Here are some key points for selecting a suitable six-dimensional force sensor for a robotic arm:
Measurement performance
• Measuring range: The appropriate measuring range should be determined based on the actual working task of the robotic arm and the magnitude of the forces and torques it may withstand. For example, if the robotic arm is mainly used for handling light items, such as on an electronic component assembly line, then a six-dimensional force sensor with a relatively small measuring range is sufficient, such as a measuring range of less than 100N in the Fx, Fy, and Fz directions, and a measuring range of less than 10Nm in the Mx, My, and Mz directions. However, if the robotic arm is used in heavy industrial fields, such as car body handling and processing of large mechanical parts, a larger measuring range is required, with the Fx, Fy, and Fz directions potentially reaching several kN or even higher, and the Mx, My, and Mz directions reaching hundreds of Nm.
• Accuracy: For robotic arm applications requiring high-precision force control, such as precision assembly and micro-manipulation, high-precision sensors should be selected. Generally, the accuracy should be at least 0.1% of full scale or even higher. For example, in the assembly process of some precision instrument manufacturing, the accuracy of a six-dimensional force sensor is required to be accurate to 0.05% FS to ensure accurate assembly of parts and avoid damage to precision components.
• Resolution: Resolution determines the smallest change in force or torque that a sensor can detect. High resolution is required for delicate operations, such as the operation of minimally invasive surgical robots, to sensitively perceive minute force changes and achieve precise motion control.
• Linearity: A sensor with good linearity ensures that the output signal has a good linear relationship with the actual force within its measurement range, which is crucial for accurate measurement and control. Choose sensors with the smallest possible linearity error, generally requiring a linearity better than 0.5% FS.
Mechanical properties
• Size and weight: Space and load limitations at the end effector or mounting location of the robotic arm must be considered. If space is limited, small, compact sensors should be selected. For example, six-dimensional force sensors with a diameter of less than 50mm and a height of about 30mm can be used for the robotic arms of some small collaborative robots. For large industrial robotic arms, the limitations on size and weight are relatively smaller.
• Installation Methods: Common installation methods include flange mounting and threaded mounting. It's crucial to ensure the sensor's mounting method matches the end effector or related components of the robotic arm for easy installation and disassembly, and to guarantee the sensor's stability and reliability after installation. For example, if the robotic arm's end effector has a standard flange structure, then a six-dimensional force sensor with a corresponding flange mounting interface should be selected.
• Stiffness: A sensor with suitable stiffness will exhibit minimal deformation when measuring forces and torques, thus ensuring measurement accuracy and the control precision of the robotic arm. Simultaneously, its stiffness matching with the overall stiffness of the robotic arm must be considered to avoid impacting system performance due to excessive stiffness differences.
Electrical characteristics
• Interface type: Select the interface based on the interface supported by the robotic arm's control system, such as analog interfaces (e.g., voltage output, current output) or digital interfaces (e.g., RS485, CANopen, EtherCAT, etc.). For example, some advanced industrial robotic arm control systems typically support EtherCAT interface sensors due to their high-speed communication and real-time performance.
• Power supply requirements: Understand the power supply voltage and power consumption of the sensors to ensure that the power supply system of the robotic arm can meet the power supply requirements of the sensors and avoid affecting the normal operation of the sensors due to insufficient or unstable power supply.
Environmental adaptability
• Temperature range: If the robotic arm works in a high-temperature environment, such as a handling robotic arm near a furnace, a high-temperature resistant six-dimensional force sensor needs to be selected. Its working temperature range should meet the actual environmental requirements. Generally, there are different levels such as -20℃ to 80℃ and -40℃ to 120℃.
• Humidity adaptability: In some humid or moisture-containing environments, such as food processing and aquaculture, robotic arms should be equipped with sensors that have good moisture resistance, and the protection level should be at least IP65 or higher.
• Vibration and shock resistance: For robotic arms that operate in environments with vibration or potential impact, such as hoisting robotic arms on construction sites, sensors with good vibration and shock resistance should be selected to ensure that they can still measure stably and accurately under harsh conditions.
In terms of reliability and stability
• Quality and Brand: Prioritize well-known brands and reliable products. These products typically undergo rigorous quality testing and market validation, ensuring high reliability and stability, as well as better after-sales service.
• Overload protection capability: The sensor should have a certain overload protection capability to prevent damage due to excessive force during the operation of the robotic arm. Generally, the overload coefficient of the sensor is required to be above 200%, and some sensors can achieve a single-axis overload capacity of 300% or even higher of the rated range.
