CN115105152A - Medical oscillating saw head - Google Patents

Abstract

The invention discloses a medical oscillating saw head, which comprises a head shell, an oscillating shaft and a reciprocating oscillating mechanism, wherein the oscillating shaft and the reciprocating oscillating mechanism are arranged in the head shell; the front end part of the swing rod is connected with the swing shaft, the rear end part of the swing rod is provided with a driven part, the driven part is matched with the driving part through a spherical pair, and the driving part and the driven part convert the rotary motion of the eccentric shaft main body into the reciprocating swing motion of the swing shaft. According to the medical oscillating saw head, through the sliding of the spherical pair and the up-and-down swinging of the second oscillating bar, the redundant resultant force of all directions except the horizontal swinging transmitted by the eccentric shaft is dissolved, so that the unnecessary vibration and noise are reduced, and the heat productivity is reduced.

Description

Medical oscillating saw head

Technical Field

The invention relates to the technical field of medical instruments, in particular to a medical oscillating saw head.

Background

In an orthopedic surgery, a medical oscillating saw is a common tool for sawing bones, and the medical oscillating saw is generally composed of a mobile phone, a machine head and a saw blade assembly, wherein a driving motor is arranged in the mobile phone. The machine head is internally provided with a swing shaft and a reciprocating swing mechanism, the reciprocating swing mechanism comprises an eccentric shaft and a shifting fork, one end of the eccentric shaft is connected with an output shaft of a driving motor, the other end of the eccentric shaft is provided with a driving part eccentrically arranged with a rotation axis of the driving part, one end of the shifting fork is connected with the swing shaft, the other end of the shifting fork is provided with a forked driven part, the driving part is clamped in the driven part, the outer side surface of the driving part is in movable contact with the inner side surface of the driven part, and rotary motion is converted into reciprocating swing motion through the eccentric shaft and the shifting fork. This kind of reciprocal beat mechanism, because the rigidity cooperation between the initiative portion of eccentric shaft and the driven part of shift fork, at the high-speed operation in-process of eccentric shaft, the vibration is big, the operation is noisy, it is violent to generate heat, is not convenient for last work for a long time, and saw cuts and shake the momentum big, if the saw bit of taking the sheath is supported in the adaptation, its accurate advantage of saw cutting can not effective performance.

Disclosure of Invention

In view of the current state of the prior art, the technical problem to be solved by the present invention is to provide a medical oscillating saw handpiece, which reduces interference of adverse factors such as vibration, noise and heat generation of the handpiece in high-speed operation, so that a doctor can use the handpiece more stably, with less noise and less heat generation, and the experience of the doctor on the product is improved.

In order to solve the above technical problem, the present invention provides a medical oscillating saw head, comprising: the reciprocating deflection mechanism comprises an eccentric input assembly and a swinging rod, the eccentric input assembly comprises an eccentric shaft, and the eccentric shaft comprises an eccentric shaft main body capable of rotating around a first axis and a driving part which is connected with the front end of the eccentric shaft main body and is eccentrically arranged with the first axis; the front end part of the swing rod is connected with the swing shaft, the rear end part of the swing rod is provided with a driven part, the driven part is matched with the driving part through a spherical pair, and the driving part and the driven part convert the rotary motion of the eccentric shaft main body into the reciprocating swing motion of the swing shaft.

According to the medical oscillating saw head, the oscillating rod is connected with the driving part through the spherical pair, the two parts can slide relatively at any angle under the action of the eccentric shaft and can be kept in reliable and stable connection, namely stable spherical contact is realized, the eccentric shaft can keep sufficient freedom degree when moving, relative impact is not generated between the two parts, and the two parts can be guaranteed to slide relatively stably.

In one embodiment, the driven part is provided with a spherical groove, the outer side wall of the driving part is spherical, and the inner side wall of the spherical groove and the outer side wall of the driving part together form the spherical pair.

In one embodiment, the inner side wall of the spherical groove is provided with a heat dissipation groove.

In one embodiment, the heat dissipation grooves comprise axial heat dissipation grooves extending along the axial direction and radial heat dissipation grooves extending along the circumferential direction, and the axial heat dissipation grooves and the radial heat dissipation grooves are communicated with each other.

