The device for reducing vibrations of sewing machines induced by dynamic forces of the crank mechanism of needle bar and the thread feeder mechanism, while the crank of the crank mechanism of needle bar and of thread feeder mechanism is attached to the upper shaft, which is rotatably mounted in arm of the sewing machine and is coupled with the balancing device.
Needle bar of sewing machine is usually driven by a crank mechanism transferring the engine rotational motion driving the machine upper shaft to a straight-line reverse motion of needle bar. Due to high rotation speed of the upper shaft at the current sewing machines the bearing of upper shaft and the arm of sewing machine are loaded by considerable dynamic forces, which are transferred to the whole machine, causing its vibrations and increasing the operational noise of the machine. The dynamic forces are composed of harmonic components of various frequencies. Frequency of the first harmonic component is identical with frequency of rotation of the crank shaft, frequency of the second harmonic component has double value, etc. The first harmonic component is usually called inertia force of first order, the second harmonic component is inertia force of second order, etc. Balancing of sewing machines is commonly solved by counterweight on the crank or on the crank shaft only balancing the centrifugal force and partially also inertia force of first order , nevertheless it results in creation of a similar inertia force in direction being perpendicular to the direction of straight-line reverse motion of the needle bar. The forces of higher orders, whose frequencies are close to resonance frequency of machine arm, remain unbalanced.
Simple damping of induced vibrations is represented by a flexible mounting of upper shaft by means of spring rings arranged between the bearing outer ring of the upper shaft and the box of arm of the sewing machine according to the
Some solutions in balancing of sewing machines use the principles used at the crank mechanisms of combustion engines.
According to the
To balance the needle bar the
According to the
According to the
The tuned vibration absorbers known for example from the sphere of crank mechanisms of combustion engines are effective only in a limited rotation speed range of machine and they partially balance only some harmonic components.
At many industrial sewing machines the effects of acting of high inertia forces must be reduced by using the machine arm of a high weight.
Mechanism of the thread feeder is usually formed of four-joint mechanism directly connected with the crank mechanism of needle bar. The main harmonic components of its motion are in motion direction of needle bar similar to harmonic components of needle bar.
A similar method of balancing creates a content of
The shortcoming at the known mechanisms for balancing the needle bar and the thread feeder is imperfect balancing or structurally complicated and thus in terms of space and price demanding solution. Due to this majority of sewing machines is produced without balancing devices, which has a negative impact to their operational properties and service life of the machines.
The goal of this invention is to eliminate the shortcomings of the present background art or to reduce them considerably.
The goal of the invention has been achieved through the device whose principle consists in that the balancing device is formed by a balancing eccentric mechanism, which comprises in an arm of the machine in a flexible and/or sliding manner mounted exit member, in which a cylindric hole is performed, in which rotatably is mounted the second eccentric, in which with eccentricity (e) the cylindric hole is performed, in which is rotatably mounted the first eccentric, which with eccentricity (r) is firmly connected with upper shaft of the sewing machine.
The advantage is a short lift of exit member of the balancing eccentric mechanism and a resulting fact that this device is not demanding as to space and it can be guided by flexible members and/or by means of a slide-way.
It is also advantageous if at the same time the eccentricity of the first eccentric is turned by 180° with respect to the crank of the needle bar crank mechanism.
Moreover this solution is simple as to its manufacturing.The balancing means are situated in close vicinity of the needle bar being balanced and due to the fact that the centre of gravity of exit member of the balancing eccentric mechanism is moving in a plane perpendicular to the upper shaft, very good balancing of the thread feeder mechanism is achieved.
The exit member in an arm of the sewing machine is flexibly mounted between in parallel manner arranged flat springs, out of which each is fastened with its one end to arm of the sewing machine and with its opposite end to the exit member.
Such solution enables an exact guiding of the exit member without play. Moreover the lateral motion of exit member of the balancing eccentric mechanism caused by deformation of the flat springs contributes to balancing of horizontal inertia forces of the thread feeder mechanism.
Exemplary embodiment according to the invention is represented in the drawing where the
The upper part of sewing machine is formed by the arm 1 of sewing machine in whose inner space in longitudinal direction is arranged the upper shaft 11 driven by the non-represented electro-motor by means of the belt 111 and belt pulley 112. The upper shaft 11 is rotatably mounted in bearings 12. On the side reversed from the belt pulley 112 on the upper shaft 11 is attached the crank 113, on whose crank journal 114 there is mounted the upper eye of the conrod 13 and the lower eye of the thread feeder 14. In vertical guiding bearings 15 displaceably is mounted the needle bar 16 with which the lower eye of the conrod 13 is connected rotatably. The upper eye of the thread feeder 14 is rotatably connected with one eye of the conrod 17 of the thread feeder 14 mechanism. The second eye of the conrod 17 is rotatably mounted on the pin 18, which is firmly connected with frame of the arm 1 of sewing machine. Thus the conrod 17 forms a pitman of four-joint mechanism, whose further members are the frame of the arm 1 of sewing machine, the thread feeder 14 and the crank 113.
