Design of a Loading System for the Tripod Leg Grinding Process

In the diploma thesis, a loading system was designed with the aim of improving process stability, automating the process and eliminating the possibility of tool breakage due to operator errors and positioning inaccuracies. Due to the specific characteristics of subsequent processing, it was determined that the tripod loading and unloading process cannot be fully automated, but it is possible to eliminate human and functional errors through the introduction of automation, which were the cause of collisions and consequent tool breakage. This confirms the hypothesis that by automating the loading process, we reduce cycle time whilst simultaneously eliminating downtime associated with manual loading onto pallets.

Problem

In the diploma thesis, a loading system was designed with the aim of improving process stability, automating the process and eliminating the possibility of tool breakage due to operator errors and positioning inaccuracies.

Solution and Method

Due to the specific characteristics of subsequent processing, it was determined that the tripod loading and unloading process cannot be fully automated, but it is possible to eliminate human and functional errors through the introduction of automation, which were the cause of collisions and consequent tool breakage. For automation, it was necessary to select a set of systems that would perform the work instead of humans, whilst simultaneously selecting a system to replace the existing system with a circular belt, which proved to be unreliable.

Before selecting the systems, it was necessary to examine what each system offers and what the weaknesses and advantages of individual systems are. Thus, for lifting the tripod, a magnetic elevator with a sliding surface and magnets on a belt beneath it was chosen, as it proved to be the only effective solution that does not cause downtime whilst enabling individual lifting of the tripod. For transitional transport, which is necessary for phase verification and tripod positioning, a standard conveyor belt with a rounded stop at the end was selected.

A smart camera is mounted above the belt, which inspects each piece and informs the system how the piece is oriented. For picking up the tripod and transporting it to the pallet, a robot was chosen due to the complex sequence of movements. At this point, the key factors for the decision were primarily the arm's dexterity and movement precision. A gripper and at least one inductive sensor must be attached to the robot. The gripper grasps the tripod, whilst the inductive sensor can determine the leg position during rotation, thereby enabling correct tripod orientation.

For correct placement, the following are crucial: smart camera, robot dexterity, inductive sensor and well-written programme. At this point, the robot also has the option to reject a piece if it receives information that it is of the wrong type. In the next step, the arm places the tripod into the pallet, which has integrated tactile sensors. ** As soon as the tripod is in the correct position, the linear module to which the pallet is attached 'carries' it to the clamping location.** During this time, the clamping head releases the piece, which falls onto the belt beneath it, and moves into the picking position.

When the tripod is in position, it descends and picks it up from the pallet. With such a system, the time between individual clampings would be reduced by at least five seconds, thereby increasing productivity. Due to the reduced workload for the worker, they would be relieved and could devote more time to maintaining quality. This provides an opportunity for better process control.

Results

This confirms the hypothesis that by automating the loading process, we reduce cycle time whilst simultaneously eliminating downtime associated with manual loading onto pallets. Because positioning with the robotic arm and linear module system is far more precise than the existing one, such a system can ensure that the tripod will always be in a suitable position for clamping, whilst the smart camera and sensors inform it how to rotate the tripod so that it is always correctly oriented. This completely eliminates the possibility of tool breakage due to human error.

With the system, we also eliminate the possibility of breakage due to incorrect position during clamping, owing to the correct tripod position. This confirms the hypothesis that the new loading system eliminates the possibility of tool breakage due to incorrect position (as well as wrong type) of the tripod. With improved tripod positioning at the clamping location, we achieve several satisfactory results, however positioning alone does not have a direct impact on process stability. If the tripod is not in the correct position, tool breakage occurs in any case, whereas in the opposite case, the tripod is additionally positioned by the good clamping system and therefore the position at the clamping location, if it is not off and clamping is completely incorrect, does not have a major impact on process stability itself. However, it does have an indirect impact, as with each collision due to increased clearance, the SPC deteriorates and corrections are needed more frequently, up to the point where it is no longer possible to maintain a stable process through correction.

However, automation has another positive impact on quality. Namely, after the introduction of the new system, the worker has time to focus on measurements and detect in time that the process is approaching the warning limit value, thereby performing correction in a timely manner. [deof_form download_text="Aljaz-Pongracic_dd.docx" download_url="https://www.academia.si/novice/wp-content/uploads/2018/09/Aljaz-Pongracic_dd.docx"]