Assembly components: Grippers, bowl feeders, and part handling components October 3, 2012 Lance Astle

Handling components Where can you learn about handling components? Material handling involves moving, selecting or packing products. Material handling robots are used to automate moving, feeding or disengaging parts or tools to or from a location, or for transferring parts from one machine to another. Where can you learn about handling components?

Bowl Feeders

Types of Bowl Feeder Tracks Multiple Track Multiple Track bowls have two or more tracks. Each track carries parts from the bottom of the vibratory bowl to its discharge. The discharge of stock bowls can have up to ten tracks. Advantages include higher production rates and the simultaneous delivery of fixed numbers of parts to the bowl's discharge. Positive Tracks Positive Tracks have a less than 90° included angle between the track and the side wall of the vibratory bowl. Track angle is expressed in degrees of slope above the horizontal plane - usually 7°, 8°, 15°, or 60°.

Radius-Form Tracks V-Form Tracks Radius-Form Tracks generally have a groove for the entire length of the track, but some just for the last quadrant. They are designed to feed a cylindrical part whose length is equal to or greater than its diameter. The track's radius should match the profile of the part being fed. V-Form Tracks V-Form Tracks contain grooves of 60°, 90°, 120°, or 150° as the included angle. Some run the entire track length, others only the latter part of the track. These tracks are designed to feed cylindrical parts.

Part Orientation

The ups and downs Ups Downs Takes high quantity of parts and feeds them out one at a time Can have multiple ramps to feed several different lines simultaneously Ramps can be made to custom fit the geometry of the part to determine orientations upon line entry Can feed parts as thin as .0015 inches at a rate of up to 24 linear feet per minute Some parts are difficult to orient properly Can be costly to try to tool your own Must be accompanied by appropriate vibratory control unit that may or may not be interchangeable with other bowls Can damage more sensitive and fragile components Limitations on part size and geometry

PROBLEMS OCCURING IN VIBRATORY FEEDERS Declining feed rate due to low amplitude. Usually this will occur gradually over a period of time. A dead spot in the bowl. Parts will not feed past a certain point in the bowl, even though they are moving elsewhere in the bowl. Intermittent operation. The feeder will spontaneously run at excessive amplitude or possibly no amplitude without apparent cause. Included in this category is for a feeder not to work at all. Noise in vibratory feeders.

Causes of Declining Feed Rate Cracked spring -creates dead spots Change in durometer -rubber feet can cure with age Cut/slice in rubber foot -foot is part of the spring system. Must be in good working order Loose feet -part of spring system Coil gap -affects amplitude Weld seam -can break on the coil when hit repeatedly by the armarture Rust and oxidation -can negatively affect amplitude when present between springs and spacers Operation without shell -amplitude is negatively affected when run without the shell/lid

Gripper: A component of a robot that grasps an object, generally through the use of suction cups, magnets, or articulated mechanisms.

Types of grippers Adhesive Double Expanding Mechanical Vacuum Hook Magnetic Hook Inflatable Ladle

Where are they used? Industrial robots –handling and manipulation Hard automation –assembling, micro assembling, machining and packaging NC machines –tool changers (see PML or CTB 101 on campus) Lifting tools –load carrying equipment

Vacuum Grippers Simple models operating off of syringes cost $60-70 -holds 3.5 ounces for ½ hr Larger models can move entire pallets of parts. Can cost thousands, but prices are generally given out to prospective customers only, as number of fittings depends on load.

Where are they used? Vacuum grippers are used in the robots for grasping the non – ferrous objects. It uses vacuum cups as the gripping device, which is also commonly known as suction cups. This type of grippers will provide good handling if the objects are smooth, flat, and clean. It has only one surface for gripping the objects. Most importantly, it is not best suitable for handling objects with holes.

What types are there? Ball joint Lever compensator These help to balance the material when it has multiple levels and also absorbs some shock.

