Hose reel irrigator Aquajet 230m Aquajet series are turbine-driven machines designed for fully mechanized and labor-saving irrigation. The main component parts such as turbine, automatic layering mechanism and crop-protecting sprinkler balancing mechanism enjoy the international patents and keep being updated. Aquajet provides the following additional features. 230M Hose Reel Irrigation,Overhead Sprinkler System,Farm Sprinkler System,Irrigation Systems For Agriculture Shandong H.T-BAUER Water and Agricultural Machinery & Engineering Co., Ltd. , https://www.ht-bauer.com
Measuring the transmission error of the machine tool is the precondition to effectively compensate the transmission error. Therefore, the precision measurement of the transmission error of the machine tool has always been an important research topic of the mechanical transmission technology. The basic measurement method of machine tool transmission error is to install sensors in the relevant parts of the machine tool, and to measure, analyze and adjust the errors of the various parts of the machine tool drive system by means of measuring instruments using mechanical, optical, and electrical principles and apply error assessment theory to find The cause of the error and the law of change.
2. Selection of sensors <br> According to the nature of movement of the end elements of the transmission chain, the correct and reasonable selection and installation of sensors is a necessary condition for accurately measuring the movement accuracy of the transmission chain. According to the working principle, the commonly used sensors for machine tool transmission error measurement can be divided into the following categories:
(1) The biggest advantage of the grating sensor grating sensor is that the signal processing method is simple, easy to use, and the measurement accuracy is high. (Foreign famous manufacturers such as Germany Heidenhain, Spain, Fagor and other companies produce grating sensors with an accuracy of 1μm/m); the disadvantage is the grating The price of the ruler is relatively expensive, and it requires a relatively high working environment. The linear expansion coefficient of the glass scale is inconsistent with the machine tool, which can easily cause measurement errors.
(2) Laser sensors Laser sensors (including single-frequency and dual-frequency lasers) have high measurement accuracy, but they also have high measurement costs and are sensitive to changes in environmental conditions (such as temperature, air flow, vibration, etc.) and are used at the production site. Measures must be taken to ensure the stability and reliability of the measurement.
(3) Magnetic grid sensor magnetic scale can be divided into two types: linear (effective measuring length 3m) and strip (effective measuring length up to 30m), its advantages are lower manufacturing costs, easy installation and use, linear expansion coefficient The same with the machine tool; the disadvantage is that the measurement accuracy is lower than the grating ruler, because the magnetic signal strength decreases with the use of time, so the need to re-record magnetic, inconvenience to use.
(4) Induction synchronizer Induction synchronizer has the advantages of low manufacturing cost, easy installation and use, and low requirement on the working environment; the disadvantage is that the signal processing method is more complex and the measurement accuracy is limited by the measurement method (measurement accuracy of the traditional measurement method. About 2 to 5 μm).
According to the different signal output methods, the sensors can be divided into analog and digital two categories. Digital sensors can be divided into incremental, absolute and signal modulation.
In a computer test system, the output signal of an analog sensor needs to be digitally processed using an analog-to-digital converter (A/D), and the cost of A/D conversion is high at high resolution, and in addition, small analog signals (such as The micro-level immunity problem is also quite difficult.
In digital sensors, absolute encoders can output parallel digital signals without A/D conversion and are easy to interface with computers. However, with the improvement of measurement accuracy, the cost of absolute encoders is getting higher and higher, and even higher than the cost of high-precision A/D conversion, so it is difficult to be accepted in many practical applications. Incremental sensors and signal modulation sensors have lower manufacturing cost and stronger anti-interference ability, and can use subdivision technology to greatly increase the resolution without changing the density of the engraved encoder. Therefore, in the measurement of transmission chain accuracy, These two types of sensors are most used. Common incremental sensors include grating incremental encoders, magnetic grid sensors, capacitive gate encoders, etc.; signal modulation sensors mainly include inductive synchronizers, laser interferometers, seismographs, and resolvers.
3. Dynamic measurement method of machine tool transmission error <br> Basic measurement principle of transmission error: Let θ1, θ2 be the input and output shaft displacement (angular displacement or linear displacement), the theoretical transmission ratio between input and output is i For example, if θ1 is used as a reference, the difference between the actual displacement of the output shaft and the theoretical displacement is the error δ of the drive chain, that is, δ=θ2-θ1/i. According to the measurement method of the displacement signal θ1, θ2, the transmission error measurement method can be divided into two major categories of phase measurement method and counting measurement method.
