Examples of grips/gripping/holding/using Mic Porter, Ergonomist, mic.porter@northumbria.ac.uk [+44/0 191 227 3155] I would not wish to suggest this list of examples is complete but I hope it does emphasise to you the range of possibilities and illustrate how important it is to consider how the design of the artefact influences the grip. I show examples that fall into the 10 categories identified by Kroemer (1986) but do not regard these examples as either exhaustive or satisfactory without images taken from the other side to clarify the whole grip/hold. An alternative classification (after Cutkosky, 1989) can be found in Zheng et al (2011). If you are interested in hand held tool design, especially for medical devices then I recommend Botney et al (2011). One area that requires particular attention, if critical errors are not to be made, is the foam modelling stage for hand held objects. Is the weight (or, more correctly Mass) of the artefact as it would be in the final product? Always add mass(weight) to the model and attempt to distribute it as it will be in the final product. For example, a prototype DVD/SKY/TV controller might have most of the mass at one end where the batteries are! The centre-of-gravity (cog) and thus the torque about the wrist (usually the fulcrum) that must be resisted by muscles needs to be simulated; essential if the weight is c4kg as my camera/lens and flash are 1. Such details of the weight distribution may critically influence usability and should be model. (Torque is measured in NM -1 ) (With foam and an evenly distributed mass you can simply push nails in but often a more sophisticated modelling of the distributed mass is required; drilling holes and inserting dead AA or AAA batteries or other materials of higher density may be one way to achieve this realism and thus contribute to making models suitable for handling trials.) An AA battery typically weights 23.5 gm and a AAA 11 gm. Never forget the distribution of the mass and the centre-of-gravity of the item. An old CRT TV packaged in a cardboard box into which handles had been cut centrally was difficult to handle but placing the cut-outs at the cog made handling much easier. This simple change of design enabled more purchasers to carry the item home thus saving on van deliveries made. (Later, I gave similar advice to a microwave manufacturer and they also folded the card to increase the radius/smoothness of the grip and thus increased comfort.) A small spherical object here an apple permits an all finger enclosed grip with the hand. This grip is also possible side on the diameter is not too large or the hand too small. How would you hold if eating this apple? Three fingers only fit thro the handle less if gloves were, for example worn. A 2.5L (say 2.65Kg full) this is easier to lift/control than a larger container. Notice how the thumb points along the handle; a common arrangement when directional control is needed here perhaps for pouring. A larger handle and now four fingers (locked with the thumb) is possible but not if gloves were worn. Full with 5L this might weigh 5.25Kg. A load not easily carried by all. A hook finger grip with thumb encircling squeezing the handle and thus improving the connection or coupling between handle and hand. Pouring is, of course, another matter and one often a focus of the designer s art. [Eg example #14 (and perhaps (I have not tested it)) #1 at: http://www.omote.co.uk/docs/?page_id=3 accessed 01.02.13 ] 1 A Canon EOS5, Mk 3 inc. battery grip, a 28-300mm f3.5/5.6 and a 580 Ex speedlite. A significant handling task for the weak wristed!
