Patent Description:
In a machine tool such as a machining center, when automatically changing a tool, whether or not a tool holder is correctly attached to a main spindle is checked to confirm suitable seating. To confirm seating, in the past, a distal end face of the main spindle which a rear end face of a flange of the tool holder closely contacts is provided with a compressed air outlet. Compressed air is supplied from the inside of the main spindle through an air supply flow channel, and the pressure of the air inside the air supply flow channel is detected. That is, if the rear end face of the flange of the tool holder and the distal end face of the main spindle closely contact each other, the amount of air leaking out from between the two surfaces is very small, so the pressure of the air supply flow channel rises to a predetermined value in a short time. As a result, it is judged that the tool holder is suitably seated. As opposed to this, if foreign matter like a chip is caught between the rear end face of the flange of the tool holder and the distal end face of the main spindle and therefore the two surfaces do not closely contact, the amount of air leaking out becomes greater and the pressure of the air supply flow channel does not rise to the predetermined value, so it is judged that the tool holder is not suitably seated.

PTL <NUM> describes a main spindle device according to the preamble of claim <NUM> able to confirm seating utilizing compressed air such as explained above. In the device of PTL <NUM>, aiming at supplying the necessary sufficient amount of air to the distal end face of the main spindle, the seating surface of the main spindle is formed with an arcuate or annular groove and the outlet of the air supply flow channel is opened at this groove.

PTL <NUM> discloses a clamp device comprising a spindle on a seating surface of which there is formed an arc-shaped air blowout groove that continues to an air supply passage. Air supplied from a compressor passes through an air piping and an air flow path of a casing, then circulates in a recessed groove of the spindle, the air supply passage and the air blowout groove toward the seating surface side, and is blown out to a holder body portion of the tool holder.

PTL <NUM> discloses a chip catching detection device for detecting catching of chips in a tool fitting structure in which a tool end face is brought into close contact with a spindle end face and a tapered part and a tapered hole are elastically deformed and brought into close contact with each other when a two-plane constraining tool is fitted to the tool fitting part of the spindle. When a chip is caught between the tapered part and the tapered hole, detection compressed air passes through a clearance space around the chip, and then is positively discharged from a tapered hole discharge groove to outside of the spindle, and change in a flow rate of the air is detected.

The inventors of the present invention have discovered that by making the depth of the annular groove such as shown in PTL <NUM> shallower, it becomes possible to detect thin foreign matter in a relatively short time, but the problem of foreign matter causing the outlet of the air supply flow channel to be blocked easily arises. If the outlet of the air supply flow channel is blocked, the pressure inside the air supply flow channel rises to almost equal to the case where the seating is normal, so regardless of interposition of foreign matter, the control device may mistakenly judge that the seating is normal. As opposed to this, the inventors of the present invention have discovered that by making the depth of the annular groove deeper, the problem of foreign matter causing the outlet of the air supply flow channel to be block becomes less frequent but the time required for detection of thin foreign matter is increased.

The present invention is made in consideration of the above situation and has as its object the provision of a main spindle device of a machine tool able to raise a reliability of confirmation of seating without increasing the time required for confirmation of seating.

To achieve the above object, according to the present invention, there is provided a main spindle device according to the appended set of claims.

According to the present invention, when supplying compressed air to an air supply flow channel to confirm seating of a tool holder with respect to a main spindle, the effect of enabling even thin foreign matter to be detected in a short time and the effect of it becoming harder for an outlet to be blocked by foreign matter covering the outlet of the air supply flow channel, which in the past were in a tradeoff relationship, can both be achieved. Therefore, according to the present invention, it becomes possible to provide a main spindle device of a machine tool raising the reliability of confirmation of seating without lengthening the time required for confirmation of seating.

A main spindle device <NUM> of a machine tool according to an embodiment of the present invention will be explained below with reference to <FIG>. <FIG> is schematic longitudinal cross-sectional view of the main parts of the main spindle device of the machine tool (below, sometimes simply referred to as the "main spindle device") <NUM> according to the embodiment of the present invention to which an air supply circuit is added, while <FIG> is a view of the end face showing a distal end face <NUM> of the main spindle device <NUM>. In the following explanation, the machine tool is a vertical machining center, but it is clear that the main spindle device <NUM> may, for example, be a main spindle device <NUM> of a horizontal machining center or other machine tool.