In one embodiment, the driven part is provided with a heat dissipation hole communicated with the heat dissipation groove.

In one embodiment, the driving portion includes a mandrel and a spherical bearing sleeved on the mandrel, a central axis of the mandrel is eccentrically disposed with respect to the first axis, and an outer side wall of an outer ring of the spherical bearing is spherical.

In one embodiment, the swing link includes a first swing link and a second swing link, a front end of the first swing link is coaxially and fixedly connected with the swing shaft, a rear end of the first swing link is connected with a front end of the second swing link, the second swing link has a rotational degree of freedom about a second axis, the second axis is located in a swing plane of the first swing link and perpendicular to an axis of the first swing link, and the driven portion is disposed at a rear end of the second swing link.

In one embodiment, the rear end portion of the first swing link and the front end portion of the second swing link are connected by a rotating shaft extending along the second axis.

In one embodiment, one of the rear end portion of the first swing link and the front end portion of the second swing link is provided with a U-shaped slot, the other of the rear end portion of the first swing link and the front end portion of the second swing link is provided with a chuck, the chuck is located in the slot, and the rotating shaft penetrates through the two rear end portions of the chuck and is fixed on two slot walls of the U-shaped slot respectively.

In one embodiment, a sliding sleeve is sleeved in the shaft hole of the chuck, and the rotating shaft is arranged in the sliding sleeve in a penetrating mode and is in clearance fit with the sliding sleeve.

In one embodiment, the rear end of the rotating shaft is provided with a cap, the front end of the rotating shaft is provided with a mounting hole extending along the radial direction, and the front end of the rotating shaft sequentially penetrates through one side wall of the clamping groove, the clamping head and the other side wall of the clamping groove and then is locked by the elastic clamping pin penetrating through the cap and the mounting hole.

In one embodiment, the second swing link has a translational degree of freedom along a second axis, and an elastic member is disposed between a rear end portion of the first swing link and a front end portion of the second swing link.

The advantageous effects of the additional features of the present invention will be explained in the detailed description section of the present specification.

Drawings

FIG. 1 is a cross-sectional view of a medical pendulum saw in an embodiment of the present invention;

FIG. 2 is a perspective view of the medical oscillating saw head shown in FIG. 1;

FIG. 3 is a top view of the medical oscillating saw head shown in FIG. 1;

FIG. 4 is a cross-sectional view taken along line A-A of FIG. 3;

FIG. 5 is a front view of the medical oscillating saw head shown in FIG. 1;

FIG. 6 is a cross-sectional view taken along line C-C of FIG. 5;

FIG. 7 is an enlarged partial view of FIG. 6 at B;

FIG. 8 is an enlarged partial schematic view at B1 in FIG. 7;

FIG. 9 is a front view of the eccentric input assembly of the medical oscillating saw head shown in FIG. 1;

FIG. 10 is a cross-sectional view of the eccentric input assembly shown in FIG. 9;

fig. 11 and 12 are perspective views of the first swing link in different directions, respectively;

FIG. 13 is a perspective view of a first swing link of the medical swing saw head shown in FIG. 1;

FIG. 14 is a perspective view of the rotatable shaft of the medical oscillating saw head shown in FIG. 1;

fig. 15-17 are schematic diagrams of the spherical bearing and the first swing link in cooperation, wherein fig. 15 is a state in which the mandrel of the eccentric shaft is rotated to the middle, and fig. 16 is a state in which the mandrel of the eccentric shaft is rotated to the bottom; fig. 17 shows a state in which the spindle of the eccentric shaft is turned to the top.

