Circuit for estimating position and orientation of a mobile object

[0001] This application claims the benefit under 35 U.S.C. § 119(e) of U.S. provisional applications No. 60/557,252, filed Mar. 29, 2004 and No. 60/602,239, filed Aug. 16, 2004, the entirety of which is hereby incorporated by reference.

[0002] Appendix A, which forms a part of this disclosure, is a list of commonly owned co-pending U.S. patent applications. Each one of the co-pending applications listed in Appendix A is hereby incorporated herein in its entirety by reference thereto.

[0003] The present invention relates generally to a system for estimating position and/or orientation of an object, and more particularly to a circuit for estimating position and/or orientation of a mobile object with respect to a local coordinate systems, such as a mobile autonomous processor unit, or an autonomous robot.

[0004] A circuit system for estimating position and orientation of a mobile object based on lights from a plurality of external light sources. The circuit comprises a position-sensitive light sensor for detecting the light sources and generating a first signal, an analog filter and amplification module (“AFA”) for filtering and amplifying the first signal and generating a second signal, a digital signal processor (“DSP”) for generating a coordinate system by extracting frequency components from the second signal.

[0005] In one embodiment, the AFA has a transimpedance amplifier (“TIA”) for amplifying the first signal from the position-sensitive light sensor, a first passive high-pass filter (“1^st PHP”) for removing DC bias from the output of the TIA, a passive notch filter (“PNF”) for removing noise signals within a predetermined range of frequencies from the 1^st PHP output, a second passive high-pass filter (“2^nd PHP”) for removing DC bias from the PNF output, a gain amplifier for amplifying the 2^nd PHP output, and a passive low-pass filter (“PLP”) for removing signals above a predetermined frequency from the gain amplifier output.

[0006] The embodiment further has a first buffer, coupled between the 1^st PHP and the PNF, for reducing undesirable interaction due to different frequency response characteristics between the 1^st PHP and the PNF, and a second buffer, coupled between the PNF and the 2^nd PHP, for reducing undesirable interaction due to different frequency response characteristics between said PNF and said 2^nd PHP.

[0010] A circuit for estimating position and orientation for a mobile object is disclosed. The overall and general methods and apparatus for position estimation using reflected light sources have been disclosed in the now-incorporated co-pending patent applications. The description that follows will elaborate on the circuit embodiments for the detection and processing of the images of the light sources in order to estimate the position and orientation of the mobile object.

[0011] Reference is first to FIG. 1, where a simplified block diagram of an exemplary circuit embodiment 10 in accordance with the present invention is shown. The circuit embodiment 10 may be implemented on a printed-circuit board (“PCB”) 15, or integrated into an application-specific integrated circuit (“ASIC”). The light is modulated at different frequencies and detected by the sensor 110 through the optics 100. It should be noted that as disclosed in the co-pending applications, the light may be generated from a variety of optical emitters, including without limitation visible light devices, invisible light devices, laser light devices, infrared light devices, polarized light devices, light-emitting diodes, laser diodes, light bulbs, halogen lights projectors and the like.

[0012] Through the optics 100, the sensor 110 detects the positions of the light spots from at least two light sources 102, 104, when the application is to determine 2-D position and orientation. The sensor 110 may be a position-sensitive detector (“PSD”), a segmented photo diode (“PD”), or an imager such as a CMOS imager. The sensor 110 is preferably a quad segmented photo diode (“PD”), e.g. Model No. S5980 from Hamamatsu Photonics, K. K. of Hamamatsu, Japan, with a web site at www.hamamatsu.com. The segmented PD may be acquired from UDT Sensors, Inc., of Hawthorne, Calif., with a web site at www.udt.com. As can be appreciated by those skilled in the art, a PSD is an optoelectronic position-sensitive light sensor utilizing photodiode surface resistance. Unlike discrete element detectors such as a CCD (“charge-coupled device”), a PSD provides continuous position data (X or Y coordinate data) and achieves high position resolution and high-speed response. The sensor 110 generates three or four (depending on the embodiment) signal currents, I_x, representative of the (X, Y) coordinate data of the light spots from the light sources 102, 104. In the case of the segmented PD, any number greater than one could be used. With two (2) segments, the user could tell in a single coordinate, e.g. X. With three (3) or more segments, X and Y coordinates could be produced.

[0013] The signal currents from the sensor 110 are then applied to the analog filter and amplification module (“AFA”) 120 in order to filter out the ambient noise, the source of which can be various kinds of non-signal lights, e.g. incandescent light or fluorescent light. Since the signal currents from the sensor 110 are typically on the order of 1 nA, they are also amplified by the AFA 120 before the signals can be further processed. The AFA 120 will be further described with reference to FIG. 2 below.

