I. Introduction
　　 Automatic online measurement of machined workpieces on CNC machine tools is an effective method to improve the automatic processing level of CNC machine tools and ensure the accuracy of the workpiece processing. Therefore, online automatic measurement system of CNC machine tools is one of the important features of measuring the technical level of CNC machine tools. Become an essential basic option for purchasing CNC machine tools. The online automatic measurement system can help the operator to set up the workpiece and set the workpiece coordinate system automatically before machining. This can simplify the fixture, save the fixture cost, shorten the auxiliary time, and improve the processing efficiency. After the neutralization processing, the workpiece size can be automatically measured online, and the error compensation data can be automatically generated and fed back to the numerical control system according to the measurement result to ensure the dimensional accuracy of the workpiece and the dimensional consistency of the batch workpiece; the on-line measurement can also be avoided The workpiece is moved to the secondary error caused by the measuring machine measurement, which can improve the processing accuracy and precision retention, and can obtain qualified products through one cutting, which greatly enhances the degree of intelligentization of CNC machine tools.
Second, the composition and working principle of the measurement system
　　 The automatic workpiece measurement system for CNC lathes generally uses a touch probe measuring system (such as the LP2 touch probe measuring system of Renishaw, UK). The trigger probe can generally be assumed to be mounted as a tool on a pocket of the tool holder for measuring the workpiece size. When the tool holder is moved and the probe touches the workpiece, the position of the probe is triggered by the numerical control system. The numerical control system calculates the workpiece size through the corresponding measurement software. On CNC lathes, the triggering measurement system can measure the outer diameter, inner diameter, length, and slot width of rotating parts. The touch probe measuring system is usually composed of touch probes, signal transmission and receivers, controller interface devices for connection to CNC systems, coordinate position data acquisition, processing and measurement error compensation systems, and automatic feedback compensation systems for measurement results. The working principle is shown in Figure 1.
Fig.1 Operational principle of triggering measurement system for CNC lathe
The triggering probe is a normally closed contact type integral unit probe, and its inside is three groups of equally divided and series contact triggering mechanisms. When working, the probe can be installed as a tool on a tool bit of the turret tool holder. When the tool holder is moved and the probe comes into contact with the workpiece, a slight offset occurs in the spindle, making one of the three equally spaced contacts. Or the two contacts are disconnected and a series circuit consisting of three contacts is open circuited to generate a step signal in an instant. This signal is transmitted through the signal transmitter in wired (wired) or wireless (electromagnetic coupling, infrared radiation) mode. Transmitted to the controller interface, the controller interface will be triggered with irregular oscillation signal after shaping the transmission to the CNC system, CNC system after receiving the trigger signal to send an interrupt signal, the machine stops moving and record the probe at this time The position coordinate, the numerical control system sends the data to the corresponding parameter unit automatically, as the variable carries on the computation processing, then the numerical control system calculates the workpiece size through the data processing software and the measurement error processing software, and feeds back the numerical control system to carry on the tool automatically Compensation or workpiece coordinate adjustment to ensure the workpiece machining accuracy.
Third, the measurement software preparation method
　　 For CNC machine users, it is very important to select or compile measurement software that is suitable for the measurement needs of their products. In general, touch-trigger probes can be purchased from professional manufacturers (such as Renishaw, etc.), but since the machine tools use different numerical control systems, the measurement software is usually compiled and provided by a numerical control system manufacturer or a numerically-controlled machine tool manufacturer. Since the current CNC system is powerful and can provide macro systems, users can also make their own measurement programs according to actual needs. Take the SINUMERIK 880 CNC system as an example. The system provides the user with parameter programming and @code that allows the user to develop and program a variety of canned cycle programs (including machining and measurement cycle programs, etc.). Parameter programming can complete parameter definition, assignment and addition, subtraction, multiplication, and division operations, while @code can perform function operations, parameter access, parameter comparisons, conditional and unconditional program jumps, logic decisions, and Boolean operations. Various functions such as system memory data input, output, and program editing can fully meet the user's need for measuring fixed-cycle programs. A brief introduction to parameter programming and the definition and use of @code is given.
1. Defining parameters and basic programming method <br> parameter programming (Parameter programming) is programmed with the parameters R ××× data as address code or data code. The role of the parameter as a substitute in programming is composed of the letter R and three digits. The R code is divided into two groups of nine groups from R0 to R999. The first category R0 to R499 are channel-specific R parameters, where R0 to R200 The basic parameters, such as: R00 ~ R49 for the transfer parameters, mainly used for the establishment of canned cycles and subroutines; R50 ~ R99 is a local parameter, mainly used for the preparation of canned cycles and subroutine calculations in the temporary calculation results; R100 ~ R199 as a global Parameters, mainly used for data storage of part programs and subroutines; R200 ~ R499 is mainly used in the system. The second major category R900 ~ R999 is the center R parameter.
The parameters can be directly assigned in the numerical control machining program, such as R01=10, and can also be assigned to each other, such as R01=R03; the parameters can perform arithmetic operations, such as R01=R02+R03, R01=R02-R03, R01=R02*R03, R01= R02/R03. E.g:
N10 R01=9.7 R02=-2.1
N20 X=20.3+R01
N30 Z=19.7-R01
Result: X=30, Z=10.
2. The definition of the @code and its basic usage @code consists of the @ sign and a three-digit number, such as @XXX, meaning: the first digit is the main group difference code, and the second digit is the subgroup code. The third digit is to define a specific function.
The first main group difference code is divided into 7 groups, which are respectively defined as: @0×× is a general instruction in the program structure; @1×× is a branch instruction in the program; @2×× is a general data transmission instruction; @3×× is data transfer instruction, from system memory to R parameter; @4×× is data transfer instruction, from R parameter to system memory; @6×× is arithmetic operation and logic operation instruction; @7×× is NC Specific instructions.
The second subgroup distinguish code and the third specific function code have different definitions in each main group, for example: 4 in the @041 represents the storage R parameter, 1 represents the parameter area to be stored; @100 The first 0 represents an absolute jump, the last 0 represents an unconditional jump; the first 1 in @111 represents a conditional jump, the comparison code is 1, and the last 1 represents the condition is equal. Another example: 4 in @440 means to set the R parameter directly to (write) the programmed coordinate value, and 0 is the specific function.
The functions and functions of the @code are very rich, and the programmer can use it flexibly according to the programming needs.
In the programming of the @ code, there are three main types to be followed by operands: K × × × is a constant; R × × × is an R parameter; P × × × is a pointer. For example, @100K1000 means jump to the 1000th sentence unconditionally, in which the positive number is the forward jump and the negative number is the backward jump.
Figure 2 shows the block diagram of the measurement software for automatic measurement system of CNC lathes. For users of the SINUMERIK 880 control system, suitable measuring programs can be programmed using @codes and parameters.
Fig. 2 The block diagram of measurement software design of CNC lathe automatic measurement system
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