How to apply ultrasonic sensors for drone landing

The drone landing assist is a function of the drone, which can detect the distance between the bottom of the drone and the landing area, determine whether the landing point is safe, and then slowly descend to the landing area. Although GPS monitoring, air pressure sensing and other sensing technologies contribute to the landing process, ultrasonic sensing is the main and most accurate basis for UAVs in this process. Most drones also have hovering and ground tracking modes, which are mainly used to capture footage and land navigation, in which ultrasonic sensors help keep the drone at a constant height above the ground.

Ultrasonic principle

Ultrasound is defined as the use of sound waves with a frequency higher than the upper limit of human hearing-see Figure 1.

Figure 1: Ultrasonic range

Ultrasound can pass through various media (gas, liquid, solid) to detect objects whose acoustic impedance does not match. The speed of sound is the distance per unit time when a sound wave propagates in an elastic medium. For example, in dry air at 20°C (68°F), the speed of sound is 343 meters per second (1.125 feet per second). The attenuation of ultrasonic waves in the air increases with frequency and humidity. Therefore, due to excessive path loss/absorption, air-coupled ultrasound is generally limited to frequencies below 500kHz.

Ultrasonic ToF

Like many ultrasonic sensing applications, the UAV landing assist system uses the time of flight (ToF) principle. ToF is an estimate of the round-trip time of the ultrasonic wave emitted from the sensor to the target object and then reflected from the object back to the sensor, as shown in Figure 2.

In Figure 2 and Figure 3, point 1. The UAV's ultrasonic sensor emits sound waves, which are expressed as saturated data on the return signal processing path. After transmission, the signal processing path becomes silent (point 2) until the echo is reflected from the object (point 3).

Formula 1 calculates the distance from the drone to the ground or from the drone to another object:

Distance (d) is the distance from the ultrasonic sensor on the drone to the ground/object, ToF(t) is the ToF defined previously, and SpeedOfSound(v) is the speed of sound through the medium. ToF(t)×SpeedOfSound(v) divided by 2. Because ToF calculates the time for the ultrasonic echo to go back and forth to the object.

Why use ultrasonic induction for drone landing?

Although many sensing technologies can detect the proximity of objects, ultrasonic sensing can work well in terms of the detection distance of the UAV landing, the cost of the solution, and the reliability of different surfaces.

The common requirement for UAV ground tracking and landing is to be able to reliably detect a distance of 5 meters from the ground. Assuming correct signal conditioning and processing, ultrasonic sensors in the 40-60kHz range can usually meet this range.

Texas Instruments’ PGA460 is an ultrasonic signal processor and sensor driver, used for ultrasonic sensing in air-coupling applications such as drones, and can meet or exceed the requirements of 5 meters. However, the coordination of ultrasonic sensing is a limitation in near-field detection of objects. All ultrasonic sensors used in air-coupling applications have an excitation period, called decay time or oscillation time, during which the piezoelectric film vibrates and emits ultrasonic energy, making it difficult to detect any incoming echo.

In order to effectively measure objects during ringing, many drone designers install separate sensors for the transmitter and receiver. By separating the receiver, the drone can detect objects during the excitation of the transmitter. So PGA460 has superior near-field detection performance-as low as 5cm or less.

Ultrasonic sensing technology is also a cost-competitive technology, especially when using integrated solutions such as PGA460, which already includes most of the required chips. PGA460 can either use half-bridge or H-bridge to directly drive the sensor, or use a transformer to drive the sensor; the latter is mainly used for sealed "closed" sensors. The PGA460 also includes a complete analog front end for receiving and conditioning ultrasonic echo. In addition, the device can also calculate ToF through digital signal processing (see Figure 4).

Ultrasonic sensing can detect surfaces that are difficult to solve with other technologies. For example, drones often encounter glass windows and other glass surfaces on buildings. Light sensing technology sometimes penetrates glass and other transparent materials, which makes it difficult for drones to hover over glass buildings. Ultrasonic waves can be reliably reflected off the glass surface.

Although ultrasonic sensing is mainly used for UAV landing assistance and hovering, its powerful cost performance is prompting UAV designers to explore other applications of this technology. The rapidly growing field of drones has huge potential.

