Stepper Motor Load Detection via PWM Zero-Crossing Phase Shift
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for detecting mechanical load on a stepper motor shaft in voltage-based operating mode without sensors are ineffective, particularly at low motor speeds and when the motor is at a standstill, due to difficulties in measuring coil currents and controlling disturbances.
Innovation Solution
A method and circuit arrangement that determine the phase shift between the actual coil current and applied coil voltage by detecting zero crossings and voltage drops across internal resistances of semiconductor switches, allowing for sensorless load measurement and load angle determination without the need for analog-to-digital converters or additional current measuring resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current-controlled operation mode is used for load detection, then measurement precision is improved, but device complexity and power loss increase due to required current measuring resistors and analog-to-digital converters
Solution Approach 1:
The invention extracts the load detection function from the current control path by measuring voltage drops across semiconductor switch resistances during voltage-based operation, eliminating the need for separate current measuring resistors and analog-to-digital converters while maintaining measurement capability
Solution Approach 2:
The semiconductor switches serve dual functions: current control switching and load detection sensing elements, as their internal resistances are used to measure coil current indirectly through voltage drop measurement during both current-controlled and voltage-based operation modes
2Use of energy by moving object
If voltage-based operating mode is used at low speeds, then energy efficiency is improved, but measurement precision deteriorates due to difficulty in measuring coil currents
Solution Approach 1:
The invention uses voltage drops across semiconductor switches as an intermediary measurement quantity to indirectly determine coil current during voltage-based operation, avoiding direct current measurement while maintaining precision through the relationship V = I × R where R is the known switch resistance
Solution Approach 2:
The invention replaces direct electrical current measurement with voltage measurement across known resistances, substituting a difficult measurement (current at low speeds) with an easier measurement (voltage) while maintaining the same information content
3Productivity
If current pulses are applied with very short duration at low currents, then productivity is improved, but measurement precision deteriorates due to difficulty in measuring actual coil current
Solution Approach 1:
The invention performs load detection during the voltage application phase before current pulses are generated, using the voltage drop across semiconductor switches to determine load conditions, thereby avoiding measurement issues during the subsequent short current pulse duration
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
Enables reliable load measurement and load angle determination in voltage-based operating mode, improving energy efficiency and reducing costs and power losses, while maintaining precision and robustness across the entire speed range.
Implementation Method 1
a first and a second voltage drop which are generated by an actual coil current flowing through internal resistances of a first and a second semiconductor switch
Implementation Method 2
a first PWM voltage is generated at a first output and a second PWM voltage in an opposite second direction (polarity) is generated at a second output, so that a resulting effective PWM coil voltage is applied to the first coil
Data Source
Figure 1~2
Figure 3(A)~3(E)
Figure 4(A)~5
AI summary
The invention relates to a method and to a circuit arrangement using which a mechanical load applied to the motor shaft of a stepper motor can be detected without a sensor in a voltage-based operating mode in which a target coil current is generated by applying a predefined coil voltage (Us) to the coil. The coil is connected in a bridge branch of a bridge circuit formed by a first to fourth semiconductor switch (S1, ... S4), wherein the predefined coil voltage (Us) is applied to the coil by switching the semiconductor switch in the form of at least one PWM voltage (U(A1), U(A2)) with a variable duty cycle (T). The motor load is detected in the form of a load indicator signal (L) which represents a phase shift between a zero crossing of the predefined coil voltage (Us) and the subsequent zero crossing of the coil current (Icoil) generated thereby, wherein a zero crossing of the coil current (Icoil) is determined if the polarity of a voltage, which falls across the internal resistors of the semiconductor switches, reverses in the time intervals (tm) in which the PWM voltage (U(A1), U(A2)) applied to the coil is zero.