centering workpiece on rotary table free sample

Is the rotary table axis above the X-Y slides as it appears? If you only need rotational motion you can flop it on your mill table anywhere convenient and clamp it down. Put a known circular object with enough weight not to move from indicator pressure on the table and get it centered by eye. Then with an indicator mounted anywhere convenient rotate the table and see how far out your object is. Tap it over toward center until you"re satisfied and now you have a circular table reference. Now mount the indicator in the spindle if it isn"t already, and move the mill"s X-Y to get your target object in line with the spindle.

If you trust the table"s outer rim sufficiently and your picture looks like rust could interfere, just mount the indicator in the spindle and with a sufficient extension sweep the rim.

If your rotary table is mounted close enough to the mill spindle centerline you could use the slides under it to re-position it sweeping the rim or your target.

This application claims priority to Japanese Patent Application No. 2011-002914 filed on Jan. 11, 2011 the disclosure of which, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.

For example, US Patent Application Publication No. 2004/0038787 describes a machine tool that includes a centering jig attachable to a tool spindle and a runout measuring device that measures a runout due to decentering of a workpiece attached on a spindle. According to a workpiece centering method implemented by this machine tool, the runout measuring device measures the runout of the workpiece by turning the spindle. Then, the tool spindle is moved to press the centering jig against the workpiece. Based on the measured runout of the workpiece, the workpiece is pushed and centered by the centering jig.

According to the workpiece centering method described above, if the centering jig is excessively pressed against the workpiece and the axis of the workpiece passes beyond the rotation axis of the spindle, the workpiece is again decentered, resulting in another runout of the workpiece. That is, in such a case, due to the rotational force of the workpiece and the pressing force of the centering jig, the distance between the axis of the workpiece and the rotation axis of the spindle may further increase, and consequently, the workpiece may fall off the spindle.

One possible option for preventing the problem described above is to lower the speed at which the centering jig pushes the workpiece. This, however, is very time-consuming. Further, because the centering jig stops pushing the workpiece before the axis of the workpiece coincides with the rotation axis of the spindle, the runout of the workpiece is not completely eliminated, causing a certain degree of centering error.

Further, because the centering jig is attached on the tool spindle, a device that automatically switches the component attached on the tool spindle between the centering jig and a tool is required. Therefore, the switching work is very time-consuming. Further, because the centering jig is attached on the tool spindle, there is a possibility that the centering jig will come into contact with other member(s) as the tool spindle moves.

The invention provides a workpiece centering apparatus and a workpiece centering method that make it possible to easily perform accurate workpiece centering.

According to a feature of an example of the invention, a centering apparatus brings a position detection probe into contact with at least three circumferentially-offset points of a peripheral face of a workpiece on a rotary table, and measures the positions of the respective contact points between the position detection probe and the workpiece. Then, the centering apparatus calculates the amount of runout of the axis of the workpiece and a phase position of the workpiece, at which the runout amount is largest, based on the measured positions of the contact points on the peripheral face of the workpiece. As such, the position of the center of the workpiece and the radius of the workpiece are determined, and therefore the amount of runout of the axis of the workpiece with respect to the rotation axis of the rotary table and the direction of the runout are accurately determined. Subsequently, the centering apparatus turns the rotary table such that the largest runout phase position of the workpiece is set in a position opposed to the workpiece contact of the centering apparatus. Then, the centering apparatus determines the relative positions of the workpiece and the workpiece contact based on the positions of the contact points of the peripheral face of the workpiece and the position of the position detection block. As such, the relative positions of the workpiece and the position detection block are determined. Then, because the positional relation between the contact face of the position detection block and the contact face of the workpiece contact, which comes into contact with the workpiece, is known, the position of the workpiece contact relative to the workpiece is accurately determined. As a result of the processes described above, the positional relation between the workpiece, the rotary table, and the workpiece contact is determined, and then the centering shaft member of the centering apparatus is moved such that the workpiece contact pushes the workpiece by a distance corresponding to the runout amount. In this way, the workpiece is centered accurately.

According to another feature of an example of the invention, the centering apparatus is mounted on a bed on which the rotary table is provided, and therefore a device that automatically switches the component fitted to a tool spindle between a centering jig and a tool, which is conventionally required, is omitted, and thus it is no longer necessary to secure a mounting space for such an automatic switching device. Further, conventionally, a centering jig is provided at a tool spindle, and therefore there is a possibility that the centering jig contact other member(s) during movement of the tool spindle. According to the above-described example feature of the invention, on the other hand, there is no possibility of such a contact, and further the relative thermal displacements of the centering apparatus and the rotary table are reduced.

According to another feature of an example of the invention, the centering apparatus moves the position detection probe to a position that is on a side opposite, across the workpiece, to where the workpiece contact is present and that is a distance corresponding to the runout amount away from the outer peripheral face of the workpiece, and keeps the position detection probe in this position. Then, the centering apparatus moves the workpiece contact to push the workpiece until the peripheral face of the workpiece contacts the position detection probe. As such, the centering apparatus is able to determine that the workpiece has been accurately pushed by the distance corresponding to the runout amount, and this reduces the cycle time of the centering.

