Roboticsystem design aspects


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Robotic system design Aspects


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Design Specific tasks in mind Overall size No. Of degrees of freedom Type of motion requirements Basic configuration etc

Informational Requirements - robot designers:

Informational Requirements - robot designers Number and weight of the work pieces to be handled. Required movements in the working space. Required working range (considering peripheral units like vibratory hoppers etc.). Required positioning accuracy. Changeover frequency of the production system. Sensor function for recognition and quality control. Gripper and tool operations. Kind of machining functions (e.g. drilling, turning). Careful examination of the production technology The kind of motions and kinematic chain. Geometrical dimensions. Velocities and accelerations. Drive system and control. Positioning accuracy

Overall design:

Overall design Some of the important considerations for the overall design are as follows Geometrical dexterity Kinematic chain and its suitability Forces and moments on the robot structure Selection of the Drive System Selection of Power Transmission System Selection of path measuring system Bearings and couplings Selection of materials

Mechanical Design Considerations:

Mechanical Design Considerations Manufacturability (production cost and ease of assembly). Ease of installation. Ease of modification or reconfiguration to adapt the robot to specific tasks. Ease of adjustment and calibration. Ease of maintenance. Ease of diagnosis and repair. Availability of spare and replacement parts. Compatibility with equipment from other vendors. Provisions for safe robot behavior in the event of component malfunctions. Likelihood that the robot will damage or destroy itself, as a result of faulty electronic hardware or software.

Task – Related Design:

Task – Related Design The requirements of industrial robots are closely related to the task Spray Painting Spot Welding Arc Welding Work piece handling

Some - specific requirements:

Some - specific requirements Handling on process: Very short cycle times. Special design, often Cartesian co-ordinate robot. Conditions of installation and accessibility are to be considered in particular. Handling of forging processes: High speed and heavy work pieces. Robot must be resistant to dirt and heat. Floor installation recommended. Handling on die casting and injection molding machine: Often gantry or console type installation. Cycle time with injection molding are shorter than with die casting machine. Very often simple movements lead to a simple programming language. Changeover frequency is low. High positioning accuracy. Insensitive to heat and dirt. Handling of machine tools: High positioning accuracy, short cycle times and also quite often heavy work pieces. Simple programming language owing to simple movements.

Design of Arm Tooling:

Design of Arm Tooling Design for quick removal or interchange of tooling by requiring a small no. of service tools (wrenches, screwdrivers, etc.) to be used. For example, use the same fastener wherever possible. Provide locating dowels, key slots or scribe lines for quick interchange, accuracy, registration and alignment. Break all sharp corners to protect hoses and lines from rubbing and cutting and maintenance of personnel from possible injury. Allow for full flexure of lines and hoses to extremes of axes of motion. Use lightweight materials wherever possible or put lightening holes where appropriate to reduce weight. Hard coat on lightweight materials for wear considerations. Conceptualize and evaluate several alternatives in design. Make sure enough effort and cost is spent to produce production worthy reliable tooling and not a prototype. Design extra motions to assist the robot in its task. Design sensors to detect part presence during transfer (limit switch, proximity, air jet, etc.).

Design of Arm Tooling:

Design of Arm Tooling For safety in part handling operations / applications, consider what effect a loss of power to tooling will have? Put shear pins or areas to protect more expensive components and reduce down time. When handling tools with robot, build in tool inspection capabilities, either in tooling or peripheral equipments. Design multiple functions into arm tooling. Provide accessibility for maintenance in design and quick change of wear parts. Use sealed bearings. Provide interchangeable inserts or fingers for part change-over. When handling hot parts, provide heat sink or shield to protect tooling and robot. Mount activators and valves on robot forearm for tooling.

Design of Arm Tooling:

Design of Arm Tooling Build in compliance in tooling or fixture where required. Design action sensors to detect open / close or other motion conditions. Analyze inertia requirements, centre of gravity of payload, centrifugal force and other dynamic considerations. Look at motion requirements for gripper in picking up parts (single action hand must be always to move part during pick-up; double action hand centre part in one direction, three or four fingers center part in more than one direction). When using electromagnetic pick-up hand, consider residual magnetism on part and possible chip pick-up. Look at insertion forces of robot in using arm tooling in assembly tasks. Maintain orientation of parts in tooling by force and coefficient of friction or locating feature. Current research is on-going to develop more flexible general-purpose grippers and tooling can adapt to a variety of sizes and shapes of parts. However, with increased sensory feedback integrate into robot tooling, more sophisticated tasks are being completed by the robot. This trend will continue in year to come.

Design of Control System:

Design of Control System Manipulator members are driven by electric motors Each drive will be powered by a single servo motor, which is controlled by a microprocessor unit governing both speed and displacement The inputs, which are the angle of rotation for the motor, i.e. the member, speed of motor, are calculated and sequentially fed by the mini-computer, which will have overall control of the system The mini-computer will be provided with software, which is interactive in nature. The values for arm rotation and speed will be sequentially fed to microprocessors controlling individual motors

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