US2966389A - Facsimile apparatus - Google Patents

Description

Dec. 27, 1960 F. P. MASON ETA].

FACSIMILE APPARATUS Filed Jan. 9. 1958 Inventor E Mason- 1.,0. Ma rd y C Attorney United States Patent Ofiice 2,966,389 Patented Dec. 27, 1960 FACSIMILE APPARATUS Frederick Percival Mason and Leonard Oswald Marden, Croydon, England, assignors to Creed & Company Limited, Croydon, England, a British company Filed Jan. 9, 1958, Ser. No. 707,891 Claims priority, application Great Britain Jan. 14, 1957 4 Claims. (Cl. 346-138) This invention relates to facsimile apparatus.

In some circumstances it is advantageous to minimize the time necessary for the translation of a facsimile scanning device, e.g. a drum, from a state of rest to a state of rotation with a desired phase. The present invention provides an improvement in apparatus designed with this object in view.

In such apparatus it is usual for a synchronous motor to drive a shaft at a constant speed, and for a rapidengagement clutch to be provided to couple a scanning device, usually a drum, which is reposing at rest in a known angular position, to the rotating shaft at an instant related to the phase position of the scanner of a co-operating machine.

The rapid-engagement clutch is of a type which will engage positively for rotation in' both directions, e.g. a dog clutch.

It is also usual for the rapid-engagement clutch to embody or be used in association with a compliant link or yielding member interposed between the clutch and the scanning device. The compliant link then limits the torque load applied to the synchronous motor at the instant of engagement of the clutch to a value such that the motor is not pulled out of synchronism.

The compliant link therefore yields at the moment of engagement of the clutch and, because the speed of the scanning device is for some time lower than that of the motor, continues to yield until the speed of the scanning device is the same as that of the motor. As the compliant link has yielded, the scanning device is not being driven at the correct phase, when it reaches the correct speed. This is corrected by the compliant link contracting and advancing the scanning device to the correct phase position. During this advance the scanning device is accelerated to a higher speed than that of the synchronous motor.

A situation then exists when the kinetic energy of the scanning device may exert a force on the clutch and the motor, either through the compliant link which is in a state of compression or through a stop or abutment pin associated with the compliant link. Thus the kinetic energy of the scanning device may cause the clutch to slip or the motor to exhibit a negative slip, or both, and correct rotational phase of the scanning device to be lost.

It is known to include, in the mechanism between the scanning device and the clutch, a second yielding member (which will be referred to as a compliant member) designed to absorb sufiicient of the force exerted by the kinetic energy of the scanning device to prevent any clutch or motor slip. However the use of two yielding members in this way causes the scanning device to be accelerated above and decelerated below the correct speed, so that it performs a number of oscillations about its correct speed and phase position. These oscillations cause distortion in a transmitted message or alternatively cause delay between the time of staring the scanning device into rotation and the time at which transmission can be started. It is the object of the present invention to provide means by which the objectionable oscillations may be reduced without re-introducing the dangers of clutch or motor slip.

According to the present invention there is provided facsimile apparatus comprising a first member arranged to be driven continuously from a motor, rapid-engagement clutch means, which will engage positively both for rotation in the direction in which said first member is driven and for rotation in the reverse direction, for coupling a second member substantially instantaneously to said first member, a scanning device arranged to be driven through said second member, yielding means interposed between said clutch means and said scanning device for limiting the forces applied by said scanning device to said clutch means and said motor, and a braking device effective to bring said scanning device substantially asymptotically to a position of rotation in which said yielding means is in a condition similar to that occupied thereby when said clutch means is disengaged and said scanning device is at rest.

The substantially asymptotic approach of the scanning device to the correct position of rotation may be defined as the reduction of the relative velocity between the scanning device and the motor to zero substantially at the instant when the phase displacement between the two becomes zero. In order to carry out this, the braking means must provide a braking torque, between the scanning device and the motor, which torque is directly proportional to the relative velocity between the scanning device and the motor.

The asymptotic approach to the correct phase position may be achieved in one of two ways. First, it may be achieved by making the braking device operative when the compliant link is contracting from its expanded position. Alternatively, the compliant link may be allowed to accelerate the scanning device through the scanning position as described above, and the braking device arranged to be operative when the second yielding member, i.e. the compliant member, is returning the scanning device to the correct phase position.

In the second case the braking device will have to be operative when the scanning device is travelling slower than the motor driving it. This is the same condition that exists when the scanning device is being started from rest and it has to be arranged that the braking device is not operative then. The difference between the two conditions is that, when the braking device is required to be operative, the scanning device is ahead of its correct phase position, and, when the apparatus is starting from rest, the scanning device is lagging behind its correct phase position. In order to apply the second method, therefore, it is necessary to provide means for determining whether the braking device is operative or inoperative according to whether the scanning device is leading or lagging with respect to the motor. It is certainly possible to do this, but complications are introduced and the first method of carrying out the invention referred to above is the simpler and is therefore preferred.

