Automation of robotic assembly processes on the basis, MAYER 2011.pdf

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ASSEMBLY Automation of robotic assembly processes on the basis of an architecture of human cognition Marcel Ph. Mayer Christopher M. Schlick Daniel Ewert Daniel Behnen Sinem Kuz Barbara Odenthal Bernhard Kausch Received: 16 February 2011 / Accepted: 1 April 2011 / Published online: 21 April 2011 Ó German Academic Society for Production Engineering (WGP) 2011 Abstract A novel concept to cognitive automation of robotic assembly processes is introduced. An experimental assembly cell with two robots was designed to verify and validate the concept. The cell’s numerical control—termed a cognitive control unit (CCU)—is able to simulate human information processing at a rule-based level of cognitive control. To enable the CCU to work on a large range of assembly tasks expected of a human operator, the cognitive architecture SOAR is used. On the basis of a self-developed set of production rules within the knowledge base, the CCU can plan assembly processes autonomously and react to ad- hoc changes in assembly sequences effectively. Extensive simulation studies have shown that cognitive automation based on SOAR is especially suitable for random parts supply, which reduces planning effort in logistics. Con- versely, a disproportional increase in processing time was observed for deterministic parts supply, especially for assemblies containing large numbers of identical parts. Keywords Cognitive automation Á SOAR Á Assembly Á Joint cognitive systems 1 Introduction In high-wage countries many manufacturing systems are highly automated. The main aim of automation is usually to increase productivity and reduce personnel expenditures. However, it is well known that highly automated systems are investment-intensive and often generate a non-negligible organizational overhead. Although this overhead is man- datory for manufacturing planning, numerical control pro- gramming and system maintenance, it does not directly add value to the product to be manufactured. Highly automated manufacturing systems therefore tend to be neither efficient enough for small lot production (ideally one piece) nor flexible enough to handle products to be manufactured in a large number of variants. Despite the popularity of strategies for improving manufacturing competitiveness like agile manufacturing [1] that consider humans to be the most valuable ‘‘factors’’, one must conclude that especially in high-wage countries the level of automation of many pro- duction systems has already been taken far without paying sufficient attention to the specific knowledge, skills and abilities of the human operator. According to the law of diminishing returns that kind of naive increase in automation will likely not lead to a sig- nificant increase in productivity but can also have adverse effects. According to Kinkel et al. [2] the amount of process errors is on average significantly reduced by automation, but the severity of potential consequences of a single error increases disproportionately. These ‘‘ironies of automation’’ which were identified by Lisanne Bainbridge as early as 1987 can be considered a vicious circle [3], where a function that was allocated to a human operator due to poor human reliability is automated. This automa- tion results in higher function complexity, ultimately increasing the cognitive loads of the human operator for M. Ph. Mayer (&) Á C. M. Schlick Á S. Kuz Á B. Odenthal Á B. Kausch Institute of Industrial Engineering and Ergonomics, RWTH Aachen University, Aachen, Germany e-mail: [email protected] D. Ewert Institute of Information Management in Mechanical Engineering, RWTH Aachen University, Aachen, Germany D. Behnen Laboratory for Machine Tools and Production Engineering, RWTH Aachen University, Aachen, Germany 123 Prod. Eng. Res. Devel. (2011) 5:423–431 DOI 10.1007/s11740-011-0316-z

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Transcript of Automation of robotic assembly processes on the basis, MAYER 2011.pdf

  • ASSEMBLY

    Automation of robotic assembly processes on the basisof an architecture of human cognition

    Marcel Ph. Mayer Christopher M. Schlick

    Daniel Ewert Daniel Behnen Sinem Kuz

    Barbara Odenthal Bernhard Kausch

    Received: 16 February 2011 / Accepted: 1 April 2011 / Published online: 21 April 2011

    German Academic Society for Production Engineering (WGP) 2011

    Abstract A novel concept to cognitive automation of

    robotic assembly processes is introduced. An experimental

    assembly cell with two robots was designed to verify and

    validate the concept. The cells numerical controltermed

    a cognitive control unit (CCU)is able to simulate human

    information processing at a rule-based level of cognitive

    control. To enable the CCU to work on a large range of

    assembly tasks expected of a human operator, the cognitive

    architecture SOAR is used. On the basis of a self-developed

    set of production rules within the knowledge base, the CCU

    can plan assembly processes autonomously and react to ad-

    hoc changes in assembly sequences effectively. Extensive

    simulation studies have shown that cognitive automation

    based on SOAR is especially suitable for random parts

    supply, which reduces planning effort in logistics. Con-

    versely, a disproportional increase in processing time was

    observed for deterministic parts supply, especially for

    assemblies containing large numbers of identical parts.

