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Automation in Food Processing 60.2 Generic Considerations in Automation for Food Processing 1045

with a variety of sensor systems, e.g., checkweighers,

vision, and metal detectors to enhance the handling pro-

cess and combine this with online inspection.

60.2.4 Joints and Seals

Careful attention should be paid to the design of joints

in automation/robotic systems to ensure that they are

both waterproof and hygienic, and avoid deep, narrow

crevices at the joints which are impossible to clean.

This is illustrated in Fig.60.2a. An improved design us-

ing a spring-energized polytetraﬂuoroethylene (PTFE)

face seal is shown in Fig.60.2b. Commercial seals are

available where the spring groove is ﬁlled with silicone

for use in food processing applications. Cover plates,

which provide access to the inside of food processing

machinery, are sealed using rubber gaskets. The screws

securing the cover plates should also be sealed. Small

screws can be sealed using a food-grade sealant. The

screws should have plain hexagon heads, which are eas-

ier to clean.

60.2.5 Actuators

Pneumatic cylinders are low costand commonly used in

the food industry to actuate ﬁxed automation machin-

ery. Accurate position control of pneumatic actuators

without the use of mechanical stops is, however, difﬁ-

cult to achieve under either proportional or pulse width

modulation control schemes [60.13, 14]. In addition,

position control using pulse-width modulation requires

rapid cycling of the solenoid valves used to drive the ac-

tuator and this wears out the valves extremely quickly.

Hydraulic actuators are not used in the food industry, as

there is a risk that hydraulic ﬂuid may contaminate the

product.

Electric motors are comparatively easy to control

and reliable in service. Brushless direct-current (DC)

motors, despite their higher initial cost, have a service

life many times greater than that of brushed mo-

tors, leading to increased reliability, lower maintenance

costs, and less down time. This makes brushless motors

more economical to use over the lifetime of the automa-

tion. The most signiﬁcant operational issue with motors

is ensuring adequate sealing to prevent the ingress of

water/solvents during cleaning etc.

60.2.6 Orientation and Positioning

For all forms of automation knowledge of the exact po-

sition of a product is vital.This is noless truein thefood

Fig. 60.1 An ABB IRB 340 used to pick and place biscuits

sector than elsewhere but in this sector a number of fac-

tors conspire to place a low value on this information.

Figure 60.3 shows a very common example of an

ordered layup of product that is taken from the produc-

tion line and placed in bins that have complete disorder.

To automate the process of recreating order from this

chaos is at best difﬁcult and expensive and at worst cur-

rently technically impossible, but humans easily cope

with this disorder. In considering examples of this type

it is clear that within a food plant many processes that

are currently considered difﬁcult or impossible could be

automated if greater attention were paid to the reten-

tion of position and orientation data. In some instances

this will involve changes to the handling process while

a) b)

Fig. 60.2a,b Unhygienic and hygienic robot joint design.

(a) Uncleanable gap, (b) PTFE face seal

Part F 60.2

1046 Part F Industrial Automation

Fig. 60.3 Food automation will often reverse traditional manufac-

turing aims that create disorder from the manufactured order

in others simple remedies such as properly adjusting

guides, transfer conveyors or feed rates will be sufﬁcient

to create the order needed to satisfy the downstream

automation. This is a process that has already been

learned (often by hard experience) in other industries

but has yet to be fully appreciated by the food process-

ing sector.

At the same time it is possible to deal with aspects

of orientation and positional inaccuracies and the vi-

sion systems that are becoming increasingly common

in other industry sectors are ﬁnding useful outlets in

Fig. 60.4 Conveying solutions

food processing also. Indeed in the food sector the rel-

atively low tolerances (due to the product variability)

mean that vision-linked handling systems could poten-

tially be even more successful in these applications than

elsewhere.

60.2.7 Conveyors

Conveyors are typically belted transport machines

to carry products, containers, packs or packaging

along a production line or between production centers

(Fig.60.4). There are a very large number of types of

conveyor designed to operate with different products,

and selection of the correct conveyor system is essential

to good automation in the food sector [60.15]. Convey-

ors can be formed as stand-alone linear or curved units

or they can be integrated into complex transportation

networks custom-designed for each factory application.

In their simplest forms the conveyor merely moves

product from point A to B but they can be integrated

with control systems, advanced drives, programmable

logic controllers (PLCs), sensors etc. and form an inte-

gral part of good automation.

