GB2222587A - A method and device for cutting a glass tube into pieces - Google Patents

Abstract

The method and device are of the type in which a continuous glass tube (T) moves along its own axis (X) at a given constant linear velocity (Vs) and a rotary cutting tool (60) is used to effect the cutting and is provided with a cutter (62) which travels along a circular orbit (O) lying in a plane (P) inclined to the axis (X) of the tube (T). In one segment of its orbit, the cutter (62) intersects the outer surface of the tube (T) which is cut upon each rotation of the tool (60) whilst the tool is driven at such an angular velocity ( omega s), termed the synchronism velocity that its cutter (62) has a linear component (Vs) of the velocity of the tube (T). The tool (60) is rotated by its own variable-speed motor. The motor imparts the synchronism velocity ( omega s) to the tool (60) for a minor fraction (I) of each revolution, which includes the said segment (S) of the orbit of the cutter (62). For the remaining, major fraction (II-III) of each revolution, however, the motor imparts to the tool (60) an angular velocity ( omega ) such that, during its next revolution, the cutter (52) reaches the said orbit segment (S) when the tube (T) has travelled the predetermined distance (Lt) from the incision made in the preceding revolution. The operating cycle of the variable-speed motor is preferably controlled by a numerical control device on which the predetermined length (Lt) of the pieces is set manually. <IMAGE>

Description

DESCRIPTION "A method and device for cutting a glass tube into pieces" The present invention relates to a method and to a device for cutting pieces of predetermined length from a continuous glass tube according to the preambles of Claim 1 and of Claim 6 respectively.

In known cutting devices, the rotary tool consists of a rotary arm which lies in a vertical plane inclined at a small angle to the axis of the tube. A hard metal or ceramic tool is mounted on the end of the arm for the purpose of making an incision in the tube at the point at which it is to be cut. During the advance of the tube, the tool-holding arm rotates about its own axis at a constant rate such that the component of its peripheral velocity in the direction of the axis of the tube is equal to the speed of advance of the tube. As it revolves, the tool touches the tube upon each revolution with a relative velocity perpendicular to the axis thereof which is sufficient to produce a small incision such as to initiate its fracture.

The tool takes its drive from the machine drawing the tube through a belt and pulley transmission. In order to modify the cutting length, in known devices it is necessary, on the one hand, to change the radius of the tool-holding arm and, on the other hand, to modify the transmission ratio between the drawing machine and the shaft of the tool. In practice, this requires the availability of a supply of pulleys of different diameters suitable for the most usual cut lengths. If cut lengths other than those which are most usual are required, then it is necessary to construct appropriate new sets of pulleys.

The object of the present invention to provide a method and a device whereby the lengths of the pieces cut can be varied at will, within a very wide range, by the simple input of data, without the line being stopped and without the need for adjustments and/or the replacement of mechanical members.

According to the present invention, this object is achieved by means of a method and a device as defined in the characterising parts of Claims 1 and 6 and the claims dependent thereon.

Broadly speaking, the concept of the invention consists of imparting the synchronism velocity to the rotary tool for only slightly longer than the time needed for the incision. Suppose that the desired cutting length corresponds to one revolution of the tool at the synchronism velocity. In this case the tool is rotated by its own motor constantly at the angular synchronism velocity. If, however, the desired cutting length is longer than that corresponding to the angular synchronism velocity, the tool is slowed down for the major part of its revolution, possibly until it is stationary, and is then accelerated again up to the synchronism velocity for such a time that the cutter is situated in the cutting zone when the tube has travelled this greater cutting length.If, however, cutting lengths shorter than that corresponding to the synchronism velocity are required, the tool is accelerated during the major fraction of its revolution and then decelerated until it returns to the synchronism velocity, so that the cutter again reaches the cutting zone when the tube has travelled the desired, shorter cutting length.

