On December 26, the US Patent & Trademark Office published Apple’s newly granted patent for ‘Hybrid low power computer mouse.’ Apple’s invention relates generally to a low powered mouse. More specifically, the invention describes an ultra low power computer mouse having an optical tracking engine and inertial tracking engine that cooperate to provide velocity data to a computing device.
Apple’s Summary
The invention described herein pertains to a wireless low power tracking device and methods of use thereof. In one embodiment, a method for operating a pointing device in a low power manner is described. The method includes receiving first tracking information from a first tracking device and periodically determining accuracy of the first tracking information. A second tracking device is activated and used to acquire second tracking information when said determining indicates that the accuracy of the first tracking information is inadequate. The first tracking device is substantially lower power device than the second tracking device.
In another embodiment, a hybrid tracking system suitably arranged to provide tracking information to a computer is described. The system includes an optical tracking engine arranged to provide the tracking information to the computer, a low power inertial tracking engine arranged to provide the tracking information to the computer, and an adaptive duty cycle signal generator coupled to the optical tracking engine and the inertial tracking engine. In the described embodiment, the adaptive duty cycle generator is arranged to compare tracking information provided by the accelerometer and provided by the optical tracking engine. When the comparison is valid, the adaptive duty cycle signal generator provides a first duty cycle signal that deactivates the optical tracking engine such that only the low power tracking engine provides the tracking information to the computer.
In yet another embodiment, computer program product for operating a pointing device in a low power manner is described that includes computer code for receiving first tracking information from a first tracking device, computer code for periodically determining accuracy of the first tracking information, computer code for activating and using a second tracking device to acquire second tracking information when said determining indicates that the accuracy of the first tracking information is inadequate, wherein the first tracking device is substantially lower power device that the second tracking device. The computer code is then stored in a computer readable medium.
A Few Detail Extracts
Although typical accelerometers are low power, they are susceptible to large tracking errors due to drift and other sources of error due to, for example, surface irregularities. Such tracking errors can be substantial after a fairly short length of time (approximately 0.5 seconds in some cases) thereby limiting the usefulness of an inertial tracking engine based computer mouse. On the other hand, low power optical tracking engines (such as, for example, the Agilent 2030) have difficulty compensating for high acceleration therefore limiting their usefulness to low acceleration (typically on the order of 0.15 G) situations.
Attempts to implement a low power computer mouse using only a low power optical tracking engine are not practicable due to the large tracking errors introduced when the computer mouse is accelerated much beyond 0.15 G as well as low power being only “lower power” that still substantially reduces on-board battery life. This extremely small range of acceptable acceleration can be appreciated when normal hand motions can induce accelerations on the order to 3 G. On the other hand, attempting to implement a low power computer mouse using a conventional accelerometer is also impractical due to the large induced tracking errors after only a short time of use especially in low acceleration cases where the signal to noise (S/N) ratios can be quite low.
The inventive computer mouse solves these problems by combining both an optical tracking engine and an accelerometer into a hybrid low power computer mouse having low power consumption requirements and long battery life. Accordingly, in a particularly useful implementation, a wireless computer mouse having an accelerometer and an optical tracking engine cooperate with each other to provide the tracking information to a computer is described. In the described embodiment, the optical tracking engine is inactive while the accelerometer is always active so as to provide continuous dead reckoning tracking information. The dead reckoning tracking information is periodically calibrated using optical tracking information provided by the now activated optical tracking engine.
For those periods of time that a dead reckoning tracking error measurement (being a difference between the dead reckoning tracking information and the optical tracking information) is greater than a pre-determined threshold, the optical tracking engine remains active to provide the optical tracking information to the computer. During these periods of time, an accumulated error value is calculated based upon a comparison of the optical tracking information and the dead reckoning tracking information that is used to reset an offset value associated with the accelerometer. By resetting the offset value, the overall accumulated error between the inertial tracking engine and the optical tracking engine is reduced.
At any time, a surface sensor monitors a surface pressure and/or a surface quality to determine whether or not the computer mouse is in contact with a suitable surface. In those situations where the computer mouse in not in contact with a suitable surface, both the accelerometer and the optical tracking engine are deactivated until such time as the sensor has determined that the computer mouse has been placed back on a suitable surface. It is contemplated that the surface sensor can be either a mechanical type sensor, an electro-mechanical type sensor, or an optical type sensor any of which would be well suited for use with the computer mouse described herein.
The invention will now be described in terms of a representative wireless computer mouse that should not be construed to limit either the scope or intent of the invention. It should be noted as well that the invention, although described in terms of a computer mouse, can be well adapted to any input device for providing any form of absolute or relative tracking information to a computing device.
Accordingly, FIG. 1 shows a representative computer mouse 100 in accordance with an embodiment of the invention. The mouse 100 includes an optical tracking engine 102 and an accelerometer 104 each of which is coupled to a microcontroller unit 106. It should be noted that the accelerometer 104 and the optical tracking engine 102 can be of any appropriate type and/or manufacture. For example, the Agilent 2030 can be used for the optical tracking engine 102 whereas the Analog Devices ADXC202 manufactured by Agilent Inc. of can be used for the accelerometer. In the described embodiment, the microcontroller unit 106 is connected to or has incorporated therein, a wireless transmitter unit 108. It should be noted that although the wireless transmitter unit 108 is configured as a Bluetooth based radio transmitter unit, any appropriate wireless transmitter can be used.
