Self-balancing line shaft of a machine tool

A self-balancing line shaft of a machine tool includes a spindle device, a cutter tool holder and at least one balancing assembly. The spindle device includes a spindle extending along and rotatable about an axis, and at least one precision lock nut threadedly engaged with and rotated with the spindle. The cutter tool holder is coaxially connected and rotated with the spindle. The balancing assembly includes an annular groove formed in one of the precision lock nut and the cutter tool holder and extending along a circle path surrounding the axis, and a plurality of weight members disposed in the annular groove to be moved in a direction opposite to a rotation unbalance during rotation of the spindle such that the center of mass of the whole rotating system is close to the axis.

FIELD

The disclosure relates to a machine tool, and more particularly to a self-balancing line shaft of a machine tool.

BACKGROUND

In order for a spindle device of a machine to reach a high rotational speed with a cutter tool holder thereof while maintaining a high machining precision, measurement and correction of any rotating unbalance of the spindle device is regularly conducted to prevent occurrence of chatter and undesired vibration. When doing so, the machine tool has to be shut off, which increases downtime of the machine tool and leads to undesirable increase in the manufacturing cost.

SUMMARY

Therefore, an object of the disclosure is to provide a self-balancing line shaft of a machine tool that can alleviate at least one of the drawbacks of the prior art.

According to the disclosure, the self-balancing line shaft includes a spindle device, a cutter tool holder and at least one balancing assembly.

The spindle device includes a spindle which extends along an axis and is driven to be rotated about the axis, and at least one precision lock nut which is threadedly engaged with the spindle in an axial direction of the axis. The precision lock nut has a ring-shaped nut body which has inner and outer ring surfaces surrounding the axis and radially opposite to each other, and two ring end surfaces interconnecting the inner and outer ring surfaces and opposite to each other along the axis. The inner ring surface has an internal thread section.

The cutter tool holder is coaxially connected with the spindle to be rotated about the axis. The cutter tool holder includes a holder body which has a mounting portion that is separably connected to an end portion of the spindle and that extends along the axis, a holding portion that is opposite to the mounting portion along the axis and for holding a cutter tool, and an annular portion that is raised radially and outwardly from the mounting portion and that is disposed between the mounting portion and the holding portion.

The balancing assembly is disposed on one of the precision lock nut and the cutter tool holder. The balancing assembly includes an annular groove which is formed in one of the nut body and the holder body and which extends along a circle path that surrounds the axis, and a plurality of weight members which are movable and disposed in the annular groove along the circle path. A total volume of the weight members is not larger than half of a volume of the annular groove such that, when the weight members are adjoined to one another in the annular groove, two terminal sides each defined by interconnecting an outermost one of the weight members and the axis cooperatively form an included angle that is not more than 180 degrees.

DETAILED DESCRIPTION

Referring toFIGS. 1 and 2, a first embodiment of a self-balancing line shaft of a machine tool according to the disclosure includes a spindle device1, a cutter tool holder2and a balancing assembly3.

The spindle device1includes a spindle11which extends along an axis (L1) and is driven to be rotated about the axis (L1), and two precision lock nuts12which are threadedly engaged with the spindle11in an axial direction (D1) of the axis (L1). One of the precision lock nuts12is disposed at a central portion of the spindle11to abut against bearings of the machine tool, and the other one of the precision lock nuts12is disposed at a rear end portion of the spindle11to position the spindle11.

The cutter tool holder2is separably and coaxially connected with the spindle11to be rotated about the axis (L1). In this embodiment, the cutter tool holder2is of BT series. The cutter tool holder2includes a holder body21.

Referring toFIGS. 2 and 3, the holder body21has a mounting portion211which is separably connected to an end portion111of the spindle11and that extends along the axis (L1), a holding portion212which is opposite to the mounting portion211along the axis (L1) and for holding a cutter tool4, and an annular portion213which is raised radially and outwardly from the mounting portion211and disposed between the mounting portion211and the holding portion212. The annular portion213has an upper end surface214engaged with the mounting portion211and facing the axial direction (D1), a lower end surface215opposite to the upper end surface214and engaged with the holding portion212, and an outer peripheral surface216interconnecting peripheries of the upper and lower end surfaces214,215. The holder2may be provided with a holding element, such as a collet, rivet, etc., in accordance with the cutter tool2, and the holder body21may be formed with a channel therein for a cutting fluid.

With reference toFIGS. 3 and 4, the balancing assembly3is disposed on the cutter tool holder2. The balancing assembly3includes an annular groove31which is formed in the annular portion213of the holder body21and extends along a circle path that surrounds the axis (L1), a plurality of weight members32which are movable and disposed in the annular groove31along the circle path, and a cover plate33.

The annular groove31is formed in and concaved from the lower end surface215of the holder body21, and has an access opening311at the lower end surface215. The annular groove31is bordered by a groove bottom wall34, a radially inner groove wall35, and a radially outer groove wall36. The groove bottom wall34is opposite to the access opening311in the axial direction (D1), and has radially inner and outer edges341,342each of which surrounds the axis (L1). The radially inner groove wall35extends from the radially inner edge341in the axial direction (D1), and the radially outer groove wall36extends from the radially outer edge342in the axial direction (D1).