60.3 Packaging, Palletizing, and Mixed Pallet Automation

One area of food production that has seen signiﬁ-

cant use of automation is end-of-line operations. For

many years, food manufacturers have successfully used

traditional hard automation, including wrappers, top

loaders, and side loaders, to package easy-to-handle

products, e.g., cartons, boxes, trays, bags, and bottles.

In this area of the food production cycle the product

has been changed from the highly variable food prod-

uct into a containerized unit. Within the end-of-line

packaging operations there are therefore a number of

Part F 60.3

Automation in Food Processing 60.3 Packaging, Palletizing, and Mixed Pallet Automation 1047

key areas that have wide application across the sector

(Fig.60.5).

These include aspects such as labeling, check-

weighing, inspection (visual, metal detection etc.), and

palletizing.

60.3.1 Check Weight

The checkweigher is an automatic machine for mea-

suring the weight of packaged commodities and hence

ensuring that the product is within speciﬁed limits

(Fig.60.6). Any packs that are outside the tolerance

are ejected from the line automatically and may be

reworked. Although there are many forms of check-

weigher they generally follow a fairly common format.

From the main production ﬂow line the product is trans-

ferred to an accelerating belt that spaces products that

are often closely located on the line. This means that in-

dividual products can be weighed without interference

from neighbors. The weigh station is an instrumented

conveyor belt incorporating a high-speed transducer

(typically a load cell), with user interface and often

data ports for Ethernet etc. At the outﬂow of the check-

weigher there is a reject conveyor to remove out-of-

tolerance packs without disrupting the normal ﬂow. The

reject mechanism is automatic and may involve a vari-

ety of approaches such as air jets and mechanical arms.

Checkweighers can have a throughput of up to 750

products per minute. The communication ports ensure

that the checkweigher can be integrated into the whole

plant operation, communicating production data etc.

and forming part of a full SCADA (supervisory control

and data acquisition) system. By controlling and moni-

toring the throughput of the checkweigher it is possible

to detect out-of-performance upstream operations and

to dynamically change the performance of the upstream

operations by adjusting their set-points. Unfortunately

this is seldom achieved and machines often run with

poor adjustments thatincrease reject rates or overﬁll and

hence gives away product. In addition, by integrating

production of several linesor monitoringdata over time,

it ispossible topermit some underweight product,as the

overall average is within tolerance and the data from the

checkweigher can validate this. This can signiﬁcantly

reduce wastage and has potential enormous savings.

60.3.2 Inspection Systems

Other inspection stations within the typical produc-

tion line include metal detection and also on occasion

Fig. 60.5 End-of-line automation

x-ray machines (Fig.60.6). These systems are primarily

installed as safety systems to prevent physical con-

tamination of food. In the instance of metal detectors

which operate by enclosing the whole of the production

conveyor belt, the product passes through the detector,

which is tuned to detect small metal shards that may

have become located in the food product. If the sen-

sor is triggered the product is automatically rejected

but in this instance there is no rework and indeed the

product is usually inspected closely to discover the

type of contamination and to ensure that this is elim-

inated. Metals detection is present on almost every

production line. X-ray machines, although slightly less

common, are used to check for nonmetallic contami-

nation, e.g., glass, plastics, bone, and ﬁbres, and also

in some meat products as a quality control system to

identify gristle.

Part F 60.3

1048 Part F Industrial Automation

Fig. 60.6 Combined check weight and metal detectionsta-

tion

60.3.3 Labeling

Labels are used on every kind of product to brand, dec-

orate or provide information, and in the food sector

it is not uncommon that a label fulﬁls all three func-

tions simultaneously (Fig.60.7). Labeling is one of the

ﬁnal aspects of the production process and may be in-

dependent or integrated with other systems such as the

checkweigher and inspection systems. There are two

main types of labeling machine: wet glue and self-

adhesive (pressure-sensitive) applicators. For the food

Fig. 60.7 Labeling stations

processing industry self-adhesive labelers are by far the

more common, using preglued labels that are supplied

on a reel of release paper or ﬁlm. This method of ap-

plication enables labels to be applied at medium/high

speed to soft packages as well as rigid containers. This

is very suited to the food sector.

