Here we present, as an application guide for ultrasonic sensors, information on the operating principle of distance detection and on the usage and applications of ultrasonic sensors in PAS (parking assist) applications, human detection, double feed detection, and more.
In addition to the above, ultrasonic sensors can be used for applications such as object detection on conveyor belts and obstacle detection in automated robot vacuum cleaners.
Operating principle of distance detection
Operating principle of distance detection
Time × speed of sound (approx. 340 m/s) = distance to object (round trip)
The time from the start of transmission until reflected waves are received is measured.
What is PAS?
Measures the distance to obstacles (walls, etc.) and reports their proximity to the driver.
PAS basic operation
Pulse signals are transmitted, the ultrasonic waves reflect off of obstacles, and the distance to the obstacles is measured based on the time until the reflected waves are received.
A clock pulse is generated when each pulse signal is transmitted, and this clock is used to measure the time.
Reflection time (s) × speed of sound (340 m/s) = distance to obstacle (round trip)
Characteristics necessary for PAS
- Must be able to detect a wall behind the vehicle while ignoring the curb.
- Each sensor must cover a wide range to reduce the total number of sensors required.
- Must be able to detect very close proximity.
Therefore, sensors with the following features are desirable:
Directionality that is narrow vertically but wide horizontally
Short resonance time
What is human detection?
The received signal waveforms are different in the 1st frame and 2nd frame.
⇒ A moving person (object) is present.
- It is necessary to record the changes at intervals over time. (A certain amount of arithmetic processing is necessary.)
- Observing changes in the minimum distance is relatively simple.
- Both MA40H1S-R and MA40S4S/R can be used.
- It is necessary to construct an algorithm.
Double feed detection
What is double feed detection?
Double feed detection is a function used in scanners and printers that determines when two sheets of paper have passed through the paper feed mechanism at the same time. Double feed detection is particularly essential in commercial scanners that are often used to scan important items such as checks or official government documents because it is necessary to prevent multiple sheets from going through the paper feed mechanism at once.
Operating principle of double feed detection
Sound waves are reflected by the paper, lessening radiated waves.
|・Single thin sheet:
||Radiated sound pressure is high.
|・Single thick sheet:
||Radiated sound pressure is low.
||Sound waves are also reflected between the two sheets because of the layer of air between them.
⇒Secondary radiated sound waves from the first sheet are substantially reduced (approx. 1/100 m in case of PPC paper).
Method other than ultrasonic sensor
■Contact type (paper thickness measurement)
|Difficult to detect the number of sheets (the difference between two thin sheets and one thick sheet).
Adjustment is necessary when using thick paper.
■Light transmission type
Accuracy can be affected by the color of the paper. Detection is not possible when using transparent sheets.
Characteristics of double feed detection
There is no abrasion because mechanical contact is not required.
No adjustment to account for paper thickness or quality is necessary.
Detection is also possible when using transparent sheets.
(The color of the paper has no effect on performance.)
We sometimes receive inquiries regarding the use of Murata products in some applications they are not intended.Murata products are not suitable for the following applications.
Water meters, fluid type detection, or fluid volume measurement
Murata products are designed to propagate ultrasonic waves through the air. They are not designed to be used with media such as liquids or solids.
Automatic doors or automatic hand washers
Although automatic door applications can utilize wide-range sensing indoors, this often leads to situations in which the doors open or close after sensing objects other than the intended persons. Nowadays, optical sensors or touch sensors are primarily used for such applications.
Ultrasonic waves are also not suitable for use in automatic hand washers because short-distance detection and drip-proof sensors are required. Optical sensors are used primarily for such applications.
Unmanned chemical sprayer robots for orchards and robot lawnmowers
Due to outdoor use, a drip-proof type is needed, but since Murata’s drip-proof type products are for automotive applications only, they cannot be used.
Industrial and distribution robots
Murata products may not be suitable due to the usage environment or durability requirements. Please contact a Murata sales representative for details.
Use of motion detection to check the well-being of persons in the bath
A drip-proof type would be necessary and transmission- and reception-only sensors would be needed. Since Murata’s drip-proof type products are for automotive applications only and are of the transmission-reception combined type, they cannot be used.