JPS6158263B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for positioning a spindle at an accurate position with reference to a contact surface, and its purpose is to detect contact of a contact inserted into the spindle. The objective is to achieve highly accurate positioning in an extremely short time using signals.

In numerically controlled machine tools, it is necessary to position the spindle at an accurate position with respect to a reference surface or reference hole provided on a workpiece or jig, and perform required machining. On the other hand, in positioning using program commands, since positioning is performed based on the program origin, the workpiece machining surface may be misaligned with respect to the program origin due to workpiece or pallet installation errors or mechanical thermal displacement, and accurate machining cannot be expected. Nakatsuta.

Therefore, if the spindle is accurately positioned with respect to the workpiece reference plane, etc., and machining is performed based on program commands based on this point, the above-mentioned errors can be eliminated and highly accurate machining can be performed.

Accurate positioning of the spindle with respect to such a workpiece reference surface is achieved by using the position where a tool or contactor inserted into the spindle comes into contact with the reference surface as a reference. In order to perform positioning at the contact detection point in this way, it is necessary to eliminate errors caused by overrun after contact detection. In order to eliminate this error, positioning by contact detection cannot increase the sending pulse frequency, resulting in a large time loss.

In view of these points, the present invention aims to ensure positioning accuracy through contact detection and to significantly shorten the time required for positioning, and will be described below based on embodiments.

Fig. 1 schematically shows a numerically controlled machine tool equipped with a contact detection function, in which 1 is a bed, 2 is a column installed on the bed 1 so as to be movable in the Z-axis direction (axis direction of the main spindle), 3 is a Z-axis motor that operates the column 2 in the Z-axis direction; 4 is a spindle head that is attached to the column 2 so as to be movable in the Y-axis direction (vertical direction); and 5 is a Y-axis motor that operates the spindle head 4 in the Y-axis direction. It is a shaft motor. Further, 6 is a work table installed movably in the X-axis direction (lateral direction perpendicular to the Z-axis direction) on the bed 1, and this work table 6 is operated in the X-axis direction by an X-axis motor 7. A rotary indexing table 8 is installed on the work table 6, and a pallet 9 on which a workpiece W is fixed is placed on the rotary indexing table 8.

A cylindrical reference hole 10 is provided on the side surface of the pallet 9.
A contactor 11 that makes relative contact with the inner circumferential surface of the reference hole 10 is replaceably mounted on the main shaft 4a of the spindle head 4. The contact 1
1 is formed into a spherical shape that is sufficiently smaller than the inner diameter of the reference hole 10, and this spherical contact surface 11a is used as a contact portion with the inner peripheral surface of the reference hole 10. During centering, the main shaft 4a is connected to the gears 4b, 4c. Main shaft motor 4 through
d while rotating the contact 11 and the reference hole 10.
are controlled by Y-axis motor 5 and X-axis motor 7, respectively.
The contact between the contactor 11 and the reference hole 10 is detected by relative movement in the axial and X-axis directions, and centering measurement is performed.

Also, a bearing 1 is attached to the spindle head 4.
A slip ring 13 that is electrically connected to the main shaft 4a is attached to the outer periphery of the main shaft 4a, which is supported via the spindle 2. A brush 14 that slides on this slip ring 13 is fixed to the nose end surface of the spindle head 4. The brush 14 is in electrical communication with the spindle head 4. The bed 1, column 2, spindle head 4, work table 6, rotary indexing table 8, pallet 9, contactor 11 and main shaft 4a are made of conductive metal material, and the slip ring 13 and The brush 14 constitutes a means for short-circuiting the electrical resistance of the bearing 12, thereby making the reference hole 1
The loop resistance of the closed loop secondary circuit 15 formed by the contact between the main shaft 4a and the contactor 11 is reduced, and the loop resistance is stabilized regardless of whether the main shaft 4a rotates or stops. Further, a coil 16 is wound around the outer circumference of the tip of the spindle head 4 in a toroidal shape, and this coil 16 is connected to an AC power source 18 via a detection resistor R. coil 16
When excited by an AC power source, a closed loop secondary circuit 15 is created due to the contact between the reference hole 10 and the contactor 11.
A current is induced in At this time, if the contact resistance between the reference hole 10 and the contactor 11 is small, the secondary circuit 1
A large current flows through the reference hole 10 and the contact 11, and if the contact resistance is large, the current becomes small, and if the reference hole 10 and the contact 11 are far apart, no current flows. Due to such a change in the secondary circuit 15, the excitation current of the coil 16, which is the primary side, also changes, resulting in a change in the voltage across the resistor R connected in series with the coil 16. That is, if the closed loop of the secondary circuit 15 is not formed, the excitation current of the coil 16 is small, so the voltage across the resistor R is low, but if the closed loop of the secondary circuit 16 is formed, the excitation current of the coil 16 is low. As the voltage increases, the voltage across the resistor R becomes higher, and if the contact detection circuit 17 detects that this voltage exceeds the set level, the contact detection between the reference hole 10 and the contact 11 becomes highly sensitive and stable. It will be done.

