In recent years, the development and application of parallel machine tools has been increasing. However, due to its complex structure and working space, when it is used to machine workpieces, it is highly likely that the interference between machine tools and workpieces will occur in the machine tool components themselves. In addition, if a peripheral tool such as an automatic tool changer is mounted on a work table like a parallel machine tool HexaM, when a workpiece is mounted, it may restrict the mounting position of the work piece, that is, the interference between the work piece and a peripheral device. There may be interference between the machine and peripheral equipment.
There have been many studies on the inspection method and the working space of the machine tool for self-interference in parallel machine tools. Among them, the author used the parallel machine tool HexaM of Toyota Toyoko Co., Ltd. as a model to explore the inspection method of the parallel machine tool's own interference, and proposed an approximate expression of the workspace. On the other hand, in 5-axis CNC machining, there are also many methods of checking the interference between the tool system (tool, chuck, and spindle) and the workpiece system (workpiece and fixture). Among them, Takeuchi takes several points from the surface of the tool system as interference check points, and the surface of the workpiece is composed of simple functions. When the interference check point is located inside the function, it can be judged that the machine tool interferes with the workpiece; The method is the opposite of this, which is to select the interference check point from the surface of the workpiece system to see if it enters the tool system to perform the interference check. Since the peripheral instruments of CNC machine tools are generally not placed on the work surface, neither of the two inspection methods considers the interference between the machine tool and the peripheral instruments during the processing.
The above studies discussed in detail the parallel inspection machine tool's own interference inspection and avoidance methods involving the machine tool and the workpiece. However, before using the parallel machine tool, there are still the following problems: 1 For the machine tool with obstacles such as peripheral equipment on the work table, Should consider the possibility of interference between the machine tool and the peripheral equipment; 2 When checking the interference between the machine tool and the workpiece, you should also consider the possible interference between the spindle plate, the clamp hinge and the connecting rod and the workpiece, but the existing CAM software does not include this Interference check; 3 When the machine tool interferes with the workpiece, the interference is usually avoided by adjusting the tool position. In fact, for the parallel machine tool, besides adjusting the tool position, various interferences can also be avoided by adjusting the installation position of the workpiece. Moreover, the biggest advantage of this avoidance method is that it does not change the existing CAM software.
Based on the tool trajectory output by general CAM software, this paper proposes a way to shorten the inspection time of the checkpoint file, and through the adjustment of the location of the workpiece to avoid possible interference, proposed to test whether the workpiece can be carried out The calculation method for the optimal mounting position of the workpiece during machining and machining.
1 Interference checking and interference Avoid installation of the parallel machine tool HexaM, peripheral instruments (magazines) and workpieces used in this article. Therefore, for the machine tool, the interference that may occur during the machining process and the installation of the workpiece has its own interference, the interference between the machine tool and the workpiece, the interference between the machine tool and the peripheral instruments, and the interference between the workpiece and the peripheral instruments.
If there is no peripheral equipment or peripheral equipment placed on the workbench of the parallel machine tool, the installation position of the workpiece will not be affected, or the interference between the machine tool and the peripheral equipment will not occur during the processing, the machine tool and the workpiece can be omitted. Instrument interference check.
1) Self-interference a. Composition of checkpoints During the machining process, all tool positions can be checked for self-interference as described in the literature. If interference occurs, avoid interference by adjusting the mounting position of the workpiece. After the installation position of the workpiece is changed, the position of the tool in the process naturally changes. Therefore, it must be checked again until no interference occurs. Since all tool positions are checked at each installation location, the calculation time must be very long. In order to shorten the calculation time, not all the tool positions, but only a small number of tool positions (hereinafter referred to as checkpoints) are checked for interference. Therefore, when the checkpoint is extracted, it must be done: if there is no self-interference at the checkpoint, no interference will occur at other tool positions. The advantage of setting checkpoints is that you can greatly reduce the number of checks.
The farther the tool is from the z-axis, the higher the position, and the greater the degree of tilt, the more likely it is that it will interfere with itself. Therefore, for the workpiece to be machined, the point at which the outermost measurement is made, the point with the higher tool position, and the point with the larger tool inclination angle are extracted from the tool path as checkpoints for judging whether or not the self-interference has occurred.
b. How to check the interference The position and posture of the tool must not interfere with each other when the position and posture of the tool are within the straight space circle and the rotation space circle, respectively. Therefore, the inspection method of self-interference is as follows: 1 Read all checkpoints, find the straight-forward space circle and the rotation space circle corresponding to each checkpoint. 2 When the tool position and orientation are within the corresponding straight-forward space circle and rotation space circle, it is determined that there is no self-interference at the checkpoint; if no interference occurs at all checkpoints, it is determined at the installation position. No interference will occur. 3 If the position or posture of a checkpoint exceeds the circle of the straight-in space or the circle of the turning space, repeat the check using the method of checking the interference described in the literature. Since the space circle is much smaller than the general inspection interference calculation, such an inspection method can shorten the calculation time for each inspection.