[0014] The output signals from the AFA 120 are voltages, V_x, which are typically on the order of ±100 mV. The voltages are first converted into digital format through an analog-to-digital converter and then applied to the DSP 130 for processing. The analog-to-digital converter 280, as can be appreciated by those skilled in the art, may be implemented either external to, or as part of, the DSP 130.

[0015] The DSP 130, upon receiving the digital signals, operates a transformation algorithm, such as the well-known Fast Fourier Transform (“FFT”), Discrete Fourier Transform (“DFT”) or the Goertzel algorithm, in order to extract the frequency components of the received signals. The Goertzel algorithm is preferred in the current embodiment, since it consumes fewer CPU resources than the continuous real-time FFTs in situations where only a few frequencies are to be detected. Using the magnitudes frequency components, the DSP 130 can calculate where the light spots hit the PSD sensor 110. Upon continuous calculation, e.g. at around 10 times per second, a global coordinate system can be developed based on the x, y positions of the light spots. With this global coordination system, the position and orientation, relative to the light sources 102, 104 of the mobile object on which the sensor 110 is positioned can be determined on a continuous basis. Such information can be used to provide navigation and guidance to an exemplary mobile object, such as an autonomous mobile robot, as disclosed in the co-pending applications.

[0016] The DSP 130, for example, may be obtained from a variety of commercial DSP vendors, such as Freescale (DSP56F802TA60), or Texas Instruments, based on the specific design requirements for each application.

[0017] AFA Module 120

[0018] Reference is now to FIG. 2, where a simplified block diagram of an exemplary AFA 120 is shown. The AFA 120 uses a combination of common analog filter components to achieve a more complex system frequency response. A preferred system is one that is capable of passing a band of frequencies, severely attenuating a different band of frequencies and finally, attenuating the remaining frequency band. This system also removes the DC component of the raw signal, leaving a well-characterized AC signal for analysis by a downstream microprocessor, e.g. DSP 130.

[0019] As can be appreciated by those skilled in the art of analog filter design, there are several trade offs that can be made when designing an analog filter:

• • [0020] Overall transfer function;
  • [0021] Cost;
  • [0022] Component count;
  • [0023] Component variation sensitivity.

[0024] The exemplary embodiment of the AFA 120 is advantageous in its ability to utilize passive (and thus low cost) filters to achieve a large (≦35 db) difference between the target frequency and the frequencies that must be ‘severely’ attenuated. This task is complicated by the proximity of the two different frequency ranges being less than 1 decade apart. This proximity requires a relatively complex transfer function. Despite this, this embodiment is able to use a minimal number of components to achieve this goal. In doing so, the embodiment achieves excellent immunity to part and process variation leading to a highly manufacturable and thus lower cost design, as will be further described below.

[0025] TIA (Transimpedance Amplifier) 200

[0026] Referring to FIG. 2, the AFA 120 expects a raw analog current be supplied to it from the sensor 110. This current is then converted into a voltage and amplified by the TIA 200. The preferred embodiment of the TIA 200 allows for an extremely small current to be measured, wherein the typical input current can be as low as 0.5 nA. FIG. 3 illustrates an exemplary circuit diagram of the TIA 200 of the preferred embodiment.

[0027] In addition, the TIA 200 makes use of a different bias voltage from the rest of the amplifiers in the AFA 120. By raising the bias voltage to near the positive rail of the op-amp (FIG. 3), the TIA 200 provides the largest amount of tolerance to DC noise. This works because the signal enters the op-amp's negative input and the actual AC signal is at most 10–20 mV at the output of the TIA 200. Thus, any DC current results in a decrease of the output bias level of the TIA 200, while maintaining the AC signal characteristics.

[0028] Before the necessary gain can be applied to the signal, the DC component should be completely removed, along with any frequencies that will produce much larger noise than the actual signal level

[0029] PHP (Passive High-Pass Filter) 210

[0030] The PHP 210 may be implemented by a passive single-pole high-pass filter. This effectively removes any DC bias that has been introduced through environmental factors. Preferably its cutoff is set at 800 Hz.

[0031] BFR (Buffer) 220

[0032] The previous stage, PHP 210, and the following stage 230, are both made up of passive components. If they were directly concatenated in the circuit, they would interact with each other, causing different frequency response characteristics. To eliminate this problem, and aid in the component variation tolerance, a single op-amp is used as the buffer 220 between them. This single op-amp buffer 220 is configured as a simple voltage follower with no gain.