According to another feature of the invention, the centering apparatus is arranged such that the centering shaft member is inclined by a predetermined angle with respect to the movement direction of the position detection probe that is orthogonal to the rotation axis of the rotary table. This arrangement prevents a contact between the position detection probe and the centering apparatus during movement of the position detection probe. Further, the contact face of the position detection block, which comes into contact with the position detection probe, is formed such that the contact face extends in a direction orthogonal to the movement direction of the position detection probe. As such, the position of the position detection block is accurately detected.

The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

A centering apparatus described in the following is used to center a columnar or cylindrical workpiece. As an example, a case where the centering apparatus is provided in a vertical grinding machine 1 will be described with reference to FIGS. 1A and 1B. Further, in the following example case, the cylindrical workpiece is centered when its outer peripheral face is ground by the vertical grinding machine 1.

As shown in FIGS. 1A and 1B, the vertical grinding machine 1 includes a bed 2, a rotary table 3, a column 4, a slider 5, a tool spindle head 6, a position detection touch sensor 7, a centering apparatus 8, and a control unit 9.

The bed 2 is generally rectangular, and is set on a floor. However, the shape of the bed 2 is not limited to a rectangular shape. The rotary table 3 and the centering apparatus 8 are mounted on the bed 2. The column 4 is provided upright at the rear side of the bed 2.

The rotary table 3 is circular, and is provided on the top of a rotation spindle 31 that is arranged at the bed 2 and extends vertically (i.e., in the Z-axis direction) such that the rotary table 3 is rotatable together with the rotation spindle 31. A rotation spindle motor 33 having a gear mechanism 32 that turns the rotation spindle 31 (rotary table 3) about the Z-axis is embedded in the bed 2. The rotation spindle motor 33 has an encoder used to detect the rotation angle of the rotation spindle motor 33. Therefore, it is possible to stop the rotation spindle 31 (rotary table 3) at a desired rotation angle position (phase). The workpiece is set on the rotary table 3, and magnetically fixed in its position.

The column 4 is shaped like a bridge, and is provided upright at the rear side of the bed 2. The control unit 9 is attached on one of leg members 41 of the column 4. The slider 5 is provided at an upper member 42 of the column 4.

The slider 5 is provided so as to be movable laterally (i.e., in the X-axis direction), that is, in the left-right direction as viewed in FIG. 1A, along a guide face 43 formed at the front side (face) of the upper member 42 of the column 4. A slider motor 52 that has a ball screw mechanism 51 used to move the slider 5 in the X-axis direction is provided at the upper member 42 of the column 4.

The tool spindle head 6 is provided so as to be movable vertically (i.e., in the Z-axis direction), that is, in the up-down direction as viewed in FIG. 1A, along a guide face 53 formed at the front side (face) of the slider 5. A tool spindle 61 extending vertically (i.e., in the Z-axis direction) is supported by the tool spindle head 6 such that the tool spindle 61 is rotatable about the Z-axis. A tool spindle motor 63 is embedded in the tool spindle head 6. The tool spindle motor 63 has a gear mechanism 62 that turns the tool spindle 61 about the Z-axis. A grinding wheel 64 used to grind the outer peripheral face of the workpiece is detachably attached at the lower end of the tool spindle 61. That is, the grinding wheel 64 is attached so as to be rotatable about the Z-axis relative to the tool spindle head 6.

The position detection touch sensor 7 is provided on the front face of the slider 5 so as to be movable vertically (i.e., in the Z-axis direction). Further, the position detection touch sensor 7 is movable also in a direction orthogonal to the rotation axis of the rotary table 3 as the slider 5 moves. The slider 5 is provided with a sensor motor (not shown in the drawings) having a ball screw mechanism used to move the position detection touch sensor 7 in the Z-axis direction. The position detection touch sensor 7 is provided with a position detection probe 71 extending downward (i.e., downward in the Z-axis direction). An axis Cp of the position detection probe 71, an axis Ct of the rotation spindle 31 (rotary table 3), and an axis Cg of the tool spindle 61 are aligned with each other on a line L extending in the X-axis direction.

The centering apparatus 8 includes a stationary portion 81, a movable portion 82, a centering shaft member 83, a workpiece contact 84, and a position detection block 85, which will be described in detail one by one. Because the centering apparatus 8 is mounted on the bed 2 on which the rotary table 3 is provided, a device that automatically switches the component attached on a tool spindle between a centering jig and a tool, which is conventionally required, may be omitted. Therefore, it is no longer necessary to secure a mounting space for such an automatic switching device. Further, conventionally, a centering jig is fitted to a tool spindle, and therefore there is a possibility that the centering jig may contact other member(s) during movement of the tool spindle. With the above-described structure of the example embodiment, on the other hand, there is no possibility of such a contact. Further, the relative thermal displacements of the centering apparatus 8 and the rotary table 3 are reduced.

The centering shaft member 83 is arranged in such a manner that the axis of the centering shaft member 83 passes through the axis Ct of the rotation spindle 31 (rotary table 3) and coincides with a line La that is inclined by a predetermined degree θ with represent to the line L. That is, the centering shaft member 83 is arranged in such a manner that the centering shaft member 83 is inclined by the predetermined angle θ with respect to the X-axis direction that is orthogonal to the rotation axis of the rotation spindle 31 (rotary table 3) and that is the direction in which the position detection probe 71 moves. This arrangement prevents a contact between the position detection probe 71 and the centering shaft member 83 during movement of the position detection probe 71.

