Servo oil cylinder friction test bench and test method

Abstract

This invention discloses a servo cylinder friction force testing bench and testing method, belonging to the field of hydraulic component testing technology. The testing bench includes a hydraulic oil source, a servo valve, a servo cylinder under test, a pressure sensor, a displacement sensor, and a controller. No external load is required during testing; in an unloaded state, the servo valve drives the cylinder to operate in preset sinusoidal motion and triangular wave motion modes respectively. The controller identifies the points of change in motion direction and the uniform motion stage based on the displacement signal, and simultaneously collects the pressure in both chambers, calculating the static friction force and dynamic friction force respectively according to the formula F=P1×A1-P2×A2. This invention eliminates complex external loading mechanisms, achieving accurate friction force measurement solely by measuring the pressure difference between the two chambers of the cylinder itself. It has advantages such as simple structure, low cost, convenient installation, and high measurement accuracy, and can effectively evaluate the friction characteristics and low-speed stability of the cylinder.

Description

Technical Field

[0001] This invention relates to the field of hydraulic component testing technology, and more specifically, to a servo cylinder friction force testing bench and testing method. Background Technology

[0002] In high-precision, high-response hydraulic servo control systems, the servo cylinder, as a core actuator, directly affects the system's control accuracy and stability through its dynamic performance. This is especially true for hydrostatic support cylinders, where resolution and hysteresis characteristics are crucial. Significant differences between the static and dynamic friction forces of the cylinder can lead to crawling and jittering during low-speed or micro-motion control, severely degrading control quality. Accurate testing of cylinder friction is key to ensuring performance and selecting qualified products. Existing testing methods often employ external loading, such as using opposing cylinders, lever weights, or force sensors to directly measure the force required to move the cylinder. These methods generally suffer from complex, bulky, costly, and inconvenient test bench structures, and the additional connecting components may introduce extra friction and errors, affecting the accuracy of the test results. Furthermore, existing technologies often struggle to effectively and conveniently distinguish and accurately measure static and dynamic friction forces. The values ​​and differences between these two forces are core indicators for evaluating the low-speed stability and micro-motion characteristics of the cylinder. Therefore, a dedicated testing device and method with a simple structure, requiring no external loading, and capable of accurately separating and measuring static and dynamic friction forces is needed. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention aims to provide a servo cylinder friction force testing platform and testing method. Based on the differential pressure method, this approach requires no external load. By driving the cylinder to perform a specific motion pattern and monitoring the pressure in its two chambers in real time, the static and dynamic friction forces can be calculated separately, thereby achieving efficient and accurate evaluation of the cylinder's friction characteristics.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A servo cylinder friction force testing platform, comprising: Hydraulic oil source; A servo valve, the oil inlet of which is connected to the hydraulic oil source; The servo cylinder under test has its inlet and outlet ports connected to the working port of the servo valve via oil lines. Pressure sensors for detecting the pressure in the chambers are installed on the oil lines of both the inlet and outlet ports. A displacement sensor is used to detect the displacement of the piston rod of the servo cylinder under test; a controller is electrically connected to the servo valve, the pressure sensor and the displacement sensor respectively.

[0005] The controller is configured to: control the servo valve to drive the servo cylinder under test to reciprocate in a preset sinusoidal motion mode under no-load conditions, and determine the point of change of motion direction based on the displacement sensor signal, and calculate the static friction force of the servo cylinder under test based on the pressure values ​​of the two chambers collected at the point of change; simultaneously, the controller also controls the servo valve to drive the servo cylinder under test to reciprocate in a preset triangular wave motion mode under no-load conditions, and determine the uniform motion stage based on the displacement sensor signal, and calculate the dynamic friction force of the servo cylinder under test based on the pressure values ​​of the two chambers collected during the uniform motion stage.

[0006] A friction force testing method based on the above-mentioned test platform includes the following steps.