60.3.4 Palletizing

The pallet is the fundamental loading and trans-

portation unit for most food operations. As such,

automation of the warehousing and palletizing op-

erations for food companies, as in most industry

sectors, is potentially one of the most proﬁtable ar-

eas. As with most industry sectors many features

inﬂuence the selection of automation for palletiz-

ing, including line speeds, factory layout, space at

the end of production lines, and of course cost, but

in food operations there is also the advantage that,

by the time the products reach the palletizing stage,

the packaging has usually created a fairly repeat-

able form that is missing in many other upstream

areas and this is therefore one of the easiest areas to

automate.

While it can be recognized that there are many fea-

tures in common with other industry sectors, one recent

trend that is particularly strongly driven in the food

sector is the assembly of mixed product pallets, which

reﬂected demand from retailers for custom pallet loads

that suit the store rather than the shipper. The mixed

load pallet is therefore emerging as one of the most ef-

Part F 60.3

Automation in Food Processing 60.4 Raw Product Handling and Assembly 1049

Fig. 60.8 Robotic palletizing

ﬁcient technologies available in the food supply chain

process.

To address these demands and opportunities and the

use of multiple feeder lines and rapid pattern changes,

the automation industry has focusedon thedevelopment

of software needed to pick the product and design the

pallet, the hardware to recognize the product (sensors

which are often visual based), hardware to manipulate

the product (often robots), and the integration of the

hardware–software solutions (Fig.60.8).

Within the robotic community there have been

important developments in the software to optimize

picking, placement, and overall construction of di-

verse pallets, with many robot manufacturers, software

houses, and systems developers introducing dedicated

software that will allow online pallet preparation to

meet thedemands of the manufacturer and, more impor-

tantly, the retailer. These software systems can be fully

integrated with external systems, e.g., machine-vision

systems and image processing or other sensors to detect

the presence of the product and its position and orienta-

tion, and this information can be directly communicated

to a manipulation system, which is typically robotic,

to allow ﬂexibility in programming and motion con-

trol. This comprehensive integration of all components

into one platform facilitates efﬁcient communication

and guarantees reliable robot operation. These software

packages typically integrate only with one robot man-

ufacturer’s product line and it is therefore necessary to

use combined hardware and software solutions. Integra-

tion suppliers can often integrate nonstandard units but

this has a signiﬁcant cost implication.

To address the increasing need for and use of robots

in the food industry a number of robot manufactur-

ers have or are developing products speciﬁcally for

these applications. However, to date very few com-

mercial robots have been developed speciﬁcally for the

food industry. Often, existing models have simply been

upgraded for use in food production and this has cre-

ated a negative impression among sections of the food

industry. Examples of industrial robots that are cur-

rently used for primary packaging and assembly of

foods include the ABB IRB 340 FlexPicker (probably

the most common robot in high-speed pick-and-place

applications and well suited to handling wrapped and

baked products) and Bosch Sigpack Delta robots, the

FANUC LRMate 200iBfood robot, Gerhard Schubert’s

TLM-F4, and more recently the FANUC M-430iA/2F,

which has a sleek proﬁle with no food particle retention

areas.

60.4 Raw Product Handling and Assembly

While the use of robots and advanced automation for

end-of-line operations such as case packing and pal-

letizing is already well established, robotics/automation

of primary handling and assembly of foods has so far

been limited. However, since ﬁnancial justiﬁcation for

the installation of an automation/robotic system is typ-

ically based on the reduction of labor costs and the

bulk of manual labor in a food production line is gen-

erally concentrated in primary packaging and assembly

operations, this is the area that requires the greatest con-

centration of effort.

As already noted products handled by traditional

automation are usually homogenous in terms of size,

shape, and weight and also tend to be rigid; however,

some or all of these conditions do not prevail in food

processing. Food is very often fragile and, unless ex-

treme care is taken during handling, products can be

damaged and in the worst case this can mean they have

to be discarded.This means thatthe handlingtechniques

used in traditional automation aregenerally not suited to

the handling of raw food products and the mechanism

of grasping the food product (rather than basic motion)

is often the key to successful automation.

Taylor [60.15] classiﬁed the gripping techniques for

nonrigid materials into three separate classes deﬁned by

the mechanism of the grasp:

Part F 60.4

1050 Part F Industrial Automation

Mechanical techniques – the product is ﬁrmly

clamped between two or more mechanical ﬁngers and

held due to the friction contact. To minimize the grip

force the gripper jaws can be compliant or speciﬁcally

shaped to the particular object. This can only be used

where variation between products is relatively small.

