REVIEW OF RELATED LITERATURE
The
purpose of the literature review is to improve the understanding of the
research that is being undertaken. This part aims to demonstrate the knowledge
of the many resources on hand from the authors and other authors.
The
Literature review is not an essay or research paper. It is not a part which
will say your method or conclusion. Because writing this part requires the
organization of your major and secondary concepts, it is important to know the
framework of your study. The framework will serve as your guide on how a
researcher can organize the concepts to be discussed in the study. In general,
the researcher may organize the concepts and include the only the works of
other authors.
a.
Major
works and Major concepts
The researcher should be able to identify the
major concepts of the study. In the same level of importance is identifying the
major works of authors supporting the discussion for the major concepts.
b.
Secondary
works supporting the major concepts
The secondary works
are resources coming from other authors with related studies. Its use is to
support the major concepts of the study. They may be identified by placing them
as subtopics of the major concepts.
c.
Comparative
literature
In the literature review, the researcher will
have to discuss through comparing the related studies. This may come through
analyzing the findings of one author to another, on whether they agree or
disagree. In this discussion, the author will express how the concepts can help
in the direction of his study.
d.
Review
The purpose why it is called a literature
review is to basically review the concepts and the related works from other
resources. Review is done in order to clearly understand the study, as well as,
this is also for the service of the readers who should be updated and clarified
with the study.
e.
Relationships
The
major concepts should be discussed with the major works and supported by the
secondary works. In this level, there should be an established relationship
with the major works and secondary works to demonstrate the discussion of the
major concepts.
To fully discuss the major concepts, the
researcher has to discuss the relationship of the major concepts to tie up the
connection to the conduct of the study. Relationships can be discuss based on
the direction of the study as discussing the effects, impacts, creating a new
design, or why the related studies are needed to explain a concept.
f.
Purpose
After the considering the major works and
secondary works for the discussion of the important concepts and after clearly
demonstrating the relationships of the concepts and the flow of the study
through the different resources, the researcher will now have to assess the
value of the literature review and explicitly express what is the importance of
the related literature to the study and how it can help in the investigation or
probing of the research.
Example of Literature Review: Ergonomic Aspects of Knob Design Hang (2015)
General types of knobs
With today’s highly developed technological
devices, user interface design has improved dramatically to the extent of
enabling even common designs such as knobs to be used in both simple and
complex tasks (Schutte and Eklund 2005). Knobs have been widely used in
adjustment applications, such as the precise adjusting application of a
microscope in a laboratory (Sillanpaa, Nyberg, and Laippala 2003).
A knob is a subclass of rotary control which
can involve continuous control knobs, selector knobs, ganged knobs and jog
shuttles (Kwahk and Han 2002). Knobs (namely selector knobs and jog shuttles)
usually have certain properties such as grids, legends and number of positions
(Kwahk and Han 2002; Keogh, Morrison, and Barrett 2007).
Knob design can be generally grouped into two
categories. One category involves the technical aspects of the design, which
include the knob’s mechanical or electrical details, while another involves the
ergonomics considerations, which include the knob’s aesthetic appearance,
usability and comfortability (Schutte and Eklund 2005; Keogh, Morrison, and
Barrett 2007). Schutte and Eklund (2005) also believe that users may select
knobs based on factors such as the attractiveness (in terms of
design/appearance), durability, safety, operability and comfortability.
A door lock consists of three basic
mechanisms, which include the main body, the lever and the door knob (Tsai,
Hsiao, and Hung 2006). Door knobs are designed to allow the user to twist and
open (or close) the door (Lobb and Woods 2012).
Knobs are also used in kitchen electrical
appliances (as control knobs of cookers for example) (Pinto et al. 2000). The
rotating control knobs on ovens are used to control temperature and timing
(Chen and Jackovin 2004).
Knobs are also used on treadmills for
controlling the resistance of the treadmill belt (Ciriello et al. 2010). The
resistance, which is controlled by turning the knob, increases with a clockwise
rotation and decreases with a counterclockwise rotation (Ciriello et al. 2010;
Mathiowetz et al. 1985). Gearshift knobs are knobs available in cars and
manipulated by drivers (Schutte and Schuder 1997).
A gearshift knob is perhaps one of the most
obvious interior parts that would easily catch the visual attention of
customers (You et al. 2006). Knobs are also used extensively in electric train
control panels (Stevenson et al. 2000). Stevenson et al. (2000) believe that a
spherical knob can allow the electric train driver to assume a more comfortable
hand position while driving the train.
Since knobs are designed for precise control
as stated by Schutte and Eklund (2005), knobs are also used in precision
medical devices such as the endoscope (Browne and O’Sullivan 2012). Levin et
al. (2000) mention that the accurate and handy characteristics of knobs make
them suitable to be used as volume adjustment controls on radios and other
types of stereos.
