Universal Motor Speed Control via Voltage Drop Measurement
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Solution Overview
Problem
Existing speed control systems for commutator series motors are costly due to the need for low-impedance precision resistors and complex circuit arrangements for current measurement, which increases the overall expense and complexity.
Innovation Solution
The method involves using voltage drops across the armature and field winding as control variables instead of motor current, eliminating the need for direct current detection, and employing a microcontroller to process voltage signals, including the use of a transistor and resistor configuration to compensate for constant voltage components, allowing for precise and inexpensive speed control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct motor current detection is used with low-impedance precision resistors, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent introduces an intermediary approach by measuring voltage drops across the armature and field winding instead of measuring current directly. This voltage measurement serves as a mediator that indirectly provides the necessary current information for speed control, avoiding the need for complex current sensing circuits while maintaining measurement accuracy.
Solution Approach 2:
The patent replaces the electrical current measurement system with a voltage measurement system. By substituting the direct current detection method (which requires precision resistors and complex processing) with voltage drop measurement across motor windings, the system achieves simpler circuitry and lower cost while maintaining the necessary measurement precision for speed control.
2Device complexity
If voltage drop measurement at armature and field winding is used, then device complexity is reduced, but measurement precision may be affected
Solution Approach 1:
The patent combines the measurement of voltage drops from both the armature winding and field winding into a single composite measurement signal. This merged voltage signal contains the necessary information for accurate speed control while being obtained through simple voltage tapping, avoiding the need for complex current measurement circuits.
Solution Approach 2:
The voltage drop measurement across the armature and field winding serves multiple functions simultaneously: it provides information about motor current, motor speed, and load conditions. This multi-functional measurement approach eliminates the need for separate sensing circuits, reducing overall system complexity while maintaining measurement precision.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces circuit complexity and costs while maintaining precise speed control, as the microcontroller processes voltage signals to adjust motor speed effectively without requiring current measurement, enhancing measuring accuracy and reducing operational expenses.
Implementation Method 1
an opposing DC voltage UG is superimposed on the measuring voltage UFA from the sum of the voltage drop at the armature and part of the field winding, which at least partially compensates for this unchanging voltage component
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a method and a circuit for regulating the speed of a commutator series-wound motor, especially a universal motor (10), which is supplied with a current from an a.c. voltage source (22) by means of a semiconductor switching element (18) mounted in series with an armature winding (12) and a field winding (14, 16) and controlled by a control unit (28) according to a nominal speed value. The control unit (28) receives, as input signals, signals corresponding to the total voltage drop (Umot) when the motor (10) is supplied with a current, and a substitute signal for the intensity of the motor current (I), corresponding to the voltage drop (Ua, Ufa) on the armature (12) alone or on the armature (12) and on a part (14) of the field winding (14, 16). The input signals of the control unit (28) are compared with motor-typical characteristic lines of the voltages on the excitation field (14) and/or on the armature, stored in the control unit, and control signals for the semiconductor switching element are formed from the deviations.