The control unit 9 includes a centering controller 90 that controls the centering operation of the centering apparatus 8, and a grinding controller 91 that controls the grinding operation of the vertical grinding machine 1. However, it is to be noted that the centering controller 90 is not necessarily incorporated in the control unit 9, that is, the centering controller 90 may be provided outside the control unit 9. The centering controller 90 executes workpiece centering control by determining the runout of the axis of the workpiece from the axis Ct of the rotation spindle 31 (rotary table 3) through control of the rotation spindle motor 33, the slider motor 52, the sensor motor (not shown in the drawings), and a movable portion motor 87b,which will be described later. The details of the workpiece centering control will be described later. The grinding controller 91 controls, through control of the tool spindle motor 63, etc., the grinding of the outer peripheral face of the workpiece by turning the workpiece and the grinding wheel 64 about the Z-axis while moving the workpiece and the grinding wheel 64 relative to each other in the Z-axis direction and X-axis direction.

Next, the details of the centering apparatus 8 will be described with reference to FIG. 2 schematically showing the structure of the centering apparatus 8. The stationary portion 81 is generally rectangular, and is fixed on the bed 2. The movable portion 82 is generally rectangular, and is provided on the stationary portion 81 such that the movable portion 82 is movable in the axial direction of the centering shaft member 83 (i.e., the direction of the line La). Paired movable portion guide rails 86aand 86b,which are parallel to each other, are provided on the top face of the stationary portion 81 so as to extend along the axial direction of the centering shaft member 83. The movable portion 82 is slidable on the paired movable portion guide rails 86aand 86b.

The stationary portion 81 is provided with a threaded shaft 87aof a movable portion ball screw, which is arranged between the paired movable portion guide rails 86aand 86band is used to move the movable portion 82 in the axial direction of the centering shaft member 83. Further, the stationary portion 81 is provided with a movable portion motor 87bused to rotate the threaded shaft 87a.Further, a nut 87cof the movable portion ball screw, which is screwed to the threaded shaft 87a,is provided in the movable portion 82. Driven by the movable portion motor 87b,the movable portion 82 moves along the paired movable portion guide rails 86aand 86b.The movable portion motor 87bhas an encoder that detects the rotation angle of the movable portion motor 87b.

The centering shaft member 83 is arranged so as to protrude from the rotary table 3-side end face of the movable portion 82 in such a manner that the axis of the centering shaft member 83 coincides with the line La. The centering shaft member 83 is movable, together with the movable portion 82, in a direction orthogonal to the rotation axis of the rotary table 3. The centering shaft member 83 may be stopped at a desired position by the movable portion motor 87bhaving the encoder.

The workpiece contact 84 is a generally rectangular parallelepiped. The workpiece contact 84 is provided at the free end of the centering shaft member 83. Thus, as the centering shaft member 83 moves, the workpiece contact 84 comes into contact with the outer peripheral face of the workpiece and then pushes the workpiece in the radial direction of the workpiece.

The position detection block 85 is shaped like a rod. The position detection block 85 is provided so as to protrude from the lower side of the workpiece contact 84, at the free end of the centering shaft member 83, in a direction orthogonal to the axis of the centering shaft member 83. A contact face 85awith which the position detection probe 71 may come into contact is formed at the free end of the position detection block 85, and is used to correct the position of the workpiece contact 84. The contact face 85aextends in a direction orthogonal to the line L, that is, to the movement direction of the position detection probe 71. With the contact face 85athus formed, the position of the position detection block 85 is detected accurately.

Next, the details of the centering controller 90 will be described with reference to the function block diagram of FIG. 3. Note that in the following descriptions on the centering controller 90, some of the structural elements of the vertical grinding machine 1 shown in FIG. 3 will be described as well. Further, note that in FIG. 3, the structural elements of the vertical grinding machine 1 shown in FIGS. 1A and 1B are denoted by the same reference numerals.

The centering controller 90 includes a shaft moving portion 92, a table turning portion 93, a probe moving portion 94, a workpiece peripheral face position measuring portion 95, a runout calculating portion 96, a block position measuring portion 97, a phase position indexing portion 98, a relative position deriving portion 99, and a pushing portion 100. The shaft moving portion 92 controls the driving of the movable portion motor 87bto move the centering shaft member 83. The table turning portion 93 controls the driving of the rotation spindle motor 33 to turn the rotation spindle 31 (rotary table 3). The probe moving portion 94 controls the driving of the slider motor 52 to move the slider 5 (position detection touch sensor 7) in the X-axis direction, and controls the driving of the sensor motor to move the position detection touch sensor 7 (position detection probe 71) in the Z-axis direction.

