Dynamic Current Limit Control for Coordinate Measuring Machine Motors
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Solution Overview
Problem
Coordinate measuring machines face challenges in protecting objects and personnel from mechanical damage while attempting to measure objects efficiently, as existing torque control methods limit motor current and speed, restricting acceleration and movement even when the measurement object is far from the coordinate measuring device.
Innovation Solution
Determine a dynamic limit value for the electric drive current based on target speed and/or target acceleration, allowing for variable movement phases and areas, enabling higher speeds and accelerations when safe and reducing current when necessary for personal or device protection, with real-time monitoring and adjustment to prevent exceeding predefined current limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the motor current is limited to a maximum value to prevent mechanical damage, then personal and device protection is improved, but the speed and acceleration of the coordinate measuring device are reduced
Solution Approach 1:
The patent applies dynamics by making the current limit value adjustable and dependent on the operational phase. The control device dynamically adapts the current limit based on whether the coordinate measuring device is in travel phase or measurement phase, allowing high speeds during travel and restricted currents during measurement. This resolves the contradiction by making the protection mechanism adaptive rather than static.
Solution Approach 2:
The patent changes the parameter of current limit value based on the operational phase. During travel phase, a higher current limit is permitted enabling faster movement, while during measurement phase, the current limit is reduced to prevent mechanical damage. This parameter change approach allows the system to optimize both speed and protection at different times in the operational cycle.
2Object-affected harmful factors
If the motor current is limited to low values for safety, then mechanical damage is prevented, but the measurement time increases due to reduced speed
Solution Approach 1:
The patent implements periodic action by alternating between two operational phases: travel phase and measurement phase. During travel phase, higher currents and speeds are permitted to cover distance quickly. During measurement phase, current and speed are limited to ensure safety. This periodic switching between phases allows the system to achieve both fast overall measurement time and safe operational conditions.
Solution Approach 2:
The patent applies preliminary action by performing the high-speed travel phase before the measurement phase. The coordinate measuring device uses higher currents to quickly position itself near the measurement object, then switches to restricted current mode for the actual measurement. This preliminary high-speed positioning reduces total measurement time while maintaining safety during the critical measurement operation.
3Device complexity
If a fixed maximum current value is used for torque control, then protection is simplified, but the coordinate measuring device cannot operate at high speeds when not near the measurement object
Solution Approach 1:
The patent makes the current limit value dynamic based on the operational phase detected by the control device. The system automatically switches between a first current limit value (higher) during travel phase and a second current limit value (lower) during measurement phase. This dynamic approach maintains relatively simple control logic while dramatically improving productivity during travel phases.
Data Source
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AI summary
The invention relates to a method for operating a coordinate measuring machine and to a coordinate measuring machine, wherein a coordinate measuring device, in particular a measuring head, of the coordinate measuring machine can be moved in at least one direction while being driven by at least one electric motor (M). An electrical drive current which flows through the electric motor (M) (via the current path of the lines C11, C21) in order to move the electric motor (M) and, in this manner, move the coordinate measuring device is measured. A limit value for the electrical drive current is determined (in the computer PC and/or in the microcontroller MC) on the basis of a desired speed and/or on the basis of a desired acceleration with which the electric motor (M) or the coordinate measuring device (5) is intended to move. If the electrical drive current reaches the limit value (IT) determined and/or if the electrical drive current exceeds the limit value (IT) determined, the coordinate measuring device (5) is changed to a predefined state, for example by virtue of the computer (PC) or the microcontroller (MC) switching off one of the switches (SW1, SW2) which are arranged in the current path.