DRONE INCLUDING ADVANCED MEANS FOR COMPENSATING THE BIAS OF THE INERTIAL UNIT AS A FUNCTION OF THE TEMPERATURE

• US 20160370404A1
• Filed: 06/07/2016
• Published: 12/22/2016
• Est. Priority Date: 06/16/2015
• Status: Active Grant

• Current Assignee: Parrot Drones
• Original Assignee: Parrot Drones
• Inventors: Quadrat, Quentin, Chaperon, Cedric, Seydoux, Henri
• Granted Patent: US 10,191,080 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B64U 10/00 Type of UAV
• CPC Class Codes: B64U 20/83 Electronic components structurally integrated with aircraft elements, e.g. circuit boards carrying loads
• CPC Class Codes: G01C 19/00 Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
• CPC Class Codes: G01C 21/183 Compensation of inertial measurements, e.g. for temperature effects
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups
• CPC Class Codes: G05D 23/1919 characterised by the type of controller

Abstract

The inertial unit, IMU, of the drone is mounted on a main circuit board. The IMU (26) includes an internal temperature sensor delivering a chip temperature signal (θ°_chip). A heating component (36) is mounted on the circuit board near the IMU, and it is provided a thermal guide, incorporated to the circuit board, extending between the heating component and the IMU so as to allow a transfer to the IMU of the heat produced by the heating component. This thermal guide may in particular be a metal planar layer incorporated to the board, in particular a ground plane. A thermal regulation circuit (44-62) receives as an input the chip temperature signal (θ_chip) and a set-point temperature signal (θ°_ref), and delivers a piloting signal (TH_PWM) of the heating component, so as to control the heat supply to the IMU. It is in particular possible to use this fast increase in temperature to perform a complete calibration of the IMU in a few minutes.

Claims

1. A drone, comprising a main circuit board (24) on which are mounted electronic components as well as an inertial unit, IMU, (26) comprising gyrometer sensors for measuring the instantaneous rotations of the drone in an absolute reference system, and/or accelerometer sensors for measuring accelerations of the drone in this reference system, the IMU (26) including an internal temperature sensor (34) delivering a chip temperature signal (θ

°

_chip),

characterized in that it comprises;

a heating component (28) mounted on the circuit board (24) near the IMU (26);

a thermal guide (30) incorporated to the circuit board (24), this thermal guide extending between the heating component (28) and the IMU (26) so as to allow a transfer (32) to the IMU of the heat produced by the heating component; and

a thermal regulation circuit (44-62), receiving as an input the chip temperature signal (θ

°

_chip) and a predetermined set-point temperature signal (θ

°

_ref), and outputting a heating component piloting signal (TH_PWM), so as to control the heat supply to the IMU as a function of the difference between chip temperature and set-point temperature.

2. The drone of claim 1, further comprising:

a memory (78) storing values of a polynomial approximating a bias/chip temperature characteristic of the IMU; and

a circuit of thermal error correction (80), adapted to apply to the raw signals (82) delivered by the gyrometer and/or accelerometer sensors of the IMU bias corrections as a function of the chip temperature, these corrections being based on the polynomial values stored in the memory.

3. The drone of claim 1, wherein the thermal guide is a metal planar layer (30) incorporated to the circuit board (24) and extending under the IMU (26) and under the heating component (28).

4. The drone of claim 3, wherein the metal planar layer is a plane of electric ground (GND_GYRO) of the IMU and of the heating component, connected to the common ground (GND) of the circuit board.

5. The drone of claim 1, wherein the heating component is a bipolar transistor associated to a stage (38) of controlled polarisation of the base of this transistor, as a function of the piloting signal (TH_PWN) delivered by the thermal regulation circuit.

6. The drone of claim 1, wherein the piloting signal (TH_PWM) delivered by the thermal regulation circuit is a PWM signal whose duty cycle is modulated as a function the difference between the chip temperature and the set-point temperature.

7. A method of calibration of the IMU (26) of a drone according to claim 1, comprising the following steps:

a) piloting the heating component (28) so as to generate a chip temperature ramp varying progressively from an initial temperature to a final temperature;

b) during this temperature ramp, reading the bias values of the IMU (26) for a plurality of chip temperature values, and establishing a bias/temperature characteristic;

c) searching for a polynomial approximating at the closest the characteristic obtained at step b); and

d) memorizing values of the polynomial found at step c), as values of IMU bias correction as a function of the chip temperature.

8. The method of claim 7, wherein the initial temperature is an ambient temperature and the final temperature is a nominal operation temperature of the IMU.

9. The method of claim 7, wherein the duration of the temperature ramp of step b, from the initial temperature to the final temperature, is lower than 3 minutes.

10. The method of claim 7, wherein step b) is executed in a static configuration of the IMU, and it is further provided, after step d), a dynamic calibration of the IMU, comprising the steps of:

e) installing the circuit board on a rotating support and applying predetermined rotations to the IMU; and

f) during these predetermined rotations, reading the raw signals delivered by the gyrometric sensors of the IMU, and applying these raw signals of a thermal correction as a function of the chip temperature, these corrections being based on the polynomial values memorized at step d).

11. The method of claim 10, wherein the heating component is deactivated during the steps e) and f).