[0007] Static friction test procedure: The controller controls the servo valve to drive the unloaded servo cylinder under test to run in a preset sinusoidal motion mode; The displacement of the piston rod is monitored by a displacement sensor to identify the points of change in the direction of motion; at the points of change in the direction of motion, the pressure values ​​of the oil inlet chamber and the oil return chamber are collected simultaneously; based on the pressure values ​​and their corresponding effective action areas, the static friction force of the cylinder is calculated.

[0008] Dynamic friction test steps: The controller controls the servo valve to drive the unloaded servo cylinder under test to run according to the preset triangular wave motion mode; The displacement of the piston rod is monitored by a displacement sensor to identify the uniform motion phase in the displacement-time curve; during the uniform motion phase, the pressure values ​​of the oil inlet chamber and the oil return chamber are continuously collected. Based on the pressure values ​​and their corresponding effective working areas, the dynamic friction force of the hydraulic cylinder is calculated.

[0009] Furthermore, in the static friction test step, the specific process of calculating the static friction force is as follows: For each direction of motion, the static friction force component at the point of change in that direction is calculated according to the formula FH = P1×A1 - P2×A2, where P1 and P2 are the pressures of the oil inlet chamber and oil return chamber at the point of change, respectively, and A1 and A2 are the effective working areas of the oil inlet chamber and oil return chamber, respectively; the absolute values ​​of the static friction force components calculated in the two directions of motion are compared, and the larger value is taken as the static friction force of the servo cylinder under test.

[0010] Furthermore, in the dynamic friction force testing step, the specific process of calculating the dynamic friction force is as follows: For each direction of motion, within the identified uniform motion phase, multiple sampling points are acquired at a preset sampling frequency; for each sampling point, the instantaneous friction force value is calculated according to the formula FG = P1×A1 - P2×A2, where P1 and P2 are the pressures of the oil inlet and return chambers of the sampling point, respectively; the arithmetic mean of the instantaneous friction force values ​​of all sampling points in the direction of motion is calculated as the dynamic friction force component in that direction; the absolute values ​​of the dynamic friction force components calculated in the two directions of motion are compared, and the larger value is taken as the dynamic friction force of the servo cylinder under test.

[0011] Furthermore, preparation steps are required before testing: connect the oil inlet and return chambers of the servo cylinder under test to the hydraulic oil source through the servo valve, and ensure that the cylinder piston rod is in a free extension and retraction unloaded state.

[0012] Furthermore, the static friction force under different motion parameters can be tested by changing the amplitude and frequency of the sinusoidal motion mode; and / or the dynamic friction force under different speeds can be tested by changing the speed of the triangular wave motion mode.

[0013] The beneficial effects of this invention are as follows: By eliminating the complex external loading mechanism, only the pressure in the two chambers of the cylinder itself needs to be measured. The test bench has a simple and compact structure, which significantly reduces manufacturing costs and floor space.

[0014] Based on the fundamental principle of balancing the pressure difference and friction between the two chambers when the cylinder is running under no-load (F = P1×A1 - P2×A2), the measurement method is direct and avoids errors in intermediate transmission links. Attached Figure Description

[0015] Figure 1 This is a three-dimensional structural diagram of the present application; Figure 2 This is a schematic diagram showing the interaction between the hydraulic cylinder under test, the pressure sensor, and the servo valve in this application. Figure 3 The curve represents a sinusoidal motion. Figure 4 The friction force curve represents sinusoidal motion. Figure 5 The curve represents uniform motion. Figure 6 The friction force curve represents uniform motion. Figure labels: 1. Hydraulic oil source, 2. Servo valve, 3. Servo cylinder under test, 4. Pressure sensor. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Reference Figures 1 to 6 The image shows a servo cylinder friction force testing platform. It should include a hydraulic oil source 1, a servo valve 2, a servo cylinder under test 3, a pressure sensor 4, a displacement sensor, and a controller.