Intrusive grippers – pins are fed into the surface or

body of the material to be lifted. The pins are precisely

located so that when inserted the object becomes locked

to the gripper. This technique is generally unsuitable

for food products, as it would often cause unacceptable

levels of damage.

Surface attraction – adhesives or a vacuum are used

to create a bonding force between the gripper and prod-

uct. Vacuum grippershave been successfully used in the

food industry and are well suited to objects with regular

or ﬂat surfaces, such as biscuits. However, not all food

items can be handled with such grippers due to difﬁ-

culties in achieving an airtight seal, bruising, and the

inﬂow of particles that could lead to microbial growth

unless equipment is sterilized regularly.

As can be seen above designing mechanisms to

grasp food products is not straightforward and the

techniques used in other industries cannot be di-

rectly applied. Different types of food product present

different challenges and as a result there are numer-

ous examples of grippers that have been developed

for use in the food industry which address these

challenges.

60.4.1 Handling Products That Bruise

There are many food products that are easy to bruise.

These are typically fruits and vegetables,but other prod-

ucts can also develop unsightly marks if grasped too

ﬁrmly. For this reason handling techniques that min-

imize forces and pressures must be developed. One

example of a product that is particularly susceptible to

bruising is the mushroom. Although not immediately

obvious a bruise can appear on a mushroom as long as

several days after being handled. This can mean that,

while a productmay appear acceptablewhen dispatched

from a factory/farm, it can appear damaged by the time

it reaches the retailer/customer.

Mushroom harvesting is typically performed manu-

ally and, despite the delicate capabilities of the human

hand, mushrooms do become bruised during manual

harvesting. An automated system for the harvesting

of mushrooms was produced by Reed et al. [60.16]

with the aim of reducing labor but also reducing

product damage. The design of the system paid par-

ticular attention to the delicacy of the mushroom

contact.

The mushroom harvesting process consists of four

main stages: ﬁrst the position of an individual viable

mushroom is obtained, followed by picking and trim-

ming of the mushroom before placing it in a container.

The location of the mushroom is obtained from a vi-

sion system mounted vertically over the mushroom

bed. Image-processing software identiﬁes and numbers

each mushroom and then determines how best to pick

them. Mushrooms below a certain size threshold are

disregarded and are left to be harvested another day.

An isolated mushroom is easy to pick, but this is not

typically thecase andusually mushroomstouch or over-

lap. The control software must therefore determine the

best way to extract each mushroom without disturb-

ing those around it. This is achieved by bending the

mushroom away from those that surround it before

picking.

The mushrooms are grasped using a vacuum cup

mounted through a compliant link to a rack and pin-

ion allowing the cup to be positioned on the surface of

the mushroom. The cup is then twisted about the verti-

cal axis to break the mushrooms base and allow it to be

removed. A turret mechanism was also included, which

allowed the most appropriately sized cup to be used for

the particular mushroom being grasped.

The contact between the vacuum cup and the mush-

room is the source of potential produce bruising and so

determining the optimum vacuum force is critical. Ex-

periments revealed that the force of the vacuum on the

mushroom produced a faint mark on the mushroom dur-

ing grasping but this was not considered by the industry

to be unacceptably severe. However, if slip occurred

between the mushroom and vacuum cup during rota-

tion this resulted in unacceptable shear damage on the

mushroom’s surface.

Once a mushroom has been removed from the

ground it is placed in a ﬁngered conveyor with the stalk

pointing vertically downwards. A blade then removes

the lower section of stalk which is discarded and the

trimmed mushroom is placed in a plastic tray ready for

dispatch. The mushrooms are not dropped as this would

result in denting and bruising. Thecomplete system was

trialled at a commercial mushroom farm in The Nether-

lands and by the Horticultural Research International

in the UK. The average picking speed of the system

was nine mushrooms per minute and in both of these

trials the amount of mushroom bruising and damage

was found to be signiﬁcantly lower than when manual

picking was used.

Part F 60.4

Automation in Food Processing 60.4 Raw Product Handling and Assembly 1051

60.4.2 Handling Fish and Meat

While less susceptible to bruising than fruits and veg-

etables, meat and ﬁsh present their own grasping

challenges. Due to the ease with which such products

deform a traditional parallel jaw gripper is typically un-

able to grasp them with sufﬁcient ﬁrmness. Similarly

vacuumgrippers havehad onlylimited successgrasping

meats since the ﬂeshy nature of meat means that un-

sightly peaks can be produced when a vacuum force is

applied. Also moisture on the surface of the meat can be

drawn into the vacuum system, causing blockages and

contamination as well as reducing the moisture content

of the product.