About the Microcontroller
FIG. 2 shows a functional block diagram of a representative microcontroller 200 suitable for use in the computer mouse 100 in accordance with an embodiment of the invention. It should be noted that the microcontroller 200 is merely an example of any of a number of possible implementations that could be used for the computer mouse 100 and should not be construed as limiting either the intent or scope of the invention. Accordingly, the microcontroller 200 includes a dead reckoning tracking error generator 202 coupled to the optical tracking engine 102 and an integrator 204 arranged to receive output data directly from the accelerometer 104 (as acceleration data).
As mentioned above, since the accelerometer 104 directly generates acceleration data, the acceleration data must be integrated to acceleration velocity data (i.e., dead reckoning tracking information) in order to be compared the velocity data provided by the optical tracking engine 102 (i.e., optical tracking information). Therefore, once the acceleration data has been appropriately integrated to form the dead reckoning tracking information, the dead reckoning tracking information error generator 202 determines the dead reckoning tracking information error E by comparing the optical tracking information provided by the optical tracking engine 102 and the dead reckoning tracking information provided the by accelerometer 104 (by way of the integrator 204) for each of a number of time intervals. In the case where the dead reckoning tracking information error E is less than a pre-determined threshold E.sub.threshold, the dead reckoning tracking error generator 202 adjusts the duty cycle signal S to deactivate the optical tracking engine 102 such that the only source of tracking information provided to the computer 112 is from the accelerometer 104. By de-activating the optical tracking engine 102, the overall power consumption of the computer mouse 100 is greatly reduced thereby providing a commensurate increase in probable battery life for battery powered computer mice.
However, in those cases where the dead reckoning tracking error E is greater than the threshold E.sub.threshold, then the dead reckoning tracking error generator 202 adjusts the duty cycle signal S to activate the optical tracking engine 102 in such a way that the only source of tracking information to the computer 112 is that provided by the optical tracking engine 102. In this mode, however, at each time interval, the dead reckoning tracking error generator 202 compares the optical tracking datum to an associated dead reckoning tracking datum in order to ascertain a corresponding dead reckoning tracking information error E for each interval to form the accumulated tracking error discussed above that is used to update the accelerometer offset value G in order to reduce accumulated positional error of the cursor 114.
Operational Cycle
FIG. 3 is a graphical illustration of a representative operational cycle 300 of the computer mouse 100 in accordance with an embodiment of the invention. For ease of discussion, the cycle 300 is illustrated using an XY graph having an X axis representing a time dimension (t) and a Y axis representing Velocity (V). For the remainder of this discussion, both the dead reckoning tracking information and the optical tracking information will be described in terms of accelerometer velocity Vacc and optical velocity Vopt.
Therefore, at an initial time interval, the optical tracking engine 102 is active and provides the optical velocity Vopt1 while the accelerometer 104 and integrator 204 provides the accelerometer velocity Vacc1. It should be noted that this initial time interval is representative of those situations where the computer mouse 100 is restarting from a stopped or otherwise inactive state. Such states can be due to the mouse 100 being powered up for the first time, being replaced upon a suitable surface after having been lifted off the surface, etc. Therefore, in order to provide an initial calibration point, the optical tracking engine 102 is activated. The initial calibration point (in this case, Vopt1) is used to compare to the accelerometer velocity Vacc1 and based upon this comparison, the optical tracking engine 102 is either de-activated (as in this example) or remains active.
In order to maintain close correlation between the accelerometer 104 and the optical tracking engine 102, a calibration operation is performed at regular intervals, referred to as a calibration interval. A typical calibration interval is approximately 80 ms during which the accelerometer 104 is calibrated against the optical tracking engine 102. In the situation shown in FIG. 3, the initial calibration indicates that the accelerometer 104 and the optical tracking engine 102 produce velocity values that are within an acceptable range. Accordingly, the computer mouse 100 is in the hybrid mode where the optical tracking engine 102 is deactivated and the accelerometer 104 is sending the appropriate tracking information to the computer 112. At a next calibration point C1, the optical tracking engine 102 is activated just prior to the calibration point C1 (in order for the optical tracking engine 102 to produce valid velocity data). A calibration check between the accelerometer 104 and the optical tracking engine 102 indicates a difference in the two velocities of such a magnitude that the optical tracking engine 102 takes over sending the tracking information to the computer 112 in place of the accelerometer 104. It should be noted, however, that for each of a number of intervals, a comparison between the accelerometer 104 and the optical tracking engine 102 is performed until such time as the measured error between the two velocities is deemed acceptable. Once the error is deemed acceptable, the computer mouse 100 is returned to hybrid mode by deactivating the optical tracking engine 102 such that the accelerometer 104 only provides the tracking information to the computer 112.
Apple lists the inventors of this patent as being Steve Hotelling, Joshua Strickon, Brian Huppi and Christoph Krah.
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Written and researched by Neo.