The workpiece peripheral face position measuring portion 95 brings the position detection probe 71 into contact with at least three positions of the outer peripheral face of the workpiece, which are offset from each other in the circumferential direction, and measures the positions of contact points between the position detection probe 71 and the workpiece with the rotation of the rotary table 3 stopped. The runout calculating portion 96 calculates the amount of runout of the axis of the workpiece, and determines the phase position of the workpiece, at which the runout amount is largest (will hereinafter be referred to as “the largest runout phase position” where necessary), based on the peripheral face contact positions measured by the workpiece peripheral face position measuring portion 95. The block position measuring portion 97 measures the position of the position detection block 85 by bringing the position detection probe 71 into contact with the position detection block 85. The phase position indexing portion 98 causes the largest runout phase position of the workpiece to be opposed to the workpiece contact 84 by turning the rotary table 3. The relative position deriving portion 99 derives the relative positions of the workpiece and the workpiece contact 84 in a state where the largest runout phase position of the workpiece is opposed to the workpiece contact 84, which has been created by turning the rotary table 3, based on the contact positions measured by the workpiece peripheral face position measuring portion 95 and the position of the position detection block 85 measured by the block position measuring portion 97. The pushing portion 100 centers, after the above-described state is created by the phase position indexing portion 98, the workpiece by moving the centering shaft member 83, based on the relative positions determined by the relative position deriving portion 99, such that the workpiece contact 84 pushes the workpiece by an amount corresponding to the runout amount.

Next, the procedure of a centering program executed by the centering controller 90 will be described with reference to FIG. 4. The centering program is executed to control the operations of the centering apparatus 8, etc. so as to center the cylindrical workpiece set on the rotary table 3, as will be described in detail below.

As shown in FIG. 4, first, the centering controller 90 first moves the position detection probe 71 of the position detection touch sensor 7 toward the workpiece set on the rotary table 3 (step S1). Then, the centering controller 90 determines whether the position detection probe 71 has come into contact with the outer peripheral face of the workpiece (step S2). At this time, if it is determined that the position detection probe 71 has come into contact with the outer peripheral face of the workpiece, the centering controller 90 then measures the coordinates of the contact point (step S3).

Subsequently, the centering controller 90 increments a measurement number n by 1 (step S4), and then determines whether the measurement number n has reached a predetermined number N (step S5). The predetermined number N needs to be three or more in terms of determining the coordinates of the center of the circular outline of the workpiece and the radius of the workpiece. It is to be noted that the predetermined number N is set to four in this example embodiment.

If it is determined in step S5 that the measurement number n has not yet reached the predetermined number N, the centering controller 90 moves the position detection probe 71 away from the outer peripheral face of the workpiece, and then turns the rotary table 3 so as to rotate the workpiece by an angle of 2π/N (step S6). Then, the centering controller 90 returns to step S1, and repeats the processes in steps S1 to S4 until the measurement number n is determined as having reached the predetermined number N in step S5.

On the other hand, if it is determined in step S5 that the measurement number n has reached the predetermined number N, the centering controller 90 calculates the amount of runout of the workpiece and the phase position of the workpiece, at which the runout amount is largest, based on the measured coordinates of the contact points (step S7). For example, as shown in FIG. 5, in a case where the coordinates of four points at an outer peripheral face Wa of a workpiece W, i.e., the coordinates A (X1, 0) of a point A, the coordinates B (X2, 0) of a point B, the coordinates C (0, Y1) of a point C, and the coordinates D (0, Y2) of a point D of the outer peripheral face Wa are measured in an X-Y rectangular coordinate system with their origin at the axis Ct of the rotation spindle 31 (rotary table 3), the coordinates (α, β) of a center C of the workpiece W and a radius R of the workpiece W are calculated according to Equations 1 to 3 shown below.

A runout amount D of the workpiece W is (α ^ 2+β ^ 2)^ 0.5, and an intersection point P between the outer peripheral face Wa of the workpiece W and a line LL extending from the axis Ct of the rotation spindle 31 (rotary table 3) through the center C of the workpiece W is the largest runout phase position. As such, because the measured contact points of the outer peripheral face of the workpiece are equiangularly offset from each other (each angular interval is 90 degrees in this example embodiment), the runout amount of the workpiece and the largest runout phase position of the workpiece are easily determined. However, it is to be noted that it is possible to determine the runout amount of the workpiece and the largest runout phase position of the workpiece even if the positions (i.e., coordinates) of contact points of the outer peripheral face of the workpiece that are not equiangularly offset from each other are measured, that is, even if the angular intervals between the respective contact points are not equal to each other.

In step S8, the centering controller 90 determines whether the runout amount of the workpiece is equal to or smaller than a reference value that is prescribed for the workpiece centering. If the runout amount of the workpiece is equal to or smaller than the reference value, the centering controller 90 determines that the workpiece has been centered and therefore exits the centering program. On the other hand, if the runout amount of the workpiece is larger than the reference value, the centering controller 90 moves the position detection probe 71 away from the outer peripheral face of the workpiece, and then causes, by turning the rotary table 3, the largest runout phase position of the workpiece, corresponding to the intersection point P shown in FIG. 5, to be opposed to the workpiece contact 84 (step S9).

Subsequently, the centering controller 90 moves the position detection probe 71 and the position detection block 85 in such directions that the position detection probe 72 and the position detection block 85 contact each other (step S10). Then, the centering controller 90 determines whether the position detection probe 71 has come into contact with the contact face 85aof the position detection block 85 (step S11). If it is determined that the position detection probe 71 has come into contact with the contact face 85aof the position detection block 85, the centering controller 90 measures the coordinates of the contact face 85a(step S12).

