selected. As the switch SW 1 is closed and switch SW 2 is open, the sampling capacitor C 1 is charged by the voltage signal. In a predetermined period of time the voltage of the sampling capacitor C 1 is the same as the voltage signal. Then the switch SW 1 is opened.

After the voltage signal is sampled, the switch SW 7 is opened and the switch SW 4 is closed for a predetermined period of time. The first current source is then connected with the first approaching capacitor C 2 and charges the capacitor C 2 to an expected level. Then the switches SW 4 and SW 6 are open, and the reference voltage is connected with the voltage division circuit. As a result the voltage of the voltage approaching element 200 is lifted close to the voltage signal but a slightly lower as determined. This is the step of coarse approaching.

At this moment, the output of the voltage approaching element 200 is lower than the output of the signal source element 100 , the output of the comparator is high. Set the control signal to high, the output of the logic gate is high, and the counter starts to count. At the same time, the switch SW 5 is open, and the switch SW 3 is closed. The second current source is connected with the second approaching capacitor C 3 and starts to charge the second approaching capacitor C 3 linearly. The voltage of the second approaching capacitor C 3 is added to the voltage output of the voltage approaching element 200 through the voltage division circuit. So the voltage output of the voltage approaching element 200 is increasing linearly to approach the voltage signal.

When the voltage output of the voltage approaching element 200 is equal to the output of the signal voltage source element, the output of the comparator turns to low, then the counter stops counting. The counted time is then used to calculate the value of the voltage signal. Consequently, the force exerted on the pointing stick device is known. The results are sent to the next processor for further processing.

In the next loop, another signal will be selected to be sensed with the same process. So the three signals can be sensed in a predetermined sequence.

In summary, the present invention provides a pointing stick device circuit which is using fewer components. The circuit is using current sources instead of voltage sources. In order to change the voltage level of a voltage source, the arrangement of the resistors has to be changed. Current source is programmable, the output level doesn't rely on any resistors. Since the output of a current source can be easily changed, one current source is able to be shared. This will be more convenient to integrate the circuit and largely reduce the cost. FIG. 5 illustrates an integrated chip with limited discrete elements to perform the function. Also, using this circuit and the relative process, the requirement of high quality and low tolerance of some critical components is reduced. The performance of the device is improved.

It is worth mentioning, in this design, the requirement of high quality and low tolerance of some critical components is reduced. Referring to FIG. 1 , in order to accurately measure the force, the tolerance of the strain gauges is requested to be less than 2% in prior art. The tolerance of the strain gauges can be larger than 10%. In the present invention, because the first approaching unit does the coarse approaching and can adjust the error introduced by the inaccuracy of the resistors, the tolerance of the strain gauges can be allowed to 20%. In this circumstance, low cost components can be selected without affecting the same performance of the device.

One skilled in the art will understand that the embodiment of the present invention as shown in the drawings and described above is exemplary only and not intended to be limiting.

It will thus be seen that the objects of the present invention have been fully and effectively accomplished. It embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the present invention and is subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.