The cover plate33has a covering portion332which is disposed in the annular groove31to close the access opening311, and a flat flange portion331which extends radially from the covering portion332to abut against the lower end surface215. The groove bottom wall34, the radially inner groove wall35, the radially outer groove wall36and the covering portion332cooperatively define a volume of the annular groove31. In assembly, the weight members32are received in the annular groove31, and the cover plate33is then secured to the lower end surface215in a fastening or welding manner to seal the access opening311.

The weight members32are restrained in the annular groove31by virtue of the cover plate33covering the access opening311, and a total volume of the weight members32is not larger than half of the volume of the annular groove31such that, when the weight members32are adjoined to one another in the annular groove31, two terminal sides, each of which is defined by interconnecting a respective one of outermost ones of the weight members32and the axis (L1), cooperatively form an included angle (θ) that is not more than 180 degrees (seeFIG. 4).

In this embodiment, the weight members32are beads and the number of the weight members32is even. The weight members32may be lubricated to reduce the impact of friction to the movement of the weight members32in the annular groove31. Alternatively, the weight members32maybe in the form of liquid, solid or a mixture of liquid and solid.

When the spindle device1is rotated with the rotational speed higher than a natural frequency of the line shaft, the weight members32of the balancing assembly3are driven by centrifugal force to move in a direction opposite to the rotation unbalance such that the center of mass of the whole rotating system is close to a central line (i.e., the axis (L1)) to alleviate chatter and undesired vibration due to the unbalance amount. Thus, the machine tool has to be shut off less often, which decreases downtime of the spindle device1and the cutter tool holder2.

In various embodiments, the number of the balancing assemblies3may be varied in accordance with the position occurring and amount of the rotating unbalance. The annular groove31may be alternatively formed in the upper end surface214to render the structure of the holder body simple without adversely affecting the rigidity thereof. With the radially outer groove wall36integrally formed as part of the holder body21not to be deformed by the centrifugal action of the weight members32during the rotation, a roundness of the annular groove31can be maintained so as to prevent deflection of the weight members32.

Moreover, in this embodiment, the annular groove31is formed in the lower end surface215of the holder body21at which a rotating unbalance often occurs, and is easily machined in a manufacturing process, which can provide the line shaft with a great self-balancing effect. With the cover plate33having the covering portion332cooperating with the groove bottom wall34to define the annular groove31, a position of the annular groove31in the axial direction (D1) can be controlled precisely during the manufacturing process.

Furthermore, the groove bottom wall34and the radially outer groove wall36may be annular so as to minimize friction of the weight members32during its rolling movement in the annular groove31. In this embodiment, the self-balancing line shaft is employed on a grinding machine tool in which a tool spindle is uni-directionally rotated at a high speed. The self-balancing line shaft may be alternatively used with other machine tools.

Referring toFIG. 5, in a second embodiment, the cutter tool holder2is of HSK series.

Referring toFIGS. 1, 6 and 7, in a third embodiment, each precision lock nut12of the spindle device1has a ring-shaped nut body121which has inner and outer ring surfaces122,123surrounding the axis (L1) and radially opposite to each other, and two ring end surfaces124interconnecting the inner and outer ring surfaces122,123and opposite to each other along the axis (L1). The inner ring surface122has an internal thread section125and two extending sections126each extending from the inner thread section125to one of the ring end surfaces124. Each of the extending sections126may have an annular gap127formed therein and around the axis (L1).

In this embodiment, two of the balancing assemblies3′ are disposed on each of the precision lock nuts12. The annular grooves31′ of the balancing assemblies3′ are formed in and concaved from the ring end surfaces124of the nut body121, respectively, and are respectively communicated with the annular gaps127. Specifically, the annular groove31′ has an access opening311′ at the ring end surface124. The annular groove31′ is bordered by a groove bottom wall34′ which is opposite to the access opening311′ in the axial direction (D1) and which has radially inner and outer edges341′,342′ each surrounding the axis (L1), a radially inner groove wall35′ which extends from the radially inner edge341′ in the axial direction (D1), and a radially outer groove wall36′ which extends from the radially outer edge342′ in the axial direction (D1). The cover plate33′ covers the access opening311′ so as to restrain the weight members32′ in the annular groove31′. Similarly, the cover plate33′ has a covering portion332′ which is disposed in the annular groove31′ to close the access opening311′, and a flange portion331′ which extends radially from the covering portion332′ to abut against the ring end surface124. The groove bottom wall34′, the radially inner groove wall35′, the radially outer groove wall36′ and the covering portion332′ cooperatively define the volume of the annular groove31′.

In various embodiments, the number of the balancing assemblies3′ may be varied in accordance with the position occurring and amount of the rotating unbalance. The annular groove31′ maybe alternatively formed in the extending section126of the inner ring surface122of the nut body121to render the structure of the nut body121simple without adversely affecting the rigidity thereof. With the radially outer groove wall36′ integrally formed as part of the nut body121not to be deformed by a centrifugal action of the weight members32′ during the rotation, a roundness of the annular groove31′ can be maintained so as to prevent deflection of the weight members32′. Moreover, in this embodiment, the annular grooves31′ are formed in the ring end surfaces124of the nut body121at which a rotating unbalance often occurs, which can provide the line shaft with a great self-balancing effect.