Parachute system for drone safty landing

Drone parachute system for commercial drone safety 10-100KG load capacity

Drone parachute is the  safety system on the market for commercial drones. Drone parachute system protects by standers on the ground, prevents loss of payload and safeguards your drone equipment by ensuring your drone always lands safely. Drone parachute system solutions are designed to comply with the future regulation that enables safe flight operations over populated areas and beyond visual line of sight. Providing the Drone Industry with the Technology to Realize its Full Potential , We believe that smart safety technologies are pivotal in ensuring that drones can operate unrestricted to explore their full economic potential while minimizing the risks associated with operating drones over populated areas. Drone parachute system develops and provides state-of-the-art drone safety solutions that fuel the growth of the booming drone economy. Drone parachute system applies real-time data analytics to identify and mitigate flight risks autonomously and increase safety for bystanders while protecting the loss of expensive drones, equipment, and payloads.

Specification

	DPS10-10KG	DPS20-20KG	DPS30-30KG	DPS40-40KG	DPS50-50KG
Installation size(mm)	82*82	116*116	116*116	116*116	145*145
Equipment size(mm)	Φ104/H100	Φ104/H150	Φ104/H165	Φ104/H180	Φ104/H210
Max Load	10KG	20KG	30KG	40KG	50KG
Interface	5 PIN	5 PIN	5 PIN	5 PIN	5 PIN
Parachute diameter	2000mm	3000mm	3500mm	4000mm	4400mm
Supply voltage	5V	5V	5V	5V	5V
Cell capacity	380mAh	380mAh	380mAh	380mAh	380mAh
Gesture perception range	±90°	±90°	±90°	±90°	±90°
Trigger angle	±80°	±80°	±80°	±80°	±80°
Fall trigger	0.5g/1.6s	0.5g/1.6s	0.5g/1.6s	0.5g/1.6s	0.5g/1.6s
operating hours	8h	8h	8h	8h	8h
Trigger method	Attitude / fall / digital serial port	Attitude / fall / digital serial port	Attitude / fall / digital serial port	Attitude / fall / digital serial port	Attitude / fall / digital serial port
data communication	TTL	TTL	TTL	TTL	TTL
PWM  pulse width	1750-2000	1750-2000	1750-2000	1750-2000	1750-2000
Power off	10s	10s	10s	10s	10s
Wake up	Yes	Yes	Yes	Yes	Yes
Ejection method	Propellant	Propellant	Propellant	Propellant	Propellant
Umbrella rope fixing method	Built-in	External transfer	External transfer	External transfer	External transfer
Weight	380g	550g	650g	780g	850g
Refresh rate	100Hz	100Hz	100Hz	100Hz	100Hz
Minimum open umbrella height	20m	30m	36m	40m	50m
Operating temperature	*-10℃—-45℃	*-10℃—-45℃	*-10℃—-45℃	*-10℃—-45℃	*-10℃—-45℃

 

	DPS60-60KG	DPS70-70KG	DPS80-80KG	DPS90-90KG	DPS100-100KG
Installation size(mm)	145*145	145*145	145*145	145*145	200*200
Equipment size(mm)	Φ130/H185	Φ130/H200	Φ130/H230	Φ130/H240	Φ180/H240
Max Load	60KG	70KG	80KG	90KG	100KG
Interface	5 PIN	5 PIN	5 PIN	5 PIN	5 PIN
Parachute diameter	4500mm	5000mm	5200mm	5500mm	6500mm
Supply voltage	5V	5V	5V	5V	5V
Cell capacity	650mAh	650mAh	650mAh	650mAh	650mAh
Gesture perception range	±90°	±90°	±90°	±90°	±90°
Trigger angle	±80°	±80°	±80°	±80°	±80°
Fall trigger	0.5g/1.6s	0.5g/1.6s	0.5g/1.6s	0.5g/1.6s	0.5g/1.6s
operating hours	12h	12h	12h	12h	12h
Trigger method	Attitude / fall / digital serial port	Attitude / fall / digital serial port	Attitude / fall / digital serial port	Attitude / fall / digital serial port	Attitude / fall / digital serial port
data communication	TTL	TTL	TTL	TTL	TTL
PWM  pulse width	1750-2000	1750-2000	1750-2000	1750-2000	1750-2000
Power off	10s	10s	10s	10s	10s
Wake up	Yes	Yes	Yes	Yes	Yes
Ejection method	Propellant	Propellant	Propellant	Propellant	Propellant
Umbrella rope fixing method	External transfer	External transfer	External transfer	External transfer	External transfer
Weight	950g	1250g	1450g	2000g	2200g
Refresh rate	100Hz	100Hz	100Hz	100Hz	100Hz
Minimum open umbrella height	65m	75m	80m	85m	85m
Operating temperature	*-10℃—-45℃	*-10℃—-45℃	*-10℃—-45℃	*-10℃—-45℃	*-10℃—-45℃