In the preferred embodiment of the invention which will he described with reference to the single figure of the accompanying drawing, the braking device is arranged to be dependent on the direction which the compliant link (or first yielding member) is being stressed.

Referring to the drawing, a synchronous motor 1. continuously drives a shaft 2. The engagement of a positive clutch 3 at a specific instant causes shaft 4 to rotate at synchronous speed with the motor shaft 2. The positive clutch 3 may, for example, be a dog clutch, but should, in any event, be a clutch which engages positively for rotation in both directions. The shaft 4 terminates in an arm which carries a yielding abutment pin 6, a spring anchor 7, a pivot pin 8, and a spring anchor 9. To spring anchor 7 is attached one end of a spring 10, the other end of which is attached to a spring anchor 11, carried by an arm 12. The pivot pin 8 carries a toothed arm 13, which is kept in engagement with a ratchet wheel 14 by the action of a spring 15 connected between the arm 13 and spring anchor 9. The wheel 14 is free to rotate upon a spindle 16 attached to arm 12. The speed at which wheel 14 can rotate is limited by the action of the mass of an escapement lever 17' which can oscillate upon a pivot pin 18 carried by arm 12. The system 13, 14 and 17 constitutes the braking device. The arm 12 is attached to a spindle 19, which carries a facsimile device such as the usual rotatable scanning drum 2%. The arm 12 is normally maintained in contact with the abutment pin 6 in an unyielded position thereof by the tension of the spring 1%.

The spring corresponds to the compliant link or first yielding member referred to in the above discussion, while the yielding abutment pin 6 corresponds to the compliant member or second yielding member. The action of the mechanism is as follows:

The motor 1 and shaft 2 are rotating at synchronous speed, clutch 3 being in a disengaged condition so that shaft 4, and all remaining members are stationary. Upon the engagement of clutch 3, shaft 4 and arm 5 are caused to accelerate substantially instantaneously to synchronous speed. As arm 5 moves away from its rest position, pin 6 moves out of contact with arm 12 which is then urged to follow pin 6 by virtue of the tension in spring 10.

Owing, however, to the large mass of drum 2% and the low acceleration of arm 12-, spring 1! is continuously ex tended until drum 2% reaches synchronous speed. As the continuous extension of spring 10 occurs, the toothed arm 13 slides over the teeth of ratchet wheel 14. After drum 2i) has reached synchronism it continues to accelerate as spring It} now contracts and were it not for the presence of ratchet -14, escapement lever 17 and toothed arm 13 drum 2!) would, by the time lever 12 meets pin 6, reach a speed so in excess of synchronism that pin 6 would be forced to yield considerably and oscillations of the drum about the correct synchronous speed would be set up. Owing, however, to the action of the toothed arm 13 on ratchet 14-, the latter is forced to rotate and the escapement lever 17 to oscillate when spring 16 is contracting. Energy is therefore dissipated and arm 1% approaches pin 6 at a facsimile device such as the usual controlled low speed.

This speed may be chosen by suitable design of the system 13, 14 and 17 so that the movement caused to yielding pin 6 by the lever 12 is very small. The drum 20 is therefore not slowed down substantially below its synchronous speed at all.

The lever 12 then rotates in contact with pin 6 which is in its unstressed position, this being the condition for ensuring correct phase relationship between this apparatus and a co-operating machine. It will be seen that the brake exerts a low braking force when the velocity of contraction of spring 10 approaches zero. This ensures that the spring 16 contracts sufficiently to enable lever 12 to adopt the correct position as described immediately above.

It will be appreciated that other forms of braking means which provide a braking torque directly proportional to the relative velocity of two parts may be used instead of the energy-dissipating escapement device shown.

While the principles on the invention have been described above in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

What we claim is:

1. Facsimile apparatus comprising a first member arranged to be driven continuously from a motor, rapide engagement clutch means, which will engage positively both for rotation in the direction in which said first memher is driven and for rotation in the reverse direction, for coupling a second member substantially instantaneously to said first member, a facsimile device, coupling means interposed between said clutch means and said facsimile device for coupling said facsimile device to said second member, said coupling means including yielding means for limiting the forces applied by said facsimile device to said clutch means and said motor, said coupling means further including a braking device for damping the said yielding means, said yielding and said braking means cooperating to bring said facsimile device substantially asymptotically to a position of rotation in which said yielding means is in a condition similar to that occupied thereby when said clutch means is disengaged and said facsimile device is at rest.

2. Facsimile apparatus as claimed in claim 1, in which said braking device comprises an energy dissipating escapement device.

3. Facsimile apparatus as claimed in claim 1, in which said facsimile device is a message-supporting drum.

4. Facsimile apparatus as claimed in claim 1, wherein said yielding means includes a compliant link which ex: pands on engagement of said clutch means, and wherein the said braking means is effective on contraction of said compliant link to exert a braking force on said facsimile device dependent on the difference in angular velocity between said motor and said facsimile device.

References Cited in the file of this patent UNITED STATES PATENTS 2,683,514 Hardway July 13, 1954

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