Figure 1: Vacuum pick and place application
Vacuum pick and place applications utilize vacuum tools for automated lift and release of workpieces. Such pick and place tools are widely seen in modern manufacturing applications for automatic material handling. Vacuum systems make such applications efficient and cost-effective and we will cover the various components that go into these systems. Vacuum systems are seen in the following types of pick and place applications:
Figure 2 represents a circuit diagram for a basic vacuum pick and place application. The selection criteria for each vacuum component is discussed below:
Figure 2: Vacuum pick and place application components: compressed air entry point (A), compressed air control valve (B), vacuum generator (C), non-return valve (D), vacuum filter (E), vacuum pressure gauge (F), external vacuum switch (G), vacuum suction cups (H), internal vacuum switch (I), & compressed air blow-off valve (J).
Compressed air is the main element to operate a pick and place application and is typically available in most facilities. Vacuum generators use compressed air to generate a vacuum between the surface of the suction cup and the workpiece, thus attaching them. The vacuum generator must ensure that enough compressed air pressure is maintained to create a vacuum throughout the operation.
The pneumatic vacuum generator can be single or multi-staged where once the compressed air is passed through one or more venturi nozzles, it expands and creates a vacuum. For a higher suction rate, a multi-stage vacuum generator is desirable for the same amount of compressed air as a single-stage vacuum generator.
Valves help in monitoring the vacuum level and ensuring the proper flow of compressed air into the system. Different types of valves are installed between the vacuum suction cup and the compressed air source serving different purposes. In a general vacuum pick and place application, the following types of valves are installed:
The flow direction of the air should be carefully considered during the installation of these vacuum valves. As the valve has one specified flow direction, the compressed air should be allowed to pass from high pressure to low-pressure port. It means, the outlet port of the valve should be connected at the vacuum side of the application. Flow rate, valve design principle, leakage rate, response time, and circuit function (2-way, 3-way) are some criteria to be carefully considered for selecting a vacuum valve.
A vacuum pressure gauge is used in pick and place applications to read the pressure readings below atmospheric. These gauges are installed near the inlet of the suction cup and/or near the outlet of the compressed air source. The negative reading (with respect to the atmospheric pressure) in the pressure gauge indicates the vacuum pressure. Generally, a Bourdon tube pressure gauge is used for moderate vacuum pressure reading. For high vacuum reading, a specially designed highly sensitive pressure gauge is used. Temperature, pressure, and accuracy required for the application are important factors in selecting a pressure gauge. For a vacuum gauge, ± 0.025 bar deviation is preferred. View Tamesons selection of pressure gauges for vacuum applications.
A vacuum generator generates the required vacuum level for the application with the help of compressed air. Thus, we first need to calculate the pressure change required by the suction cup and the response time required. A low suction rate will create weak adhesion in the suction cup. The response time can increase with the increased length of the vacuum line. Prior knowledge of this data is necessary to make the vacuum generator selection. View Tamesons selection of vacuum generators.
A vacuum suction cup is a component that comes in direct contact with the workpiece in a pick and place application. The vacuum generator removes the air between the surface of the suction cup and the workpiece creating a vacuum. The atmospheric pressure becomes more than the pressure between the cup and the workpiece causing the vacuum suction cup to attach against the workpiece.
Figure 6: Pick and place production line
In general, the force exerted by the vacuum suction is calculated as:
Load orientation and the type of suction cup used to hold the workpiece also affect the force. Commonly used vacuum suction cup types include flat vacuum, oval vacuum, and bellow vacuum suction cups. The required safety factor and coefficient of friction are also required to be known when calculating the needed lifting force. View Tamesons selection of vacuum suction cups.
Pneumatic hoses are required to convey compressed air for the pick and place application. These hoses must be able to withstand high pressure to operate with compressed air without leakage. It is not advisable to use thin tubing as it can collapse under a vacuum even on moderate heat. The hoses must be sized to meet the flow volume requirement and the size of the suction cups. View Tamesons selection of pneumatic hoses.
Vacuum tools are generally accompanied by fixed or detachable fittings to connect them to a compressed airline. The properly installed fittings prevent leakage and ensure a proper flow path for the compressed air. These fittings should be able to handle light workpieces without causing any bending stress in the suction cup. Push-in pneumatic fittings and other pneumatic couplings (manifolds, safety couplings, etc.) are often used. They are available in a wide variety of sizes and should be selected based on the size and type of the suction cup being used. The type of material being handled (porous, non-porous) is also a critical consideration. It is equally important to ensure the bore size of the fitting and the vacuum line are properly sized. The temperature and pressure required for the application should also be considered. Aluminum and brass are the widely used material for such fittings. View Tamesons selection of pneumatic couplings and push-in fittings.