The main spindle device <NUM> is provided with a support member <NUM> supported by a column of the machine tool (not shown) to be able to move in a Z-axial direction, a main spindle <NUM> rotating about a rotational axis Rz extending in the Z-axial direction, a plurality of bearings <NUM> arranged between the support member <NUM> and the main spindle <NUM> and rotatably supporting the main spindle <NUM>, a draw bar <NUM> arranged inside of the main spindle <NUM>, a collet <NUM> arranged between the draw bar <NUM> and a tool holder <NUM>, a plurality of dish springs <NUM> biasing the draw bar <NUM> upward in the Z-axial direction, a not shown actuator pushing the draw bar <NUM> downward in the Z-axial direction, etc. The main spindle device <NUM> in the present embodiment clamps the tool holder <NUM> with respect to the main spindle <NUM> by constraining the two surfaces.

<FIG> is a view similar to a view enlarging <FIG>. There, the tool holder <NUM> is clamped to the main spindle <NUM>. The tool holder <NUM> in <FIG> is shown in a longitudinal cross-sectional view in the state where the rotary tool <NUM> for machining use is fixed by a known method, but the inside structure is not shown. Only the contours are shown. The tool holder <NUM> is of a type clamped from two surfaces, so has a tapered shank part <NUM> and a flange part <NUM> forming a positioning surface perpendicularly intersecting the rotational axis Rz. The tool holder <NUM> is clamped at the main spindle <NUM>, as is well known, by insertion of the shank part <NUM> of the tool holder <NUM> into a corresponding shank insertion hole <NUM> provided at the main spindle <NUM> and pulling up the tool holder <NUM> by a draw bar <NUM> until the outer circumferential surface of the shank part <NUM> of the tool holder <NUM> and the inner circumferential surface of the shank insertion hole <NUM> closely contact each other and further the positioning surface of the flange part <NUM> of the tool holder <NUM>, that is, the rear end face, closely contacts the distal end face <NUM> of the main spindle <NUM>. Further, while changing the tool holder <NUM>, the above-mentioned closely contacting surfaces are sprayed with coolant from a not shown coolant spray port so as to wash off any chip or other foreign matter which may deposit there.

The main spindle device <NUM> of the present embodiment is further provided with, for confirming seating, an air supply flow channel <NUM> for supplying the distal end face <NUM> of the main spindle <NUM> with compressed air from the inside, a pressure detector <NUM> detecting the pressure of the air supply flow channel <NUM>, a compressed air source <NUM>, a control device <NUM>, and a not shown solenoid valve opening and closing the air supply flow channel <NUM>. The air supply flow channel <NUM> is comprised of a pipe portion 21a from the compressed air source <NUM> to the support member <NUM>, a support member inside part 21b formed at the inside of the support member <NUM>, and a main spindle inside part 21c formed at the inside of the main spindle <NUM>. An outlet 21d of the air supply flow channel <NUM> is formed as the outlet 21d of the main spindle inside part 21c. The outlet 21d of the air supply flow channel <NUM> opens in an annular recess <NUM> formed at the distal end face <NUM> of the main spindle <NUM> centered about the rotational axis Rz. The annular recess <NUM> is shown in <FIG>, more particular, is shown in <FIG> schematically explaining it.

The main spindle device <NUM> of the present embodiment is controlled so that, when the main spindle <NUM> stops, the rotational angle of the main spindle <NUM> is controlled by the control device <NUM> so that the outlet of the support member inside part 21b of the air supply flow channel <NUM> and the inlet of the main spindle inside part 21c are positioned in terms of angle. Furthermore, while not shown, an embodiment configured so that when the main spindle <NUM> is at a standstill, the outlet of the support member inside part 21b of the air supply flow channel <NUM> and the inlet of the main spindle inside part 21c closely contact each other, while when the main spindle <NUM> is rotating, they separate is also possible. In this case, the flow channel part of the air supply flow channel <NUM> including the outlet of the support member inside part 21b is formed inside a plunger (not shown) able to advance and retract in a direction perpendicular to the rotational axis Rz. The plunger is actuated to retract during rotation of the main spindle <NUM> and to advance and contact the main spindle <NUM> when the main spindle <NUM> stops.

Next, the annular recess <NUM> formed at the distal end face <NUM> of the main spindle <NUM> will be explained with reference to <FIG> is a view schematically showing the distal end face <NUM> of the main spindle <NUM>, while (B) is a cross-sectional view laying out flat the cross-section curved by the line X-X extending in the circumferential direction in (A). The annular recess <NUM> is formed so that when the tool holder <NUM> is attached to the main spindle <NUM>, it is completely covered by the rear end face of the flange part <NUM> of the tool holder <NUM>. The annular recess <NUM> has a relatively shallow first section 25a and a second section 25b deeper than the first section 25a. At the bottom surface of the second section 25b, a diameter <NUM> outlet 21d of the air supply flow channel <NUM> opens. In the present embodiment, a depth D<NUM> of the first section 25a is <NUM>, while a depth D<NUM> of the second section 25b is <NUM>. The widths of the first section 25a and second section 25b are both <NUM>. However, an embodiment differing in width W of the first section 25a and the second section 25b is also possible.

