The hydraulic cylinder is a hydraulic actuator that converts hydraulic energy into mechanical energy and does linear reciprocating motion (or oscillating motion). It has a simple structure and works reliably. When it is used to realize reciprocating motion, it can avoid the deceleration device, and there is no transmission clearance, and the movement is stable, so it is widely used in the hydraulic system of various machinery. The output force of the hydraulic cylinder is proportional to the effective area of the piston and the pressure difference between its two sides, and the hydraulic cylinder is basically composed of cylinder barrel and cylinder head, piston and piston rod, sealing device, buffer device and exhaust device. Buffers and exhausts vary depending on the application, but others are essential.
Among them, the piston and piston rod can make the piston rod and piston of the hydraulic cylinder with short stroke integrate, which is the simplest form. However, when the stroke is long, the processing of this integral piston assembly is more cumbersome, so the piston and piston rod are often manufactured separately and then connected into a single piece. As shown in the figure:
So how to determine the stroke of the hydraulic cylinder? The working degree of the hydraulic cylinder refers to the maximum moving distance of the piston of the hydraulic cylinder, which can be determined according to the working needs and the characteristics of the hydraulic system. In general, the hydraulic cylinder stroke should be at least 50mm more than each working stroke.
When determining the stroke of the hydraulic cylinder, it is also necessary to take into account factors such as the angle of rotation, the position of the load, and the speed. At the same time, it is also critical to determine the material, sealing performance and lubrication conditions of the cylinder according to the design requirements to ensure that the cylinder can work properly and has long-term reliability.
In industrial production, the measurement of displacement and speed of hydraulic cylinder pistons is often encountered. At present, differential transformer displacement sensors and conductive plastic resistive sensors are used to measure piston displacement and velocity in most cases, but these measurement methods have the problem of noise interference and the difficulty of improving the frequency response. Especially when measuring the displacement of the piston of hydraulic cylinders with large displacements, it is difficult to obtain satisfactory measurement results with other sensors. The use of ultrasonic to measure the displacement of the piston of the hydraulic cylinder can meet the needs of the large displacement measurement of the hydraulic cylinder, and the measurement accuracy is high, the frequency response is fast, the degree of automation is high, the installation is convenient, the price is cheap, etc.
Analysis and application of ultrasonic ranging principle in hydraulic cylinder stroke detection: ultrasonic ranging belongs to the category of non-contact detection, it has incomparable advantages of contact measurement in many occasions, and compared with laser, infrared, radio and other non-contact detection, ultrasonic testing is not affected by light within a certain distance range, simple structure, low cost and other characteristics. Ultrasonic ranging is a relatively new detection method, the attenuation of ultrasonic waves in air and hydraulic oil is analyzed, and several factors affecting the measurement accuracy in air and hydraulic cylinders are analyzed.
The main factors affecting the ranging accuracy in air and hydraulic cylinders include: the frequency of ultrasonic waves, the ambient temperature, the systematic error of the ultrasonic transducer itself (i.e., the probe fixation error), the hardware time delay, the electrical noise and acoustic noise of the work site, the overvoltage and dielectric pressure noise of the mains, and the spike and surge noise of the mains. With the wetted ultrasonic position sensors for short-stroke hydraulic cylinders, you can monitor the clamping process of the workpiece directly, continuously and quickly.
By emitting ultrasonic waves into the hydraulic oil, the sensor generates reliable information about the clamping status and enables early detection of deviations. By monitoring the entire clamping process, pressure fluctuations in the hydraulic unit, defects in the rotating mechanism and seal defects can also be detected and intervened in a timely manner. The MB1300 has a high output power and real-time automatic calibration for changing environments (temperature, voltage, acoustic and electrical noise) to ensure that the most reliable (air-in-air) readings are taken every time. The XL-MaxSonar-EZ/AE sensor has low voltage requirements (3.3~5.5V) and can provide long- and short-range detection and ranging in a small and compact form factor. The MB1200 and MB1300 sensors are capable of detecting objects from 0 cm (1) to 765 cm (25.1 ft) or 1608 cm (35 ft) apart (select module) and provide sonar ranging information with a resolution of 1 cm from 20 cm (2) to 765 cm or 1608 cm (select module). In general, the distance information of objects that are considered to be between 0 cm (1) and 20 cm (2) is 20 cm. The sensors are available in the form of a pulse-width output (MB1200 series), a real-time analog output envelope (MB1300 series), an analog voltage output, and a serial digital output.