    Keywords Cognitive automation SOAR Assembly Joint cognitive systems

    1 Introduction

    In high-wage countries many manufacturing systems are

    highly automated. The main aim of automation is usually to

    increase productivity and reduce personnel expenditures.

    However, it is well known that highly automated systems are

    investment-intensive and often generate a non-negligible

    organizational overhead. Although this overhead is man-

    datory for manufacturing planning, numerical control pro-

    gramming and system maintenance, it does not directly add

    value to the product to be manufactured. Highly automated

    manufacturing systems therefore tend to be neither efficient

    enough for small lot production (ideally one piece) nor

    flexible enough to handle products to be manufactured in a

    large number of variants. Despite the popularity of strategies

    for improving manufacturing competitiveness like agile

    manufacturing [1] that consider humans to be the most

    valuable factors, one must conclude that especially in

    high-wage countries the level of automation of many pro-

    duction systems has already been taken far without paying

    sufficient attention to the specific knowledge, skills and

    abilities of the human operator.

    According to the law of diminishing returns that kind of

    naive increase in automation will likely not lead to a sig-

    nificant increase in productivity but can also have adverse

    effects. According to Kinkel et al. [2] the amount of

    process errors is on average significantly reduced by

    automation, but the severity of potential consequences of a

    single error increases disproportionately. These ironies of

    automation which were identified by Lisanne Bainbridge

    as early as 1987 can be considered a vicious circle [3],

    where a function that was allocated to a human operator

    due to poor human reliability is automated. This automa-

    tion results in higher function complexity, ultimately

    increasing the cognitive loads of the human operator for

    M. Ph. Mayer (&) C. M. Schlick S. Kuz B. Odenthal B. Kausch

    Institute of Industrial Engineering and Ergonomics,

    RWTH Aachen University, Aachen, Germany

    e-mail: [email protected]

    D. Ewert

    Institute of Information Management in Mechanical

    Engineering, RWTH Aachen University, Aachen, Germany

    D. Behnen

    Laboratory for Machine Tools and Production Engineering,

    RWTH Aachen University, Aachen, Germany

    123

    Prod. Eng. Res. Devel. (2011) 5:423431

    DOI 10.1007/s11740-011-0316-z

  • planning, teaching and monitoring, and hence leading to a

    more error-prone system. To reduce the error potential one

    could again extend automation and reinforce the vicious

    circle. During the first iteration it is quite likely that the

    overall performance of an automated system will increase,

    but the potential risk taken is often severely underesti-

    mated. Additional iterations usually deteriorate perfor-

    mance and lead to poor system robustness.

    The novel concept of cognitive automation by means of

    simulation of human cognition aims at breaking this

    vicious circle. Based on simulated cognitive functions,

    technical systems shall not only be able to (semi-) auton-

    omously carry out manufacturing planning, adapt to

    changing supply conditions and be able to learn from

    experience but also to simulate goal-directed human

    behavior and therefore significantly increase the confor-

    mity with operator expectations. Clearly, knowledge-based

    behavior in the true sense of Rasmussen [4] cannot be

    modeled and simulated, and therefore the experienced

    machining operator plays a key architectural role as a

    competent problem solver in unstable and non-predictable

    situations.

    2 Experimental assembly cell

    One of todays challenges in manufacturing is the

    increasing complexity of assembly processes due to an

    increasing number of products that have to be assembled in

    a large variety in production space [5]. Whereas in con-

    ventional automation each additional product or variant

    significantly increases the organizational overhead, cogni-

    tively automated assembly cells are theoretically able to

    autonomously plan, execute and replan the expected tasks

    on the basis of a digital model of the product to be

    assembled in conjunction with a set of production rules. No

    explicit knowledge on how to solve the assembly problem

    is needed. Therefore, these systems allow for flexible, cost-

    effective and safe assembly.