To advantage, these operating cycles are achieved, according to the invention, by means of a control device, which is preferably numerical, on which it is necessary only to set a number corresponding to the desired cutting length by means of a preselector with wheels or a keyboard.

The invention will better be understood from a reading of the detailed description which follows, with reference to the appended drawings, given by way of non-limiting example, in which: Figure 1 is a side elevation of part of a glass-tube drawing line provided with a cutting device according to the invention, Figure 2 is a front elevation partially sectioned in the plane indicated II-II in Figure 1, Figure 3 is a fragmentary and partially cut-away side elevational view of the part enclosed by the circle III in Figure 2, Figure 4 is a cross-section taken in the plane indicated IV-IV in Figure 3, Figure 5 is a perspective view showing the essential parts of the device of Figures 3 and 4, Figure 6 is a plan view of a portion of the tube from above, showing the incision, Figure 7 is a diagram showing the tube, the cutting device and its electrical and electronic parts, Figure 8 is a series of four graphs in which the cutting lengths and the times are shown on the abscissae and the angular velocity of the cutting tool is shown on the ordinates, for four different cutting lengths according to a type of control which gives a trapezoidal trace, and Figure 9 is a series of graphs similar to those of Figure 8 but relating to a type of control which gives a substantially sinusoidal trace.

With reference to Figures 1 and 2, a drawing line includes a strong pillar 10 which supports a strong horizontal cantilever beam 12. The pillar 10, on the one hand, and the free end of the beam 12, on the other hand, support respective support brackets 14 and 16 which in turn support a lower horizontal beam 18. The beam 18 supports brackets 20, 22, 24 whose positions are adjustable along the beam.

The brackets 20 carry grooved bearing rollers 26. The bracket 22 carries a grooved guide roller 28 and the bracket 24 carries, inter alia, a grooved bearing roller 30.

A glass tube T travels along its own longitudinal axis over the rollers 20 and 30 and under the roller 22 in the direction of the arrow A.

The upper beam 12 acts as a guide for a slide 32 which can be positioned micrometrically along the beam 12 by means of a lead screw 34 driven by a wheel 36.

The slide 32 in turn carries a slide 38 arranged crosswise and whose vertical position is adjustable micrometrically by means of a lead screw 40 driven by a wheel 42.

The slide 38 carries a lower vertical arm 44 which in turn carries a support bush 46.

With reference to Figures 3 and 4 as well as Figures 1 and 2, a horizontal shaft 48 is rotatably mounted in the bush 46. A tool-holder assembly, generally indicated 50, is keyed to one end of the shaft 48 which is situated above the roller 30. A flanged electric motor 52, of which more will be said below, is fixed to the opposite end of the bush 46. The shaft of the motor 52 is coupled directly to the shaft 48.

The tool-holder assembly 50 includes a clamp 54 for keying to the shaft 48. A radial tool-holder arm 56 is fixed to the clamp 54 on one side and counterweights 58 for balancing the arm 56 are fixed to its opposite side.

At its free end, the arm 56 carries a hard metal or ceramic tool 60. The tool 60 has a substantially sharp-edged cutter 62 arranged parallel to the axis of the shaft 48.

As will be explained better below, the cutter 62 is intended to form transverse incisions in the surface of the tube T to constitute fracture initiators, the fracture occurring in a region downstream of the drawing unit of Figure 1 (not shown). The incisions are formed under wet conditions, water being sprayed onto the tool 60 in a manner not shown. In order to prevent the water from spurting into the environment, the tool-holder assembly 50 is covered by a hood 64.

The exact arrangement of the tool-holder assembly 50, which cannot be seen in Figures 1 to 4, is shown in Figure 5. As can be seen from Figure 5, the horizontal shaft 48 is so arranged that the cutter 62 of the tool 60 travels along a circular orbit 0 which lies in a plane P. The plane P is inclined to the axis C of the tube which is travelling in the direction of the arrow A. The angle of the plane P to the axis X is indicated C(and is preferably 160.