3.1 Machine tool transmission error ratio phase measurement method The phase relationship between the two sensor output signals θ1, θ2 reflects the transmission chain transmission error. When the transmission error TE = 0, that is, the transmission ratio is constant, θ1, θ2 maintain a constant phase relationship; when the transmission ratio i changes, the phase relationship between θ1, θ2 also changes. The ratio phase measurement method indirectly measures the transmission error TE by measuring the phase relationship between θ1 and θ2. With the development of digital technology and computer technology, the phase contrast measurement method has experienced the development from analog phase to digital phase to computer digital phase.
(1) Analog phase ratio The commonly used trigger phase meter uses the analog phase method. The principle of analog phase comparison: After two channels of signals have been frequency-divided, they become the phase of the same frequency signal. The time difference Δt between them depends on the phase difference δ(t) between θ1 and θ2. After the flip-flop identification, Δt is transformed into an analog quantity Δu corresponding to the duty ratio of the square wave of the phase-to-phase, and the change of the duty ratio reflects the transmission error of the transmission chain.
Analog phase ratio measurement system has the following problems: 1δ(t) is a periodic function with 2π as a period and changes according to a certain rule. Let f be the frequency of phase change, and ω=2πf is the angular frequency, then δ(t)=δ ( Ωt). When the two signals are compared with each other, the phase measurement is a repeated measurement with a period of 1/f. It can be known from the condition 0 ≤ δ(ωt) ≤ 2π that Δu has a linear relationship with δ(t). Since δ(ωt) changes periodically, the time constant τ of the analog recording head is required to be smaller than the period of the measured phase difference, that is, τ≤1/f, otherwise, if no accurate reading is obtained within the previous phase change period, The latter cycle has begun to repeat, so that the phase difference cannot be recorded in real time. Therefore, the analog phase-phase dynamic measurement performance is poor, and it cannot adapt to the dynamic measurement requirements of real-time analysis and processing. 2 The measurement resolution and measurement range are mutually restricted. If the resolution is increased, the range will be reduced. To do this, configure the range selection circuit so that the phase difference of the measured signal must be less than 360°. (3) It is required that the frequency of the two-phase signal of the phase comparison signal is the same, that is, only the frequency-phase ratio can be performed. Therefore, the frequency-dividing/multiplier of the two-way signal must meet the change requirements of the transmission ratio, the circuit structure is complex, and the anti-interference ability is poor. The range is smaller.
(2) Digital phase comparison Digital phase comparison is implemented using logic gates and counters. The phase difference is directly output in digital form. The principle of phase ratio: the two frequency signals θ1 and θ2 are amplified and shaped to obtain two sets of pulse signals u1 and u2, which are respectively controlled by a logic gate circuit to open and close the counter. The counting result of the counter is the time interval Δt between θ1 and θ2, which is proportional to the phase difference δ(t). Let the period of the phase signal be T, then δ(t) = 2πΔt/T.
The main features of the digital ratio phase measurement method are: 1 Because the Δt value depends not only on the phase difference δ(t) of the two signals, but also on the frequency of the two signals. Therefore, in order to obtain higher-accuracy measurement results, it is necessary to ensure that both the two-phase pulse signals and the clock signal have higher accuracy. Within a phase period T, any factor that causes a change in the frequency of the phase signal will affect the measurement result. 2 Although the digital ratio compensates for some deficiencies in the analog phase, the measurement stability and reliability are improved, but it can only be applied to the same frequency ratio phase.
(3) Microcomputer Subdivision and Phase Comparison Since the 1980s, the micro-computerization of test instruments has become an important trend in measurement technology. In the machine tool transmission error measurement, the microcomputer subdivision method has begun to be widely applied.