    Due to their design for assembly, many of todays

    industrially processed components in mass and medium lot

    size production are purposefully constrained so that their

    assembly is only possible in a particular sequence or only a

    few procedural variations are allowed (see [6]). The

    assembly of these components is too simple to fully dem-

    onstrate the flexibility and effectiveness of cognitive

    automation. To fully develop and validate the novel con-

    cept, mountable assemblies were chosen that can be gen-

    erated in an almost unlimited number of variants in small

    series production. One of the requirements for the build-

    ing blocks is that they allow arbitrary configuration and

    are completely interchangeable. LEGO building bricks,

    from the Danish company of the same name, fulfill this

    requirement and were therefore used for system design and

    evaluation. Unlike complex free forming components (e.g.

    interior elements in an automobile), the bricks are also easy

    to describe mathematically. Nevertheless they allow for

    very complex work processes because of the huge number

    of permutations of assembly steps. This is easily shown by

    a simple example: Building a small pyramid of only five

    LEGO bricks with a foundation of two by two bricks can

    be done using 24 different assembly sequences.

    In order to study cognitive automation, an experimental

    assembly cell was designed and a manufacturing scenario

    was developed [7]. The scenario is as follows: An engineer

    has designed a mechanical part of medium complexity with

    a CAD system. The part can contain an arbitrary number of

    bricks. The task for the assembly cells cognitive control

    unit (CCU) is to autonomously develop and execute a time

    and energy efficient assembly sequence on the basis of the

    CAD model using the available technical resources in

    terms of robots, manipulators, grippers and clamping

    devices, as well as supplied bricks, etc. The supply of

    bricks can change dynamically.

    In our assembly scenario (see Fig. 1), two robots carry

    out a predefined repertoire of coordinated pick and place

    operations. One robot is stationary (robot 1), the other

    robot sits on a linear track (robot 2). A conveyor system

    equipped with four individually controlled transfer lines,

    pneumatic track switches and light barriers completes the

    experimental system. The transfer lines are arranged so that

    the parts can cycle around the working area. First, the

    stationary robot grasps the bricks from a pallet and puts

    them on a conveyor belt. The second robot, which is

    waiting on the linear track for the part, has to identify the

    brick, i.e. match it to a known library of bricks with respect

    to color and shape. If the brick is included in the final state

    of the product to be assembled, the robot will pick it from

    the conveyor (which in a later step will comprise the task of

    tracking the unknown position and synchronizing the robot

    to a running track) and will put it on the working area

    either at the corresponding position in the assembly or in a

    buffer area for further processing. Otherwise, the brick can

    keep circulating on the conveyor belt to reappear later or to

    be removed.

    3 Simulation of human cognition

    An important foundation of cognitive automation is a

    suitable simulation model of human cognition. Such a

    model is also termed a cognitive architecture. In order to

    simulate cognitive functions in a robotic assembly cell,

    distinct criteria must be met.

    When a function that was allocated to a human operator

    has to be automated due to frequent human errors, the

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    123

  • reliability of the automated function clearly is the most

    important technical criterion. We distinguish between two

    aspects of reliability: reliability of the execution of the

    assembly processes and reliability of the cognitive simu-

    lation model controlling the process. Concerning the for-

    mer aspect, we do not aim at high-fidelity modeling of

    human cognition including (solely from a technical point of

    view) inherent weaknesses like oblivion or decision bias,

    but rather want to plan and execute predictable processes

    on the basis of robust symbol processing. Hence, when

    accessing knowledge in the artificial memory, access

    should be unlimited, so that even rarely used knowledge

    can be retrieved quickly and will not be forgotten.

    Concerning the latter aspect of reliability we regard the

    level of maturity of a cognitive architecture as an important

    criterion. Even though no absolute measure is known for

    the level of maturity of such a symbolic processor, the

    amount of applications, the existence of a large and active

    user community and the time the architecture has been

    under continuous development are all taken as sub-indi-

    cators. Moreover, since the automated assembly cell should

    be controlled directly via the cognitive simulation model,

    another criterion is the availability of suitable interfaces for

    sensors and actuators.

    There are many cognitive simulation models that can be

    used to automate assembly processes. A systematic review

    was carried out by Chong et al. [8]. The most popular are

    ACT-R [9], ICARUS [10] and SOAR [11].

    In the framework of a robotized assembly cell, SOAR

    was chosen as a suitable simulation model because it sat-

    isfies most of the aforementioned criteria. The design of the

    CCU based on SOAR as well as selected simulation results

    will be presented in Sects. 4 and 5.

    There are applications for SOAR in other domains. In

    the military domain, TACAIR-SOAR is used for training

    [12]. The system is capable of executing most of the air-

    borne missions that the U.S. military flies in fixed-wing

    aircraft. A speech-enabled agent is used for indirect fire

    training for a Forward Observer by providing fire direction

    center support using the SOARSpeak voice interface [13].