The motor 52 rotates the tool-holder assembly 50 in the sense of the arrow B.

The height of the axis of the shaft 48 is adjusted by the micrometric adjustment of the slide 38 in dependence on the diameter of the tube T so that the orbit 0 just intersects the outer surface of the tube T when the tool 60 is in the lowest part of its rotation, as shown in Figure 5.

The micrometric adjustment of the slide 32 serves, however, to put the cut pieces "in phase" with a collector situated downstream (not shown). This phase-setting is carried out so that successive offcuts are always deposited on the collector, in the same position regardless of their weight and inertia.

In Figure 6, the tube T, its axis X, the plane P and the angle o( are shown again.

The cutting device is arranged so that the cutter 62 forms a transverse incision S in the tube T at each revolution (Figure 6). For this purpose, as shown in Figure 5, when the tool 60 is in the cutting zone, it must have a tangential velocity Vp with a component Vs which is equal to the velocity with which the tube T is moving. The transverse incision S is thus effected by virtue of the transverse component Vt of the velocity of the cutter 62.

When the tangential velocity Vp of the cutter 62 satisfies all the above conditions, the tool 60 and its whole assembly have an angular velocity which will hereinafter be referred to as the synchronism velocity #s.

Reference will now be made to Figure 7 in order to describe the electrical and electronic part of the device.

In Figure 7, the tube T is again indicated B; the cutting assembly is again indicated 50 and the tool is again indicated 60. The motor of the cutting assembly 50 is again indicated 52. This consists of a stepped motor, preferably with five phases and 250 steps. In practice, as will be seen, the shaft 48 of the motor 52 can be rotated in quarter steps which means that one revolution of the shaft 48 of the tool-holder assembly 50 can be divided into 1000 fractions or steps.

An electronic control 70 is associated with the motor 52 and constitutes the heart of the cutting device. An encoder 72 is associated with the controller 70 for detecting the angular velocity CP of the tool-holder assembly 50. The encoder 72 generates a feedback signal which is applied to the controller 70 to enable its self-regulation.

Another encoder 74 is associated with the wheels of the drawing machine, as indicated conventionally at 76, in order to detect the speed of movement of the tube T and to apply a corresponding linear velocity signal to the controller 70.

Finally, a data-input system 78 is associated with the controller and may consist of a digital preselector with wheels or a keyboard. The preselector 78 serves for the manual input to the controller 70 of a delivery signal which is proportional to the desired cutting length of the pieces. In practice the figures shown on the keys or on the wheels of the preselector enable the desired cutting length to be set directly, for example in millimeters (for example from 600 to 3000 mm).

Once the desired cutting length has been set, the controller 70 is arranged to carry out the necessary calculation, based on the linear velocity signal provided by the encoder 74 and on the angular velocity signal of the tool-holder assembly 50 provided as feedback from the encoder 72.

As a result, the controller 70 applies to the motor 52 a train of pulses whose rate varies between a value corresponding to the angular synchronism velocity bO s and, according to circumstances, a value corresponding to a lower angular velocity, down to zero, or to a higher angular velocity.

Naturally, by virtue of the linear velocity signal provided by the encoder 74, the controller 70 adapts the values of oD s to the instantaneous linear velocity V5 so that any fluctuations in the latter do not affect the cutting length set.

All this will be explained by a practical example with reference to Figure 5 and Figure 8.

In Figure 5, the orbit 0 has been divided into three sectors I, II and III. The sector I corresponds to 300 steps of the motor 52 and each of the sectors II and II correpsonds to 400 steps of the motor 52.

The angular synchronism velocity #s must satisfy the equation Vs = , s R cos where R is the radius of the tool (Figures 3 and 4).

The controller 70 must impart this angular synchronism velocity 3 s to the tool 60, or rather to its cutter 62, at least in the zone in which the incision N is made, and preferably in a segment S of the orbit (Figure 6) which starts before and finishes after that zone. This segment S corresponds to the sector I or, at least, is included therein.