Things to consider for vacuum grippers Theoretical force Shear force Holding force Weight of workpiece Work conditions Suction area Difference in ambient pressure and system pressure Coefficient of friction Workpeice material and geometry

Suction Force Theoretical Force: Force perpendicular to the surface Shear Force: Force adjacent to the surface

Holding Force F=∆P*A F = Holding force (without safety factor, purely static) ∆P = Difference between ambient pressure and pressure of the system A = Effective suction area (the effective area of a suction cup under vacuum)

Diameter and suction force Horizontal Vertical D=1.12√(MS/PN) M = mass of the workpiece in kilograms S = safety factor P = vacuum in bar N = number of suction cups D=1.12√(MS/PNµ) M = mass of the workpiece in kilograms S = safety factor P = vacuum in bar N = number of suction cups µ=coefficient of friction

Hey kids, it’s problem time A certain line has glass, stone and plastic table tops that must be sorted into separate lines. They scratch easy so vacuum grippers must be used. The stone platters can sometimes come out a little moist. They will be lifted in a vertical direction The manufacturer wants to know how many suction cups he will have to use to be safe in all circumstances. The diameter of available vacuum grippers is 95mm or 150mm. The 95mm device costs $160 and the 150mm device costs $190. The masses are as follows Glass-40kg, stone-32kg, plastic-5kg Workpiece surface Friction coefficient approx. μ Glass, stone, approx. 0.5 plastic (dry) Moist or oily 0.1-0.4 surface Vacuum pressure is -0.4 bar Calculate all diameters in cm. Which device is the better choice financially while still achieving a factor of safety of at least 2 in all scenarios?

What is the limiting factor? which table tops will require the most vacuum grippers? When the factor is found, which will cost more? compare pricing for both sizes

D=1.12√(MS/PNµ) N = MS/(Pµ(D/1.12)^2) Evalute both at 95mm N(glass) = (40*2)/(.4*.5*(9.5/1.12)^2) = 5.5596 6 N(wet stone) = (32*2)/(.4*.1*(9.5/1.12)^2) = 22.2387 23 Wet stone table is limiting factor Evaluate wet stone at 150mm N(wet stone) = (32*2)/(.4*.1*(10.5/1.12)^2) = 18.2 19

What costs more? 95 mm: 15o mm: 23 x $160.00 = $3680.00

Problems with grippers Contact with grippers can cause static electricity Multiple contacts with sensitive surfaces can cause scratches rendering defective products Contact on food surfaces can increase the spread of bacteria

Current solutions Pneumatic Non-Contact Grippers “Uses air flow as the medium to apply a lifting force to pick up and grip a work piece, because air flow is free from magnetism and generates little heat.”

Disadvantages Losses when converting electric energy to compressed air: When air is compressed and transported it experiences “mechanical energy loss in the compressor, thermal energy loss due to heat transfers when air (is) being compressed, energy loss due to viscous friction and turbulence in the transmission and depressurization” -Kagawa Must be taken into careful consideration whether or not implementing such a device can be justified financially

Robotics and Computer-Integrated Manufacturing Volume 29, Issue 1, February 2013, Pages 63–70 Development of a new noncontact gripper using swirl vanes Xin LiCorresponding author contact information, E-mail the corresponding author Toshiharu Kagawa Precision and Intelligence Laboratory, Tokyo Institute of Technology, R2-14, 4259 Nagatsuta-chou, Midori-ku, Yokohama, 226- 8503, Japan http://dx.doi.org/10.1016/j.rcim.2012.07.002, How to Cite or Link Using DOI

Swirl Vane

Pneumatic non-contact gripper Energy required to produce a 0.2N lifting force: Required air flow: 1.17×10−3 m3/s (ANR) Compressor pressure: 200 kPa (abs.) Air power formula: PaQln(Ps/Pa) (Q=volume flowrate, Pa=abs atm, Ps=abs calculated positon) At 90% efficiency the energy required to produce 0.2N lifting force is: 90 watts

Swirl vane non-contact gripper At 24 Volts and 0.08A the swirl vane produces a lifting force of 0.2N using only: 2 Watts

Link to article for Swirl vane http://www.sciencedirect.com/science/article/pii/S0736584512000865

Questions?

References Grippers Vacuum grippers Bowl feeders http://books.google.com/books?hl=en&lr=&id=mJyOOe2ohq8C&oi=fnd&pg=PR5&dq=robotic+grippers&ots=uyfb_pr- H6&sig=YOtBzNxGOjs8I001Z5GPK18jd6o#v=onepage&q=robotic%20grippers&f=false  http://www.answers.com/topic/gripper-1 Vacuum grippers http://www.roboticsbible.com/vacuum-grippers.html http://www.numatics.com/common/pdf/Numatics-Vacuum-Products-Catalog.pdf http://www.lynxmotion.com/p-825-vacuum-gripper-kit-with-wrist-rotate.aspx Bowl feeders http://www.autodev.com/assets/downloads/trouble-shooting-guide.pdf Swirl vane non-contact gripper http://www.sciencedirect.com/science/article/pii/S0736584512000865 Material handling http://www.robots.com/applications/material-handling/15