Navigation systems for wheeled carts
View Patent ↗Examples of systems and methods for locating movable objects such as carts (e.g., shopping carts) are disclosed. Such systems and methods can use dead reckoning techniques to estimate the current position of the movable object. Various techniques for improving accuracy of position estimates are disclosed, including compensation for various error sources involving the use of magnetometer and accelerometer, and using vibration analysis to derive wheel rotation rates. Various techniques utilize characteristics of the operating environment in conjunction with or in lieu of dead reckoning techniques, including characteristic of environment such as ground texture, availability of signals from radio frequency (RF) transmitters including precision fix sources. Navigation techniques can include navigation history and backtracking, motion direction detection for dual swivel casters, use of gyroscopes, determining cart weight, multi-level navigation, multi-level magnetic measurements, use of lighting signatures, use of multiple navigation systems, or hard/soft iron compensation for different cart configurations.
1. An anti-theft system for a human-propelled cart, the anti-theft system comprising:
a vibration sensor configured to measure vibration data of the human-propelled cart;
a communication system configured to communicate with a wheel of the human-propelled cart, the wheel comprising a brake system configured to inhibit rotation of the wheel in response to receipt of a locking signal; and
a hardware processor programmed to:
analyze the vibration data to determine the cart has received an impulse;
analyze the vibration data to determine a vibration signature indicative of ringing of the cart in response to the impulse;
estimate, based at least partly on the analysis of the vibration data, whether the cart is loaded or unloaded;
determine whether the cart has crossed a confinement boundary;
determine, based at least partly on the estimate of whether the cart is loaded or unloaded and whether the cart has crossed the confinement boundary, an anti-theft instruction to communicate to the brake system or to an external surveillance system; and
communicate the instruction.
2. The anti-theft system of claim 1 , wherein the vibration sensor comprises an accelerometer.
3. The anti-theft system of claim 1 , wherein to analyze the vibration data to determine the cart has received an impulse, the hardware processor is programmed to identify a vertical component of acceleration with magnitude exceeding 0.5 g and having a duration less than 10 ms.
4. The anti-theft system of claim 1 , wherein to analyze the vibration data to determine a vibration signature indicative of ringing of the cart in response to the impulse, the hardware processor is programmed to identify a horizontal component of acceleration having a frequency greater than 1 kHz that occurs within 10 ms of the impulse, the horizontal component being in a direction of cart motion.
5. The anti-theft system of claim 1 , wherein to estimate whether the cart is loaded or unloaded, the hardware processor is programmed to determine whether a component of the vibration signature occurring in a direction of cart motion is above or below a threshold vibration amplitude.
6. The anti-theft system of claim 1 , wherein the anti-theft instruction comprises an instruction to actuate the brake system if the cart is estimated to be loaded.
7. The anti-theft system of claim 1 , wherein the anti-theft instruction comprises an instruction to actuate the brake system, wherein the instruction further comprises an indication of a speed or force at which the brake system is to be applied to slow the cart, and wherein the indication of the speed or force depends at least partly on the estimate of whether the cart is loaded or unloaded.
8. The anti-theft system of claim 1 , wherein the anti-theft instruction comprises an instruction to not actuate the brake system if the cart is estimated to be unloaded.
9. The anti-theft system of claim 1 , wherein the anti-theft instruction comprises an instruction to actuate the external surveillance system if the cart is estimated to be loaded.
10. The anti-theft system of claim 1 , further comprising a navigation system configured to determine a location of the cart.
11. The anti-theft system of claim 10 , wherein the navigation system comprises:
a magnetometer configured to determine a heading of the cart, wherein
the hardware processor is further programmed to:
estimate a speed of the cart based at least in part on the vibration data from the vibration sensor; and
estimate a location of the cart based at least in part on the estimated speed and the heading of the cart.
12. The anti-theft system of claim 11 , wherein to estimate the speed of the cart, the hardware processor is programmed to:
analyze a spectrum of the vibration data;
identify a first peak in the spectrum of the vibration data, the first peak associated with vibration data for vibrations associated with forward or rearward movement of the cart;
determine a rotation rate of the wheel to be a harmonic frequency of the frequency of the first peak in the spectrum of the vibration data; and
estimate the speed based on the rotation rate and a circumference of the wheel.
13. A method for determining whether a human-propelled wheeled cart is loaded or unloaded, the method comprising:
measuring, with a vibration sensor, a Z-vibration signature representative of an impulse applied to the cart in a vertical, Z-direction;
measuring, with the vibration sensor, an X-vibration signature representative of ringing of the cart that occurs in response to the impulse, the X-vibration signature being in a horizontal, X-direction parallel to a direction of motion of the cart; and
determining whether the cart is loaded or unloaded based at least partly on the X-vibration signature.
14. The method of claim 13 , wherein the Z-vibration signature comprises an acceleration in the Z-direction having a magnitude greater than 1 g and a duration of less than 10 ms.
15. The method of claim 13 , wherein the X-vibration signature has a frequency greater than 1 kHz and occurs within 10 ms of the impulse.
16. The method of claim 13 , wherein determining whether the cart is loaded or unloaded comprises comparing an amplitude of acceleration associated with the X-vibration signature to a threshold.
17. The method of claim 16 , wherein the threshold is 1 g.
18. The method of claim 13 , further comprising estimating a weight of the cart or a weight of the cart load based at least partly on the X-vibration signature.
19. The method of claim 13 , further comprising: in response to determining that the cart is loaded, actuating a brake system configured to inhibit motion of the cart.
20. The method of claim 19 , further comprising providing an indication of a speed or force at which the brake system is to be applied to slow the cart, wherein the indication of the speed or force depends at least partly on the determination that the cart is loaded.
21. The method of claim 13 , further comprising:
estimating a speed of the cart based at least in part on vibration data from the vibration sensor; and
estimating a location of the cart based at least in part on the estimated speed and a heading of the cart.