The most usual linear velocities Vs are from 30 to 300 m/min.

In order to illsutrate the concept, it is assumed that: - Vs = 120 m/min = 1 m/sec; ~ #s = 12.56 rad/sec (equal to 2 revolutions/sec); S - R - 0.083 m = 83 mm.

As will be understood, under these conditions, if the tool rotates constantly at the synchronism velocity an an an incision will be made every half meter, that is 0.5 m pieces of tube will be produced.

If pieces of a longer length are desired, for example with a length Lt of lin, this value (e.g. 1000) is input through the keyboard and the controller 70 produces a cycle such as that of Figure 8a. Assuming that the tool 60 is stationary at the highest point of its orbit, indicated IV in Figure 5, the controller 70 sends a train of 400 pulses at an increasing rate to the motor 72 so as to accelerate it up to the synchronism velocity td s which is reached at the S beginning of the sector I. Throughout the sector I, the controller 70 sends the motor 72 a train of 300 pulses at a constant rate so as to make it travel along the entire sector I at the synchronism velocity The The controller 70 then sends the motor 72 a train of 400 pulses at a decreasing rate, making it decelerate until it stops at the point IV. In order to effect a new cutting or incision cycle, the controller 70 restarts the motor 72 and accelerates it again along the sector II, and the cycle is repeated.

Naturally, the sector III must be traversed in such a manner that the tool 60 reaches the cutting zone after the tube T has travelled the desired cutting length, in the present case 1 m.

Figure 8b shows a graph which corresponds to a cutting length lit of 0.8 m. In this case there is no longer a pause at the point IV and, after decelerating to zero along the sector II, the motor immediately accelerates again along the sector III.

Figure 8c shows the case in which the cutting length Lt is 0.65 m. In this case, between two successive incisions, the tool decelerates along the sector II and accelerates again along the sector III without stopping at the point IV.

As already stated, if the cutting length Lt is 0.5 m the tool rotates at a constant velocity, that is to say, the trace of the graph coincides with the straight line on the ordinate at buds Figure 8d shows the case in which the cutting length Lt is 0.4 m. This means that, whilst the tool 60 must still have the synchronism velocity ov s along the S sector I, it accelerates along the sector II and decelerates along the sector III.

Naturally, there is a lower limit for the cutting length since it is not possible to accelerate the motor 52 above a certain critical speed, that is to say, that it is not possible to shorten the distance between the segments at the level bOs of Figure 8d to less than a S certain limit.

As can be seen from Figure 8, the control of the motor 72 occurs with a periodic variation in the angular velocity of the tool whose amplitude, which may inter alia assume a zero value1 is directly proportional to the linear velocity of the tube and whose frequency, which may inter alia assume a zero value, is directly proportional to the cutting length, that is to the batch signal input through the preselector 78.

According to Figure 8, the controller 70 causes the angular velocity to vary periodically with a trapezoidal trace. This solution enables the controller 70 to be made with quite simple electronics but may have the disadvantage of causing the accelerations and decelerations to be too abrupt and harmful to the mechanical members of the device.

A more satisfactory solution lies in the generation, by means of the controller 70, of trains-of pulses for controlling the motor 72, which cause the angular velocity to vary substantially sinusoidally.

This second solution is shown in Figure 9 of which the graphs a, b, c, d correspond to the graphs a, b, c, d of Figure 8. The same notations have been used as in Figure 8 so that it can clearly be understood.

As will be understood, with the solution of Figure 9, the accelerations and decelerations occur without discontinuity so that the mechanical members of the device are less stressed.