In the embodiment of <FIG>, the first section 25a has a considerably wide area in a plan view of about <NUM> times the second section 25b. The inventors of the present invention have discovered that this is because if the depth of the annular recess <NUM> is large, as explained later, the detection time or judgment time when thin foreign matter is interposed becomes longer. In other words, reducing the area of the considerably deep second section 25b enables the judgment time to be shortened.

Next, how the main spindle device <NUM> according to the present invention confirms seating will be explained with reference to the flow chart of <FIG>.

The process of confirmation of seating is started by the main spindle <NUM> clamping the tool holder <NUM> (S10). Note that, in the present embodiment, compressed air continues to be supplied from before the process of confirmation of seating is started.

Next, in this state, a predetermined wait time is waited. The predetermined wait time is determined in accordance with the thickness of the smallest chip targeted for detection etc. (S20).

Next, the control device <NUM> judges if the air pressure in the air supply flow channel <NUM> detected by the pressure detector <NUM> has exceeded a predetermined threshold value (S30).

If the detected pressure is a predetermined threshold value or less, the control device <NUM> judges that the seating is unsuitable and emits an alarm (S40).

On the other hand, if the detected pressure is over the predetermined threshold value, the control device <NUM> judges that the seating is suitably performed (S50) and ends the seating confirmation step and tool changing step (S60).

Here, before explaining detail the action and effect of the main spindle device <NUM> of the present invention, the action and effect of an annular recess in a main spindle device (not shown) according to the first and second related art of the present invention will be explained referring to the graphs of <FIG> and <FIG>. Note that, the main spindle device of the first and second related art according to the present invention differ from the main spindle device <NUM> according to the embodiment of the present invention in only the configuration of the annular recess, so preparation of drawings is eliminated. For the reference notations of the component element, the ones of the main spindle device <NUM> are employed.

<FIG> shows graphs showing the change along with time of the air pressure in the air supply flow channel <NUM> detected when seating and clamping the tool holder <NUM> to the main spindle <NUM> of the main spindle device according to the first related art of the present invention. The pressure of the ordinate is the pressure detected by the pressure detector <NUM>. <FIG> shows the graph as a whole, (B) is an enlarged view of a relatively high pressure region of (A). The main spindle device according to the first related art differs from the main spindle device <NUM> according to the present invention in the annular recess <NUM> formed at the distal end face <NUM> of the main spindle <NUM> not being provided with the second section 25b and being only comprised of the first section. The outlet 21d of the air supply flow channel <NUM> opens at the bottom surface of the annular recess <NUM>. Further, the annular recess <NUM> is formed to a depth of <NUM>.

The six lines in the graphs in <FIG> show the following six types of conditions, that is:.

Note that, in this Description, the "thickness" of a chip indicates the thickness including bending and warping of the chip.

From <FIG>, it will be understood that the pressure rapidly rises due to the tool holder <NUM> being clamped while seated at the main spindle <NUM> and stabilizes at about <NUM> to <NUM> second. The pressure is the highest in the case of the condition (a) where the tool holder <NUM> is suitably seated at the main spindle <NUM> and the rear end face of the clamp of the tool holder <NUM> and the distal end face <NUM> of the main spindle <NUM> closely contact in state and is the lowest in the case of the condition (e) where the foreign matter interposed between the two surfaces is thick. In the case of the condition (f) where the foreign matter is thick and covers the outlet 21d of the air supply flow channel <NUM>, the pressure becomes somewhat high, but does not reach the threshold value, so the presence of the foreign matter is detected.

On the other hand, in the case of the condition (c) where the foreign matter is thin and is interposed between the two surfaces at a location far from the outlet 21d of the air supply flow channel <NUM>, the pressure exceeds the threshold value once and rises to a value substantially equal to the state of close contact (a), but after about <NUM> seconds, falls to the threshold value or less. Therefore, the presence of foreign matter is detected. However, in this way, about <NUM> seconds are required until correct results of detection are obtained, so the above-mentioned wait time may be set to for example <NUM> seconds with the addition of an extra margin. This <NUM> seconds of wait time is not a practical value for a user of a machine tool with a high tool changing frequency, but is a value where shortening is desired. In the case of the condition (c), the pressure rises once probably due to the coolant present in the annular recess <NUM>. That is, due to the coolant present in the annular recess <NUM> obstructing the flow of air, the pressure temporarily rises, but it is believed the pressure falls as the coolant is expelled from the annular recess <NUM> by the compressed air.