Then, because the positional relation between the contact face 85aof the position detection block 85 and the contact face of the workpiece contact 84, which comes into contact with the workpiece, is known, the centering controller 90 derives the relative positions of the largest runout phase position of the outer peripheral face of the workpiece and the contact face of the workpiece contact 84, based on the coordinates of the contact points of the outer peripheral face of the workpiece and the coordinates of the contact face 85aof the position detection block 85 (step S13).

Then, the centering controller 90 moves the workpiece contact 84 toward the workpiece such that the contact face of the workpiece contact 84 contacts the largest runout phase position of the outer peripheral face of the workpiece and pushes the workpiece by an amount corresponding to the runout amount (step S14). Subsequently, the centering controller 90 returns to step 1 and repeats the above-described processes of the centering program until the runout amount of the workpiece becomes equal to or smaller than the reference value. Through the processes described above, the workpiece W is centered accurately.

In the meantime, because the largest runout phase position of the workpiece is set to the position opposed to the workpiece contact 84 by turning the rotary table 3 in step S9, the relative positions are easily derived in step S13. However, it is to be noted that the angle by which the rotary table 3 is turned to bring the largest runout phase position of the workpiece to the position opposed to the workpiece contact 84 is obtained in advance, and therefore the process in step S9 may be executed after the process in step S13.

As described above, in the centering program, the position detection probe 71 is made to contact at least three circumferentially-offset points of the outer peripheral face of the workpiece on the rotary table 3, and the positions of the respective contact points between the position detection probe 71 and the workpiece are measured. Then, the amount of runout of the axis of the workpiece and the largest runout phase position of the workpiece are calculated based on the measured positions of the contact points on the outer peripheral face of the workpiece. As such, the position of the center of the workpiece and the radius of the workpiece are determined, and therefore the amount of runout of the axis of the workpiece with respect to the rotation axis of the rotary table 3 and the direction of the runout are accurately determined.

Subsequently, the rotary table 3 is turned so as to set the largest runout amount phase portion of the workpiece in the position opposed to the workpiece contact 84 of the centering apparatus 8. Then, the relative positions of the workpiece and the workpiece contact 84 are derived based on the positions of the contact points on the outer peripheral face of the workpiece and the position of the position detection block 85. As such, the relative positions of the workpiece and the position detection block 85 are determined. Then, because the positional relation between the contact face 85aof the position detection block 85 and the contact face of the workpiece contact 84, which comes into contact with the workpiece, is known, the position of the workpiece contact 84 relative to the workpiece is accurately derived. As a result of the processes described above, the positional relation among the workpiece, the rotary table 3, and the workpiece contact 84 is determined. Therefore, the centering shaft member 83 of the centering apparatus 8 is moved such that the workpiece contact 84 pushes the workpiece by an amount corresponding to the runout amount. In this way, the workpiece is centered accurately.

Next, an interrupt program that may be additionally executed in step S8 of the centering program described above will be described with reference to FIGS. 6, 7A, 7B, and 7C. As shown in FIG. 6, the centering controller 90 moves the position detection probe 71 to the side opposite, across the workpiece W, to where the workpiece contact 84 is present (step S21). Then, the centering controller 90 determines whether the position detection probe 71 has come into contact with the outer peripheral face Wa of the workpiece W (step S22).

As shown in FIG. 7A. if the position detection probe 71 has come into contact with the outer peripheral face Wa of the workpiece W, the centering controller 90 then moves the position detection probe 71 to a position that is away, in the X-axis direction, from the outer peripheral face Wa of the workpiece W by a distance a corresponding to the runout amount D, and keeps the position detection probe 71 in the position (step S23), as shown in FIG. 7B. Then, the centering controller 90 moves the workpiece contact 84 toward the workpiece W so that the front end face of the workpiece contact 84 contacts a largest runout phase portion P of the outer peripheral face Wa of the workpiece W, and pushes the workpiece W toward the center C using the workpiece contact 84 (step S24).

Then, the centering controller 90 determines whether the outer peripheral face Wa of the workpiece W has come into contact with the position detection probe 71 (step S25). At this time, if it is determined that the outer peripheral face Wa of the workpiece W has come into contact with the position detection probe 71 as shown in FIG. 7C, the centering controller 90 finishes the interrupt program. In this way, through the interrupt program, the centering controller 90 is able to determine that the position detection probe 71 has pushed the workpiece W accurately by the distance corresponding to the runout amount D, and this reduces the cycle time of the centering.

The centering apparatus 8 is inclined by the predetermined angle θ with respect to the line L in order to prevent a contact between the position detection probe 71 that moves on the line L running in the X-axis direction and the centering apparatus 8 in the foregoing example embodiment. However, the centering apparatus 8 may be provided on the line L if a contact between the position detection probe 71 and the centering apparatus 8 is prevented by, for example, controlling the movement of the position detection probe 71.

Further, while the workpiece is centered through the centering program described above using the centering apparatus 8 in the foregoing example embodiment, the workpiece may be centered through the centering program described above using a runout prevention apparatus or a shoe grinding machine, which is often used to machine a workpiece on the basis of its outer diameter, in place of the centering apparatus 8.

Further, while the centering is performed on the basis of the outer diameter of the workpiece to grind the outer peripheral face of the workpiece in the foregoing example embodiment, the centering program described above may be implemented in the same manner as above also when the workpiece is centered on the basis of the inner diameter of the workpiece to grind the inner peripheral face of the workpiece.