c. Method of avoiding interference Since the position of the tool is on the z-axis in the same horizontal plane, it is least likely to interfere with oneself. Therefore, if there is a self-interference at a certain checkpoint, the connection between the checkpoint and the z-axis is used as the avoidance direction. Then, move the mounting position of the workpiece 10 mm in the avoidance direction. If the included angle in the avoidance direction is greater than 150° in two consecutive passes, the avoidance direction is considered to have reversed, and there is no position to be installed in the horizontal plane. Therefore, the mounting position of the workpiece can only be increased upward. In this article, increase 10mm at a time. If you interfere with the interference between the main motor and the lower end of the slewing screw, it means that the workpiece is too high or the mounting position of the workpiece is too high. It cannot be processed by this machine.
2) Interference between the machine tool and the workpiece a. Parts that may interfere with the machine tool and the workpiece include a tool, a chuck, a spindle head, a spindle clamp, a clamp hinge, and a connecting rod. Workpieces can be considered to consist of machined surfaces and non-machined surfaces. Among them, the machined surface is composed of a non-machined point by a machining point and a non-machined surface that may interfere with the machine tool. Here, the machining point and the non-processing point are collectively referred to as an inquiry point.
Interference between the enquiry point and the tool, chuck, spindle head, and spindle plate is called Type 1 interference. This kind of interference is only related to the position of the tool, regardless of the mounting position of the workpiece. Therefore, if such interference is checked, it can only be avoided by adjusting the tool posture. This requires modification of the CAM software beyond the scope of this article.
Interference between the query point and the splint hinge or link is called type 2 interference. This kind of interference can be avoided by adjusting the mounting position of the workpiece. The following describes the composition of the checkpoints for these two types of interference. There is a cone whose apex is the center of the tool, and the cone angle q0 is the smallest angle that contains the tool, chuck, spindle head, and spindle plate; the center of the tool is the smallest from the hinge of the plywood. The distance is d0; the minimum distance in the direction of the tool axis is h0, then q0, d0, and h0 can be found according to the parameters of the machine tool components and the splint hinge's maximum rotation angle.
For any machining point P, the length P of the connecting line PQ of the P and all query points Q and the included angle q of the tool axis, the length d of the line segment, and the projected length h of the line segment PQ in the tool axis direction are calculated. Therefore, the condition q is satisfied
b. Method for checking interference When checking whether Type 1 interference occurs, the tool, chuck, spindle head and spindle clamp (referred to as the tool system) and the checkpoint for interference of type 1 are first projected on the xz plane, and then the inspection is performed. Checkpoints that fall within the projection of the tool system interfere with the tool system. Because Type 1 interference is independent of the mounting position of the workpiece, only one such inspection calculation is required before calculating the mounting position of the workpiece. Due to the difference in the mounting position of the workpiece, the position of the splint hinge and the connecting rod must be Changes in posture. Therefore, after each adjustment of the workpiece mounting position, it must be checked whether Type 2 interference will occur. Therefore, how to reduce the checkpoint for Type 2 interference is the key to shorten the inspection time. In this paper, the condition for judging the second type of interference checkpoint is to satisfy d0 and h0, which can greatly reduce the number of inspection points for a small workpiece or a relatively flat workpiece.
c. Ways of Avoiding Interference When there is interference, the avoidance method is the same as the avoidance method when one's own interference occurs.
3) Interference between machine tools and peripheral instruments a. Checkpoint composition Fig. 3 is a top view of peripheral instruments, workpieces, and toolpaths during machining in the HexaM parallel machine tool. From Fig. 3, it can be seen that the peripheral instruments are set at the first stage of the workbench. In the quadrant, the out-point (·) of the 1st quadrant in the center of the tool path is used as a checkpoint for interference.
b. Methods of Checking Interference The machine parts that may interfere with peripheral instruments include: cutters, chucks, spindle heads, splint hinges, connecting rods, and spindle clamps. They are in the shape of a polyhedron consisting of a cylinder and a bounding plane, and peripheral instruments. The shape is polyhedron. Therefore, the interference inspection method of "boundary plane and cylinder" and "boundary plane and bounded plane" can be used between peripheral instruments and machine tool parts. That is, at all checkpoints, it is calculated whether there is an intersection between the bounding plane forming the peripheral device and the cylinder or bounded plane of the machine tool part. If there is an intersection, there is interference; if there is no intersection, there is no interference. As described above, the difference in the mounting position of the workpiece will inevitably lead to changes in the position and posture of the machine tool. Therefore, each time a new workpiece mounting position is set, it must be checked again whether there is interference between the machine tool and peripheral instruments.
c. Method of avoiding interference If the machine tool interferes with peripheral equipment, use the normal direction of the front surface of the peripheral equipment as the avoidance direction. The avoidance method is the same as the avoidance method in the case of self-interference.