The action and effect of a main spindle device according to the second related art will be explained with reference to <FIG>. In the second related art, the annular recess <NUM> formed at the main spindle <NUM> does not have the second section 25b and only has the first section. The depth of the annular recess <NUM> is <NUM> in the first related art, but the depth of the annular recess <NUM> in the second related art is <NUM>. The rest of the configuration is equal to the first related art. <FIG> is a graph similar to <FIG>. The conditions (a) to (f) are also the same.

In <FIG>, unlike <FIG>, in the case of the condition (c) as well, the pressure will never exceed a threshold value. Therefore, it becomes possible to judge the interposition of thin <NUM> foreign matter in a short time, for example, even if shortening the wait time down to about <NUM> second. On the other hand, in <FIG>, in the case of the condition (f) causing the deposition of a thickness about <NUM> aluminum alloy chip so as to cover the outlet 21d of the air supply flow channel <NUM>, despite foreign matter being sandwiched in, the pressure exceeds the threshold value and stabilizes. This is because a chip of aluminum alloy thicker than the depth of the annular recess <NUM> is pushed against the outlet 21d of the air supply flow channel <NUM> and block it. As a result, the problem arises of the control device <NUM> mistakenly finding that seating has been suitably performed.

The rise in pressure in the main spindle device <NUM> according to the embodiment of the present invention will be explained using <FIG> similar to <FIG> and <FIG>. The annular recess <NUM> of the distal end face <NUM> of the main spindle <NUM> of the main spindle device <NUM>, as explained above, is comprised of the first section 25a with the depth D<NUM> of <NUM> and the second section 25b with a relatively small area, but the depth D<NUM> of <NUM> deeper than the first section 25a, in which second section 25b, the outlet 21d of the air supply flow channel <NUM> opens. According to <FIG>, even in the case of the condition (c), which is a problem in the case of the first related art, the pressure never exceeds a threshold value. Therefore, interposition of foreign matter can be judged in a short time. Further, even in the case (f), which is a problem in the case of the second related art, the pressure will never exceed the threshold value. Therefore, seating being suitably performed will never be mistakenly recognized.

In this way, according to the main spindle device <NUM> according to the embodiment of the present invention, the effect of enabling even thin foreign matter to be detected in a short time and the effect of it becoming harder for the outlet 21d of the air supply flow channel <NUM> to be blocked by foreign matter covering the outlet 21d, which in the past were in a tradeoff relationship, can both be achieved. This is because, according to the present invention, by providing the second section 25b in the annular recess <NUM>, the outlet 21d of the air supply flow channel <NUM> becomes harder to block, so the first section 25a can be made shallower.

A number of modifications of the main spindle device <NUM> according to the embodiment of the present invention will be explained below. In these modifications, the form of the second section of the annular recess of the main spindle <NUM> differs from that in the above-mentioned embodiment.

First, an annular recess <NUM> of a first modification will be explained with reference to <FIG> is a view schematically showing a distal end face <NUM> of the main spindle <NUM>. (B) is a cross-sectional view laying out flat the cross-section curved by the line X-X extending in the circumferential direction in (A). Here, the depth of the second section 125b of the annular recess <NUM>, as shown in <FIG>, becomes gradually deeper the closer to the outlet 21d of the air supply flow channel <NUM>.

In a second modification, a second section 225b of an annular recess <NUM>, as shown in <FIG>, is formed in steps so as to become deeper the close to the outlet 21d of the air supply flow channel <NUM>. In <FIG>, one step is formed at the second section 225b, but several steps may also be formed.

In a third modification, a second section 325b of an annular recess <NUM> is formed as a circular recess surrounding an outlet 21d of the air supply flow channel <NUM> such as shown in <FIG>.

A modification comprised of the above first to third modifications combined is also possible. For example, the first modification and third modification may be combined and the circular recess may be formed as a frustoconical recess becoming gradually deeper the closer to the outlet 21d of the air supply flow channel <NUM>.

Claim 1:
A main spindle device (<NUM>) of a machine tool using compressed air to confirm seating of a tool holder (<NUM>), comprising:
a main spindle (<NUM>) having a distal end face (<NUM>) which a flange (<NUM>) end face of the tool holder (<NUM>) closely contacts;
an annular recess (<NUM>) formed at the distal end face (<NUM>) of the main spindle (<NUM>) so as to be covered by the flange (<NUM>) end face of the tool holder (<NUM>);
an air supply flow channel (<NUM>) connecting with the annular recess (<NUM>) and supplying the annular recess (<NUM>) with compressed air;
a compressed air source (<NUM>) supplying air to the air supply flow channel (<NUM>); and
a pressure detector (<NUM>) detecting pressure of the compressed air inside the air supply flow channel (<NUM>),
characterized in that
the annular recess (<NUM>) has a first section (25a) deeper than the distal end face of the main spindle and a second section (25b) deeper than the first section (25a), the air supply flow channel (<NUM>) opening at the second section (25b).