[0018] Hydraulic oil source 1 provides pressurized oil. The servo valve receives electrical signal commands from the controller and controls the flow rate and direction to the two chambers of the servo cylinder 3 under test, thereby driving the piston rod to move according to a predetermined pattern. The inlet and return chambers of the servo cylinder 3 under test are connected to the two working ports of the servo valve 2 via oil pipes.

[0019] In order to obtain the most direct pressure signal and reduce the impact of pipeline pressure loss, pressure sensor 4 should be installed as close as possible to the oil port of the cylinder body to detect the pressure P1 and P2 of the two chambers in real time.

[0020] The displacement sensor is used to detect the displacement L of the piston rod in real time, and its signal is fed back to the controller.

[0021] The controller is typically a combination of an IPC or PLC and a motion control card / data acquisition card, with built-in testing software. It generates sine and triangular wave position commands and sends them to the driver of servo valve 2; simultaneously, it synchronously acquires data from pressure sensor 4 and displacement sensor, and processes, calculates, displays, and stores the data in real time according to a preset algorithm.

[0022] Friction test basis: Theoretically, the pressure P1 of the oil inlet chamber of the oil cylinder multiplied by the effective working area A1 of the oil inlet chamber of the oil cylinder is equal to the pressure P2 of the oil return chamber of the oil cylinder multiplied by the effective working area A2 of the oil return chamber of the oil cylinder, that is, P1×A1=P2×A2. However, since the oil cylinder itself has friction, P1×A1≠P2×A2. The oil cylinder friction force F=P1×A1-P2×A2. The oil cylinder friction force is divided into static friction force and dynamic friction force.

[0023] Static friction force (FH) test procedure: Servo valve 2 drives the piston rod of cylinder 3 to perform a smooth sinusoidal reciprocating motion according to the command. The displacement sensor provides real-time feedback on the actual position. The controller monitors the displacement signal in real time. When the piston rod moves to the peak or trough of the sine wave, its instantaneous velocity is zero, i.e., the point of change of motion direction. At the identified point of change of direction A and point B, the controller synchronously triggers data acquisition, recording the inlet oil chamber pressure P1 and the return oil chamber pressure P2 at this moment.

[0024] The static friction force FH should be determined based on the measured values ​​at two points where the motion direction changes during sinusoidal motion. The larger of the absolute values ​​of FH1 and FH2 is the static friction force FH of the cylinder. This value directly reflects the maximum static friction resistance that the cylinder needs to overcome to start.

[0025] Dynamic friction force (FG) test procedure: Servo valve 2 drives the piston rod of cylinder 3 to perform triangular wave reciprocating motion. The corresponding speed curve includes: acceleration-uniform speed-deceleration-pause (or reverse acceleration)-uniform speed-deceleration stages. The controller identifies the uniform speed motion stage by analyzing the stability of the slope based on the collected displacement-time data. Within the identified uniform speed motion stage, the controller continuously collects pressures P1 and P2. For the extension uniform speed segment, the instantaneous dynamic friction force FG1 is calculated at each sampling point within the segment. Then, the arithmetic mean of all FG1 values ​​in that segment is calculated as the dynamic friction force component in the extension direction. Similarly, the same processing is performed on the retraction uniform speed segment to obtain the dynamic friction force component in the retraction direction. The larger of the two absolute values ​​is the dynamic friction force FG of the cylinder. This value reflects the average frictional resistance of the cylinder under stable motion conditions.

[0026] By comparing static friction and dynamic friction (FG), the friction hysteresis of the cylinder can be calculated, thereby comprehensively and quantitatively evaluating its low-speed stability and micro-motion characteristics.

