Complete Modular Servo System

Complete Modular Servo System

The MS150 Modular Servo System is designed to study the theory and practice of automatic control systems. It has been designed for teaching the theory of open and closed-loop, speed and positional control systems using modular units, both mechanical and electronic, that can be configured to demonstrate the various methods of control techniques.

The MS150 comprises a baseplate and twenty units which may be supplied in different configurations, such as: a complete system MS150-3, a dc system only MS150, an ac system only MS150A, a Digital system in a MATLAB™ environment 33-008 or conversion sets to enable a change from one system to another.

Each unit is fitted with a magnetic base which holds the unit to the plastic coated steel baseplate, irrespective of the angle at which the baseplate is positioned. Individual units may be so arranged to create operating block schematic systems and interconnections between the units are made by jumper leads terminated in 4mm stackable plugs.

The modular concept of the MS150 system permits the study of individual units and also, by combination, the investigation and performance testing of complete systems. A series of instructional manuals is supplied to provide comprehensive coverage of servo system theory and assignments for a wide range of student abilities. The d.c system MS150 is the basic set from which all other systems are derived. It is used for demonstrating and teaching automatic control techniques to students and technicians at all levels, e.g. Technical and Craft schools Science and Physics courses Industrial training courses Universities, Teachers’ Training Colleges, Military Training Schools, etc.

The MS150 comprises modular units for individual study and construction of speed and position controls using d.c error signals. The MS150 system is extendible to cover: AC servo systems, Hybrid servo systems, Digitally controlled servo systems, Relay (on/off) servo systems, Sampled data systems, Three-term control.

Instruction manuals give a detailed coverage of theory and practice from basic introduction to advanced study. Most work is non-mathematical and in the few cases where some knowledge is required, the formulae are of the elementary kind.

To cover the full range of demonstrations and experimental work a function generator and a means to display the dynamic responses are essential. Feedback function generator FG601 is suitable. We recommend that the display oscilloscope has d.c coupled X and Y channels and has a simple storage facility.

The ac system MS150A is used in more specialised and advanced control engineering courses where some detailed knowledge of ac carrier systems is required. It has the same basic form as the dc system and in fact uses some common components. As ac systems are fundamentally more complex than dc systems the theoretical work possible with the MS150A is to a higher level than that for the MS150 dc system.

The MS150A will have particular relevance to control engineering for Military and Aviation schools and for universities and colleges catering for the aerospace and advanced electronic industries. The Instruction Manuals contain progressive exercises with full theoretical explanations at each stage.

The MS150RST consists of three modules which enables the MS150 to be converted into an ac / dc hybrid servo. The 150RST produces a continuous rotation position control system with ac error channel using two synchros and a demodulator. These three units enable mainly qualitative assignments to be carried out; they cover exploratory work on synchros for data transmission and on associated equipments.

When the Conversion Units 150UVW are added the ac system is converted into a suppressed carrier ac system. The system uses a two-phase motor (150U), an ac pre-amplifier (150V) and a compensator unit (150W). The equipment is supplied with full theoretical explanations and suggested courses of practical work.

The SR150G is an additional unit which greatly increases the scope of the dc MS150 by converting it into a relay (bang-bang or on-off) type control system with 2-step & 3-step control characteristics; it provides a wide range of electronically generated non-linear characteristics. The SR150G may also be used on its own to demonstrate specific control system characteristics. The unit is provided with selector switches and controls that allow the generation of the following characteristics: Input drive voltage ±10V triangle waveforms at 5Hz nominal frequency.

A further add-on unit is the PID150Y three-term control unit which can be used also with other d.c control systems. It provides a practical programme covering proportional, integral and derivative functions. Each path in the unit can be isolated from the others and is accessible via a monitoring socket. The three paths are combined in a summing amplifier with low-pass filtering characteristics and an inverter is used to give 0 & 180 degree outputs. Variable time constants are provided in the integral and derivative functions to allow investigation of control loop characteristics.

The addition of the SH150M enables the MS150 dc Modular Servo System to demonstrate the application of the principles of sampling theory to control systems. The unit consists of a zero order hold circuit and compatible pulse generator. The generator has an operating range of 0.1 to 100Hz in three decades.