Gravity assist with this under hand grip. Consider also a cricket ball and, if you have the knowledge, the various grips the spin bowler uses. A bigger diameter prevent the encirclement of the apple sized object but here the friction is high enough to permit the form of the all hand squeezed grip. Gravity assist with an under hand grip. Easy? The trained waiter, of course, carries a tray this way; except that the hand will be totally flat. Similar to the spherical object this bottle does not quite permit the en-circling grip. A bottle of smaller diameter does permit en-circling well almost!) Another common, all finger, span grip. Contrast with the extreme span adopted when carefully handling 12 inch (LP) vinyl records. Thumb working with two fingers each of which moves independently to open/close the sticks. Note that the sticks also rest on the forefinger, towards the junction with the thumb. Fork or spoon arrangement hold between two fingers and against the thumb. Is this how a bodhrán player holds the tipper or is it more like the pen (next image)? Classic pen/pencil grip. The pen is held in the triangular space created between two fingers and the thumb. Note that the pen also rests on the rear of the hand where forefinger and thumb meet. How might this grip vary with a left-handed person? 2/7
Classic pinch grip between tip of the thumb and the forefinger tip side. Again the classic pinch grip but here the thumb is working against the forefinger s middle section. Gripping (and turning a key) is often a problem for those with arthritis a common problem of old age. Thumb pinching against the second finger while the forefinger points (to aid control) and rides on the top of the knife ready to apply force, when required. Picking up a stamp. Initially the thumb grips by friction as the stamp is slide towards the edge of the paper and pinch grip established. As previously but note, in both cases, that in the thumb is pinching against the side of the forefinger. Like the pen grip but here the hand is ready to provide more force and rotary action (from the wrist) as the whisking is undertaken. Thumb against the tip of the forefinger and the second finger stabilising to prevent sideways movement. This egg is stone but a more fragile object would receive less force. Gripping a shopping bag, all fingers and a flexible handle can permits good coupling In fact the force per unit area may be too high for comfort, especially with plastic bags where the area of bag/hand contact can be very low. Clearly the walking stick is not being used for weight bearing getting ready to wave?! Thumb pointing, for control, and the lack of applied force, transferred via the palm, are key indicators as to the current purpose of the stick! 3/7
An all hand grip on a saw. Note that the thumb usually points and thus helps to control the tool when cutting.- in this case timber. Considerable push forces may be transferred via the pulp in the palm of the hand. Three fingers curled round and opposing the thumb grip and control the spray while the forefinger works the button More commonly this spray must be pointed downwards when used. Incidentally, but perhaps not surprising, the Home Office reported that in early trials of CS Spray Police Officers spayed themselves in 50% of discharge incidents; simply they were unclear which way the spray would emerge from the canister! Squeeze grip on a mastic gun can be problematic if the span required is too great to get all the fingers round the moving part. Again the force is applied between fingers and the palm of the hand but the force demanded can be too great for the user when it is demanded at full stretch. The squeeze completed now fatigue can demand a prompt release of the fingers and prevent fine control towards the end of the action. Consider hand span and the use of pliers or scissors; especially the larger paper-hanging or fabric cut out scissors.. Hammer grip, again the forefinger points in the direction of the hammer head and helps control the action. Note that if the hammer is heavy and the user weak (or inexperienced) then they often hold closer to the hammer head. When forging or shaping with heavy hammers a rhythm is established. Watch a blacksmith using an anvil, often one hit is made on the object is followed by two/three bounced on the anvil while the next guided blow considered/aimed. Here the curled grip of three fingers round the handle and the compromise between curling and control aiding pointing of the forefinger/thumb is evident. Eggs are fragile so great control of the forces applied by this thumb against three finger grip. 4/7 Notice how the little finger is curled round to provide an end stop against which to hold the egg.