[0027] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A servo cylinder friction force testing platform, characterized in that, include: Hydraulic oil source (1); Servo valve (2), whose inlet is connected to the hydraulic oil source (1); The oil inlet and return ports of the servo cylinder under test (3) are connected to the working port of the servo valve (2) through oil circuits respectively. Pressure sensors (4) for detecting the pressure of the chamber are installed on the oil circuits of the oil inlet and return ports. A displacement sensor is used to detect the displacement of the piston rod of the servo cylinder (3) under test; The controller is electrically connected to the servo valve (2), the high-precision pressure sensor (4), and the displacement sensor respectively. The controller controls the servo valve (2) to drive the servo cylinder (3) under test to reciprocate in a preset sinusoidal motion mode under no-load conditions. The controller determines the point of change of motion direction based on the displacement sensor signal and calculates the static friction force of the servo cylinder (3) under test based on the pressure values ​​of the two chambers collected at the point of change. The controller also controls the servo valve (2) to drive the servo cylinder (3) under test to reciprocate in a preset triangular wave motion mode under no-load conditions. The controller determines the uniform motion stage based on the displacement sensor signal and calculates the dynamic friction force of the servo cylinder (3) under test based on the pressure values ​​of the two chambers collected during the uniform motion stage.

2. A friction force testing method based on the servo cylinder friction force testing bench according to claim 1, characterized in that, Includes the following steps: Static friction test steps: The controller controls the servo valve (2) to drive the unloaded servo cylinder (3) to run in a preset sinusoidal motion mode; the displacement of the piston rod is monitored by the displacement sensor to identify the point of change of motion direction; at the point of change of motion direction, the pressure values ​​of the oil inlet chamber and the oil return chamber are collected synchronously; based on the pressure values ​​and their corresponding effective action areas, the static friction force of the cylinder is calculated. Dynamic friction test steps: The controller controls the servo valve (2) to drive the unloaded servo cylinder (3) under test to run in a preset triangular wave motion mode; the displacement of the piston rod is monitored by the displacement sensor, and the uniform motion stage in the displacement and time curve is identified; during the uniform motion stage, the pressure values ​​of the oil inlet chamber and the oil return chamber are continuously collected; based on the pressure values ​​and their corresponding effective action areas, the dynamic friction force of the cylinder is calculated.

3. The friction force testing method according to claim 2, characterized in that, The specific process for calculating static friction in the static friction test procedure is as follows: For each direction of motion, the static friction force component at the point of change in that direction is calculated according to the formula FH = (P1×A1 - P2×A2), where P1 and P2 are the pressures of the oil inlet and oil return chambers at the point of change, respectively, and A1 and A2 are the effective working areas of the oil inlet and oil return chambers, respectively. Compare the static friction components calculated in the two motion directions, and take the larger value as the static friction force of the servo cylinder (3) under test.

4. The friction force testing method according to claim 2, characterized in that, The specific process for calculating the dynamic friction force in the aforementioned dynamic friction force test procedure is as follows: For each direction of motion, during the identified uniform motion phase, multiple sampling points are acquired at a preset sampling frequency; for each sampling point, the instantaneous friction force value is calculated according to the formula FG = (P1×A1 - P2×A2), where P1 and P2 are the pressures of the oil inlet chamber and oil return chamber of the sampling point, respectively. Calculate the arithmetic mean of the instantaneous friction force values ​​at all sampling points in the direction of motion, and use it as the dynamic friction force component in that direction; Compare the dynamic friction force components calculated in the two motion directions, and take the larger value as the dynamic friction force of the servo cylinder (3) under test.

5. The friction force testing method according to claim 2, characterized in that, Before the static friction test step and the dynamic friction test step, a preparation step is also included: connecting the oil inlet chamber and oil return chamber of the servo cylinder (3) to be tested to the hydraulic oil source (1) through the servo valve (2), and ensuring that the cylinder piston rod is in a free extension and retraction no-load state.

6. The friction force testing method according to claim 2, characterized in that, By changing the amplitude and frequency of the sinusoidal motion pattern, static friction under different motion parameters is tested; and / or, by changing the speed of the triangular wave motion pattern, dynamic friction under different speeds is tested.

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