[0033] PNF (Passive Notch Filter) 230

[0034] The second large source of undesired noise is produced in a very small band of frequencies, specifically in this application, frequencies between 100 and 120 Hz. This noise is produced by incandescent light bulbs in the environment and can be 100 times larger than the actual signal amplitude. Although the incandescent light bulbs run on 50 Hz and 60 Hz of household electricity, they emit light due to the heating of the resistive tungsten, even when the current reverses its direction. Therefore, the light coming from the light bulbs can have an effective frequency of 100 and 120 Hz, the removal of which is the primary function of the PNF 230.

[0035] To that end, the PNF 230 is implemented to remove this 20 Hz wide band. Normal notch filters of this type have a much narrower band, i.e. 1–3 Hz; this design implements slightly ‘detuned’ values to widen the band. There is a negative impact on the band depth and thus the effective attenuation, but detuning allows a single part population to cover circuits for the entire world and aids in component tolerance sensitivity.

[0036] GAIN (Gain Amplifier) 240

[0037] The previous stage, PNF 230, and the following stage, PHP 250, are both made up of passive components. If they were directly concatenated in the circuit, they would interact with each other causing different frequency response characteristics. To eliminate this problem, and aid in the component variation tolerance, a single op-amp is used as a buffer 240 between them. This op-amp is also configured to provide gain to the signal in preparation for the signal being measured with the Analog-to-Digital converter 280. In some applications, a single op-amp may be utilized as a buffer instead, where the op-amp is configured as a simple voltage follower without any gain.

[0038] PHP (Passive High-Pass Filter) 250

[0039] The previous notch stage, PNF 230, produces a DC bias due to variations in part values. In some situations this would not have been a problem; however, the current application requires a large, 100×, gain to be applied to the signal. With this large magnitude of a gain, even the smallest offset, e.g. 20 mV, would be magnified and result in an op-amp saturating at a rail. To eliminate this problem, and allow for a large gain in the following stage, the passive high-pass filter 250 is utilized, effectively AC coupling the signal.

[0040] GAIN (Gain Amplifier) 260

[0041] Prior to this point, the actual signal level is still much too small to measure with the Analog-to-Digital converter 280. The gain amplifier 260 amplifies the signal to a measurable level and attempts to maximize the op-amp dynamic range and system SNR.

[0042] PLP (Passive Low-Pass Filter) 270

[0043] This PLP 270 stage adds an extra pole to the transfer function. This increases the rate of gain roll-off from the maximum system gain of 40 db @ 2 k Hz. There are inherent poles in the TIA 200 and GAIN 260 stages, making this the 3^rd pole in the transfer function. This provides a roll-off of 60 db/decade in the frequency response. With this added pole, the system provides 0 db of gain @ 40 kHz and attenuates all frequencies above this. Without this pole, the crossover point would have been moved out to over 80 kHz, allowing more high frequency noise to enter the system.

[0044] Although this invention has been described with reference to these specific embodiments, the descriptions are intended to be illustrative of the invention and are not intended to be limiting. Various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention.

[0045] The following patent applications, commonly owned and filed on the same day as the present application, are hereby incorporated herein in their entirety by reference thereto:

[0046]

	Application No. and
Title	Filing Date	Attorney Docket No.
“Methods And Apparatus For Position Estimation	Provisional Application	EVOL.0050PR
Using Reflected Light Sources”	60/557,252
	Filed Mar. 29, 2004
“Circuit for Estimating Position and Orientation	Provisional Application	EVOL.0050-1PR
of a Mobile Object”	60/602,238
	Filed Aug. 16, 2004
“Sensing device and method for measuring	Provisional Application	EVOL.0050-2PR
position and orientation relative to multiple light	60/601,913
sources”	Filed Aug. 16, 2004
“System and Method of Integrating Optics into an	Provisional Application	EVOL.0050-3PR
IC Package”	60/602,239
	Filed Aug. 16, 2004
“Methods And Apparatus For Position Estimation	Utility Application	EVOL.0050A
Using Reflected Light Sources”	Serial No. TBD
	Filed Mar. 25, 2005
“Sensing device and method for measuring	Utility Application	EVOL-0050A2
position and orientation relative to multiple light	Serial No. TBD
sources”	Filed Mar. 25, 2005
“System and Method of Integrating Optics into an	Utility Application	EVOL.0050A3
IC Package”	Serial No. TBD
	Filed Mar. 25, 2005