This simple phone rests on two fingers with a third used as a stop to prevent the phone from sliding, when the thumb presses. The width, even of the most sophisticated phone, is limited by the reach of the thumb. Note, if the cog was under the screen then the phone would be much harder to use, battery placement is critical. What happens when holding a, much larger, lager multifunctional communications device? Holding a basket ball requires, for most, two hands working in opposition. However, proplayers will have a span grip large enough to hold the ball, in one hand, and by friction alone. Two handed grip of a cake tin and cake. Notice the span grip of the hands which are, of course, working in opposition. As before, notice the thumb on the top of the tin to steady the load and to hold the lid on. Here the tin is, virtually empty so only a light grip is required. Detail of the right hand grip and force application when using a lever style cork-screw. Note that this would be easier if the bottle was lower. Using a wine waiters friend style corkscrew opening a bottle of wine is a two handed task. Here the left hand, span grip, holds/steadies while the right is a curled grip; considerable force may be demanded. A straight pull, simple corkscrew will often need the whole upper body to pull the cork from the bottle held between the legs! Here holding the bottle higher up and holding it down again surface. In the previous picture the bottle was not supported. Static, plus dynamic loading (as here) of the musculoskeletal system can be problematic and, possibly, injurious. Using a broom is a two-handed task. Notice the near c90 disposition of the two hands so that forward/back and side-toside actions are facilitated. Easy grip here as the hand can easily curl round the small diameter handle. 5/7
Span grip detail. Here the hand span is less than half the diameter so finger/bottle friction become critical to holding the bottle still as the force is applied to lift the corkscrew and cork. Using a thumb nail to open this (tight) but empty, tin. Notice the span grip holding the tin would be problematic if the tin contained a 70cl bottle of whiskey! Two hands to get a CD out of its case. Notice the span grip on the right hand and the left forefinger finger pushing the release button. Compare with the aerosol. Holding and opening a large (2L) bottle of water. A helpful strategy can be to grip tight the top and turn the bottom. The greater diameter gives a greater leverage/torque than turning the top. (A 2L/2Kg the bottle may be too heavy for many to hold. Small bottle are easier to hold and grip but, gain, turning the base and holding the top can be helpful. Here the squared bottle helps grip and thus coupling. Small jars can cause the fingers to tangle and thus limit the quality of the coupling/grip and the ability of the hand to apply the torque required to open the jar, especially when new and still holding the vacuum. Here the problem of the last example is solved by the squareness of the jar. Notice that the all finger grips are established at 90 to each other. The span grip is used to hold the jar but the thickness of the lid limits the left hand s grip. Thumb against forefinger (in part only) and the second finger. Two pinch grips flexing a pill package until the pill appears. Then a single hand pinch grip will be used to transfer, in this case, the tablet to the mouth. 6/7
The tablet emerges. Note that the person starts to cup the hand in case the tablet drops or flies! This is also a case where the correct material specification and design can make a bid difference. Does the foil crack or tear open? In my experience cheap medicines (eg Aspirin) tear but the 280 chemotherapy tablets (Xeloda @ (?) 20 each) I needed just snapped out! In several of these examples attention has been drawn to the load and how it affects grip/posture/movement. Next time you watch TV, Film or a Movie ask yourself which objects are loaded (and loaded evenly) and which are not. It is very common for a suitcase to be empty when carried by the actor (note how fast it swings) but full when opened! What other indications might you observe that will tell the observer if the object is lighter or heavier than expectations? The point about static, plus dynamic loading of the musculoskeletal system being problematic is because the tensed muscle stop blood supply to the muscles/joints and this is needed not only to supply nutrients but also to remove the waste products. Finally an ethical note. Consent forms exist for these images and I would advise you to always ensure that people/body parts in any of your photographs are covered by comprehensive and signed consent forms. A little pre-planning can prevent problems later! This generic feedback and a full set of the Design School u/g ethics forms can be found on the bloggy thingy: www.designforindustry.wordpress.com (Note that Departments/Faculties differ and will favour different forms although the content and advice will be similar.) Any further questions? An example of a grip taxonomy/classification. Grasp taxonomy Zheng et al (2011) after Cutkosky (1989) References Botney, R, Privitera, MB, Berguer, R and Radwin, RG (2011) Hand Tool Design, Chapter 16 in Weinger, MB, Wiklund, ME and Gardner-Bonneau, DJ (2011). Handbook of Human Factors in Medical Device Design. CRC Press, Boca Raton. Cutkosky, MR (1989) On grasp choice, grasp models and the design of hands for manufacturing tasks. IEEE trans. Robotics and Automation 5(3), 269-279. Kroemer KHE (1986) Coupling the hand with the handle: An improved notation of touch, grip and grasp. Human Factors 28 337 339. Zheng, Joshua Z., De La Rosa, Sara and Dollar, Aaron M (2011) An Investigation of Grasp Type and Frequency in Daily Household. IEEE International Conference on Robotics and Automation (May 9-13), Shanghai International Conference Center. Proceeding p 4169-4175Online at: http://www.eng.yale.edu/grablab/pubs/zheng_icra2011.pdf (Accessed: 01.02.13) 7/7