GB1601632A

GB1601632A - Escapement carriage control for photocomposition machine

Info

Publication number: GB1601632A
Application number: GB1465178A
Authority: GB
Original assignee: Multigraphics Inc
Current assignee: AB Dick Co
Priority date: 1977-06-02
Filing date: 1978-04-13
Publication date: 1981-11-04
Also published as: JPS542718A; DE2824080B2; FR2392812A1; DE2824080A1

Description

(54) ESCAPEMENT CARRIAGE CONTROL FOR PHOTOCOMPOSITION MACHINE (71) We, AM INTERNATIONAL INC., formerly ADDRESSOGRAPH MULTIGRAPH CORPORATION, a Corporation organized and existing under the laws of the State of Delaware, United States of America, of 1900 Avenue of the Stars, Los Angeles, California 90067, United States of America, formerly of 20600 Chagrin Boulevard, Cleveland, State of Ohio 44122, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement:- This invention relates to a photocomposition machine in which character spacing is achieved by means of an escapement carriage driven by a stepper motor.The invention also relates to a method of controlling the pulsing of the stepper motor and to a method of establishing data for this purpose that is stored in the machine.

The invention is generally concerned with the avoidance of a phenomenon referred to herein as 'ringing' and explained hereinafter.

Photocomposition is accomplished by projecting a series of images along a line of composition. The images are projected onto a photosensitive surface.

In the composition, the characters must be spaced from one another. The spacing varies according to assigned width values. Word spacing is a larger value than character spacing.

Spacing is accomplished by many differing means in various photocomposing machines.

One successful machine is the machine sold under the Trade Mark Comp/Set by Addressograph Multigraph Corporation (now AM International Inc.) of Cleveland, Ohio, U.S.A. United States patent No. 4,008,480 illustrates the lens and escapement system of that machine, wherein a mirror carriage is reciprocated by a stepper motor operation through a cable system, the mirror serving to direct the characters to be imaged onto a photosensitive surface at a position determined by the position of the carriage. Reference should be made to U.S. Patent 4,008,480 for further detail. The structure disclosed in the mentioned U.S. patent was first used with a direct entry keyboard and did not operate at high speed. Hence there was no problem with the mirror being in ringing movement when a character is projected. The system simply uses a delay to allow any ringing to cease before character projection.

However, if the system is operated as a unit separate from a direct entry keyboard, such as under tape input, at a much greater speed, the elasticity or resilience in the carriage drive system that leads to ringing becomes of greater significance. Even though in practice the drive cables are stable woven wire, and the carriage is very light in weight, speeds of 80 lines per minute as required in faster operation, will magnify the inertia and elastic nature of the system.

'Ringing' is a term which signifies the settling characteristic of the carriage. After attaining speed, the carriage inertia will cause the cables to stretch and retract when the drive is stopped. The continued inertial carriage movement will then cause rebound. On an oscilloscope the forward and reverse movement appears as a diminishing wave form similar to the acoustical wave form of a bell.

The present invention is generally concerned to provide measures aimed at avoiding ringing and undertakes this task by controlling the velocity/time profile, i.e. the velocity versus time relationship of the carriage as it is driven over a given distance. The distance is equivalent to a certain number of pulsations of the stepper motor and the profile is obtained by controlling the timing of the motor pulses.

According to one aspect of the invention there is provided a photocomposition machine in which character spacing is achieved by an escapement carriage driven by a stepper motor, comprising: a memory storing data defining the respective velocity/time profiles of carriage movement for a plurality of distances travellable by the carriage as represented by the respective numbers of motor steps required to travel said distances; logic means responsive to a call for a given distance movement of the carriage to select the respective profile data from the memory to control the carriage movement by controlling of the pulsing of the stepper motor; wherein said stored data is obtained by pulsing the motor for each of said numbers of steps in accord with various pulse timings to accelerate and subsequently decelerate the carriage so as to bring the carriage to rest with essentially no ringing while noting the total time of travel in each case and selecting for data storage that sequence of pulse timings for each number of steps which satisfies the no ringing criterion with the minimum of total travel time in each case.