4) Interference of workpieces and peripheral instruments In order to quickly check whether there is interference between the workpiece and the peripheral instruments during installation, first project the workpiece to the xy plane and use a bounded polygon to envelope the projection of the workpiece. Then, use the "bounded plane and bounded plane" to check the interference of the workpiece with the peripheral instruments. This interference check must be performed every time the workpiece mounting position is given.
If the workpiece interferes with a peripheral device, the normal direction of the front surface of the peripheral device is used as the avoidance direction, and the avoidance method is the same as the avoidance method when the interference occurs.
5) Interpolation of checkpoints It is known from the above that except for the interference check between the workpiece and the peripheral equipment, other interference check is to calculate whether there is interference at the checkpoint. Therefore, if the distance between the checkpoints is too large, there is no interference at the checkpoint, and interference occurs between the checkpoints, and such interference is not discovered. This is absolutely not allowed during actual processing.
To solve the possible interference problems between checkpoints, there are mainly two methods: First, the simple function and the polyhedron to achieve the intersection of two methods; the second is to narrow the distance between checkpoints. The first method is particularly effective for checking the interference between the machine tool and the workpiece, but it cannot be used to solve the interference of oneself; the second method is suitable for all kinds of interference inspections, but if the distance between the checkpoints is too small, the checkpoint is The number is huge and the calculation of inspection interference can take a long time. Therefore, a safe distance is set in this article. According to this safety distance, the distance between checkpoints is shortened so as to achieve the purpose that the inspection result must be reliable and the inspection time must be short. The specific method is as follows.
When judging whether two objects interfere, first expand one of them by 5mm. If there are intersections between the two objects after expansion, it is determined that the two objects have interference. If the intersection is within 5mm from the surface of the object, there is still no interference. That is, if it is determined that there is no interference between the two objects, then the distance between the two objects should be 5 mm or more. Here, this 5mm is called a safety distance.
For the query points and tool trajectories output by the CAM system, if the distance between the adjacent query points or the distance between the tool trajectories is greater than the safety distance, some points are interpolated between the query points or tool trajectories. That is, the distance between the interpolated query points and the tool path is less than the safety distance. Therefore, when no interference occurs at the two check points, no interference occurs between them. Therefore, judging whether it is necessary to interpolate with a safe distance can not only prevent missed interference but also increase the calculation time.
2 How to Calculate the Workpiece Installation Position 1) Optimal Workpiece Mounting Position This document uses the “lowest pad height; the shortest distance from the center of the worktable†as the standard for measuring the optimal mounting position of the workpiece. Specifically, first, the bottom surface of the workpiece is placed on the workbench (in this case, the height of the pad is 0), and the projection center of the tool path on the xy plane coincides with the center of the table (the distance from the center of the table is 0). , as the best installation position of the workpiece. If interference cannot be installed at this position, to ensure that the height of the spacer is the lowest, the workpiece is moved from the inside to the inside within the same level to find an installation position where no interference will occur. If no installation position is found in the same level without interference, move the workpiece gradually upwards (increase the height of the spacer) and then continue to search in the same level until you find the installation position or get on the machine. The conclusion of the processing.
2) The calculation method of the best installation location is based on the concept of the best installation location of the workpiece. This article proposes the following calculation steps for the installation location of the workpiece during machining:
a. Read basic data. Including: tool, chuck radius and extension length; query point; tool path; position of the peripheral instruments and projection on the xy plane.
b. Determine if the machine can be machined. According to the query point of the workpiece and the tool trajectory, the dimension of the workpiece in the xyz direction and the movement distance of the tool are calculated. When the external dimension of the workpiece or the moving distance of the tool is too large and a warning that the workpiece cannot be machined is given, the system operation is ended.
c. Generate a checkpoint file that checks for various types of interference. Among them are checkpoint documents that check for interferences of themselves, between Class 1 and Class 2 interferences between machine tools and workpieces, and between machine tools and peripheral instruments.
d. Check if there is a Class 1 interference between the machine and the workpiece. If it exists, since the interference cannot be avoided by moving the workpiece mounting position, the system operation is ended after the warning “There is an unavoidable Type 1 interference†is given.
e. Set the initial position of tool path center C(x,y,z). In order to satisfy the definition of the optimal installation position of the workpiece, the initial setting of C(x,y,z) is: x=0; y=0; z=s. Where s is the distance from the center of the tool path to the bottom of the workpiece.
f. Calculate the position of tool path center C. According to the interference checking method and the avoidance method, the installation position of the center of the tool path is constantly moved until an installation position where interference does not occur is found or a warning is given that the workpiece cannot be machined on the machine.
g. Output the mounting position of the workpiece. If the position of the center of the tool path where interference does not occur is found in (6), the mounting position of the workpiece is calculated and output based on this value and the structure size of the workpiece.