Further, while the position detection touch sensor 7 is provided at the slider 5 in the foregoing example embodiment, for example, the same effects and advantages as those described above may be obtained even if a position detection touch sensor having a device for moving the sensor in the X-axis direction is used in place of the position detection touch sensor 7. In this case, for example, the position detection touch sensor is provided at the bed 2.

When using a rotary table on a mill, whether to mill an arc or drill holes in some circular pattern, there are two things that must be done to set up the workpiece. First, the workpiece must be centred on the rotary table. Second, the rotary table must be centred under the spindle. Then the mill table can be moved some appropriate distance and you can start cutting.

You could centre the table under the spindle first, by indicating off the hole in the centre of the table. Then you could mount the workpiece on the table and indicate off the workpiece. There are two problems with this approach. First, you are assuming that the hole in the table is true and centred. That may or may not be true. Second, this approach risks a sort of accumulation of errors, as you"re measuring from two different features (the rotary table"s hole and some feature on the workpiece). My suggestion is to centre the workpiece on the rotary table first, and then centre the rotary table under the spindle.

As shown in this photo, a DTI has been positioned with its tip against the inside of a hole in the workpiece. The DTI is held in the mill spindle, but that"s just for convenience. (When I do this, I put a little wooden wedge between the spindle pulley and the headstock, to make sure the indicator remains stationary.) It could as easily be held on a test stand. Indeed, the measurement doesn"t have to be done on the mill at all.

To centre the workpiece on the rotary table, spin the rotary table and watch for deflection of the indicator pointer. Adjust the chuck jaws as required, until the needle no longer deflects.

After the workpiece is centred on the rotary table, you now turn the spindle by hand, so the DTI tip sweeps the inside of the hole. Adjust the position of the mill table as required until no needle deflection is noted.

Again in this photo, a DTI is measuring from the inside of a hole. As in the previous illustration, the rotary table is spun and the workpiece"s position on the rotary table is adjusted until the DTI shows no deflection.

After the workpiece is centred on the rotary table, you now turn the spindle so the DTI tip sweeps the inside of the hole. Adjust the position of the mill table as required until no needle deflection is noted.

You can, of course, use the pointed end of a centre finder to position over a point on the workpiece. When centring the table under the spindle, if you are indicating off a larger hole or other curved feature, you may need to mount the indicator on a short arm, so you can sweep a large enough radius.

Years ago, before I learned CNC, I owned a Phase II 8″ horizontal/vertical rotary table that I purchased from Kap Pullen’s Getmachinetools.com store. He has them at a good price, BTW, and he’s a darned nice fellow to deal with as well as being a frequent HSM contributor. Anyway, its a nice little table, but I hadn’t done a whole lot with it for quite a while after purchasing it. As is so often the case, one day, a project landed on my doorstep and I was glad to have it.

Before I could get started, however, I had to make some accessories for it. Basically, I needed some T-Nuts to fit the table, as well as a little fixture that makes it easy to hold a plate up off the table through a hole in the center so you can machine it. The latter, what I call a “plate machining fixture”, was inspired by something similar I saw the Widgitmaster of CNCZone fame using to make Dremel clamps for his mini-router:

The Plate Maching Fixture and 3 Homemade T-Nuts. T-Nuts are easy to make: square a block to the proper dimensions, mill the side reliefs, drill, and tap. These are much smaller than the mill’s Bridgeport standard T-slots, so I made them myself and I’m using 1/4-20 bolts with them. They’re made of mild steel.

I turned the round spigot using the 4-jaw on the lathe. I’m making the fixture out of MIC-6 aluminum plate, which is pre-ground very flat on the sides. This is a 5 inch by 3 inch piece. I’ve clamped it to the rotab using my T-nuts and the regular mill clamps and step blocks. It is sitting on parallels to make sure I don’t cut into the table. You can also see how I’ve clamped the rotary table to the mill table using a big cast iron V-block I have. You can never have to many blocks with precision faces hanging around!

Having a 4-jaw chuck on your rotary table is mighty handy! Because it’s a 4-jaw, you can dial in the workpiece by adjusting the jaws until it is perfectly concentric with the table’s axis of rotation. The best way is to make an adapter plate that attaches to the back of the chuck in the same way that your lathe does so you can exchange lathe tooling with the rotab. Here is an example:

For the example, the chuck is threaded onto the adaptor plate, and then the holes in the adapter plate’s flange are used to bolt down to T-nuts on the table.

In my case, I bought a 4-jaw from Shars brand new, and simply drilled some through-holes in the chuck to mount to the table directly without an adapter plate:

First, you want to make sure your part is properly centered on the table. To do that, I clamp the table down on the mill table (no special place is needed), put my Indicol indicator holder on the mill spindle, and find some round feature on the part to indicate on. For example, on the plate milling fixture above, indicate on the round boss, or on the center hole. Spin the table and bump the part in until spinning the table doesn’t move the indicator.

Second, locate the center of rotation directly under the mill spindle. You can simply use the X and Y table handwheels to do this. Use that Indicol to indicate off of a circular feature you want centered under the spindle. Turn the indicol around on the spindle and adjust the handwheels until the indicator stays put relative to the spindle position. A Blake Coaxial indicator will make this last even simpler.

