Automatic compensation method for automatic tool setting and tool wear of CNC planer

June 06 13:08:12, 2024

When machining planes and simple parts with CNC planers, there is usually no precise positioning of the tool and compensation of tool wear, but when used to machine parts with a cross-sectional contour that is complex (such as the cross-sectional contour of the Roots pump rotor) The four-section circular arc, the four-section outer cycloidal line and the four-section involute curve, the contour line of the large water ring pump impeller blade is composed of a plurality of straight lines and arcs, and their dimensional accuracy, profile position accuracy and shape accuracy are all on the workpiece. There is a high requirement), the cutting edge relative to the starting position of the workpiece directly affects the machining accuracy of the workpiece. Due to the large size and large margin of the workpiece, the rough finishing is often carried out on the same machine. The rough machining requires different tools. The tool chipping phenomenon sometimes occurs, so even if the same workpiece is machined, the tool sometimes Need to be replaced multiple times. Each time the tool is changed, the tool tip is required to be at the same starting position. In addition, when the same tool is used to machine multiple workpieces or one large workpiece, the wear of the tool sometimes exceeds the allowable degree during the machining process, and the tool wear is not compensated, and the size of the workpiece may be out of tolerance. To achieve high-precision machining of the workpiece, the precise positioning of the tool and the compensation of the tool wear must be well solved. Generally, there are usually two solutions to the problem of positioning of the CNC planer after the tool is installed and replaced: one is the trial cutting method; the other is the adjustment method of the tool block. But the two methods are not accurate, or inconvenient to operate. The wear compensation of the tool can usually be carried out knowing the amount of tool wear, but the online detection of tool wear itself is a complicated problem that is not easy to implement. For this reason, the automatic tool setting and tool wear automatic compensation device with simple structure and convenient operation are studied.

Figure 1 Tool and tool wear compensation device

Figure 2 knife signal detection circuit

1 Structure of the device


Figure 1 shows the automatic tooling and tool wear automatic compensation device for CNC planer designed by the author. The structure of the device is very simple, consisting of three parts: the tool block, the insulator and the base. The entire device is fixed to the table by screws through the base. The tool setting device and the table are moved horizontally by the X-direction servo motor, and the tool is moved up and down by the Z-direction servo motor control. There is a terminal for each of the block and the base, and the two are insulated by an insulator. The groove of the tool block consists of two bevels and a plane, called the bevel of the tool and the bottom of the tool. The bottom surface of the knife is parallel with the table top of the worktable, and the inclined surface of the cutter is parallel to the forward and backward movement direction of the planer. In order to ensure the accuracy of the tool, high flatness and low roughness are required for both the bevel and the bottom of the block.
The tool signal detection circuit is shown in Figure 2. It consists mainly of a photocoupler and two current limiting resistors. The two signal output lines on the block are respectively connected as input signals to the two input ends of the signal detecting circuit to form a switching circuit, and the output signal is connected to the parallel interface 8155 of the numerical control system. From the circuit point of view, in Fig. 1, since the base is connected to the tool through the table and the bed, the terminal 2 is also connected to the tip. When the tool tip is in contact with any pair of knives, the LED of the signal detecting circuit illuminator will be turned on and illuminate, and the phototransistor will also be turned on, and the output terminal level will be changed from high to low. When the tool tip leaves the tool face, the path of the LED is turned off, the light stops, and the output returns to a high level. This signal is used as the input signal of the numerical control system. The numerical control system judges whether the tool tip and the tool block are in contact according to the level of the input signal.

2 tool setting method


The tool setting is to adjust the position of the tool so that the tool tip is placed at a certain spatial position relative to the workpiece (the origin of the tool) when the tool is changed and the tool is changed. If the position of the workpiece mounted on the table is determined, the position of the tool tip relative to the workpiece is determined as long as the position of the tool tip relative to the table is determined. Therefore, the purpose of the tool can also be achieved by adjusting the position of the tool relative to the table. The tool setting of the planer requires the position of the tool tip to be determined in two orientations, one is the vertical orientation and the other is the horizontal orientation. For the tool setting device shown in Figure 1, the vertical orientation of the tool tip is determined by the position of the tool tip relative to the bottom surface of the tool blade, and the horizontal orientation is determined by the position of the tool tip relative to the two pairs of blade bevels.
The process of setting the knife is to use the tip of the knife to find a problem with a midpoint between the bottom surface of the knife and the inclined surface of the knife. Set the tool origin to 20mm above the middle of the two pairs of knife bevels. The tool setting method is as follows:
  1. First control the table and tool movement so that the tool is above the bottom of the tool (no limit on height);
  2. Control the tool to move down, and during each move down, take one step down to check if the tool tip and the bottom face are in contact. When it is detected that the tool tip touches the signal of the tool face, the control tool stops moving downward, the Z coordinate value is cleared, and then the tool is moved upward by 5 mm;
  3. The control table is moved to the left to move the right tool slant to the tool. When it is detected that the tool tip touches the right tool slant, the table stops moving and the X coordinate value is cleared.
  4. The control table moves in the opposite direction, and at the same time, the displacement amount L in this direction is recorded. When it is detected that the cutter head is in contact with the left counterblade slope, the table stops moving.
  5. The control table is moved to the left to the middle of the opposite side of the blade (ie at L/2).
  6. Control the tool to move up 15mm and clear the two coordinate values ​​of X and Z. The position where the tool tip is located at this time is the set tool origin.

In the above six steps, the first step is to use the manual function of the CNC system. The other steps are to design a tool setting program to complete automatically.

3 tool wear compensation


The longitudinal wear of the tool tip will shift the position of the tool nose to the lowest point, which is equivalent to the tool origin moving up; the lateral wear of the tool tip will cause the left or right deviation of the tool nose center position, which is equivalent to the tool origin. Left or right. By setting the tool, the tool origin can be automatically restored and the tool wear is automatically compensated. In the case of faster tool wear speed, in the process of machining, multiple tools can be used to achieve online compensation of tool wear.
The automatic compensation function for tool and tool wear is designed as a function module when designing the CNC system. For a CNC system using a PC as the host, if there is no tool setting program, a tool setting program can be designed separately. General PCs and various CNC systems have parallel I/O interfaces, so in addition to optocoupler devices, there is no need to add other interface circuits to achieve this function.
After understanding the idea of ​​tool and tool wear compensation, you can design a program to achieve this. The design of the tool setting program is not a difficult problem. The design of the specific program is not introduced here.

4 Conclusion


The tool setting method has the characteristics of simple structure, low cost and convenient operation, and can simultaneously solve the problem of automatic compensation of the tool automatic tool setting and tool wear, and the precision of the tool and tool wear compensation is high, so the pair of tools The method has strong usability and has high promotion and application value in the planer numerical control system. The tool setting method has been applied in the planer numerical control system developed by the author and has achieved good results.

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