According to a second aspect of the invention there is provided a method of establishing data for controlling the carriage movement of a photocomposition machine of the kind in which character spacing is achieved by means of an escapement carriage driven by a stepper motor and which comprises: a memory for storing data defining the respective velocity/ time profiles of carriage movement for a plurality of distances travellable by the carriage and represented by the respective numbers of motor steps required to travel said distances; and logic means responsive to a call for given distance movement of the carriage to select the respective profile data from the memory to control the carriage movement by controlling the pulsing of the stepper motor which method comprises pulsing the stepper motor of a photocomposition machine of the aforementioned kind for each of said numbers of steps in accord with various pulse timings to accelerate and subsequently decelerate the carriage so as to bring the carriage to rest with essentially no ringing while noting the total time of travel in each case, selecting that sequence of pulse timings for each number of steps that satisfies the no ringing criterion with the minimum amount of travel time in each case; and storing data defining the selected sequences as velocity/time profiles in the memory of a photocomposition machine of the aforementioned kind.

It is preferred that the velocity/time profiles should comprise a portion at a selected constant velocity between acceleration and deceleration portions.

In a further aspect of the invention there is provided a method of controlling carriage movement in a system having an escapement carriage coupled through an intermediary drive system to a stepper motor to be driven by the motor.

the method comprising: pulsing the motor in accord with predetermined data relating to the timing of the pulses for a required travel distance of the carriage that provides the phases of: accelerating the motor for a period at the end of which the motor velocity is in excess of that of the carriage; decreasing the rate of acceleration of the motor for a period during which the carriage velocity surpasses the motor velocity; increasing the rate of acceleration of the motor and then decreasing the rate of acceleration to bring the motor and the carriage to an equal selected velocity; subsequently decelerating the motor for a period at the end of which the motor velocity is less than that of the carriage; decreasing the rate of deceleration of the motor until the velocity of the motor surpasses the carriage velocity; and increasing the rate of deceleration of the motor and then decreasing the deceleration of the motor to bring the motor and carriage to a halt with essentially no ringing of the carriage.

The invention and its practice will now be described with reference to the accompanying drawings, in which: Figure 1 is a side elevational view of the optical system of a photocomposition machine with the font source and flash system shown schematically and showing the carriage-mounted lens and mirror arrangement; Figure 2 is a section view taken along line 2-2 of Figure 1; Figure 3 is a perspective illustration of the mechanical motion drive system for the escapement carriage of the composer of Figure 1; and Figure 4 is a velocity versus time chart of a master profile; and Figure 5 is an acceleration curve for the motor velocity curve of Figure 4.

For justification of a composed line of type it is necessary to increase the space between words in order to spread the amount of extra space that would ordinarily appear at the end of a line into those spaces throughout the line for better appearance.

These spacing problems and their solutions were not possible on a standard typewriter, and were solved by the use of a manual strike-on typewriter using a mechanical memory. The most successful of such machines was sold under the VariTyper trademark and was the forerunner of modern phototypesetting.

In phototypesetting, the same problems occur and the same solutions are used with respect to spacing of the letters. However, the spacing of the letters and the provision of extra spaces between words is done by projecting the image of a letter rather than by hardware which strikes a paper sheet. In order to accomplish kerning as well as word spacing and letter spacing for the difference between wide letters and narrow letters, a very fine escapement capability is required. Because phototypesetting machines are operated by electrically driven prime mover devices, the logical solution is a stepper motor which can be programmed to step the precise number of units from a given starting point according to a controller program for the machine.

Figure 1 shows a font source 10, a flash source 12, shown diagrammatically as a bulb, lenses 16 and 18, and a decollimating lens 20 by which the selected font character is imaged onto a sheet of photosensitive material via reflection at a mirror 22. The mirror 22 and lens 20 are mounted on an escapement carriage driven through a cable system by a motor 30 to move the carriage parallel to the medium 26 whereby positioning of characters at required spacings is achieved. The mechanical drive system for the carriage is further illustrated in Fig- ure 3.

This mechanism employs a stepper motor 30 to operate the mechanical motion reduction system 32. System 32 is a pulley arrangement very similar to a double acting block and tackle.