Description of reference numerals: 1. a sheath saw blade; 2. a machine head; 21. a handpiece housing; 211. a first shell; 212. a second shell; 22. a pendulum shaft; 221. a drive pin; 23. an eccentric input assembly; 230. an eccentric shaft; 231. an eccentric shaft main body; 232. an input interface; 233. a mandrel; 234. a spherical bearing; 234a, an outer sidewall; 235. a first bearing; 236. a second bearing; 237. a sleeve; 237a, an installation interface; 24. a first swing link; 241. a flat aperture; 242. clamping a head; 243. a shaft hole; 244. a first mounting groove; 25. a second swing link; 251. a driven part; 251a, a spherical groove; 251b, radial heat dissipation grooves; 251c, axial heat dissipation grooves; 251d, heat dissipation holes; 252. a card slot; 253. a second mounting groove; 26. a rotating shaft; 261. a cap portion; 262. mounting holes; 27. an elastic bayonet lock; 28. a sliding sleeve; 291. an elastic washer; 292. a first gasket; 293. a second gasket; 3. a mobile phone; 31. a handset housing; 32. a drive motor; 321. an output shaft; 322. and (6) an output interface.

Detailed Description

In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. It is apparent that the specific details set forth in the following description are merely exemplary of the invention, which can be practiced in many other embodiments that depart from the specific details disclosed herein. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without any inventive step, are within the scope of the present invention.

In this document, when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The directional terms front, rear, upper and lower are defined as the positions of the components in the drawings and the positions of the components relative to each other, and are used for the sake of clarity and convenience in technical solution. It is to be understood that the use of the directional terms should not be taken to limit the scope of the claims.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

As shown in fig. 1, the medical pendulum saw in the embodiment of the present invention includes a hand piece 3, a handpiece 2 and a sheath-protecting saw blade 1, wherein the hand piece 3 includes a hand piece housing 31 having a shape similar to a pistol and a driving motor 32 disposed in the hand piece housing 31, the driving motor 32 has an output shaft 321 extending in an axial direction, and an output interface 322 is disposed at a front end of the output shaft 321. The machine head 2 comprises a machine head shell 21, a swing shaft 22 arranged in the machine head shell 21 and a reciprocating swing mechanism, wherein a machine head interface is arranged on the swing shaft 22. The reciprocating swing mechanism is used for converting the rotation of the output shaft 321 into the rotation reciprocating swing motion of the swing shaft 22. The sheath-protecting saw blade 1 comprises a saw blade body and a sheath, wherein a saw blade interface is arranged at the rear end of the saw blade body and connected with the machine head interface. When the saw is in work, the machine head 2 drives the saw blade body to swing so as to drive the saw teeth to swing to form sawing.

As shown in fig. 2, 3, and 4, the handpiece housing 21 includes a first housing 211 and a second housing 212, a center line of the first housing 211 is perpendicular to a center line of the second housing 212, and the second housing 212 is connected to a front end of the first housing 211. The swing shaft 22 is arranged in the second shell 212 in a manner of reciprocating swing around a swing axis, a machine head interface matched with the saw blade interface is arranged at the upper end of the swing shaft 22, and the machine head interface in the embodiment comprises a plurality of driving pins 221 arranged at the upper end of the swing shaft 22 at intervals along the circumferential direction. The reciprocating deflection mechanism is positioned in the first housing 211 and includes an eccentric input assembly 23, a first swing link 24 and a second swing link 25.

As shown in fig. 4, 6, 9 and 10, the eccentric input assembly 23 includes an eccentric shaft 230, the eccentric shaft 230 includes an eccentric shaft main body 231 rotatable about a first axis X1, an input interface 232 disposed at a rear end of the eccentric shaft main body 231, and a driving part connected to a front end of the eccentric shaft main body 231, the input interface 232 is engaged with the output interface 322 on the output shaft 321, and a central axis of the driving part is disposed eccentrically from the first axis X1. The front end of the first swing link 24 is coaxially and fixedly connected with the swing shaft 22, the first swing link 24 can swing around a swing axis, specifically, the front end of the first swing link 24 is provided with a flat hole 241 (see fig. 13), the outer side wall of the swing shaft 22 is flat (see fig. 6), and the front end of the first swing link 24 is sleeved on the swing shaft 22 to realize coaxial and fixed connection. The rear end of the first swing link 24 is connected to the front end of the second swing link 25, the second swing link 25 has a rotational degree of freedom along a second axis X2, the second axis X2 is located in the swing plane of the first swing link 24 and perpendicular to the axis of the first swing link 24, the rear end of the second swing link 25 is provided with a driven part 251, and the driven part 251 and the driving part are matched through a spherical pair.