A washing machine is equipped with dial knobs
for simple and efficient function controlling (Ha et al. 2009). Functions like
wash mode, dry mode, wash time and water level can be selected using the
control knob (Ha et al. 2009). The tactile sensation of the control knob for
washing machines was studied by Kleiss (2008), who investigated the preferred
sensation of the users when turning the knob.
Knobs are also used in the shower for water
temperature control. According to Green and Kemp (2002), it appears that when a
handle is attached on a knob, the turning operation for the knob becomes
easier. Gas valve control knobs are invented for the convenience of the users
who adjust the gas flow rate without directly accessing the gas valve (Harris
and Miller 1985). Harris and Miller (1985) believe that it would be safer and
more ergonomic for users to control the knob rather than the gas valve since
users can easily adapt to the use of the knob’s turning operation. Gas valve
control knobs are economically produced and easily obtainable (Harris and
Miller 1985).
Other types of commonly available knobs
include circular knobs, ridge knobs, butterfly nuts and tap knobs (Peebles and
Norris 2003). Knobs for furniture are designed for handling purposes and fixture
appearance (Matijevic 2008). Screw knobs are used to join/ connect objects
together with an adjustable screw mechanism (Shih and Ou 2005; Keogh, Morrison,
and Barrett 2007; Shivers, Mirka, and Kaber 2002) and were frequently used in
the intravenous stand designed by Jost and Tseng (1990), who designed the pole
to be adjustable according to the patient’s height.
Various types of knobs are used on the
control panel of aircrafts (Stanton et al. 2009). The design of knobs in an
aircraft is important as it can potentially evade the occurrence of human
errors (Stanton et al. 2009). The use of knobs can be found on consumer
electronics products as well, such as telecommunication devices and home
appliances (Kwahk and Han 2002). These knobs are considered as the interface
components of consumer devices, and their usability has become an important
factor to gaining acceptance in the market (Kwahk and Han 2002).
Knobs are used for height adjustment in office
chairs as well (Groenesteijn et al. 2009). The difficulty of height adjustment
in office chairs using knobs has also been investigated by some researchers, as
this factor is one of the design considerations that improves the ergonomics
and comfort of chairs (Groenesteijn et al. 2009).
Ergonomics factors
Today, knobs do not only act as input control
devices, but are also ergonomically designed to adapt with the user’s
convenience. Knobs, which are designed ergonomically, can prevent accidents
from happening, improve working efficiency and avoid muscle injuries. The
following subsections present several ergonomics factors considered in knob
designs and other research pertaining to knobs.
Human
perception and hand activities. Different types of knob manipulation have been studied in relation to
actions that involve pushing, pulling and turning (Browne and O’Sullivan 2012).
However, improper handling and excessive repetition in knob manipulation can
cause injury to the hands (Browne and O’Sullivan 2012).
Certain factors, such as finger push strength,
pinch-pull strength, hand grip strength, opening strength, wrist-twisting
strength and push-pull strength, are often considered so as to conform to the
ergonomics aspects of the design (Ng et al. 2014; Peebles and Norris 2003).
Peebles and Norris (2003) discovered that turning torque can be increased by
adding knurls or ridges on the object since the grip is improved (knobs or
lids).
Studies have also found that knurling has no
effect on torque when the object’s diameter is smaller than 86 mm (Peebles and
Norris 2003; Nagashima and Konz 1986; Imrhan 88 Y.H. Tan et al. Imrhan and
Jenkins (1999) state that knurled handle torques are larger than smooth handle
torques by approximately 1.15 times.
Stereotype control behaviour is the
relationship between the control movements made by users and their effects on
the display based on the instincts of the users (Chan, Shum, and Poon 2002).
According to Chan, Shum, and Poon (2002), a rotary control with a linear
display is commonly used in many devices and equipment in the industry.
There are a few major stereotype principles
that have been suggested for rotary control and linear display combinations,
which include the Warrick’s principle, clockwisefor-right principle,
clockwise-for-increase principle and the scale side principle (Chan, Shum, and
Poon 2002). A short adjustment time, where the control and display interfaces
become compatible with each other, should preferably be achieved (Chan, Shum,
and Poon 2002). Figure 1 presents a pictorial idea of the different types of common
knobs.
Ergonomic knobs
In industries, such as the automotive
industry, ergonomists and functional designers have been working on improving
control and display systems in order to minimise and prevent human error that
often cause accidents to happen (Schutte and Eklund 2005; Kim et al. 2011; Ng
et al. 2013e). It has been found that around 75% of all accidents are
associated with human errors (Stanton et al. 2009). Researchers believe that
the ergonomic design of the control interface can also reduce the stress and
tiredness of drivers (Schutte and Eklund 2005).
