RTCP, in five-axis CNC system, think RTCP is Rotated Tool Center Point, namely we often say the tip Point of the following functions.In the process of five-axis machining, the additional motion of the tool tip is generated due to the rotary motion when pursuing the track of the tool tip and the attitude between the tool and the workpiece.The control points of the numerical control system often do not coincide with the tool tip, so the numerical control system should automatically correct the control points to ensure that the tool tip moves according to the set trajectory of the instructions.The technology is also known as TCPM, TCPC or RPCP.In fact, the functional definition of these terms is similar to that of RTCP. Strictly speaking, RTCP function is used in the structure of double swing head, which is compensated by the rotating center point of the swing head.Rpcp-like functions are mainly used in the form of double turntable machine tools, compensation is due to the workpiece rotation caused by the change in the linear axis coordinates.In fact, these functions are the same, are to keep the tool center and the tool and the workpiece surface of the actual contact point unchanged.Therefore, for the convenience of expression, this paper unifies this kind of technology as RTCP technology.
So what does RTCP do?Machine tools with RTCP technology, operators do not need to accurately align the workpiece with the turntable axis line, arbitrary clamping, automatic compensation offset machine tool, greatly reduce the auxiliary time, while improving the processing accuracy.At the same time post-processing production is simple, as long as the output tool point coordinates and vector on the line.As we said before, in the mechanical structure, the five-axis CNC machine tools mainly have double pendulum head, double turntable, a pendulum a turn and other structures.
Below, we will take the dual-turntable five-axis CNC system as an example to introduce the RTCP function in detail.
Define the concept of the fourth axis and the fifth axis in the five-axis machine tool: the rotation of the fourth axis affects the attitude of the fifth axis in the double-rotary table structure, and the rotation of the fifth axis cannot affect the attitude of the fourth axis.The fifth axis is the rotation coordinates on the fourth axis.
All right, so after we look at the definition let's explain it.As shown in the figure above, the fourth axis of the machine tool is A axis, and the fifth axis is C axis.The workpiece is placed on the c-axis turntable.When the fourth axis A rotates, the attitude of the C axis will also be affected because the C axis is installed on the A axis.Similarly, for the workpiece placed on the turntable, if we program the cutting tool center, the change in rotational coordinates will inevitably lead to the change in the X, Y, and Z coordinates of the linear axis, resulting in a relative displacement.In order to eliminate the displacement of this section, the machine must compensate for it, RTCP is to eliminate the compensation generated by the function.
So how does the machine compensate for this offset?Now let's analyze how this offset is generated.
According to the above, we all know that it is the change of rotation coordinates that causes the deviation of the straight spool coordinates.It is important to analyze the center of rotation of the rotation axis.For a double-turntable machine tool, the control point for the c-axis, also known as the 5th axis, is usually at the rotary center of the machine tool table.The fourth axis usually chooses the midpoint of the fourth axis axis as the control point.
In order to realize the five-axis control, the numerical control system needs to know the relationship between the fifth axis control point and the fourth axis control point.That is, the initial state (position 0 of axis A and C of machine tool), the position vector [U,V,W] of the control point of axis 5 under the rotating coordinate system of axis 4 with the control point of axis 4 as the origin.We also need to know the distance between the axes of axis A and axis C.For a double turntable machine tool, the example is shown in the figure below.
With that said, you can see that for a machine tool with RTCP function, the control system keeps the tool center always in the programmed position.In this case, the programming is independent, independent of machine movement.When you program on a machine tool, you don't have to worry about machine movement and tool length; all you have to worry about is the relative motion between the tool and the workpiece.The rest of the work control system will do for you.Here's an example:
As shown in the figure above, the control system does not consider the tool length without the RTCP function.The cutter rotates around the center of the shaft.The tip of the knife will be removed from its position and will no longer be fixed.
As shown in the figure above, with RTCP function on, the control system only changes the direction of the tool and the position of the tip remains unchanged.The necessary compensating motion along the X, Y, and Z axes has been calculated automatically.