In the reciprocating deflection mechanism of the present invention, the second oscillating bar 25 has a rotational degree of freedom, and the second oscillating bar 25 is connected with the driving part through a spherical pair, which enables the two to slide relatively at any angle under the action of the eccentric shaft 230 and keep a reliable and stable connection, i.e. a stable spherical contact, so that the eccentric shaft 230 can keep a sufficient degree of freedom during movement, not enable the two to generate relative impact, and also ensure the two to slide relatively stably.

Referring to fig. 11 and 12, the driven part 251 is provided with a spherical groove 251a as an example, the outer side wall of the driving part is spherical, and the inner side wall of the spherical groove 251a and the outer side wall of the driving part together form the spherical pair. Alternatively, the spherical groove 251a may be provided on the driving portion, and the driven portion 251 may be provided with a spherical outer sidewall engaged with an inner sidewall of the spherical groove 251 a.

The inner side wall of the spherical groove 251a is provided with heat dissipation grooves 251b and 251c, and the heat dissipation grooves 251b and 251c can reduce the spherical contact area between the inner side wall of the spherical groove 251a and the outer side wall 234a of the spherical bearing 234, convert high pair contact of two spherical contacts into low pair contact with less friction, and are beneficial to heat dissipation; moreover, the heat-resistant solid lubricating oil or grease is placed in the heat dissipating grooves 251b and 251c, so that the cooperative lustering and sliding performance of both spherical surfaces can be effectively increased. In order to increase the heat dissipation effect, the heat dissipation grooves 251b and 251c include axial heat dissipation grooves 251c extending in the axial direction and radial heat dissipation grooves 251b extending in the circumferential direction, and the axial heat dissipation grooves 251c and the radial heat dissipation grooves 251b communicate with each other. In order to further increase the heat dissipation effect, the driven portion 251 is provided with heat dissipation holes 251d communicating with the heat dissipation grooves 251b, 251 c.

Referring to fig. 9 and 10, the driving portion includes a spindle 233 and a spherical bearing 234 fitted over the spindle 233, a center line of the spindle 233 is eccentrically disposed with respect to the first axis X1, and an outer sidewall 234a of an outer ring of the spherical bearing 234 is spherical. With such a structure, the spherical outer side wall 234a and the inner groove wall of the spherical groove 251a have rolling friction, and the friction force is smaller than that of sliding friction of the spindle 233 directly contacting the driven portion 251.

Referring to fig. 9 and 10, the exemplary eccentric input assembly 23 further includes first and second bearings 235 and 236 fitted over the front and rear ends of the eccentric shaft main body 231, the first and second bearings 235 and 236 supporting the eccentric shaft 230. Preferably, the eccentric input assembly 23 further includes a sleeve 237, a front end of the sleeve 237 being inserted and fixed in a rear end of the first housing 211, and a rear end of the sleeve 237 being provided with a mounting interface 237 a. The mobile phone 3 is provided with a mobile phone interface (see fig. 1) matched with the mounting interface 237a, the mounting interface 237a is inserted into the mobile phone interface during mounting, and the input interface 232 of the eccentric shaft 230 is connected with the output interface 322 of the output shaft 321 of the driving motor 32.

As shown in fig. 7 and 8, the rear end of the first swing link 24 and the front end of the second swing link 25 are connected by a rotating shaft 26 extending along the second axis X2. Specifically, a U-shaped slot 252 (see fig. 11 and 12) is disposed at the front end of the second swing link 25, a chuck 242 (see fig. 13) is disposed at the rear end of the first swing link 24, a shaft hole 243 is disposed on the chuck 242, and the two ends of the rotating shaft 26 are respectively fixed on two groove walls of the slot 252 after passing through the shaft hole 243. Alternatively, the positions of the engaging groove 252 and the engaging head 242 may be reversed, that is, the engaging groove 252 is disposed on the rear end portion of the first swing link 24, and the engaging head 242 is disposed on the front end portion of the second swing link 25.

As shown in fig. 14, the rear end of the rotary shaft 26 is provided with a cap portion 261, the front end is provided with a mounting hole 262 extending in the radial direction, and the front end of the rotary shaft 26 is sequentially passed through one groove wall of the locking groove 252, the locking head 242, and the other groove wall of the locking groove 252 and then locked by the elastic locking pin 27 passed through the mounting hole 262 through the cap portion 261.

