When selecting a robot, customers should not only focus on its payload but also on its maximum end effector workspace, which includes the reach of the robot's end effector and its maximum pickup height. The reach refers to the maximum working diameter of the parallel robot's end effector in the horizontal plane. The maximum working radius, which is half the reach, is the distance from the farthest point (point P) of the robot in the horizontal plane to the center of the robot's base. The maximum pickup height, or maximum vertical range of motion, refers to the range between the lowest point (usually below the robot's moving platform) and the highest point that the robot's end effector (point P) can reach.
However, in practical applications, different robots and different application scenarios all influence the choice of robot reach. Especially when selecting a robot, the following technical points should be paid special attention to:
1. The robot's reachable workspace is divided into full workspace and effective workspace.
Taking a parallel robot as an example, the entire workspace is the set of points reachable by the robot's end effector given all poses. It can be obtained using the method of intersecting circular arcs, and its shape is a three-dimensional space resembling an umbrella, represented by the symbol W.
The definition of effective workspace is predicated on the limiting conditions of the robot's drive mechanism. These conditions are defined by a safe limiting angle that excludes unusual postures of the robot's end effector and interference from physical components. Therefore, effective workspace refers to the maximum effective working area that the robot's end effector can reach within the safe limiting angle range. To visually represent effective workspace, it is simplified into a cylindrical space composed of a cylinder and an inverted frustum (icon D).
Considering the actual application scenarios of customers, the effective workspace diagram D defined in this paper mainly consists of one cylinder and two inverted frustums (as shown in the figure above), where the inverted frustum shown in D3 approximates an inverted cone. The robot's end effector lies within the effective workspace D, resulting in the following general rule for the overall rigidity of the robot: In the horizontal direction, the rigidity of point P gradually decreases from the center point of the base to the farthest point; in the vertical direction, the rigidity of point P gradually decreases from the center point of the base to the lowest point. The degree of rigidity reduction varies depending on the actual structure of the robot's components.
2. In practical applications, the pick-up and drop span needs to be at least 20cm less than the arm span.
Every company provides the robot's range of motion, but when integrating the robot into a real-world solution, factors such as load, pick-and-place span, pick-and-place cycle time, and conveyor belt speed are all important factors affecting the selection of the arm span.
Taking the following diagram as an example, the overlapping part of the robot's workspace and the conveyor belt's workspace constitutes the effective pickup space of the integrated solution. Due to their different positions, the two items A and B located on the conveyor belt spend different amounts of time in the effective pickup space when passing through the conveyor belt. When the robot's arm span is small, blind spots are likely to occur when picking up items from the conveyor belt. A larger arm span also means a larger effective pickup space.
3. Parallel operation offers greater space and floor space advantages, and a longer boom span also allows for higher speeds.
Compared to other industrial robots, end-effector freedom and workspace are not areas where parallel robots are inherently strong; and a large arm span inevitably restricts movement speed, preventing a substantial improvement in production efficiency; ultra-large arm spans are mostly used in scenarios involving the handling of heavy objects, and the extreme operating range, high speed, and high load place extremely high demands on structural stability. However, these difficulties were changed with the advent of the D-2600 in January 2019, whose 2600mm ultra-large arm span is among the first in the field of parallel robots.
This unit is a custom-made model belonging to the 3+1 axis product series. Originally initiated in November 2018 to address the customer's need to reduce floor space, it has recently completed the final in-house testing phase after two months of development. In addition to achieving an arm span of 2600mm, the maximum pickup height reaches 890mm, the standard cycle time (25-305-25 gantry trajectory) is 120 times/minute, and the repeatability is ±0.1mm. It will soon be put into testing at the customer's site.
To ensure optimal speed and load performance even with a large reach, the Bokent Robotics Research Institute has achieved new breakthroughs in mechanical structure. In addition to inheriting the structural advantages of Bokent's existing three-plus-one axis design, inspired by the mortise and tenon joints of traditional Chinese architecture, the institute boldly experimented with a composite stationary platform featuring high rigidity. This structure significantly improves the stability of the large reach structure during operation, avoiding rigidity errors under high loads and high speeds. The integrated design of the reducer and motor results in a lightweight, compact design with high rotational accuracy and high torque. The modular rotating unit配套的 ...
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