Classifications

• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B19/00—Programme-control systems
  • G05B19/02—Programme-control systems electric
  • G05B19/18—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form
  • G05B19/19—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path
  • G05B19/21—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path using an incremental digital measuring device
  • G05B19/23—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path using an incremental digital measuring device for point-to-point control
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B19/00—Programme-control systems
  • G05B19/02—Programme-control systems electric
  • G05B19/18—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form
  • G05B19/414—Structure of the control system, e.g. common controller or multiprocessor systems, interface to servo, programmable interface controller
  • G05B19/4142—Structure of the control system, e.g. common controller or multiprocessor systems, interface to servo, programmable interface controller characterised by the use of a microprocessor
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B2219/00—Program-control systems
  • G05B2219/30—Nc systems
  • G05B2219/34—Director, elements to supervisory
  • G05B2219/34215—Microprocessor
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B2219/00—Program-control systems
  • G05B2219/30—Nc systems
  • G05B2219/37—Measurements
  • G05B2219/37152—Combination 00-01-10-11, previous, actual pulses, or two series of pulses, and rom

Definitions

• This invention relates to position control systems and to methods of controlling the position of an object.
• the invention is concerned with achievingposition control digitally by using a microcomputer.
• the invention is especially adapted for the positional control of a dc motor coupled to an object which is to be controlled.
• the position control method and system of the present invention finds wide application, and can be used in any field where fast-response position control is required.
• One particular application of the method and system is to the control of a "daisy" print-wheel, as will be described in greater detail hereinafter.
• the method and system of the present invention are also applicable to manipulators, robotics, and other situ ⁇ ations where a fast response, coupled with a high degree of accuracy, is required.
• the present invention achieves this object by the use of a novel algorithm which uses the microcomputer in an unconventional way and which requires a minimum of additional circuitry.
• the algorithm used in the present invention is based on state transition concepts.
• a method of controlling the position of an object which includes feeding a microcomputer with information representative of a desired position or sequence of positions of the object, monitoring the position of the object by sensing incremental movements of the object in each of two opposed directions and feeding this position status information to the icro- computer, and using the microcomputer to generate signals for motive means arranged to drive the object to the desired position, characterised in that the position status information upon which the microcomputer acts includes a single multi-bit word representative both of the current sampled object position and of the pre-• ceding sampled object position and determinative of whether and in which direction movement has taken place in the time interval between said samples.
• the multi-bit word forms part of a status byte including additional bits
• the status byte is accessed by a single input instruction, in the sub ⁇ sequent instruction the status byte is used as an index to a look-up table of addresses of action routines, and in the subsequent instruction the microcomputer enters the appropriate routine.
• the sensing of the object position produces two trains of coded logic signals of relatively different phase
• the time interval between two changes of logic level of either the one or the other signal represents a predetermined incremental movement of the object, and " if a change in logic level occurs too early the motive means is decelerated whilst if a change in logic level has not occurred after the designated interval then the motive means is acceler- ated.
• the method includes generating as the position status information an 8-bit status byte con ⁇ sisting of four bits of movement information representing past and present position status, one bit representing a home position, one bit indicative of whether a change in the logic levels of certain of said first four bits has occurred within a preset time interval, and two bits representing- forward and reverse drive respectively.
• logic signals from said sensor means representative of current position are fed to a first por of the microcomputer, and corresponding bits of a second port with logic levels representative of the preceding position are cross-wired to said first port to provide a status byte input having present and past status infor ⁇ mation.