The system employs a flexible line 34 which is secured to a drive spool 36 mounted on and driven by the output shaft of the motor 30.

The line 34 is then reeved around a pulley 38 which pulley may be considered to be a stationary position turning surface. It is better that the surface be a rotatable pulley to eliminate sliding friction drag. The carriage for the decollimating or converging lens 20 and mirror 22 has mounted on the bottom thereof a rotatable pulley 40 and line 34, after looping around the pulley 38, is directed around the pulley 40 and back to a fixed anchoring point 42 on the frame of the machine.

Assume at this point that there is a force tending to move the carriage for the lens 20 and mirror 22 in the direction of pulley 38A in Figure 3. Then, as the motor turns the spool 36 to take up the line 34, the mechanical nature of the system will cause the pulley 40 and hence the carriage to move toward the fixed position pulley 38, but the line 34 will remain tight.

Then, by wrapping the counterpart line 34A around the pulley 36 in the opposite direction from the line 34, and threading the line about the fixed position pulley 38A, the second guide groove on the pulley 40 and back to ground position 42A, it will be seen that as the spool 36 takes up on line 34 it lets out on line 34A, and the system is balanced. When the motor reverses the opposite is true, and the line 34A will be taken up and the line 34 will be paid out.

As a result, an exact movement of the pulley 40 is achieved, but due to the mechanical advantage nature of the pulley system construction, the movement of the pulley 40 is only half of the movement of the pulley 36. This is a known mechanical phenomenon.

Although the structure of Figure 1 is an exact illustration of an operating, successful direct entry photocomposing system, it is elastic in nature in that the motor 30 and cables 34 and 34A are capable of some degree of elasticity or resilience. The carriage which carries the lens 20 and the mirror 22 is ofvery lightweight construction, but nonetheless has a degree of inertia.

The inertia of the system, including the carriage and its burden, causes the carriage to overshoot and then elastically return if the carriage is suddenly stopped. The internal elasticity of the motor is also a contributor. Such overshooting and retum at the target position is known as 'ringing' because of the similarity to the decay wave form of the acoustic sound wave of a bell that has been struck. Such ringing motion will cause a misplaced character projection unless the projection is delayed until the ringing motion stops. Waiting for such settling time is detrimental to the rapid speed desired for the escapement carriage.

It is now proposed to pulse the drive motor as rapidly as it can accept the load without slipping so as to accelerate the escapement carriage as rapidly as possible. Acceleration should continue to a maximum speed which can then be held for a period and then deceleration is caused to take place to bring the carriage to the exact escapement position, and no further.

It is theoretically possible to impart an acceleration to the carriage for a finite period of time, and then apply a braking motion to the carriage, including windage and friction, to bring the carriage to a precise target position without ringing. It is required to perform such an operation so as to achieve the least travel time for any given distance to be moved.To this end, for each distance, as represented by a certain number of motor steps, the stepper motor was pulsed to accelerate and thereafter decelerate the carriage with various pulse timings, and a velocity/time profile for the motor and carriage was plotted in each instance in order to determine empirically that series of times between pulses to accelerate and decelerate a given mass of the carriage and drive system such that it moves a selected number of steps and arrives at the new desired position essentially without ringing and in the minimum amount of time. In practice a great number of arbitrarily chosen step patterns, i.e. pulse timing sequences, were applied to the motor, and the resultant carriage travel traced on an oscilloscope.Therefore, a great number of arbitrary stepping pulses was established by means of a programmable control to develop a series of acceleration and deceleration curves whereby the carriage was brought to a maximum selected velocity (not necessarily the maximum system velocity as explained below) in the shortest period of time possible.

From this empirical study it was concluded that a preferable velocity/time profile was achieved when the motor velocity led the carriage velocity for a period of time, whereafter the motor acceleration is reduced to a point where the elastic nature of the system caused the carriage not only to catch up but to surpass the velocity of the motor due to the releasing of the stored elastic energy. Then, the acceleration of the motor is increased and then again reduced until the velocity/time curves of the motor and carriage merge at a selected maximum velocity, whereafter the acceleration of both is at zero.