For the above reasons a number of alternative ap-

proaches have been proposed to address the problem

of handling meat. Khodabandehloo [60.17] proposed

a gripper with similar functionality to the human hand

which could use its ﬁngers to grasp a product. A full

dexterous hand would be unnecessarily complex and

as yet no such system has been demonstrated in an

industrial environment, however the principle still ap-

peared promising and a multiﬁngered gripper was

developed [60.17], formed from a solid piece of ﬂexi-

ble rubber. An internal cavity was created at the ﬁnger’s

knuckle which could be pressurized by an external air

supply. As the cavity was ﬁlled with air it expanded,

causing the rear surface of the ﬁnger to elongate. Due to

the location of the cavity the front surface of the ﬁnger

remained unextended. As the ﬁnger was formed from

one solid piece of rubber this difference in extension

caused the knuckle to ﬂex.

A hand consisting of four such ﬁngers was devel-

oped and tested at the University of Bristol, UK. It was

positioned so that two ﬁngers were located on each side

of the piece of meat to be lifted. When activated, the

ﬁngers curled around the meat, creating a grasp. Due to

the compliant nature of the ﬁngers they did not create

damage to the surface of the meat as there was no hard

contact. Due to the low number of mechanical parts and

lack ofmoving linkagesthe gripperwas very wellsuited

to the hygiene requirements of the food industry as the

gripper could be washed or hosed down without risk of

damage.

Whilst proving effective at handling some cuts of

meat the Bristol University gripper was unsuited to

grasping steaks or thin slices of meat as they deform

too much for the ﬁngers to produce a secure grasp.

An alternative approach is the Intelligent Portion

Loading Robot produced by AEW Delford Systems

Ltd. [60.18]. This system is robot based and is able

to handle and manipulate a broad range of meat types

including both bone-in and boneless portions, ﬁsh,

cheese, and sliced products. Meat is fed to the system

on a conveyor where a vision system determines the po-

sition and orientation of the product to be handled. An

ABB IRB 340 FlexPicker robot ﬁtted with a novel end-

effector developedby AEW Delford is then used to pick

each product and transfer it to packaging or a further

processing machine.

The end-effector’s design is simple with a low num-

ber of parts, making it well suited to the needs of the

food industry. The end-effector is essentially a high-

speed paralleljawed gripper. Each jaw consists of a very

thin plate which, when the gripper activates, is forced

under the product as can be seen in Fig.60.9a,b. The

low proﬁle of the jaws means they can be inserted under

the product without damaging it. Although the lateral

force applied to the product as the jaws are closed is rel-

atively low it is still possible that this might dislodge the

product slightly.In order to prevent this, a spring-loaded

guide plate rests on the upper surface of the product

being lifted whilst the jaws close.

Fish pieces can be particularly difﬁcult to handle as,

due to their structure, they can crumble when handled,

breaking into many pieces. Gjersted [60.19] developed

a needle gripper for the picking and packing of pieces

of fresh, cooked and uncooked ﬁsh.

The gripper operates using a surface hooking prin-

ciple [60.19] and uses numerous pins which enter the

product simultaneously from opposite sides. The pins

are angled slightly towards the center of the product

Chicken

portion

Guide plate

Jaw

Fig. 60.9a,b AEW Delford gripper raised (a) and lowered

with jaw closed

(b)

Part F 60.4

1052 Part F Industrial Automation

and as a result when inserted they physically lock the

ﬁsh ﬁrmly in place, which means it can be handled and

accelerated rapidly without fear of being dropped. The

only way thatthe product can be dropped whilst the pins

are still inserted is if the product breaks apart, but this

is unlikely to happen as, whilst the pins are in the prod-

uct, they form an internal support structure which helps

keep the product in one piece.

The gripper was developed according to European

Hygienic Engineering and Design Group (EHEDG)

principles for hygienic design, meaning it meets with

the stringent requirements of the food industry. The

gripper has been tested successfully with both salmon

and cod and demonstrates excellent holding capability

with minimal impact on the product surface and the

overall product quality. In fact the impact on product

appearance and quality was judged to be less than when

conventional human handling was used.