Claims (16)

1. A method for cutting a continuous glass tube which is moving along its own axis at a given linear velocity into pieces of predetermined length, in which a rotary cutting tool is used to effect the cutting and is provided with a cutter which travels along a circuilar orbit lying in a plane inclined to the axis of the tube and which intersects the outer surface of the tube in one segment of its orbit, and in which the outer surface of the tube is cut by the cutter upon each revolution of the tool when the cutter is in the said segment of the orbit and whilst the tool is driven at such an angular velocity, termed the synchronism velocity, that the linear component of the velocity of its cutter substantially coincides with the linear velocity of the tube, in which the synchronism velocity is imparted to the tool for a minor fraction of each revolution which includes the said segment of the cutter's orbit and, for the remaining major fraction of each revolution, an angular velocity is imparted to the tool such that, during its next revolution, the cutter reaches the beginning of the said orbit segment when the tube has travelled the predetermined distance from the incision made in the previous revolution.

2. A method according to Claim 1, in which the tool is rotated by its own variable-speed motor.

3. A method according to Claim 1 or Claim 2, in which there is imparted to the tool a periodic variation in the angular velocity whose amplitude, which may inter alia assume a zero value, is directly proportional to the linear velocity of the tube and whose frequency, which may inter alia assume a zero value, is directly proportional to the predetermined length of the pieces.

4. A method according to Claim 3, in which the angular velocity varies trapezoidally.

5. A method according to Claim 3, in which the angular velocity varies sinusoidally.

6. A device for cutting a continuous glass tube, which is moving along its own axis at a given linear velocity along a drawing line, into pieces of predetermined length, including a rotary cutting tool and respective means for rotating it, the tool being provided with a cutter which travels along a circular orbit lying in a plane inclined to the axis of the tube and which intersects the outer surface of the tube in one segment of its orbit and in which the outer surface of the tube is cut by the cutter upon each revolution of the tool when the cutter is in the said orbit segment and whilst the tool is driven at such an angular velocity, termed the synchronism velocity, that the linear component of the velocity of its cutter coincides substantially with the linear velocity of the tube, in which the means for rotating the tool have associated means for controlling the angular velocity of the tool so that the tool is rotated at the synchronism velocity for a minor fraction of each revolution which includes the said segment of the orbit of the cutter and the tool is rotated for the remaining major fraction of each revolution at an agular velocity such that, during the next revolution, the cutter reaches the beginning of the orbit segment when the tube has travelled the predetermined distance from the cut made in the previous revolution.

7. A device according to Claim 5 or Claim 6, in which the means for rotating the tool are constituted by its own variable-speed motor.

8. A device according to Claim 6 or Claim 7, in which the control means have associated means for the manual input of the predetermined length of the pieces.

9. A device according to Claim 8, in which it includes means for detecting the linear velocity of the tube and for emitting a linear velocity signal, the input means are arranged to emit a delivery signal proportional to the input length of the pieces and in which the control means are arranged to control the tool with a periodic variation in its angular velocity whose amplitude, which may, inter alia, assume a zero value, is directly proportional to the linear velocity of the tube, and whose frequency, which may inter alia assume a zero value, is directly proportional to the delivery signal.

10. A device according to Claim 9, in which the periodic variation in the angular velocity caused by the control means is trapezoidal.

11. A device according to Claim 9, in which the periodic variation in the angular velocity caused by the control means is sinusoidal.

12. A device according to any one of Claims 8 to 11, in which the variable speed motor is a stepped electric motor and the control means are arranged to apply to the motor step pulses whose rate varies like the periodic variation of the angular velocity.

13. A device according to any one of Claims 6 to 12, in which it includes means for detecting the angular velocity of the tool, the means applying a feedback signal to the control means for their self-regulation.

14. A device according to any one of Claims 6 to 13, in which it includes a structure which is associated with the drawing line of the tube and supports the tool by means of a pair of crossed slides whose positions are adjustable micrometrically so as to adjust the position of the tool in a direction parallel to the tube and in a direction radial of the tube respectively.

15. A method of cutting a continuous glass tube into pieces substantially as described herein with reference to the accompanying drawings.

16. A device for cutting a continuous glass tube into pieces, substantially as herein described with reference to, and as shown in the accompanying drawings.