11 Gripping Technology Flashcards

Question

Disadvantages of Anthropomorphic Grippers

Answer 1

- Very complex design - Complex gripping setup - Complex process control - Very expensive

Answer 2

Gripping force is created through a negative pressure between gripper and part Technical details and applications * Gripping force is defined through the diameter and the quantity of the suction cups * Pick and place applications * Plastics, glass, metal sheets, wood and textiles

Answer 3

- Quick process control - Large handling forces possible - Low wear (no moving parts) - Working fluid most times by default at the machine available

Answer 4

- Only suitable for air impermeable parts - Susceptible to dirt - Failures in the vacuum system lead to loss of handling force - Deformation of the handled part is possible - Time to create the vacuum

Answer 5

 Used to create negative pressures  Smooth-walled pipe with a cross-section narrowing  Take-off tube at the smallest cross section

Answer 6

* Smallest cross-section: maximum dynamic pressure; minimum static pressure * The fluid’s velocity increases by the ratio of the cross-sections when entering the constricted area (constant volume) * Static pressure decrease in the outlet pipe

Answer 7

* Simple and robust design * Low generation of noise * Energy supply via air pressure, which is usually available, thus no need for additional energy supply * Lower need for maintenance

Answer 8

The gripper is pressed against the part. Through a negative pressure, the gripper gets stiff and lays itself around the part Technical details and applications * Combination of form and force closure * Large variety of objects, while the part can be enveloped partly * Soft and deformable parts with low surface pressure

Answer 9

- Possible to handle multiple parts at the same time - Large flexibility regarding possible parts geometries

Answer 10

- No defined handling pose - Just suitable for small, light parts - Susceptible to dirt - Failures in the vacuum systems leads to loss of handling forces

Answer 11

* A negative pressure is created through a positive pressure at the gripper itself * Equilibrium between force of the negative pressure and the weight force of the part * Used to handle very sensitive parts, e.g. solar cells

Answer 12

- Contact less handling of the part - No residue on the parts - Smooth handling of sensitive parts

Answer 13

- Precise positioning is difficult - Uncontrolled blowoff of dirt particles - Handling small parts is difficult - Possibility of surface damage - Only suitable for flat and plane parts

Answer 14

Through the attraction of magnetic components results a magnetic handling force. Technical details and applications  Handling through magnetic force closure  Force can be created with: * Permanent magnets: needs fixture to release the part, not suitable for a precise positioning * Electromagnets: no additional actuators needed, looses handling force at failure  Used for mostly smooth and ferromagnetic parts

Answer 15

- Simple design - No additional actuator needed

Answer 16

- Remaining magnetism possible - Low positioning and repeating accuracy - High tare weight of the gripper - Just ferromagnetic parts - Need of an additional fixture to release parts

Answer 17

 Adhesive bond between frozen water and part  Adhesive force depends on the wettability of the active medium  Heat extraction through a Peltier element  Release through a polarity reversal in the Peltier element  Suitable to handle textiles and fiber composite materials

Answer 18

- No damage to the surface - Relatively small handling forces

Answer 19

- Long process times due to the inertia of the semiconductors - Parts surface must be able to absorb water

Answer 20

 Thermo-electric conductor  Peltier element consists of two materials with different conductivity (mostly semiconductors)  Semiconductors are connected in alternating order; junctions alternating on the line  Jean C. A. Peltier: “Emergence of heat and cold on the boundary of two semiconductors of different conductivity when current is applied”  Current flow through two junctions in a row: thermal absorption (cooling) at one junction, heat dissipation at the other

Answer 21

On the gripper surface are many very thin hairs, which establish a force of attraction with the parts surface Technical details and applications  Based on the Van der Waals forces  No remaining stains on the part  Suitable to handle light sheets or platins

Answer 22

- Also suitable for porous materials - No additional medium/power needed for the handling force

Answer 23

- More elaborative release strategies as the gripper can’t be turned on and off - Needs clean and smooth surface - Limited handling forces

Answer 24

The soft fingers change their forms through an applied negative pressure and envelope themselves around the part. Technical details and applications  Form closure with low surface pressure  No defined position, as the fingers are flexible  Suitable to handle different forms, soft and light parts  Mostly used in the food industry

Answer 25

- Parts do not need a defined pose to be grabbed - Gripper adapts to the form of the part - Handling of sensible and soft parts

Answer 26

- No defined pose of the parts - Small gripping forces - Parts must be able to be enveloped

Answer 27

o Prevents the release of the part at energy loss. o Different variants of retentions, depending on the type of gripper o Direction of retention depends on the application (o.d. or i.d. gripping)

Answer 28

o Pneumatic and electric transmission for robotic application o Enables multiple turns of a gripper o Integrated slip ring contacts and air transmission supplies the gripper with energy

Answer 29

 Multiple turnings of the robot axis possible, without hoses wrapping around the axis  Less interference contours due to hoses or cables

Answer 30

Exchange systems for grippers and tools are used in systems to execute multiple tasks with different tools per machine cycle.

