The reason for the uncoordinated movements of the robot - the KUKA robot

In the case of industrial robots and machine tools, it may involve the precise and harmonious movement of multiple axes in a specific space to complete the task at hand. Robots generally have 6 axes, and these axes must be harmonious and orderly, and if sometimes the robot moves along a trajectory, there will be 7 axes.

The reason for the uncoordinated movements of the robot - the KUKA robot

The reason for the uncoordinated movements of the robot - the KUKA robot

In CNC machining, 5-axis harmony is common, but some applications use up to 12 axes where things and workpieces move relative to each other in a specific space. Each axis consists of a servo drive, a motor, and sometimes, a gearbox between the motor and the shaft joint, perhaps the end effector. Then, the system is interconnected through industrial Ethernet, and the LINE topology is generally selected. The motor manipulator converts the desired spatial trajectory into a single azimuth reference required for each servo axis, which is then cycled over the network.

Manipulation cycles

These applications operate at the specified cycle time, which is typically equal to, perhaps several times the fundamental stewardship/pulse width modulation (PWM) switching cycle of the underlying servo motor drive. In this environment, end-to-end network transmission delay is an important parameter. During each cycle, the motor operator must transmit the new bearing datum and other relevant information to the individual nodes. Then, the moment in the PWM cycle when the demand is satisfied is sufficient for each node to update the servo control algorithm with the new azimuth reference and any new sensor data. Each node then passes through a distributed clocking mechanism that relies on the Industrial Ethernet protocol to apply the updated PWM vector to the servo drive at the same point in time. Depending on the detailed control architecture, part of the control loop algorithm can be completed in the PLC, and if any relevant sensor information is updated on the network, the demand can only be completed at the moment when the requirements are met.

Data transfer is delayed

Assuming that the only traffic on the network is a periodic data flow between the machine tool manipulator and the servo node, the network deferral (TNW) consists of the number of network jumps to the farthest node, the network data rate, and the deferral resolution suffered by each node. In the case of robots and machine tools, the delay in signal transmission caused by the line is negligible, due to the relatively short cable length. The primary postponement is bandwidth postponement; i.e. the moment required to transfer data to the line. With regard to the smallest Ethernet frames (generally suitable for machine tools and robot manipulation), bandwidth delays regarding 100 Mbps and 1 Gbps bit rates. This is equal to the packet scale/data rate. For multi-axis architectures, the typical data payload from the manipulator to the servo consists of a 4-byte speed/azimuth reference update and a 1-byte manipulator update for each server, i.e., a payload of 30 bytes for a 6-axis robot. Of course, some applications include more information and/or have more axes, in which case the size of the packet is larger than the minimum scale.

In addition to bandwidth delays, other deferred elements occur due to Ethernet frames passing through the PHY and dual-port switches of each servo network interface. The part of the frame movement that appears in these postpones is through the PHY into the MAC, and when the policy address is parsed, only the preamble and policy part of the frame need to be timed. Route A indicates the interception of the payload data of the current node, and path B indicates the journey of the frame to the destination node. Only the payload transmitted to the application in A is displayed, and B shows the majority of the frame being transmitted; This suggests that there may be subtle differences between Ethernet protocols. The path indicates that the frame is transmitted outbound, through the transport queue, through the PHY, and back to the cable. This assumes that pass-through packet exchange is chosen instead of store-and-forward, which has a longer delay because the entire frame is counted on the switch before being forwarded.

Displays the time-lapse element of the frame in a timeline that depicts the entire transmission moment of the frame through an axis node. TBW indicates a bandwidth delay, and TL_1node indicates a delay in the frame passing through a single node. In addition to the delays associated with the physical transmission of bits through the line and the inclusion of address bits for the execution of policy address profiling, PHY and switch component delays are other factors that affect transmission delays within the system. As the number of nodes increases as the bit rate on the line increases, these delays have a greater impact on the overall end-to-end frame transmission delay.

Low postponement treatment options

ADI introduces two new Industrial Ethernet PHYs designed to operate robustly in harsh industrial conditions over a wider range of ambient temperature scales (up to 105°C) with superior power and deferred standards. ADIN1300 and ADIN1200 are designed to handle the challenges mentioned in this article and are ideal for industrial applications. With the FIDO5000 real-time Ethernet, multi-protocol embedded dual-port switch, Analog Devices has developed a processing solution for deterministic moment-sensitive applications.

PHY and switching, provided that the receive buffer profile is based on the policy address and that a 100 Mbps network is selected.

For example, factoring these postponements into a line network of up to 7 axes, and factoring the total payload into the final node, the total transmission postponement becomes

During that time 58 × 80 ns indicate that the preamble and policy address bytes are read after the remaining 58 bytes of the payload.

This accounting assumes that there is no other traffic in the network, and perhaps the network will be able to prioritize access to always-sensitive traffic. It relies to some extent on protocols, and there are slight differences in the values calculated according to the Industrial Ethernet protocols that are used in detail. In retrospect, when the cycle time of the mechanical system is reduced to 50 μs to 100 μs, the transmission of frames to the farthest node may take up nearly 50% of the entire cycle, resulting in a reduction in the time left for the next cycle to update the motor control and motion control algorithm calculations. Minimizing this transmission time is important for optimizing the function, as it allows for longer and more messy manipulation calculations. Given that the delay associated with line data is fixed and dependent on bit rate, the use of low-latency components such as ADIN1200 PHY and fido5000 embedded switches will be key to optimizing functionality, especially as the number of nodes is added (e.g., a 12-axis CNC machine) and the cycle time is shortened. Switching to Gigabit Ethernet can dramatically reduce the impact of bandwidth delays, but adds to the share of overall delays caused by switching and PHY components. For example, a 12-axis CNC machine with a gigabit network has a network transmission delay of about 7.5 μs. In this case, the bandwidth element is negligible, and there is no difference in the use of minimum or maximum Ethernet frame sizes. The value of minimizing the delay of these elements is highlighted by the fact that network latency can be roughly evenly split between PHY and switch, with the shift to gigabit network speeds in industrial systems, the reduction in the number of operating cycles (12.5 μs for WEtherCAT®), the increase in the number of nodes due to the addition of Ethernet-connected sensors to the control network, and the increasing flattening of the network topology.

In the application of high-performance multi-axis synchronous movement, the control timing needs to be very precise, deterministic and time-critical, and the end-to-end delay needs to be minimized, especially when the control cycle time is shortened, and the clutter of the control algorithm is added. Low-latency PHYs and embedded pass-through switches are important components for optimizing these systems. To address the challenges described in this article, ADI has introduced two new robust Industrial Ethernet PHYs, ADIN1300 (10 Mb/100 Mb/1 Gb) and ADIN1200 (10 Mb/100 Mb).

The reason for the uncoordinated movements of the robot - the KUKA robot

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