Referring to fig. 8, preferably, the shaft hole 243 of the chuck 242 is sleeved with the sliding sleeve 28, the rotating shaft 26 is inserted into the sliding sleeve 28 and is in clearance fit with the sliding sleeve 28, and the sliding sleeve 28 may be made of a wear-resistant material (such as copper) to increase the service life.

Preferably, an elastic member is disposed between the rear end of the first swing link 24 and the front end of the second swing link 25, so that vibration and noise are reduced by the elastic member, transmission of swing motion is more flexible, and the problem that parts of the handpiece 2 and the saw blade are damaged due to excessive instantaneous load is reduced. As shown in fig. 8, the elastic member includes an elastic washer 291 fitted around the rotation shaft 26 between two side surfaces of the chuck 242 and two groove walls of the engaging groove 252. Preferably, the elastic washer 291 is a disc spring. In the process that the second swing link 25 drives the first swing link 24 to swing left and right, the instantaneous rigid force transmitted by the second swing link 25 is converted into elastic deformation force through the action of the elastic washer 291, and then the elastic deformation force is converted into the swing motion of the swing shaft 22 and the saw blade. The structure can effectively reduce instantaneous load and impact during left-right swinging of high-speed and high-frequency, reduce vibration and noise, enable the transmission of swinging motion to be more flexible, and reduce the bad condition that parts and saw blades of the machine head 2 are damaged due to overlarge instantaneous load.

Preferably, the elastic member further includes a first washer 292 and a second washer 293 sleeved on the swing stem 233 at both sides of the elastic washer 291. The first and second washers 292 and 293 may increase the elastic force on the one hand and reduce the wear of the elastic washer 291 on the other hand. Preferably, two side surfaces of the chuck 242 are provided with first mounting grooves 244, two groove walls of the U-shaped clamping groove 252 are provided with second mounting grooves 253, and the first gasket 292 and the second gasket 293 are respectively mounted in the first mounting grooves 244 and the second mounting grooves 253. The first pad 292 and the second pad 293 may be made of hardened wear-resistant polymer materials such as rubber, PC and the like; the elastic washer 291 may be made of rubber, or a stainless steel spring or a disc spring coated with a surface layer by surface-flexible coating.

As shown in fig. 16-17, when the eccentricity of the eccentric shaft 230 moves from zero to the maximum eccentricity position, the spherical bearing 234 on the eccentric shaft 230 exerts a force to swing left and right in the horizontal direction through the spherical pair due to the limit reaction of the first swing link 24, the rotating shaft 26, the first washer 292, the second washer 293, the elastic washer 291, and the like in the horizontal direction; meanwhile, the second swing link 25 continuously swings up and down around the sliding sleeve 28 (the rotating shaft 26) mounted on the rotating shaft 26 with the variation of the eccentricity of the eccentric shaft 230, and at this time, the inner spherical surface of the second swing link 25 and the outer spherical surface of the spherical bearing 234 form a spherical pair and flexibly slide. Through the sliding of the spherical pair and the up-and-down swinging of the second swing link 25, the excessive resultant force in all directions other than the horizontal swinging transmitted by the eccentric shaft 230 is resolved, thereby reducing unnecessary vibration and noise.

Moreover, when the eccentricity of the eccentric shaft 230 moves from zero to the maximum eccentricity position, at this time, the second oscillating bar 25 is pressed along one side of the rotating shaft 26 in the horizontal direction under the sliding fit action of the spherical bearing 234, at this time, the fit inner side surface of one side of the second oscillating bar 25 compresses the elastic washer 291 through the second washer 293 and further compresses the first washer 292, so that the first oscillating bar 24 swings to one side, and the primary swing of the oscillating shaft 22 is realized, thereby driving the saw blade body mounted on the oscillating shaft 22 to swing and saw in a single direction; when the eccentric shaft 230 rotates to the other direction, the second swing link 25 is pressed to the other side, so as to further drive the swing shaft 22 and the saw blade body to saw in the opposite direction, thereby completing one complete sawing cycle. In the process that the second swing link 25 drives the first swing link 24 to swing left and right, the instantaneous rigid force transmitted by the swing shaft 22 is converted into elastic deformation force through the action of the first spacer 292, the second spacer 293 and the elastic washer 291, and then the elastic deformation force is converted into the swing motion of the swing shaft 22 and the saw blade body. The conversion through this structure can effectively reduce instantaneous load and striking when the high-speed high frequency left and right oscillations, reduce vibration and noise, can make the transmission of swing motion more flexible, reduce the bad condition that aircraft nose 2 spare part and saw bit take place the damage because of receiving too big instantaneous load.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.