60.4.3 Handling Moist Food Products

Within the food manufacturing industry it is extremely

common that the materials to be handled are moist. This

can be a result of washing, cooking or cutting or in-

deed just due to the nature of the product. This moisture

can often make traditional grippers ineffective and so

a number of novel techniques have been developed.

Sliced tomatoes and cucumbers used in a wide

varietyof products,e.g., saladsand sandwiches, are typ-

ically washed and sliced in a secondary part of a factory

using large-scale slicing machines capable of process-

ing many kilos per minute. Once sliced the product is

deposited into trays and delivered to production lines.

The high water content of most vegetables and the

nature of the cutting process means that slices have

a high residual moisture on their surfaces and cannot

be placed directly into the product, which would be-

come soggy reducing customer appeal, although it has

no signiﬁcant hygiene issues. To reduce this sogginess

and improve shelf life the sliced vegetable trays are left

to drain, for at least 2h, before being used. The ef-

fectiveness of this method is highly variable, with the

upper layers of ingredients draining more thoroughly

than those towards the middle or bottom of the tray.

After draining, the trays are delivered to the assem-

bly lines, where operators pick individual slices from

the trays and place them in the assembled product, e.g.,

sandwiches. It is extremely difﬁcult to do this without

further damaging the slices and as a result it is not un-

common for the center of tomatoes to become detached.

Furthermore the moisture causes the slices to stick to-

gether and the operators have to separate them, slowing

the overall process. For this reason a production line

working at 50 sandwiches per minute can typically have

four operators just placing tomato slices and a similar

number handling cucumber.

Davis et al. [60.20] proposed an automated sys-

tem for the handling of sliced tomato and cucumber

based on a novel end-effector. The solution involves

cutting slices on the actual assembly line for imme-

diate use. A slice would only be cut when required

and thus the need to pick an individual slice from

a tray is removed. Once cut, each slice is grasped us-

ing a noncontact Bernoulli gripper and a robot places it

as required (Fig.60.10).

A Bernoulli gripper operates using compressed air

and a ﬂat gripping face. Deﬂectors on the surface of the

gripper direct the supplied air so that it radiates from the

center of the gripper across the surface. When the grip-

Fig. 60.10 (a) Noncontact Bernoulli gripper. (b) Gripper

handling tomato

Part F 60.4

Automation in Food Processing 60.4 Raw Product Handling and Assembly 1053

ping surface is brought close to an object to be grasped

the gap through which the air travels becomes reduced.

To maintain the volumetric air ﬂow through the gripper

this results in an increase in air velocity. The rapid ﬂow

of air between the object and gripper generates an at-

tractive force in line with Bernoulli’s principle. It is this

force which allows the object to be grasped.

As well as lifting the products the gripper is also

able to remove moisture from the object being handled

using the air-knife principle where moisture is atomized

by the air and blown off the surface.

Another technique developed for lifting moist

products is the cryogenic gripper. Stephan and

Seliger [60.21] developed a freezing gripper for use

in the textile industry which created a bond between

the gripper and products by freezing moisture on the

surface of the product using a Peltier element. The re-

ported grip forces were as high as 3.5N/cm

after 3s

of freezing with release after 1s.

Although this gripper was developed for use in the

textile industry the technique appeared to have potential

in the food industry. To assess this, the Food Refriger-

ation and Process Engineering Research Center at the

University of Bristol, UK [60.22] carried out tests on

cryogenic grippers for the food industry. They were

particularly interested to determine whether such tech-

niques could be used to lift sheet-like food materials

such as lasagne, sliced ﬁsh, cheese, and ham. Similar

results to the work of Stephan et al. [60.21] regarding

grasp times were obtained, however, unforced release

times were found to be poor and mechanical release

methods were found to produce unacceptable damage

to the products’ surface. Nonetheless it is suggested

that with further development work a viable gripper can

probably be developed that has the potential to be very

useful in some sectors of the food industry, e.g., frozen

foods.

60.4.4 Handling Sticky Products

Many food products are sticky and, whilst there is

usually no problem developing automated systems for

grasping such objects, releasing them can often present

a challenge. The glacé cherry is an example of one such

product. When handled with a traditional two-jaw grip-

per the cherry is found to stick to one of the jaws when

released [60.23]. This meant that the cherry could not

be positioned accurately. Reed et al. [60.23] developed

a unique gripper for the production of Bakewell tarts.