Figure 5 illustrates the fact that, although the velocity of the motor never falls on the start of ajourney, the acceleration actually reduces almost to zero, then declines to zero at the selected steady velocity level. The reverse takes place on deceleration.

Accordingly, further arbitrary empirical times were established wherein the motor steps were pulsed at greater intervals to thereby cause the motor to lag behind the speed of the accelerating carriage and act as a braking force on the carriage.

The Figure 4 is an illustration of the resultant relationship between the motor and the carriage. Figure 4 is not a scale drawing of the exact relationship, but rather is a teaching illustration which symbolizes the mass of oscilloscope curves developed for the actual production of data to enter into a memory system for controlling the motor stepping.

After the mass of empirical data is assembled to bring the carriage to a velocity of acceptable magnitude, the times between steps to accelerate and decelerate the given mass of the carriage and drive system is placed in memory as a step profile for each possible number of steps, i.e. each distance to be travelled. The memory contains the information for each possible profile starting from the second step to any chosen maximum which may therefore be designated 'N' steps. Then, a control logic is provided to call out the steps in memory for any particular distance which is desired for carriage movement, and the stored steps and frequency of steps will then be applied to the motor under the control logic, to accomplish the acceleration and deceleration of empirically established.

It is theoretically possible to pulse the motor continually, always leading the carriage, until a maximum velocity is reached from which it is then possible for the motor to be decelerated sufficiently to bring the carriage to a proper stable target position. This could be accomplished by the motor leading the carriage until the latest period of time when it is necessary, as found by empirical methods, to apply a braking action to bring the carriage to the target position. Such a continuously accelerating and then decelerating curve would produce the most rapid movement from point to point. However, the amount of storage data to contain the mass of information for such a set of curves would be very massive and excessively expensive. It has been estimated that possibly 14,000 different profile patterns would be required to satisfy the necessary photocomposition requirements.

Therefore, a compromise was selected wherein in 16 steps from start a useful, although not maximum, velocity could be achieved. The number 16 was selected because it is binary and because the amount of memory necessary to contain all of the steps from zero to the velocity obtained at 16 steps is within economic balance for the cost of the market to be served.

It is also to be understood that the concept of this compromise includes profiles from the second step through the 16 steps necessary for the 16 steps to reach maximum velocity, and 16 steps to decelerate to zero velocity. It is not possible to profile one step, and therefore we are concerned with a range of two steps through an arbitrary maximum number, which has been selected as 32 steps in actual practice.

After the carriage and the motor have reached equilibrium at the selected velocity which is produced by the 16 input steps, then a determination is made empirically of the time between steps necessary to maintain each component of the system at a constant velocity such that the components are in equilibrium with one another at this velocity with minimum acceleration of each component of the system, whereby any number of steps can be travelled at substantially constant velocity.

It should be noted from Figure 4 that the series of acceleration steps for the motor which produces the velocity of the constant velocity portion of the curve, followed by the deceleration portion of the curve to bring the carriage to a non-ringing target position, is then simply stretched out for different distances by the number of steps at constant velocity and the same deceleration then applied to arrive at the chosen target position.

At less than 16 steps there is no need to match the carriage and motor acceleration at a selected velocity. Hence, only the matching of deceleration to shape the curves to match at zero velocity is required.

The profiles of motor velocity versus time selected in accord with the teachings given above enable a mirror carriage drive mechanism to be realised which is competitive with the lower inertia oscillating mirror structures such as are disclosed in U.S. Patent 3687025. The displacement path of the carriage in the present case is parallel to the photosensitive medium and there is no need to accept lower quality focussing or the provision of focus compensation devices such as in the just-mentioned patent.

