Research On Technique Of The Standard Force Source With Double Levers

Research on technique of the standard force source with double leversThe force measurement is to ensure that measured value of standard force measurement apparatus or equipment is accurate and reliable. The standard force machine is the necessary system in order to establish benchmark and standard for force measurement. Force standard machine is the working device equipped with a standard power source and to complete the verification to the measuring instruments. And the force standard machine is the highest standard device in the national force measurement and the force value passed the field. Its level of accuracy and performance is an important indicator to measure the national force measurement testing.Lever type force standard machine use the principle of enlarging lever and the dynamics theory to generate the force value with two methods:the one is enlarging the accurate weight with same ratio of the lever, the other is weight fixed move on the lever by amplifying the lever ratio. Traditional lever-type force standard machine is the composition with the leverage structure amplified and dead-weight force standard machine, which is the lever ratio fixed, changing the weight to achieve force loading. However, this lever-type force standard machine has some shortcomings and deficiencies in the technology, mainly including the low efficiency and automation, poor performance, high cost, no advanced technologies and new methods. These deficiencies seriously impact on scientific research, production and measurement. In this context, we developed a new type of force standard machine with two levers, to solve the problems with low efficiency and automation, poor performance and low accuracy and so on.1. The principle of double lever-type force standard machineAccording to lever amplification principle, rely on a single block of fixed weight (jockey-weight) by changing the jockey-weight position on the main lever beam to change the lever ratio, and achieve force loading. As long as the precisely control jockey-weight position, the goal of precise load can be achieved. The two main characteristics of the double lever-type force standard machine are two lever systems, namely, the main lever system and the balance lever system. The main lever system uses the second lever principle to achieve the loading force. The balance lever system uses the first lever system to balance all the weigh generated by the main lever system. As long as structural parameters of system determined the initial balance location of jockey-weight (zero position) is uniquely determined and not be influenced by Installation workpiece or other factors. Therefore, the zero position is natural balance. Using the double lever-type force standard machine can not only realize precise loading force, but also in structure optimization, reducing size, cost greatly reduced.2. Error analysis the error and assessment of degree of uncertaintyMainly analyze geometric error and force error of the double lever-type force standard machine, the main source of geometric errors are from the equilibrium position deviating from the lever system, the deviation of placement from the centerline of the workpiece, the elastic deformation of lever and mechanical manufacturing and processing accuracy and so on. Force errors are mainly from the equilibrium position deviating from the lever system, friction torque of knife-edge bearing, displacement resolution and elastic deformation of lever. Some errors can be eliminated by improving the system stiffness and optimization design; and other can be compensated by precisely traveling the jockey-weight position. Since the existence of force error, force value in the measurement process can not be fully identified, which need to be expressed with degree of uncertainty.Force uncertainty express the range that the error exist in the measurement, the error may fall on that range. According to the assessment methods of degree of uncertainty, force uncertainty mainly caused by physical factors and force error.3. Zero position calibration and force calibrationZero position balance, calibration and force calibration of double lever-type force standard machine play a very significant impact on the machine work performance. According to the lever balance principle, complete zero position balance the zero position calibration by changing the weight position on the main lever beam. Initial zero position be adjusted just only one before starting work.Once the balance, the installation or replacement of the tested samples will not affect the initial equilibrium position. The double lever-type force standard machine realizing zero position balance, calibration and force calibration mainly base on the principles and methods through keeping initial equilibrium, breaking the balance and then recovering balance.Force calibration methods include:fractional weight placed on the reverse rack placed and changing the additional weight on the balance lever. This method is simple and reliable.4. Automatic control analysis and realization of visualization human-machine interfaceAccording to the requirements of the high-precision, high efficiency, automation requirements, develops a fully automated control system based on computer. This control system fundamentally solve poor automation, low reliability, complex operation and other questions existing in the traditional lever-type force standard machine. Particularly expound the hardware, control analysis and visualization human-computer interface. Control analysis includes setting mathematical model and calculating transfer function of each control component in the closed-loop control system. According to all the transfer function derived, we know the control system is a second-order system, then make transfer function of second-order system to the standard forms for time-domain analysis.5. The load characteristics experiment of the load cell and applicationWe design a 50kN double lever-type force standard machine through above theory and principle, and through a large number of load characteristics experiment of load cell demonstrate performance indicator of 50kN double lever-type force standard machine.The experimental show that:the loading time and equilibrium time did not exceed 10s, force Repeatability error is less than 0.002%. Then use the precisely loading technology of the 50kN double lever-type force standard machine complete the experiment of plastic measure pressure and solve the problem about precise loading and calibration of copper pillar. Plastic pressure experiment of copper pillar also shows that deformation of copper pillar has very good repeatability in any loading, and the parallelism error is less than 5μm.In summary, the double lever-type force standard machine is a working device with high precision, high efficiency, high reliability, high automation and low-cost. It completely compliance with international and national requirements for the standard force source...