• Fig. 1 is a block diagram of a position control system embodying the present invention
• Fig. 2 shows an optical disc with 96 stripes for use as a position signal generating element in theposition control system of Fig. 1;
• Fig. 3 shows the analog and digital encoded signals obtained upon rotation of the optical disc shown in Fig.2;
• Fig. 4 is a circle diagram to illustrate certain moves of the optical disc; and, Fig. 5 is a graphical representation of the respons of the position control system in terms of numbers of incre mental steps plotted against time.
• the position control system des cribed hereinafter is described in relation to the control of a daisy print-wheel, the print-wheel having 96 charac ⁇ ters on individual “petals”.
• the optical disc indicated generally at 10 in Fig. 2 which has 96 stripes, thus corresponds to the print-wheel, and rotation of the optica disc 10 through a given angle will correspond to an equal rotation of the print-wheel.
• the disc 10 has the.96 stripes arranged equally spaced around its circumference around the rim of the disc.
• the central opaque zone of the disc is provided with a single radial slot which, as will be explained, is used for the generation of a "home" signal. As shown in Fig.
• the disc 10 is mounted on a shaft 12 extending from a dc motor 14.
• the dc motor 14 drives the print-wheel.
• the optical disc 10 serves as a slave disc monitoring the movements of the print-wheel as controlled by the motor 14.
• three optical sensors Associated with the optical disc 10 are three optical sensors. These may comprise photocells posi ⁇ tioned on one side of the disc, with a ligh source or sources on the other side of the disc. Two of the sensors, indicated at A and B in Fig. 1, are positioned at a radial distance from the centre of the disc 10 such that their line of sight is traversed by the stripes, while the third sensor, indicated at H in Fig.
• the three photoelectric trans ⁇ ducers generate analog signals a_, ' b and h respectively, as illustrated in the upper half of Fig. 3.
• the ' a. and b signals are in quadrature, i.e. there is a 90 relative phase difference between these two signals.
• the signal generated by the third photoelectric transducer H is referred to hereinafter as the h signal.
• the field of view of each sensor is equal to the width of one of the stripes on the disc 10, which itself is equal to the width of the gap between each stripe.
• the maximum amplitude occurs when the optical sensor is exactly aligned with the gap between two stripes, the minimum amplitude Occurs when the sensor is exactly aligned with one of the stripes, and the points of zero amplitude occur when the sensor is half covered by one of the stripes.
• a step is chosen to be the time interval between two daisy characters, i.e. the time taken for the disc 10 to rotate from one of the sensors A or B being in alignment with a stripe to that same sensor being in alignment with the next adjacent stripe (see Fig. 3) .
• a move is the " time interval between any two changes of either the a or b signal (again see Fig. 3) There are thus 4 moves to each step. For the move shown in Fig. 3, it is initiated by the ' b signal changing from 1 to 0 and is terminated by the a. signal changing from 0 to 1.
• the three signals from the pulse shaper 16 are fed to a microcomputer 18 having a first 8-bit port PO and a second 8-bit port Pi.
• the microcomputer may be based for example on an Intel 8035 with external memory or a mask programmed, single chip Intel 8048.
• the microprocessors usedtherein are particularly well-suited to handling the algorithm on which the present invention is based.
• Position demand i.e. the position to which the user wishe the controlled object to move, is fed into the microcompute 18 via the data bus and control lines, one of which TO is shown. In the case of a printer the position demand signals would be issued by a master processor which is concerned with overall system co-ordination and possibly with editing functions.
• bits 0 and 1 of port P are hard-wired to bits 2 and 3 of port 0.
• the system of the present invention involves a sampling technique inwhic the condition or status of the sensors is monitored.
• Bit O and 1 of port PO represent the current status of sensors A and B respectively, and it is arranged that the corres ⁇ ponding bits 0 and 1 of port PI represent the 'old' status of those sensors, i.e. their preceding sampled logic values.
• bits 2 and 3 of port PO are 'old a.' and
• Bits 6 and 7 of port PO act together to supply a drive forward (DF) or drive reverse (DR) signal to apply • maximum drive voltage to the motor 14.
• the motor 14 is here driven by a four-transistor amplifier 20, together with two integrated circuit operational amplifiers 21 and 22. A connection is provided between the output from sensor A and one side of operational amplifier 21, and a phase advance circuit 24 is connected across this amplifier. By this means one can accommodate level conversion of logic signals and phase advance of linear signals.