WHAT WE CLAIM IS: 1. A photo composition machine in which character spacing is achieved by an escapement carriage driven by a stepper motor, comprising: a memory storing data defining the respective velocity/time profiles of carriage movement for a plurality of distances travellable by the carriage as represented by the respective numbers of motor steps required to travel said distances; logic means responsive to a call for a given distance movement of the carriage to select the respective profile data from the memory to control the carriage movement by controlling of the pulsing of the stepper motor; wherein said stored data is obtained by pulsing the motor for each of said numbers of steps in accord with various pulse timings to accelerate and subsequently decelerate the carriage so as to bring the carriage to rest with essentially no ringing while noting the total time of travel in each case and selecting for data storage that sequence of pulse timings for each number of steps which satisfies the no ringing criterion with the minimum of total travel time in each

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. were established wherein the motor steps were pulsed at greater intervals to thereby cause the motor to lag behind the speed of the accelerating carriage and act as a braking force on the carriage. The Figure 4 is an illustration of the resultant relationship between the motor and the carriage. Figure 4 is not a scale drawing of the exact relationship, but rather is a teaching illustration which symbolizes the mass of oscilloscope curves developed for the actual production of data to enter into a memory system for controlling the motor stepping. After the mass of empirical data is assembled to bring the carriage to a velocity of acceptable magnitude, the times between steps to accelerate and decelerate the given mass of the carriage and drive system is placed in memory as a step profile for each possible number of steps, i.e. each distance to be travelled. The memory contains the information for each possible profile starting from the second step to any chosen maximum which may therefore be designated 'N' steps. Then, a control logic is provided to call out the steps in memory for any particular distance which is desired for carriage movement, and the stored steps and frequency of steps will then be applied to the motor under the control logic, to accomplish the acceleration and deceleration of empirically established. It is theoretically possible to pulse the motor continually, always leading the carriage, until a maximum velocity is reached from which it is then possible for the motor to be decelerated sufficiently to bring the carriage to a proper stable target position. This could be accomplished by the motor leading the carriage until the latest period of time when it is necessary, as found by empirical methods, to apply a braking action to bring the carriage to the target position. Such a continuously accelerating and then decelerating curve would produce the most rapid movement from point to point. However, the amount of storage data to contain the mass of information for such a set of curves would be very massive and excessively expensive. It has been estimated that possibly 14,000 different profile patterns would be required to satisfy the necessary photocomposition requirements. Therefore, a compromise was selected wherein in 16 steps from start a useful, although not maximum, velocity could be achieved. The number 16 was selected because it is binary and because the amount of memory necessary to contain all of the steps from zero to the velocity obtained at 16 steps is within economic balance for the cost of the market to be served. It is also to be understood that the concept of this compromise includes profiles from the second step through the 16 steps necessary for the 16 steps to reach maximum velocity, and 16 steps to decelerate to zero velocity. It is not possible to profile one step, and therefore we are concerned with a range of two steps through an arbitrary maximum number, which has been selected as 32 steps in actual practice. After the carriage and the motor have reached equilibrium at the selected velocity which is produced by the 16 input steps, then a determination is made empirically of the time between steps necessary to maintain each component of the system at a constant velocity such that the components are in equilibrium with one another at this velocity with minimum acceleration of each component of the system, whereby any number of steps can be travelled at substantially constant velocity. It should be noted from Figure 4 that the series of acceleration steps for the motor which produces the velocity of the constant velocity portion of the curve, followed by the deceleration portion of the curve to bring the carriage to a non-ringing target position, is then simply stretched out for different distances by the number of steps at constant velocity and the same deceleration then applied to arrive at the chosen target position. At less than 16 steps there is no need to match the carriage and motor acceleration at a selected velocity. Hence, only the matching of deceleration to shape the curves to match at zero velocity is required. The profiles of motor velocity versus time selected in accord with the teachings given above enable a mirror carriage drive mechanism to be realised which is competitive with the lower inertia oscillating mirror structures such as are disclosed in U.S. Patent 3687025. The displacement path of the carriage in the present case is parallel to the photosensitive medium and there is no need to accept lower quality focussing or the provision of focus compensation devices such as in the just-mentioned patent. WHAT WE CLAIM IS:

1. A photo composition machine in which character spacing is achieved by an escapement carriage driven by a stepper motor, comprising: a memory storing data defining the respective velocity/time profiles of carriage movement for a plurality of distances travellable by the carriage as represented by the respective numbers of motor steps required to travel said distances; logic means responsive to a call for a given distance movement of the carriage to select the respective profile data from the memory to control the carriage movement by controlling of the pulsing of the stepper motor; wherein said stored data is obtained by pulsing the motor for each of said numbers of steps in accord with various pulse timings to accelerate and subsequently decelerate the carriage so as to bring the carriage to rest with essentially no ringing while noting the total time of travel in each case and selecting for data storage that sequence of pulse timings for each number of steps which satisfies the no ringing criterion with the minimum of total travel time in each

case.

