Phase compensation in a time of flight system

Abstract

Systems and methods are provided for imaging a surface via time of flight measurement. An illumination system includes an illumination driver and an illumination source and is configured to project modulated electromagnetic radiation to a point on a surface of interest. A sensor system includes a sensor driver and is configured to receive and demodulate electromagnetic radiation reflected from the surface of interest. A temperature sensor is configured to provide a measured temperature representing a temperature at one of the illumination driver and the sensor driver and located at a position remote from the one of the illumination driver and the sensor driver. A compensation component is configured to calculate a phase offset between the illumination system and the sensor system from at least the measured temperature and a model representing transient heat flow within the system.

Having described the invention, we claim: 
     
         1 . A time of flight system comprising:
 an illumination system, comprising an illumination driver and an illumination source, configured to project modulated electromagnetic radia-tion to a point on a surface of interest;   a sensor system, comprising a sensor driver, configured to receive and demodulate electromagnetic radiation reflected from the surface of interest;   a temperature sensor configured to provide a measured temperature representing a temperature at one of the illumination driver and the sensor driver, the temperature sensor being located at a position remote from the one of the illumination driver and the sensor driver such that a change in temperature at the one of the illumination driver and the sensor driver is not instantaneously detected at the temperature sensor; and   a compensation component configured to calculate a phase offset between the illumination system and the sensor system from at least the measured temperature and a model representing transient heat flow within the system.   
     
     
         2 . The time of flight system of  claim 1 , wherein the model represents the phase offset as a function of a time derivative of the measured temperature such that the compensation component is configured to calculate a numerical representation of the time derivative of the measured temperature for at least one time. 
     
     
         3 . The time of flight system of  claim 2 , wherein the model represents the phase offset as a linear combination of a time derivative of the measured temperature, a final stable temperature at the temperature sensor after transition in temperature, and a calibration temperature for the temperature sensor at which the phase offset is expected to be zero. 
     
     
         4 . The time of flight system of  claim 3 , wherein the linear combination comprises a product of a static coefficient with a difference between the final stable temperature and the calibration model, the static coefficient representing an expected amount of change in the phase offset associated with a given deviation of the measured temperature from the calibration value when the temperature of the system is not in transition. 
     
     
         5 . The time of flight system of  claim 3 , wherein the linear combination comprises a product of the time derivative of the measured temperature and a thermal time constant associated with the temperature sensor. 
     
     
         6 . The time of flight system of  claim 3 , wherein the linear combination comprises a product of the time derivative of the measured temperature, a thermal time constant associated with the temperature sensor, and a term linearly dependent on a time since the beginning of a transition in temperature. 
     
     
         7 . The time of flight system of  claim 6 , wherein the linearly dependent term comprises the different between one and a product of the time since the beginning of a transition in temperature and a difference between the respective multiplicative inverses of the thermal time constant associated with the temperature sensor and a thermal time constant associated with the sensor driver. 
     
     
         8 . The time of flight system of  claim 1 , the model representing the phase offset as a nonlinear function of a time since the beginning of a transition in temperature. 
     
     
         9 . The time of flight system of  claim 6 , the model representing the phase offset as an exponential function of a time since the beginning of a transition in temperature. 
     
     
         10 . The time of flight system of  claim 1 , wherein the temperature sensor is a first temperature sensor configured to provide a first measured temperature and the system further comprising a second temperature sensor configured to provide a second measured temperature, the model representing the phase offset as a function of the first measured temperature and a second measured temperature. 
     
     
         11 . The time of flight system of  claim 10 , wherein the model representing the phase offset as a function of each of first measured temperature, the second measured temperature, a thermal time constant associated with the first temperature sensor, a thermal time constant associated with the second temperature sensor, a thermal time constant associated with the sensor driver, and a thermal time constant associated with the receiver driver. 
     
     
         12 . The time of flight system of  claim 1 , further comprising a time of flight calculation component configured to determine a distance to the point of the surface of interest from the demodulated electromagnetic radiation and the phase offset. 
     
     
         13 . A method for determining a distance to a surface of interest with a time of flight system, comprising:
 projecting modulated electromagnetic radiation to a point on the surface of interest via an illumination system;   receiving electromagnetic radiation reflected from the point on the surface of interest at a sensor system;   demodulating the received electromagnetic radiation at the sensor system;   measuring a temperature at a position remote from respective drivers associated with each of the illumination system and the sensor system;   calculating a phase offset between the illumination system and the sensor system from at least the measured temperature and a model representing transient heat flow within the system; and   determining a location of the point on the surface of interest, relative to the time of flight system, from the received electromagnetic radiation and the calculated phase offset.   
     
     
         14 . The method of  claim 13 , wherein calculating the phase offset comprises calculating a numerical representation of the time derivative of the measured temperature for at least one time. 
     
     
         15 . The method of  claim 13 , wherein the method is iteratively repeated across a plurality of iterations, and calculating a phase offset between the illumination system and the sensor system comprises calculated the phase offset from at least the measured temperature, a measured temperature from a previous iteration of the method, and a model representing transient heat flow within the system. 
     
     
         16 . The method of  claim 13 , further comprising determining a plurality of system parameters for the model from a reference system via a curve fitting analysis. 
     
     
         17 . The method of  claim 16 , wherein measuring the temperature comprises measuring the temperature at a temperature sensor located on a circuit with the sensor system, but remote from the driver associated with the sensor system, the plurality of system parameters comprising a thermal time constant associated with the temperature sensor. 
     
     
         18 . The method of  claim 16 , the plurality of system parameters comprising one of a thermal time constant associated with the driver associated with the sensor system and a calibration temperature for the measured temperature at which the phase offset is expected to be zero. 
     
     
         19 . The method of  claim 18 , the plurality of system parameters comprising a static coefficient representing an expected amount of change in the phase offset associated with a given deviation of the measured temperature from the calibration value when the temperature of the system is not in transition. 
     
     
         20 . A time of flight system comprising:
 an illumination system, comprising an illumination driver and an illumination source, configured to project modulated electromagnetic radiation to a point on a surface of interest;   a sensor system, comprising a sensor driver, configured to receive and demodulate electromagnetic radiation reflected from the surface of interest;   a temperature sensor configured to provide a measured temperature representing a temperature at one of the illumination driver and the sensor driver, the temperature sensor being located at a position remote from the one of the illumination driver and the sensor driver, such that a change in temperature at the one of the illumination driver and the sensor driver is not instantaneously detected at the temperature sensor;   a compensation component configured to calculate configured to calculate a numerical representation of the time derivative of the measured temperature for at least one time and a phase offset between the illumination system and the sensor system from at least the measured temperature, the calculated time derivative of the measured temperature, and a model representing transient heat flow within the system; and   a time of flight calculation component configured to determine a distance to the point of the surface of interest from the demodulated electromagnetic radiation and the phase offset.