3 Analysis, Experiment Results When using vertical machining, the general-purpose CAM software CAMAND is used to generate the tool position and tool position during machining (the same as the normal point of the machining point). In the figure, the number of position points in the tool path is 123,201 points. The tool is a ball-end milling cutter with a diameter of 10 mm, a length of 50 mm from the chuck, a chuck diameter of 60 mm, and a 45 mm extension from the spindle.
According to the above algorithm, this article has developed a system for calculating the position of the workpiece when the parallel machine tool is being machined. The installation position of the workpiece shown in Fig. 4 was calculated and the calculation time (CPU of the computer: AMD A THLON 850 MHz) was about 15 minutes.
1) Check points In the tool path generated by the CAMAND software, there is no need for interpolation auxiliary points since there is no adjacent tool path larger than the safety distance. Also, with the exception of the machined surface, the rest of the surfaces are not likely to interfere with the machine tool. Therefore, the query points are all composed of tool path points. The number of self-interference check points extracted from the query points was 2,382; the number of check points for interference between the machine tool and peripheral instruments was 248; and the number of check points for the first type and the second type of interference between the machine tool and the workpiece was 0 points. The interference check between the workpiece and the peripheral equipment becomes a problem of two quadrilateral intersections.
2) Analysis of the installation position and the experimental results The process of changing the position of the workpiece is shown in Fig. 5. From the calculation process, it is known that when the workpiece mounting position is low and near the center of the table, interference between the machine tool and the peripheral instruments is likely to occur; if the workpiece mounting position is far from the center, the machine tool itself is likely to interfere. Finally, when the mounting height of the workpiece reached 70 mm, the installation position where no interference occurred was found.
The center of the workpiece bottom is not at the center of the table, but is offset from the center of the table (-42.05, -42.05, 70) mm. This is because, to avoid the interference between the machine tool and the peripheral instruments placed in the first quadrant of the table, the workpiece must be moved to the third quadrant of the table, and also must be moved upwards. During the installation, the workpiece must be placed 70 mm high. Pads.
Whether or not there will be interference after the installation position and the proper rounding of this position, this article uses the machine tool HexaM for experiments. Among them, the minimum gap is obtained by visual inspection.
No. Mounting position (mm) Whether to interfere with the minimum distance (mm)
Xyz analysis experiment 1 -42.05 -42.5 70 â—‹ â—‹ 7
2 -40 -40 70 â—‹ â—‹ 6
3 -35 -35 70 × ○ 3
4 -20 -20 80 â—‹ â—‹ 7
5 0 0 90 â—‹ â—‹ 13
Note: ○ indicates no interference; × indicates interference occurs. Except when the workpiece is installed outside the position of line 3 (x=-35, y=-35, z=70) mm, the analytical result is the same as the experimental result, that is, not Interference will occur. When the workpiece was mounted on the third row, it was known from experiments that the minimum clearance between the machine tool and the peripheral equipment was 3mm, which was less than the safety distance set by this analysis system and was naturally judged to be interference during the analysis. Although the analytical results are different from the experimental results, it can still be considered that the analytical results are reasonable and correct. Therefore, it can be said that the calculation method proposed in this paper and the developed workpiece position calculation system are effective and can be used in actual processing.
4 Conclusions This paper uses the parallel machine tool HexaM of Toyota Toyoko Co., Ltd. as a model to explore the methods of checking the interference of the machine tool itself, the machine tool and the workpiece, the machine tool and peripheral instruments, and the interference between the workpiece and the peripheral instruments when using parallel machine tools. The method of avoiding interference by adjusting the mounting position of the workpiece. Finally, through a series of analytical results and experimental results, it is proved that the algorithm and software developed for calculating the location of the workpiece proposed in this study are correct. From the above discussion process, the following conclusions can also be drawn:
· The developed system can automatically calculate whether a given workpiece can be processed on the machine tool according to a given machining trajectory.
• When it is judged that machining is possible, the position where the workpiece is installed without interference can be calculated.
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