When you’re rounding partially by cranking a part around on the rotary table, it’s really easy to go a little too far and screw things up. The answer is to drill the end points to make the exact stopping point on the rotab a lot less sensitive:

Centering with a Blake indicator is really fast, but what if you don’t have a Blake, or worse, what if your mill is too small to accomodate one? Here is a nice solution I found on a German site. This fellow has made an ER collect fixture for his rotary table, and has taken care that when installed on the table, the axis of the collet is aligned with the table’s axis. He can then place a dowel or other straight pin in the collet and line up until it will go into a similarly sized collet on the spindle. Nice trick! It’s similar to how Widgitmaster showed me to align a drill chuck on a QCTP to the lathe centerline with a dowel pin held in the lathe chuck.

then, to centre the workpiece itself, you first decide what accuracy level of centring you need.....just using a pointy mill wiggler in the spindle and aligning it with scribed lines on the workpiece can get you within .005 if you"re careful.

if you need to be closer, take a step back in history....."button up" the job with a toolmakers button......drill and tap for the button in the workpiece"s approx centre, snug up the button, adjust the button to the exact desired relationship with whatever surface or other feature of the workpiece defines your centre, and tighten up the button.

when your workpiece is placed on the rotary table, sweep the button with an indicator in the spindle, adjust position til your indicator zeroes out, and you"ll have it centred within the possible accuracy of the setup.

Most small rotary tables have some sort of center hole, sometimes with a cylindrical bore but often with a Morse taper. If the part you"re wanting to center has its own center hole, you might be able to make a plug that fits the rotary table center hole and the part center hole.

The more common way of centering a workpiece on a rotary table requires that you measure the difference between workpiece radii that are 180 degrees apart, and then adjust the workpiece location on the rotary table to split the difference. The most common tool used to make the measurements is a dial gage or dial indicator that must be held stationary; most often the dial gage is anchored to the machine spindle while the rotary table base is clamped to the table.

After you center the work on the rotary table by eye, set a dial indicator up to probe the reference surface. Adjust the indicator holder or move the table so that the dial gage plunger is pressed about half way into its range of travel before zeroing the indicator. Now turn the rotary table top and workpiece (as an assembly) a half turn before reading the dial gage.

Now you want to move the workpiece relative to the rotary table surface until the dial gage reads one-half of the second value. Let"s say your two dial gage readings are A. 0.000 inch, and B. 0.138 inch . . . you want to move the workpiece until the dial gage reads 0.069 inch at BOTH positions A and B.

Next, you need to repeat the measure-rotate 1/2 turn-measure-split the difference process at positions C and D, which must be on a line perpendicular to that connecting A and B.

Since it"s about impossible to move the part on the table exactly the right amount in the right direction, it"s vital that you recheck and readjust A and B after you adjust along C and D . . . and then you"ll need to check and readjust C and D again, and so on and so on. While you"re learning, it"ll seem like you"re chasing your tail, but it is a skill you"ll learn.

To reiterate, the important part is that when adjusting the part on the table you need to rotate the part and table together when you make your measurements, NOT the machine table.

Then later, if you need to center the table under the spindle, you rotate the spindle to measure and move the machine table, which has the rotary table and part bolted to it, to make the adjustment.

Leading development partner for the transportation industry with a global operating workforce of over 5,600, EDAG (Detroit, MI / Fulda, Germany) recently was faced with the task of designing a heavy-duty ring for a new production concept. Featuring a distinctly large central opening, the WEISS CR2600 heavy duty ring rotary table is a unique combination for this size of a classic rotary table and shuttle system in which robots can access the workpiece from both sides.

The system, designed for small lot production of vehicle components, was required to not only bear the weight of car body tools weighing up to four tons, but also provide sufficient room at its center for a heavy-duty robot.

Hahl commissioned industry leading specialist for rotary tables and automation WEISS North America, Inc. (Willoughby, OH), and its’ parent company WEISS (Buchen, Germany), to initiate detailed and collaborative engineering discussions with them to develop a complete, integrated solution for EDAG’s unique production system.

Based on its‘ powerful CR series range of heavy-duty rings, which feature large open centers, WEISS North America began customized engineering specifications on a unique CR2600 rotary table that could ultimately accommodate four tools−and a robot in the center.

The table should also feature sufficient space in the center for a robot to carry out both machining and logistics functions−thus permitting space saving while enhancing the flexibility and productivity of the system.

Key specifications for the new CR2600 heavy duty ring table quickly came into focus:A permissible vertical axial 500kN dynamic and 1000kN static force on the drive plate

Additionally, the new member of the WEISS CR family would inherit all the positive design characteristics of the series’ range: a flat design, zero backlash and optimum power transmission, as well as a drive unit positioned far to the outside which can easily be taken into operation with WAS.

According to Stanislav Cafuta, a WEISS system developer, “The key was designing the ring’s central opening with a diameter of two meters, tool weights of up to 20 tons, and a reach of up to 2.5 meters – demands which even our largest heavy-duty rings were unable to meet at the time.”

Several technical hurdles had to be overcome before the new-generation CR2600 was able to achieve its production goals. With its very high vertical integration rate, WEISS was able to monitor and guarantee quality while procuring large parts with long delivery times more quickly.