In exemplary embodiment between the bearing 12 of upper shaft 11 being adjacent to the needle bar 16 and the crank 113 the balancing device is arranged, which is formed by the balancing eccentric mechanism 19 which comprises the first eccentric 191 firmly connected with upper shaft 11, while the centre s1 and thus the axis of the outer cylindric surface of the first eccentric 191 intersects the straight line p passing through the axis of the crank journal 114 and the axis of upper shaft 11 outside the join of axes of the crank journal 114 and axis of the upper shaft 11 behind the axis of the upper shaft 11.
The first eccentric 191 by its outer circumference is rotatably mounted in cylindric cavity of the second eccentric 192, which by its outer circumference is rotatably mounted in cylindric cavity of the exit member 193 of the balancing eccentric mechanism 19.
The eccentricity r of the first eccentric 191 is given by the distance of axis of the upper shaft 11 and the centre s1 of the first eccentric 191. The eccentricity e of the second eccentric 192 is given by the distance of the centre s2 of the second eccentric 192 and the centre s1 of the first eccentric 191. The eccentricity r of the first eccentric 191 is several times smaller than the length R of the crank 113. Similarly the eccentricity e of the second eccentric 192 is several times smaller than the length I of the conrod 13. In similar ratio the weight of the exit member 193 of the balancing eccentric mechanism 19 is greater than the weight of the needle bar 16.
The exit member 193 is formed of a flat square body to whose opposite external walls the ends of two flat springs 194 are fastened. Opposite ends of springs are firmly connected with frame of the arm 1 of sewing machine, thus also with frame of the sewing machine. At this solution deformation of the flat springs 194 arising as a result of the side motion of the exit member 193 of the balancing eccentric mechanism 19 may partially balance the horizontal inertia force of mechanism of the thread feeder 14.
In the not represented embodiment the exit member 193 of the balancing eccentric mechanism 19 is formed of a body of any spatially convenient shape arranged so that its centre of gravity is in direction of axis of the upper shaft 11 as close as possible to centre of gravity of the needle bar 16.
In another not represented embodiment the exit member 193 of the balancing eccentric mechanism 19 is guided in a straight-lined slide-way, at the same time in direction of this way it may be mounted in a spring manner between two pressure springs.
Upon rotating of the upper shaft 11 the needle bar 16 performs the working lifts. The size of a whole lift of the needle bar equals to double length of crank R of the crank 113, while the exit member 193 of the balancing eccentric mechanism 19 performs a lift, which equals to double of eccentricity r of the first eccentric 191. At this activity the cyclic springy deformations of the flat springs 194 occur which the vertical motion of the exit member 193 of the balancing eccentric mechanism 19 enable through their elasticity. At the same time the flat springs 194 generate also the force which reduces the inertia forces between the eccentrics 191, 192 and the exit member 193 of the balancing eccentric mechanism 19.
The first eccentric 191 in principle balances the centrifugal force of the crank 113, the balancing eccentric mechanism 19 as a whole balances the inertia forces of the needle bar 16, of conrod 13 and partially also the inertia forces of thread feeder 14 mechanism.
The device for reducing vibrations of sewing machines induced by dynamic forces of the crank mechanism of needle bar 16 and of thread feeder 14 mechanism according to the invention creates an integral unit which can be easily built-in into an arm of the sewing machine 1 with assumption of low acquisition costs, good efficiency and reliability. It is advantageous that the centre of gravity of exit member 193 of the balancing eccentric mechanism 19 is situated in a minimum distance from the needle bar 16. At the same time this centre of gravity moves in a plane perpendicular to the upper shaft 11, through which a better balancing of the thread feeder 14 can be achieved. The balancing eccentric mechanism according to the invention also reduces forces exerting load to bearings of the upper shaft 11.
It is obvious that the exemplary embodiment does not restrict the scope of protection given by the patent claims. In compliance with the claims for example the external shape of individual parts of the mechanism, type of spring elements for guiding of exit member, geometric parameters, etc. may be modified.
The invention may be applied at all types of sewing machines using the crank or link mechanism for drive of needle bar. It is especially applicable at industrial high-speed sewing machines.
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.