Since the ergonomics properties of mechanical
knobs are highly important in modern designs, many companies are putting up
more effort in designing comfortable and userfriendly knobs (Ha et al. 2009).
For instance, the dial knob of a washing machine is designed according to some
design considerations like torque profile, aesthetical appearance,
functionality, physical properties and sound effects (Ha et al. 2009).
The visual appearance and ergonomics aspects
of a vehicle’s interior design are one of the main concerns of the customers
(You et al. 2006). The material used in a knob therefore plays a crucial role,
as customers tend to judge the quality of the knob by its appearance and
tactile sensation (You et al. 2006; Ng et al. 2013f). Researchers have also
found that the softness, shininess and surface texture of knobs are factors
related with the appearance judgment of customers (You et al. 2006; Ryu et al.
2003; Tanoue, Ishizaka, and Nagamachi 1997).
Certain ergonomic control knobs are designed
with force feedback features to provide torque resistance and physical
sensation to the user (Levin et al. 2000). The force feedback features are
controlled by integrated electrical motors and microprocessors that allow
different kinds of tactile sensation to be programmed accordingly (Levin et al.
2000). Some control knobs are also designed with multiple degrees of freedom,
which enable rotary, transverse and linear directional movements (Levin et al. 2000).
The rotary movements allow knobs to be rotated about the rotating axis, while
the transverse movements (perpendicular to the axis) and the linear movements
allow the knobs to be pushed or pulled (Levin et al. 2000).
Normally, an index line or mark is indicated
on a knob when the position of a rotary control knob is to be discerned
(Kroemer, Kroemer, and Kroemer-Elbert 2001). In consideration of these factors,
Harris and Miller (1985) designed a gas valve knob which includes an index mark
and pointer for safety and ease of identification, so as to display the angular
displacement of the gas valve knobs to the user.
Since there can be multiple knobs of
different functions available on a control panel, knobs need to be shape-coded
for safety purposes and in order to reduce operational errors (Burgess-Limerick
et al. 2010). Researchers have discovered that 5% of coal mine accidents were
caused by control activation errors on bolting machines (Burgess-Limerick et
al. 2010; Helander, Krohn, and Curtin 1983). Shape-coding can facilitate the
identification of the knobs and allow them to be differentiated easily by
operators according to shape, size, operation mode, labelling and colour
(Kroemer, Kroemer, and Kroemer Elbert 2001; Ng et al. 2013c; Ng and Saptari 2012).
The ergonomic design of control knobs has
been an emphasis of designers for many years (Kleiss 2008). According to
researchers, in order to idealise the ergonomic design of a particular knob,
the size and shape of the knob are crucial factors to be considered (Woodson,
Tillman, and Tillman 1992; Kleiss 2008; Amaral et al. 2013).
Studies show that elderly individuals of 65
years and above can only exert a capacity of 75% of the strength and endurance
that they were able to exert in their younger years (<30 years old) (Shaheen
and Niemeier 2001; Haigh 1993). Lee and Su (2008) postulate that the difficulty
of the adjustment of control knobs is determined by the size and tolerance of
the knob. However, Kroemer, Kroemer, and Kroemer-Elbert (2001) opine that if
the turning resistance is low and the knob can be easily operated, the size of
the knob is inconsequential. On the other hand, if the space is constrained,
the knobs are required to be small and with low turning resistance to allow the
user to manipulate it easily (Kroemer, Kroemer, and Kroemer-Elbert 2001).
The function of a knob is often given more
attention to rather than the sensory quality of the knob, as designers
generally do not consider it to be a critical factor to improve for optimised
performance (Kleiss 2008). It was found that about 58% of elderly people obtain
some form of disability in control and sensation when manipulating knobs
(Shaheen and Niemeier 2001). A secure sensation is often one of the factors
that should be considered, especially in knob designs that emphasise on
providing a smooth tactile experience to knob users (Kleiss 2008). Beside this,
the compatibility of control knobs with display devices is highly important for
the reduction in human error and response time (Chan, Shum, and Poon 2002).
Kroemer,
Kroemer, and Kroemer-Elbert (2001) suggest
that continuous knobs should be considered in machine design if little turning
torque and fine adjustments are required. Kroemer, Kroemer, and Kroemer-Elbert
(2001) however explain that the knob position should be set in such a way that
it is not affected by vibration or involuntary movements. In reflection of the
abovementioned considerations, Bull (1987) designed a control knob with a
push–pull mechanism, where the control knob was required to be pushed or pulled
in order to engage. This prevented inadvertent and accidental adjustments to
the device.