In Fig. 2, reference hole 1 is used as the contact surface.
The principle diagram is shown in the case of centering in which a contactor 11 attached to the main shaft and having a concentric spherical contact surface 11a is brought into contact with the inner circumferential surface 10a of the main shaft 0 to align the main shaft center S with the reference hole center 0. Centering is accomplished by positioning the spindle center at the center of the contact point at each of two points on the X and Y axes. In such centering, contact detection is required at a total of four points, and positioning is performed for each contact point.

As shown in the cycle diagram in Fig. 3, this positioning is performed at high speed until the first contact is detected, then returned by a small amount at high speed upon contact detection, and after confirming that there is no contact, the second contact is detected. The object is fed at a slow speed until the contact is detected, and then the feed is stopped and positioning is performed. This slow feed is performed using a feed pulse with a cycle longer than the time required for one rotation of the main shaft. This reduces time and ensures positioning accuracy.

Here, if the spindle rotation speed is 600 revolutions per minute, the feed pulse for slow forward movement must be 10 PPS or less. If the setting unit of one pulse is 1 μm and a feed pulse of 10 PPS is given to the feed servo motor and the feed servo motor is moved 1 mm before contact is detected, it will take 100 seconds. On the other hand, if the high-speed feed in the method of the present invention is to apply a feed pulse of 200PPS, it will take 5 seconds to detect the first contact, and if the high-speed retraction amount is 40 μm, it will take 0.2 seconds, but even if non-contact confirmation is included, it will take 5 seconds to detect the first contact. 0.5 seconds, and if the slow advance is 10PPS and advances 40 μm to the second contact detection, it is 4 seconds, and the total time required is 9.5 seconds, which is 10 minutes per positioning cycle compared to when the method of the present invention is not adopted. Highly accurate positioning is possible within 1 minute of time.

Similarly, the second point _P2 is moved at a high speed until the first contact is detected, and then returned to the point where there is no contact and is moved at a slow speed until the second contact is detected.

Each positioning point P ₁ positioned in this way,
By counting the feed pulses between _P2 , the distance between both positioning points can be detected, and by returning to the midpoint, centering in the X-axis direction can be performed. By positioning points P ₃ and P ₄ in the Y-axis direction and returning them to the midpoint, the spindle center S can be aligned with the reference hole center 0.

In this way, in the case of centering to control the machining operation using the center of the reference hole as the origin, the positioning method according to the present invention performs positioning based on the inner peripheral surface of the hole. The surface may be a work reference plane or a reference plane on a reference block provided on a pallet or the like.

Note that the contact detection method is not limited to the method shown in the above embodiment, and for example, contact may be detected using a detection signal associated with the amount of change in the contact. This is effective for detecting contact between unobtainable items.

According to the method of the present invention, high-speed feed can be used to position the contact at the position where it contacts the reference surface, which can significantly shorten the time, and also eliminate positioning errors due to overrun, etc. This has the effect of achieving accurate positioning.

[Brief explanation of the drawing]

FIG. 1 is an overall view of a numerically controlled machine tool equipped with a contact detection function, FIG. 2 is an explanatory diagram of the principle of centering by contact detection, and FIG. 3 is a cycle diagram of the positioning method of the present invention. 1...Bed, 2...Column, 4...Spindle head, 4a...Main shaft, 10...Reference hole, 11
...Contact element, 17...Contact detection circuit.

Claims (1)

[Claims] 1 Equipped with a contact detection function that detects when a tool or contactor attached to the main shaft of a numerically controlled machine tool approaches a contact surface, and detects contact by relatively feeding the two in the direction of approaching each other. This is a positioning method in which the feed is stopped at a certain position, and the approach operation is performed at high speed until the first contact is detected, and after the first contact is detected, the high speed feed is stopped and a very small amount is moved until the non-contact position is reached. A high-speed positioning method characterized by moving the object backward, then approaching the object again at a slow speed, and then stopping the feeding and positioning by detecting a second contact.