Browse Prior Art Database

Closed-Loop Control of Acceleration And Deceleration in a High-Speed Printer

IP.com Disclosure Number: IPCOM000102720D
Original Publication Date: 1990-Dec-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 4 page(s) / 155K

Publishing Venue

IBM

Related People

Green, TA: AUTHOR [+3]

Abstract

A DC motor controller capable of continuous closed-loop velocity profiling is disclosed here. This invention provides new techniques for expression of three control constants as functions of position so that load velocity can be profiled up and down while retaining stable control. Control algorithms devised based on these techniques provide for a low-cost implementation of a high performance motion control system, using low resolution optical encoders, low-cost motors and drive electronics and a minimum of control logic.

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Closed-Loop Control of Acceleration And Deceleration in a High-Speed Printer

       A DC motor controller capable of continuous closed-loop
velocity profiling is disclosed here.  This invention provides new
techniques for expression of three control constants as functions of
position so that load velocity can be profiled up and down while
retaining stable control. Control algorithms devised based on these
techniques provide for a low-cost implementation of a high
performance motion control system, using low resolution optical
encoders, low-cost motors and drive electronics and a minimum of
control logic.

      The digital control method employed in many DC motor systems
incorporates the feedback structure illustrated in the drawing.

      In this sampled-time velocity control system, motor speed (or
the time between successive encoder counts) must be relatively
constant for guaranteed system stability. Therefore, algorithms
implementing this type of closed-loop control provide for additional
routines for acceleration and deceleration up to and down from the
required steady- state speed.  Typically, these routines are
open-loop, although adaptive or bang-bang variations have been
implemented in designs with critical start/stop requirements.

      Cost-effective design of high performance machines dictates
high acceleration and deceleration rates, tight control of start and
stop distances, and velocity profile tailoring for optimization of
transient response and system jerk.  None of these criteria are met
adequately by piecewise algorithms in which the system switches
between open-loop and closed-loop control laws.

      Three control constants are expressed as functions of position
so that load velocity can be profiled up and down while retaining
stable control.  From the figure, these three constants are "Ref.",
GD and PWM Offset.  "Ref." is an inverse-velocity representation of
the desired velocity.  It is made a function of position, calculated
according to encoder pulses, to meet given motion profile
requirements.  Next, GD, the gain control factor is calculated for
given encoder positions to maintain stability over the range of
velocities.  Finally, the PWM Offset which is constant for a given
velocity, is made a function of position so that "nominal" motor
voltage is supplied when ERROR=0, across the range of speeds in a
given profile. Therefore, the control loop is capable of dynamic
adjustment of the motor voltage to provide the commanded velocity
profile.

      THEORETICAL DETAILS For the control system in the figure to
exhibit sufficient dynamic response and stay stable, the system DC
gain must be bounded.  For systems operating only in steady-state,
the best value for DC gain may be determined by using a number of
analytical techniques.  The desired gain is then implemented by
setting the Gain Divide (GD) factor in the digital filter.

      DC gain in terms of system parameters is expre...