The DS150J is a differential synchro unit for use with the MS150A ac Modular Servo System. It is used in conjunction with the ST150T synchro transmitter and ST150R synchro transformer for demonstrating synchro operation. The DS150J is similar in appearance to the ST150R but it is fitted with a differential synchro in place of the synchro transformer and has a knob to set the differential angle. It can be inserted in the normal link between the ST150R and ST150T to illustrate the positioning of a transformer to an angle equal to the difference between the angles set on the transmitter and differential synchros. As there is an internal torque generated which tends to align the rotor and stator to zero differential, the dial is fitted with a braking pad. Six connections, three rotor and three stator, are brought out to the top panel.

• Features

  • Comprises selfcontained units with mimic diagrams of function blocks.
  • Magnetic base on each unit provides firm fixing to baseplate enabling pratical visualisation of system block configurations.
  • Units may be investigated individually before building a system
  • Easily extended to cover Digital systems
  • No mechanical skills required to construct a working system
  • ‘Hands-on’ assembling of working systems
  • Variable factors such as gain, damping, friction and inertia are immediately demonstrable by their effect on performance
  • Demonstrations of stable and unstable modes by using switch-in time constant network
  • Speed or position configurations may be built
  • System protected against incorrect connections and accidental shortcircuits

• Curriculum Coverage

  MS150 DC system:

  • Operational Amplifiers
  • Motor Speed Characteristics
  • DC Error Channel
  • Simple Position Control
  • Closed-Loop Position Control
  • Simple Speed Control
  • Deadband and Step Response
  • Velocity Feedback
  • Analysis of Simple Position Control
  • Speed Response
  • Position Response
  • Closed-Loop Frequency Response
  • Measurement of Motor Time Constant
  • Measurement of Velocity Error Constant
  • Frequency and Transient Response
  • Measurement of Following Error
  • Stability Considerations and the Use of Lead
  • Lag and Combined Networks
  • Tacho-Generator Feedback and its Effects on System Performance Including Acceleration Feedback
  • Linearisation of System
     

  MS150A ac System:

  • Motor Characteristics
  • AC Tacho-Generator
  • Motor Speed Control
  • AC Pre-Amplifiers
  • Position Control System
  • The Importance of Correct Phasing on Performance
  • Compensation Using the Adjustable Notch Filter
  • Notch Filter Design Exercises
  • Frequency Selective
  • Characteristics for the Elimination of Noise and Harmonics
  • Detailed Analysis of Carrier System
  • Frequency Transformation for Compensator Techniques
  • Principles and Measurement of Compensation Unit Characteristics
  • Measurement of System Characteristics
  • Instability
  • Reduction in Steady Following Error

  150RST:

  • The Synchro Link
  • The Demodulator
  • Error Channel Sensitivity
  • Closed-Loop System
  • Steady State Following Velocity Feedback Effect
  • Improved Steady State Following with Acceleration Feedback
  • Use of Synchro Link with ‘Defined Time Constant’ System

  150UVW:

  • Characteristics of a Two-Phase Motor
  • General Behaviour of a Closed Loop System
  • Effects of Gain and Damping on Stability
  • The Importance of Correct Phasing on Torque and Speed Control
  • Compensation Using the Adjustable Notch Filter
  • Notch Filter Design Exercises
  • Frequency Selective Characteristics for Elimination of Noise and Harmonics

  150G:

  • Relay Characteristics - Deadband - Hysteresis
  • Relay-Operated Control System
  • l Following Characteristics of Relay System
  • Effect of Backlash on System Stability
  • Relay-Operated Speed-Control System
  • Phase-Plane Analysis
  • Motor Characteristics – Trajectories
  • Trajectory for a Sequence of Switchings
  • Phase-Plane Analysis of Relay Operated Systems
  • Rotation of Switching Lines by Velocity Feedback
  • Deadband with Variable Slope
  • Backlash with Fixed Unity Slope
  • Two-Step and Three-Step without Hysteresis (overlap)
  • Two-Step and Three-Step with Hysteresis (overlap)

  150Y:

  • Speed Control of an MS150 Servo
  • Position Control
  • Following Error

  MS150M:

  • Waveform Sampling
  • Sampled Data Servo Control System
  • Simulated Sampled Data Control System
  • Sampled Data Process Control System - Transfer Functions of Hold Circuits and the Sampling Theorem