Answer 31

 Increase the flexibility of an industrial robot  Open up new fields of application  Combination of handling and machine tasks  Consideration of gripper and tool change within a programmed procedure

Answer 32

 Increase of auxiliary process time for tool change  Technical effort for the implementation of the exchange system

Answer 33

o Pneumatic bearded adapter plates between robot and tool o In case of a collision, the adapter plate yields and the robot is stopped

Answer 34

o High precision joining of parts with transition or press fit o Position and angular compensation o Anti-twist device is used if torque occurs

Answer 35

o Proximity switches o Distance sensor o Force/torque sensors o Optical sensors

Answer 36

o Gripping phase: Status of the gripper (open/closed/gripped) o Securing the part: Applying a defined gripping force o Recognizing the part: Camera systems recognize the position and orientation of the part

Answer 37

 Design usually realized as a “reed switch”  Magnetic field magnetizes and deflects ferromagnetic contacts  Magnetic force needs to overcome spring force of the contacts  Required field force for opening switch much smaller than for closing

Answer 38

 Query of predefined positions  Detection of a gripper’s finger position via a permanent magnet mounted on the piston rod or gripper jaws  Not applicable for areas with magnetic interference fields (welding)

Answer 39

 Capacity change affects the oscillator’s frequency  Disturbance filter removes unwanted switching signals, however it also reduces the possible switching frequency to 1-100Hz  Compensation electrode to balance out influence of dirt

Answer 40

Electroconductive object:  Object forms counter electrode to the sensor electrode  System corresponds to a series circuit of 2 capacitors  Overall capacity is greater than undamped sensor Isolating object:  Object increases capacity as a function of dielectric constant 

Answer 41

 Query of predefined positions  Creation of high frequency alternating magnetic field  If an electrically conductive material enters the field, energy is absorbed so that the amplitude is reduced  The sensor is switched on, if there is a significant change

Answer 42

 Query of predefined positions  Creation of high frequency alternating magnetic field  If an electrically conductive material enters the field, energy is absorbed so that the amplitude is reduced  The sensor is switched on, if there is a significant change

Answer 43

 Compact design  High repetition accuracy  Non-sensitive towards influence of light, sound, temperature change or humidity

Answer 44

 For applications with high magnetic fields (welding), an additional protection is required  Switching distance depends on the construction of the proximity switch and the material of the supervised object -> Correction factor might be necessary

Answer 45

 Sensor emits light by optical fiber  Position detection of the supervised gripper by evaluation of the reflected light or time

Answer 46

 Inexpensive  Non-sensitive towards influence of sound, temperature change, humidity and magnetic fields

Answer 47

 Sensitive towards daylight, dirt, fog or particles in the air

Answer 48

 Light source sends light ray to the receiver (direct or through a reflector)  If the ray is interrupted the sensor switches

Answer 49

 The light of the source is reflected by the object and detected by the receiver  Time between sending and receiving is measured

Answer 50

o Measurement of the gripper’s finger position o Sensor is penetrated by a permanent magnet mounted to the jaw of the gripper -> Level of penetration depends of the distance between magnet and sensor o Output if jaw is in 1 of 5 programmable ranges o Software allows the determination of the exact position

Answer 51

o Assembly of intermediate jaws between basic jaw and gripper finger o Contact forces induce flux along the intermediate jaws o Measurement of deformation by clever orientated strain gauges inside the middle jaw o Deformation is transformed into an analog signal by an electronic device

Answer 52

o Human robot collaborations is regulated in many guidelines and standards o Safety principles -> A gripper never hurts a human while gripping -> A gripper never looses its part -> A gripper recognizes contact with a human every time o Equipped with different sensors, e.g. capacitive sensors, camera systems, force limitation and force measuring o Information is processed in real-time and the software can, because of the information, distinguish between a human and an object

Answer 53

- Computer vision solutions can recognize undefined objects and can identify robust gripping positions through knowledge of prior gripping operations - Vision based systems are especially attractive for processes with small quantities of parts, for which manual gripping programming or arranged part feeding would not be cost-efficient - Complexity of the needed system depends on general conditions -> Order state of the parts -> Knowledge of the parts’ shape - AI based systems enable a higher flexibility than standard algorithms, but need a lot more and top-quality data in order to run properly

Answer 54

Unordered -> Bulk Material, random orientation and overlapping possible (e.g. Silo) Partially ordered -> Parts are not ordered, but all on one plane without overlapping (e.g. Conveyer Belt) Ordered -> Parts are ordered and can be picked up all the time at the exact same spot (e.g. magazines)

Answer 55

Unknown -> Shape is completely unknown, the system needs to define gripping positions independently Similar parts known -> The shape is not completely known, although the system has gripped similar parts before and can use this data Known -> The shape is completely defined

Answer 56

Parts are transferred from an unordered to an ordered condition o Idea: Parts are delivered unordered, get recognized from a camera system and are gripped depending on their position and orientation Reference process can be divided in 4 steps: 1. Recognizing the object -> Object must be recognized, localized and separated from the environment 2. Determine the orientation -> Pose relative to the robot must be determined 3. Identification of gripping positions -> Gripping positions are evaluated on the abse of previous gripping tasks and one position is chosen 4. Path planning -> kinematic restrictions and objects in the direct way must be included

Answer 57

- External Handling - Integrated Handling - Semi integrated Handling

Answer 58

 Handling system separate from the machine tool (above/next to machine tool)  Enables workpiece feed of multiple machines with one centralized handling system)  Connected to machine tool via interface  Suitable with mobile handling systems

Answer 59

 Handling system is integrated in the machine tool  Usage as design element in the machine  No additional safety area necessary  Machine spaces does not get larger  Cost reduction at a serial use 3-5 times against an external handling

Answer 60

 Handling partly integrated into machine tool  Exemplary handling systems * Handling as shuttle (telescopic system) * Tool storage * Removal robot

Answer 61

o Workpieces are prepared on a pallet by a worker o The complete pallet is loaded into the clamping system in the machine o Positioning with a reference point system

Answer 62

o Parts can be postprocessed with a robot parallel of the machining process o Cost-efficient in combination with long cycle times o Mostly classic tasks for robots -> Brushing and deburring of work pieces -> Part measurement -> Part description -> Part cleaning o Parts are held by a robot or are placed in separate systems

11 Gripping Technology Flashcards

(86 cards)