• the motor 14 is required to be at rest, i.e. if drive forward and.drive reverse are both zero, then the signal a from photocell A is fed back through the drive amplifier to apply a proportional voltage to the motor, locking the system into its final settling position.
• control algorithm used in the system of the present invention is based on a state defined in terms of the present and previous a and b logic values, the h logic value, the present drive direction, a count related to the time elapsed since the last change of a or b, and a count of the distance yet to go.
• a relationship is defined between the distance to go and required velocity, and the problem reduces to one of velocity control.
• OMPl a required time interval between changes of a or b. If a change occurs too soon, deceleration must be applied, whilst if a change has not occurred after the allotted time then the motor must accelerate. A further co pon- ent of the state can thus be considered to be 'time out', indicating that a change has not occurred soon enough. In other words, 'time out' indicates 'accelerate';. 'not time out' indicates 'decelerate'.
• the status byte is accessed by a single input instruction, is in the next instruction used as an index to fetch an address from a look-up table in read-only memory, and in the following instruction the processor has entered the appropriate routine - which in the case of 'time out' may be this routine itself looping until the status byte indi ⁇ cates that a change has occurred.
• bit 5 of port PO is not connected, that does not mean that it is not used.
• the same output instruction which sets the drive direction will also set bit 5 high or low (1 or 0) to indicate 'time out* or 'not time out'. This value is therefore present in the status word or byte when it is input, and serves its purpose in addressing the look-up table.
• the program and 'cat's cradle' of linkage addresses thus operates more clearly as a finite automaton than a conventional system.
• One further instruc ⁇ tion must be inserted in the above sequence; in order that the 'old' values can be presented in the status byte, the input is followed by an output to the second port Pi, of which the bits 0 and 1 corresponding to a. and b are cross- wired to Old a_' and 'old b" bits 2 and 3 of the first port PO.
• the sixteen combinations of the signals b' " a ' b_a can therefore be grouped into four classes - 1110, 1000, 0001 and 0111 indicate clockwise moves, 1101, 0100, 0010 and 1011 are all anti-clockwise moves, 1111, 1010, 0000 and 0101 represent no move at all, whilst 0011, 0110, 1100 and 1001 are all illegal. two of the legal moves are selected as 'counting' moves.
• the b signal is low whilst the analog form of the a signal is fed back through the operational amplifiers 21, 22 and the phase advance circuit 24 to hold the system near the a transition. If the signal is displaced by half a stripe in either direction the position counter must therefore count either up or down.
• This counter takes place when a. changes whils b is high.
• 1110 represents a clockwise counting move and 1011 represents an anti-clockwise counting move; each time a move of such a type is detected the position counter is adjusted accordingly.
• the least significant four bits of the status byte can thus be interpreted as representing one of the following eight conditions -
• the 8-bit status byte can now be interpreted as for example, clockwise counting move, no time out, drive forward, and a simple look up in the decision table will swiftly execute the appropriate routine.
• ACTION ROUTINES For each value of the status byte there will correspond in the look up table the address of a suitable action routine.
• the routine includes a test of the control line TO ( Figure 1) which is used to indicate that a new command is being issued.
• the detailed decision matrix of Table 2 shows which routine is to be entered under each status condition and the routines themselves are summarised afterwards.
• Fig. 5 shows the speed response of a daisy wheel position control system in accordance with the invention.

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• Engineering & Computer Science (AREA)
• Human Computer Interaction (AREA)
• Manufacturing & Machinery (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Automation & Control Theory (AREA)
• Computer Hardware Design (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Control Of Position Or Direction (AREA)

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• 1981
  • 1981-02-16 WO PCT/GB1981/000021 patent/WO1981002347A1/en not_active Application Discontinuation
  • 1981-02-16 GB GB8104808A patent/GB2070285B/en not_active Expired
  • 1981-02-16 EP EP19810900434 patent/EP0045761A1/de not_active Withdrawn

Non-Patent Citations (1)

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