One of these critical parts was the bearing. The development of a so-called YRT bearing, a combination of two axial bearings and a radial bearing, is a time- consuming matter. To overcome this issue, the WEISS engineers decided to speed up the process by giving the bearing supplier Schaeffler (Fort Mill, SC), a helping hand by assuming responsibility for the development of the bearing cages themselves. As a result, the total development time and delivery for the new CR2600 heavy duty ring table was compressed to six months.

Featuring a distinctly large central opening, the CR2600 heavy duty ring table is a unique combination for this size of a classic rotary table and shuttle system in which robots can access the workpiece from both sides. The system is currently running with two tools for two components, so that the rear hatches and bonnets can be manufactured in a combined process.

According to WEISS North America’s Vice President, Bill Eppich,“Ultimately, the CR 2600’s unique configuration opens up other possibilities for the installation that sparks the imagination. This is due to the user-programmability of the table, as well as savings in floor space brought about by the option of positioning even large robots at its center.”

EDAG’s Hahl expanded on these possibilities stating,“For example; if an opening of two meters can accommodate one large robot, then there is of course room for two or more small robots. In addition, four or more different tools can be used instead of the current 2+2. As a result, it is possible to either produce four different door types for small lots on one installation, or provide four different tools in quick succession in a similar manner as a turret on a machining center.”

Hahl concluded in stating,“The free positions can also naturally be used for logistics and equipping the tools. Therefore, the heavy-duty ring’s low height of only 300 millimeters is very convenient−enabling ergonomically favorable, stepless manual loading alongside automatic loading.”

G234 Tool Center Point Control (TCPC) lets a machine correctly run a contouring 4- or 5-axis program when the workpiece is not located in the exact location specified by the CAM-generated program. This eliminates the need to repost a program from the CAM system when the programmed and the actual workpiece locations are different.

G234 Tool Center Point Control (TCPC) is a software feature in the Haas CNC control that allows a machine to correctly run a contouring 4- or 5-axis program when the workpiece is not located in the exact location specified by a CAM-generated program.

This eliminates the need to repost a program from the CAM system when the programmed and the actual workpiece locations are different. The Haas CNC control combines the known centers of rotation for the rotary axes (MRZP) and the location of the workpiece (e.g., active work offset G54) into a coordinate system.

TCPC makes sure that this coordinate system remains fixed relative to the table; when the rotary axes rotate, the linear coordinate system rotates with them. Like any other work setup, the workpiece must have a work offset applied to it. This tells the Haas CNC control where the workpiece is located on the machine table.

TCPC is activated with G234. G234cancels the previous H-code. An H-code must therefore be placed on the same block as G234. G234is canceled by G49, G42, and G44.

TCPC G-code is programmed from the tool tip. The control knows the centers of rotation for the rotary axes (MRZP), the location of the workpiece (active work offset), and the tool length offset. The control uses this data to calculate the position of tool tip relative to the active work offset and maintains a static tool tip position through rotary feed moves.

G234 Tool Center Point Control (TCPC) is a software feature in the Haas CNC control that allows a machine to correctly run a contouring 4- or 5-axis program when the workpiece is not located in the exact location specified by a CAM-generated program. This eliminates the need to repost a program from the CAM system when the programmed and the actual workpiece locations are different.

The Haas CNC control combines the known centers of rotation for the rotary table (MRZP) and the location of the workpiece (e.g., active work offset G54) into a coordinate system. TCPC makes sure that this coordinate system remains fixed relative to the table; when the rotary axes rotate, the linear coordinate system rotates with them. Like any other work setup, the workpiece must have a work offset applied to it. This tells the Haas CNC control where the workpiece is located on the machine table.

For clarity, the illustrations in this section do not depict workholding. Also, as conceptual, representative drawings, they are not to scale and may not depict the exact axis motion described in the text.

The straight line edge highlighted in is defined by point (X0, Y0, Z0) and point (X0, Y-1., Z0). Movement along the Y Axis is all that is required for the machine to create this edge. The location of the workpiece is defined by work offset G54.Location of Workpiece Defined by G54

TCPC is invoked in . The Haas CNC control knows the centers of rotation for the rotary table (MRZP), and the location of the workpiece (active work offset G54). This data is used to produce the desired machine motion from the original CAM-generated program. The machine follows an interpolated X-Y-Z path to create this edge, even though the program simply commands a single-axis move along the Y Axis.G234 (TCPC) On and the B and C Axes Rotated

Invoking G234 (TCPC) rotates the work envelope. If the position is close to the travel limits, the rotation can put the current work position outside of travel limits and cause an over travel alarm. To solve this, command the machine to the center of the work offset (or near the center of the table on a UMC), and then invoke G234 (TCPC).

Our product range includes single and multiple axes, tilt/rotating tables, and indexing and high-speed spindles. Additionally, we offer customized solution tables for customer requests or OEM projects.

Customer satisfaction is our highest priority. Due to a high degree of vertical integration, our customers have one point-of-contact and the guarantee that all components are manufactured and assembled to your specifications.

Even for EDM machines that have been in use for decades, we will work with you to determine the ideal rotary indexing table and/or rotating/indexing spindle solution.

Our state-of-the-art rotary indexing tables and customizable reference and clamping systems provide endless application possibilities and highly efficient solutions.

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