In summary, the ergonomics considerations
incorporated in knob designs are useful based on several aspects. Knobs with
sensory feedback capabilities (such as haptic knobs) can aid users to perceive
input levels and influence their usability and comfort when manipulating a
device. For a functional knob design, the operating degrees of freedom
(pushing, pulling and turning) need to be considered so that the knob is of good
quality, reliable and user-friendly. The appearance and choice of materials for
the knob are also important in order to provide a quality tactile experience
for the users.
Knobs, which are attached to industrial
equipment and machines, need to consider certain surface temperature changes
that may be caused by the heat transferred from the machines. This forethought
is important given that some knob surfaces may get too hot and uncomfortable
for handling and operation, and even lead to injuries. The surface of these
knobs requires the use of heat resistant materials to ensure the comfort and
safety of the user.
Certain knob designs are highly beneficial to
the users for shape-coding, indication, compatibility and positioning. Knobs,
which are built with appropriate friction and torque requirements (such as
knurled knobs), are much easier to be operated (Swanson, Matev, and Groot 1970;
Ng et al. 2013d; Ng, Saptari, and Yeow 2012). Safety features such as push–pull
locking mechanisms are also available on some knobs to prevent accidental
activations of input controls. Apart from that, in order to accommodate more
precise adjustments, a continuous knob design would be preferable.
Theoretical implications
The compilation of this literature review on
knobs can be a good foundation for future research on knobs, pinch techniques
and related studies on musculoskeletal disorders. The knowledge on knobs can
also be a basis for developing theories in union with other biomechanical
studies. This literature review can also serve as preliminary groundwork for
designers and engineers to design and build creative and unique designs that
utilise knobs.
As an example, researchers who conduct
studies on the forearm posture can relate their research with the manipulation
of knobs and invent new guidelines to allow more comfortable and user-friendly
knob operations that potentially reduce the risks of workrelated injuries with
inappropriate forearm postures. Beside this, a new avenue for future studies is
also created through this literature review with the aim to encourage
researchers from various disciplines to conduct more investigations on the
research related to knobs.
Practical implications
With this anthology of various knob designs,
an improved knob design can be developed by designers and engineers. The
comfortability and working efficiency while manipulating knobs can be improved
and optimised radically with the development of an ergonomic knob. These
aspects improve their selling points and attract the attention of buyers who
often look into the aesthetics and user-friendliness of a design. An ergonomic
knob can also help reduce the occurrence of human errors with its convenience
of use. This can potentially improve the safety level of the workplace. Lesser
workplace accidents and errors will eventually lead to healthcare cost
reduction, increased productivity and improved product quality. Workers will be
able to experience an improved quality of life and higher job satisfaction with
a safer working environment.
Directions for future research
For future research, it is proposed that an
empirical study is carried out to investigate the user preference on knobs
among manual workers. An empirical study will help researchers to directly
understand the perspectives of manual workers and how they actually visualise
the design of an ergonomic knob. More quantitative findings are also required in
order to support the substantiations of this literature review.
Biomechanical instruments can also be used to
collect strength data from manual workers who often use knobs while operating
their equipment. For instance, force sensors can be attached to their fingers to
measure the feedback of the pinch force when the worker operates a knob. Using
statistical analyses, researchers can conduct hypothesis tests and identify the
effects of certain knob designs on the biomechanical pinch force of a human
hand.
Safety guidelines can also be developed from
the results of observation research and statistical analyses. These guidelines
will be useful for manual workers. With the correct understanding of knob
designs, pinch force exertion, pinch posture and handling method, manual
workers can execute their tasks safely and more efficiently. With these
guidelines, the knowledge on knob-handling safety will eventually become a norm
among industrial workers and motivate designers and ergonomists to design more
user-friendly knobs.
Generally, this literature review provides a
summary on the variation of knobs that are available in the industry and
everyday life. It appears that knobs are used differently in various
applications. Their shapes and designs serve a variety of purposes. This
literature review suggests that the biomechanics of hand movements and natural
consciousness of humans are major elements that contribute to the design of an
ergonomic knob. Designers should develop an apperception on the importance of
ergonomics considerations when designing knobs. The ergonomics considerations
for an ergonomic knob can include the comfortability, usability and aesthetics
of the design. Since hand-related musculoskeletal disorders are affected by
commonly assumed working postures, it is essential for ergonomists, designers
and engineers to consider the position of their knob designs in regards to the
working posture and handling position of the equipment or apparatus.
Relevance to ergonomics theory
This literature review serves as a reference
for designers to improve their designs such that inappropriate and less
ergonomic working postures can be avoided. Considering ergonomics aspects in
knob designs reduces human error and risks of workplace accidents. Ergonomics
researchers can also use this literature review as a guideline for future hand-related
designs and research.