Claims (12)

1. A medical oscillating saw head, comprising:

the reciprocating deflection mechanism comprises an eccentric input assembly and a swinging rod, the eccentric input assembly comprises an eccentric shaft, and the eccentric shaft comprises an eccentric shaft main body capable of rotating around a first axis and a driving part which is connected with the front end of the eccentric shaft main body and is eccentrically arranged with the first axis;

the front end part of the swing rod is connected with the swing shaft, the rear end part of the swing rod is provided with a driven part, the driven part is matched with the driving part through a spherical pair, and the driving part and the driven part convert the rotary motion of the eccentric shaft main body into the reciprocating swing motion of the swing shaft.

2. The medical oscillating saw head of claim 1, wherein the driven part is provided with a spherical groove, the outer side wall of the driving part is spherical, and the inner side wall of the spherical groove and the outer side wall of the driving part jointly form the spherical pair.

3. The medical pendulum saw head of claim 2, wherein a heat sink is disposed on an inner sidewall of the spherical recess.

4. The medical pendulum saw head of claim 3, wherein the heat sink includes an axial heat sink extending in an axial direction and a radial heat sink extending in a circumferential direction, the axial heat sink and the radial heat sink being in communication with one another.

5. The medical oscillating saw head of claim 3, wherein the driven portion is provided with heat dissipation holes communicating with the heat dissipation grooves.

6. The medical oscillating saw head of claim 1, wherein the driving portion comprises a mandrel and a spherical bearing sleeved on the mandrel, a central axis of the mandrel is eccentrically arranged with respect to the first axis, and an outer side wall of an outer ring of the spherical bearing is spherical.

7. The medical pendulum saw head of claim 1, wherein the pendulum comprises a first pendulum and a second pendulum, a front end of the first pendulum is fixedly connected coaxially with the pendulum shaft, a rear end of the first pendulum is connected with a front end of the second pendulum, and the second pendulum has a rotational degree of freedom about a second axis, the second axis is located within a swing plane of the first pendulum and perpendicular to an axis of the first pendulum, and the driven portion is disposed at a rear end of the second pendulum.

8. The medical pendulum saw head of claim 7, wherein the rear end of the first pendulum and the front end of the second pendulum are connected by a rotating shaft extending along the second axis.

9. The medical oscillating saw head according to claim 8, wherein one of the rear end portion of the first oscillating bar and the front end portion of the second oscillating bar is provided with a U-shaped slot, the other of the rear end portion of the first oscillating bar and the front end portion of the second oscillating bar is provided with a clamp, the clamp is located in the slot, and the rotating shaft passes through the rear end portions of the clamps and is fixed on two slot walls of the U-shaped slot respectively.

10. The medical oscillating saw head as claimed in claim 9, wherein a sliding sleeve is sleeved in the shaft hole of the chuck, and the rotating shaft is inserted into the sliding sleeve and is in clearance fit with the sliding sleeve.

11. The medical oscillating saw head according to claim 8, wherein the rotating shaft is provided at a rear end thereof with a cap, and at a front end thereof with a mounting hole extending in a radial direction, and the front end of the rotating shaft is sequentially passed through one side wall of the locking groove, the locking head, and the other side wall of the locking groove and then locked by the cap and an elastic locking pin passed through the mounting hole.

12. The medical oscillating saw head according to any one of claims 7 to 11, wherein the second oscillating bar has a translational degree of freedom along a second axis, and an elastic member is provided between a rear end portion of the first oscillating bar and a front end portion of the second oscillating bar.

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