Hybrid Direct-Indirect Axis Control for Precise Machine Positioning
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Solution Overview
Problem
Machine axes with a combination of indirect and direct drives face challenges in integrating direct drives due to size and cooling complexity, leading to high costs and reduced competitiveness, especially for main axes of robots, while existing controller structures lack detailed designs for optimizing drive dimensioning and dynamics.
Innovation Solution
A controller structure that includes a third determination device for calculating force pre-control values based on axis inertias and scaling factors, allowing the first and second drives to be controlled by summing force pre-control values with their respective setpoints, thereby optimizing drive dimensioning and improving dynamics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct drives are integrated into machine axes, then positioning dynamics and accuracy are improved, but device complexity and costs increase due to size and cooling requirements
Solution Approach 1:
The drive system is segmented into two independent drives: a first drive (indirect drive via transmission) and a second drive (direct drive). Each drive operates independently with its own control loop, allowing the direct drive to provide high dynamics and positioning accuracy without requiring a complete direct drive system, thus reducing overall complexity and cooling requirements
Solution Approach 2:
The patent combines indirect drive and direct drive systems into a hybrid configuration where both drives act on the same machine element. The indirect drive provides cost-effective power transmission while the direct drive enhances positioning dynamics, achieving improved performance without the full complexity of a complete direct drive system
2Productivity
If direct drives are used for main axes, then productivity and dynamics are improved, but costs increase reducing competitiveness
Solution Approach 1:
The direct drive is applied locally only where high dynamics are most beneficial for positioning accuracy, rather than requiring all main axes to have expensive direct drives. The indirect drives handle applications where cost is more critical, creating a cost-effective hybrid system that improves productivity where needed without unnecessarily increasing costs across the entire system
Solution Approach 2:
The control system dynamically coordinates both drives with different control cycles (first control cycle for indirect drive, second control cycle for direct drive). This dynamic control approach allows the system to optimize performance and productivity while managing costs through selective use of each drive type based on operational requirements
3Speed
If mixed direct/indirect drive is implemented, then positioning dynamics are enhanced, but control complexity increases
Solution Approach 1:
The control system implements dynamic coordination between drives with different control cycles. The first speed controller operates with a first control cycle for the indirect drive, while the second speed controller operates with a second control cycle for the direct drive. This dynamic multi-cycle control approach enables enhanced positioning dynamics while managing control complexity through structured hierarchical control architecture
Solution Approach 2:
The control system uses feedback from both drives to coordinate their operation. Speed feedback from both the first and second drives is utilized to adjust control signals, ensuring synchronized operation and enhanced positioning dynamics while managing control complexity through feedback-based coordination
4Power
If force pre-control values are determined with different weighting, then drive dimensioning is optimized, but calculation complexity increases
Solution Approach 1:
The system determines force pre-control values with different weighting factors applied to each drive based on their respective characteristics. The first force pre-control value uses different weighting than the second force pre-control value, allowing optimization of drive dimensioning and power distribution. This parameter-based approach enables flexible optimization without requiring complex real-time calculations, managing calculation complexity through pre-determined weighting strategies
Data Source
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AI summary
A first drive (1) acts on a machine element (4) of a multi-axis machine, which is adjustable about one axis, via a transmission device (3), and a second drive (2) acts directly. A position controller (8) receives a setpoint position (x*) and an actual position (x) of the machine element (4) and uses these values (x*, x) to determine a setpoint velocity (v*) for the machine element (4). A first detection device (11) receives the setpoint velocity (v*) and uses it to determine a resultant setpoint velocity. A first velocity controller (12) uses the difference between the resultant setpoint velocity and the actual velocity (v) of the first drive (1) to determine a first force setpoint (F1*) and controls the first drive (1) according to this force setpoint (F1*).A second speed controller (9) determines a second force setpoint (F2*) based on the difference between the resulting setpoint speed and the actual speed (v) of the machine element (4) and controls the second drive (2) depending on this force setpoint (F2*). The invention is characterized in that a second force feedforward value (F2V) is determined based on a second axis inertia JMot,ab and a second scaling factor (1 - α), and a first force feedforward value (F1V) is determined based on a first axis inertia JMot,an, the second axis inertia JMot,ab, and a first scaling factor (α).