These small cakes require a decorative cherry to be

place at the center of each cake and therefore a method

of picking and reliably releasing a single cherry was

developed.

The gripper developed is a two-ﬁngered parallel jaw

mechanism as shown in Fig.60.11a. As with a standard

gripper the jaws are closed and an object is held by

a frictional grasp. However, the unique feature of this

gripper is that the contact surface of each jaw is covered

in a polyester ﬁlm. This ﬁlm takes the form of a narrow

tape which is wound onto spools (Fig.60.11). When the

gripper releases an object a length of tape is wound off

the inner spools and onto the outer spools as shown in

Fig.60.11.

To release anobject thespools arerotated and there-

sultant motion of the polyester tape on each jaw causes

the object being grasped to be transported downwards.

At the tips of the jaws the tape doubles back on itself

and this causes it to peel away from the object being

held and therefore release it. The sharpness with which

the tape doubles back on itself is vital. If insufﬁciently

sharp it would be possible for the object to remain stuck

to one of the tapes and be transported along the out-

side of the jaw. An appropriately tight turn ensures that

the contact area between the tape and object is so small

that the resulting adhesive force is not large enough to

support the weight of the object.

In addition to its ability to handle sticky objects

this gripper can be used to position objects in con-

ﬁned spaces as the jaws of the gripper do not need

to be opened during product release. This makes the

gripper particularly well suited to placing objects into

boxes. Reed et al. demonstrated how the gripper could

be used to place petits fours and fondants into presenta-

tion boxes [60.23].

Another sticky product that has a reputation of be-

ing particularly difﬁcult to handle is fresh sheets of

lasagne. Clamping-type end-effectors cannot be used as

Jaws

Spools

a) b)

Polyester

tape

Fig. 60.11a,b Parallel jaw gripper grasping (a) and releas-

ing

(b) a sticky object

Part F 60.4

1054 Part F Industrial Automation

Roller

Pasta

Conveyor

Blade

a) b)

Fig. 60.12 (a) Lasagne lifting. (b) Motions in the automated handling of a lasagne pasta sheet

they would damage the surface of the pasta, and for

similar reasons vacuum cups are also unsuitable.

Moreno-Masey et al. investigated the possibility

of automating the manufacture of lasagne ready (mi-

crowave) meals and developed a method based on the

rolling action common in making pastry [60.24]. By

rolling a sheet of lasagne onto a roller and then grad-

ually unrolling it above a product it was shown that

the sheet could be positioned accurately and with lit-

tle damage. The conceptual design with the envisaged

sequence of operations is shown in Fig.60.12a, with the

automation system shown in Fig.60.12b.

The gripper is initially positioned so that the spat-

ula arm, needed to lift the front edge of the pasta, is

located close to the pasta sheet. The gripper then moves

horizontally a short distance towards the pasta, forcing

the spatula under the leading edge of the sheet. The

gripper continues moving in the horizontal direction

and simultaneously rotates the roller. By coordinating

the two motions the pasta is rolled onto the gripper

in a controlled manner. To release the pasta and de-

posit it into a tray the roller is simply rotated in the

opposite direction. The weight of the sheet causes the

lasagne to peel free of the roller in an equally con-

trolled manner. The machine constructed based on this

design is shown in Fig.60.12b. The motion of all actu-

ators are pneumatically powered with PLC control over

the joints using input sensing on the position of the

lasagne sheets. The machine is sufﬁciently simple and

low cost that nine identical machines could be used to

produce ready meals at a typical production rate of 60

per minute.

60.5 Decorative Product Finishing

Many food products include components or features

which add nothing to the taste or quality of the prod-

uct but are purely decorative. Cake manufacture is an

example of a production process where the product’s

appearance is as (perhaps even more) important as its

ﬂavor. There are many decorative features used, rang-

ing from discrete components which are place on the

surface of the cake to intricate patterns or text produced

using icing.

Park Cakes in the UK is a large bakery produc-

ing cakes for special occasions which often include

hand-written messages on their upper surface such as

“Happy Birthday” or “Congratulations”. These mes-

sages are produced by skilled staff using icing-ﬁlled

pastry bags. The operators apply pressure to the bags

in order to produce a constant ﬂow of icing with which

to write the messages. In order to be able to undertake

this task to the required high standard requires both ex-

Part F 60.5