Workpiece carrier

In transfer systems linked to rigid work transfer systems, the workpieces and/or partly assembled components run through the assembly process on workpiece carriers in clocked cycles. The assembly stations are placed on a circuit or next to each other parallel to the transfer device. Rigid work... 

For longitudinal transfer systems, the transfer movement usually results from the friction between the workpiece carrier and the transfer equipment (belt, conveyor, etc.). The workpiece carriers transport the workpieces through the assembly system and also lift the workpieces in the assembly stations. The workpiece carrier is isolated and stopped in the assembly station in order to carry out the assembly process. The coding of the workpiece is executed by mechanical or electronic write/read units on which up-to-date information about the assembly status or manufacturing conditions can be stored. 

The coding of the workpiece carrier is executed by means of mechanical or electronic write/read units. In this way, it is possible to record up-to-date information about the assembly status or manufacturing procedure on every workpiece carrier and to process this information through the assembly control system. Figure 8 shows a workpiece carrier with a coding device. 

Figure 8 Example of a Workpiece Carrier with a Coding Device. (Source Robert Bosch GmbH)...

The following example shows the possibilities of material flow simulation. In the model of an assembly system which is designed to produce 140 pieces/hr, the number of the workpiece carriers is increased. The result is a higher production level at some of the examined stations, but at some locations the higher number of workpiece carriers cause a blockage of stations that have successor stations with a higher cycle time. Thus, the increase of workpiece carriers has to be done in small steps with a separate simulation after each step to find the optimum. In this example, a 10% increase in the number of workpiece carriers and the installation of a second, parallel screwing station lead to a production increase from 120 to 150 pieces/hr. 

Multiple workpiece carriers for standard SMT process chains Chip-on-MID placement technologies Embedded components MID housing... 

It may well be necessary to design a workpiece carrier for station-to-station transport of the circuit carrier along the production line and also for loading the devices into the individual stations. Depending on circumstances, it can be very difficult to convey small MID parts and complex 3D bodies dependably on the PCB conveyor belt. Reusable carriers are one way of shortening cycle times, with each carrier accommodating multiple interconnect devices. 

SMD Pick Place Machine with Manually Operated Workpiece Carrier... 

One way of extending the 3D capability of an SMD pick place machine is to use a workpiece carrier with defined angular settings for the individual process surfaces of the MID (Fig. 4.15). These settings are presets deriving from the design of the... 

FIGURE 4.15 Manually operated workpiece carrier in an SMD pick place machine... 

TABLE 4.2 Properties of the Kinematics of an SMD Pick Place Machine with Manually Operated Workpiece Carrier... 

Kinematics, MID side Workpiece carrier with manual rotation a about x... 

The Space 400 3D precision assembly module from Xenon is a versatile in-line system with a four-axis gantry system and a component manipulator for 3D applications (Fig. 4.17). The conveyor brings carrier-mounted MID to the component manipulator. The manipulator grips the workpiece carrier and can then position the interconnect device s process surfaces about two rotary axes and along one linear axis. There are two parallel process axes for dispensing and component placement [5j. 

Automated production requires a workpiece carrier that can be used all the way along the production line. Consequently, the design is such that the carrier can be conveyed by the printed-circuit board conveyor to all the machines in the process chain. The appropriate number of workpiece carriers is required if production is to be continuous. An interface for energy supply and communication between the automatic machines and the workpiece carrier is necessary, particularly for the dispensing unit and the automatic placement machines. The electronics built into the workpiece carrier render it unsuitable for reflow soldering, so a handling step has to be included so that the MID can be lifted on to a separate, passive workpiece carrier for this process. This transfer can be manual or by means of an industrial robot such as the Scara robot. 

An alternative to progressing down a production line is to integrate stationary work-piece carriers into the placement machines, in this arrangement the MID incoming from the printed-circuit board conveyor are readied for component placement by being transferred by the placement machine to the workpiece carriers. 

The workpiece carrier can be used in an existing SMD placement machine and the machine itself can still be used for assembling planar printed-circuit boards, and this versatility affords manufacturers two-fold benefit from having an efficient, cost-effective solution for MID production. 

Gantry system Placement head Workpiece carrier... 

FIGURE 4.21 Automated workpiece carrier in SMD pick place machine Siplace HF... 

Carrier thermal mass or, more accurately, capacity becomes important when work-piece carriers (Fig. 4.22) are used along the entire production line. The soldering proces s in particular is very much affected by this thermal capacity. The temperature profile has to be adapted to ensure dependable electrical and mechanical interconnecting that will also result in the requisite reliability. If the choice is going to be in favor of an automated workpiece carrier, it is important to bear in mind that the integrated drives and the electronics are not suitable for the soldering process. 

FIGURE 4.22 Use of workpiece carriers in vapor-phase soldering of MID parts (graphic left courtesy of 2E mechatronic]... 

Consequently, prior to soldering the MID will have to be transferred to a passive workpiece carrier, for example. 

It may well be necessary to adapt an optical inspection system to accommodate the three-dimensional layout of MID process surfaces. Class 2l D MID can be inspected without additional kinematics and adaptation of the optical inspection system. This holds true only if the process surfaces are plane-parallel in the inspection plane of the sensor array. Classes n x 2D and 3D call for changes to the AOI system if the electronic components are widely spaced. This could well mean integrating an extra handling and positioning unit for MID, for example an automated workpiece carrier. 

With the exception of the injection-molding step, production is on the line for hot-emboss MID set up in the framework of the AHMID research project funded hy the BMBF. The line includes a dispenser, an SMD pick place robot, and a vapor-phase soldering unit. The preassembled interconnect devices are set in groups of twenty on a purpose-built workpiece carrier and checked. The high level of quality is confirmed by what is now eight years of fault-free operation in the field. 

Pfeffer, M., Goth, C., Craiovan, D., Franke, J. 3D-Assembly of Molded Interconnect Devices with Standard SMD Pick Place Machines Using an Active Multi Axis Workpiece Carrier. In Proceedings 2011 IEEE International Symposium on Assembly and Manufacturing, ISAM 2011, Tampere (Finland), 25-27 May 2011. 

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