Microcomputer subdivision and phase comparison is a digital phase-phase microcomputer application. Because the computer has powerful logic, numerical calculation function and control function, it is easy to realize high-frequency clock subdivision, phase comparison and output of two-way signals, so the production of peripheral circuits is relatively simple. The transmission error is δ(t)=2πNt/N. In the phase comparison process, the high-frequency pulse φ is no longer generated by the external oscillation circuit, and the internal computer clock CP is directly used; the count of the pulse CP is no longer a logic gate circuit counter, but a programmable timer/counter in the computer is used. Microcomputer subdivision ratio phase measurement method has the following advantages: 1 The two phase signals do not need to have the same frequency (that is, the transmission ratio of the tested transmission chain can be any value). In the calculation of the transmission chain error, the transmission ratio is a constant. The phase ratio of 2 can be any value, and the phase difference must not be less than 360°. 3 The integration of clock subdivision and phase comparison is realized, which greatly simplifies the hardware interface circuit. Since the frequency of the programmable counter can be controlled by computer software, the sampling frequency can be easily adjusted to adapt to the measurement of the drive chain error at different speeds. 4 The subdivision accuracy and measurement accuracy of the system are relatively high, which facilitates the formation of an intelligent, multi-functional measurement system.
3.2 Measuring method of machine tool transmission error count The analog and digital ratio phases are the same frequency ratio phase. In order to obtain the same frequency ratio phase signal, it is necessary to first perform the transmission ratio frequency; in order to ensure that the error range does not occur 2Ï€ phase inversion, it also needs Divide the range. Since the frequency division will reduce the measurement resolution, it must be multiplied before the frequency division, which makes the measurement system more complicated. In addition, non-integer gear ratios cannot be measured because they cannot be divided.
The digital counting measurement method adopts the non-infra-frequency ratio phase, so it is not necessary to perform frequency division processing on the two pulse signals, and it is possible to directly use the quantitative relationship between the two sensor output pulses to transmit the computer bed transmission error.
(1) Direct counting measurement method The principle of direct counting measurement method is to set the number of output signals per input of the input and output shaft sensors as λ1 and λ2, select the output shaft θ2 as the reference axis, and the sampling interval T is equal to the period of the θ2 pulse signal or it The integer multiple. According to the definition of transmission error, the transmission error at the j-th sampling is: δ(j)=[N1(tj)-N2(tj)(iλ1/λ2)]2π/λ1.
Since θ1 and θ2 are time-discrete pulse sequences, the count N1 (tj) of the θ1 pulse in the sampling time interval (N2 θ2 pulses) varies with time and is usually a non-integer. In this way, the error Δ2π/λ1 caused by the fractional part Δ is ignored. In addition, the actual transmission system (iλ1/λ2) is not always an integer, ie, the frequency of the pulse θ1 is not necessarily an integer multiple of θ2. If the N1 theory is treated as an integer, it will cause a theoretical error, thereby limiting its application range.
(2) Microcomputer Subdivision Counting Measurement The measurement steps of the subdivision count counting method are as follows: 1 Before a θ2 pulse is used as a door opening signal, the latter θ2 pulse is used as a closing signal, and the number of pulses θ1 is counted by a counter N0; 2 Using the clock pulse CP, the pulse sequence θ1 is subdivided by interpolation, and the fractional cycle count value TΔ and the integer cycle count value T2 of the θ1 pulse signal are respectively counted; 3 The transmission error is calculated: δ(t)=(N0+TΔ/T2-iλ1) /λ2) 2π/λ1.
Microcomputer subdivision count measurement method has the following advantages: 1 can effectively reduce the measurement error Δ; 2 can make full use of computer internal resources and software control to simplify the external hardware circuit; 3 to integrate measurement sampling, data processing and results analysis to achieve Intelligent measurement.
Machine tool transmission error measuring instrument and measuring method
1. Introduction <br> The transmission error of a machine tool refers to the difference between the actual displacement of the output shaft and the theoretical displacement under the condition that the input shaft of the machine tool drive chain is driven completely and rigidly. The drive chain of the compound motion required to realize the forming of the workpiece surface on the machine tool—the two ends of the “internal contact†drive chain must always strictly maintain the motion relationship that satisfies the given requirements. Transmission chain transmission accuracy refers to the accuracy of its transmission movement, which can be measured by transmission error. Due to the actual transmission chain error of the machine tool, there is an error in the forming trajectory of the workpiece surface, which is finally reflected on the workpiece to be processed, that is, the shape error of the forming surface is caused. Since the machine tool transmission chain is mainly composed of a gear pair, a worm gear pair, and a thread pair, the error of the transmission chain mainly comes from the processing precision and installation accuracy of these transmission elements. From a kinematics point of view, everything that causes the instantaneous gear ratio to deviate from a given drive's requirements is the source of drive chain error.