2. A photocomposition machine as claimed in Claim 1 in which the velocity/time profiles are selected from profiles comprising a portion at a selected substantially constant velocity between acceleration and deceleration portions.

3. A photocomposition machine as claimed in Claim 1 or 2 in which the velocity/time profiles are selected from profiles in which the acceleration and deceleration of the motor each do not exceed a predetermined number of motor steps.

4. A method of establishing data for controlling the carriage movement of a photocomposition machine of the kind in which character spacing is achieved by means of an escapement carriage driven by a stepper motor and which comprises: a memory for storing data defining the respective velocity/time profiles of carriage movement for a plurality of distances travellable by the carriage and represented by the respective numbers of motor steps required to travel said distances; and logic means responsive to a call for given distance movement of the carriage to select the respective profile data from the memory to control the carriage movement by controlling the pulsing of the stepper motor; which method comprises pulsing the stepper motor of a photocomposition machine of the aforementioned kind for each of said numbers of steps in accord with various pulse timings to accelerate and subsequently decelerate the carriage so as to bring the carriage to rest with essentially no ringing while noting the total time of travel in each case, selecting that sequence of pulse timings for each number of steps that satisfies the no ringing criterion with the minimum amount of travel time in each case; and storing data defining the selected sequences as velocity/time profiles in the memory of a photocomposition machine of the aforementioned kind.

5. A method as claimed in Claim 4 in which the pulse timings for each number of steps are selected to obtain velocity/time profile having a portion at a selected substantially constant velocity between acceleration and deceleration portions.

6. A method as claimed in Claim 4 or 5 in which in the selected velocity/time profiles the acceleration and deceleration of the motor each do not exceed a predetermined number of motor steps.

7. A photocomposition machine in which character spacing is achieved by an escapement carriage driven by a stepper motor and which comprises a memory storing data defining the respective velocity/time profiles of carriage movement for a plurality of distances travellable by the carriage and represented by the respective numbers of motor steps required to travel said distances; and logic means responsive to a call for a given distance movement of the carriage to select the respective profile data from the memory to control the carriage movement by controlling the pulsing of the stepper motor; wherein the stored data is established by means of the method of Claim 4,5 or 6.

8. A method of controlling carriage movement in a system having an escapement carriage coupled through an intermediary drive system to a stepper motor to be driven by the motor, the method comprising: pulsing the motor in accord with predetermined data relating to the timing of the pulses for a required travel distance of the carriage that provides the phases of:: accelerating the motor for a period at the end of which the motor velocity is in excess of that of the carriage; decreasing the rate of acceleration of the motor for a period during which the carriage velocity surpasses the motor velocity; increasing the rate of acceleration of the motor and then decreasing the rate of acceleration to bring the motor and the carriage to an equal selected velocity; subsequently decelerating the motor for a period at the end of which the motor velocity is less than that of the carriage; decreasing the rate of deceleration of the motor until the velocity of the motor surpasses the carriage velocity; and increasing the rate of deceleration of the motor and then decreasing the deceleration of the motor to bring the motor and carriage to a halt with essentially no ringing of the carriage.

9. A method as claimed in Claim 8 in which having achieved said equal selected velocity, the motor and carriage are maintained at said selected velocity for a period prior to deceleration.

10. A method as claimed in Claim 9 in which the number of motor steps for the acceleration and deceleration phases does not exceed a predetermined value and the remaining motor steps are realised in said selected velocity phase.

11. A method as claimed in Claim 8,9 or 10 in which the intermediary drive system is a cable system.

12. A photocomposition machine substantially as hereinbefore described with reference to the accompanying drawings.