    An unmanned air vehicle controlled onboard by SOAR was

    developed and tested by Putzer [14]. A detailed overview

    of using SOAR for the control of unmanned vehicles can

    be found in Onken and Schulte [3].

    In the field of mobile robotics, a gait control system

    based on SOAR was developed for a six-legged robot that

    is able to move on unlevel terrain, avoid obstacles and walk

    to a pre-specified GPS location [15].

    However, the only application of SOAR that can be

    related to manufacturing systems is the system called

    ROBO-SOAR [16]. It is able to solve the three blocks

    problem with outside guidance from a human operator.

    The system incorporates camera surveillance and a robot

    performing pick-and-place operations. No explicit knowl-

    edge on how to solve the problem has to be input to the

    system beforehand. This also holds true for the self-

    developed CCU, which will be presented in the next

    section.

    4 Architecture of cognitive control unit

    Cognitive systems for the automation of production pro-

    cesses have to meet many functional and non-functional

    requirements [17] through the design of the software

    architecture. The system has to work on different levels of

    Fig. 1 Design of theprototypical assembly cell [7]

    Prod. Eng. Res. Devel. (2011) 5:423431 425

    123

  • abstraction. This means, for instance, that the reasoning

    mechanism cannot work on the raw sensor readings.

    Instead an intermediate software component is required to

    fuse and aggregate the sensor data. To meet the require-

    ments, a multilayer software architecture [18] was devel-

    oped, as depicted in Fig. 2.

    The software architecture is separated into four layers

    which incorporate the different mechanisms needed to

    simulate human cognition. The presentation layer includes

    the humanmachine interface and an interface for the

    modification of the knowledge base. The planning layer is

    the deliberative layer in which the actual decision for the

    next action in the assembly process is made. The coordi-

    nation layer provides services to the planning layer that can

    be invoked by the latter to start action execution. The

    reactive layer is responsible for a low response time reac-

    tion of the whole system in case of an emergency situation.

    The knowledge module contains the necessary domain

    knowledge of the system in terms of production rules.

    At the beginning the human operator assigns the desired

    goal g* to the CCU via the presentation layer. The desired

    goal is compiled and enriched with additional assembly

    information, which will be discussed in more detail in the

    following section. It is then transferred to the planning

    layer where the reasoning component derives the next

    action u* based on the actual environmental state y* and

    the desired goal g*. The actual environmental state is

    estimated on the basis of sensor readings from a technical

    application system (TAS). In the coordination layer the raw

    sensor readings y are fused and aggregated into an envi-

    ronmental state y*. Hence, all decisions in the planning

    layer are based on the environmental state y* at a given

    time. The decision process must therefore be short, because

    the state of the TAS may have changed significantly. The

    next best action u* derived in the planning layer is sent

    back to the coordination layer, where the abstract

    description of the next best action u* is translated into a

    sequence of actuator commands u, which are sent to the

    TAS. In the TAS, the sequence of commands is executed

    and the changed environmental state is measured again by

    the sensors. If the new vector y of sensor readings indicates

    an emergency situation, the reactive layer processes the

    sensor data directly and sends the corresponding actuator

    commands to the TAS.

    4.1 Development of the reasoning component

    As shown by Mayer et al. [19], it is crucial for the human

    operator to understand the subgoals and the planned actions

    of the CCU to supervise the robotic assembly cell. This

    raises the question of how the symbolic representation of

    the knowledge base of the CCU must be designed to ensure

    conformity with the operators expectations. Proprietary

    programming languages that are used in conventional

    automation have to be learned for each domain and do not

    necessarily match the mental model of the human operator.

    In terms of a human-centered description for matching the

    procedural knowledge to the mental model, one promising

    approach is the use of motion descriptors, since motions are

    familiar to the human operator from manual assembly

    tasks. These motions are also easy to anticipate in human-

    robot interaction. In mass production it is best practice to

    break down complex tasks into fundamental motion ele-

    ments. To do so, the MTM method [20] as a library of

    fundamental movements is often used in industry. This

    method was chosen to define the motion descriptors that

    can be used by the CCU to plan and execute the robotic

    assembly processes also used in small lot production [21].

    Based on this concept, we followed the so-called Cog-

    nitive Process method (CP method [14]). This method is

    able to integrate software engineering and cognitive sys-

    tems engineering. To do so, the structure of the behavioral

    model is retained and the software code is developed on the

    basis of a cognitive process. The a priori knowledge that is

    needed to control the assembly cell was implemented in

    SOAR following the four steps of the static model of the

    CP method. Moreover, in the actual executable it is pos-

    sible that a production rule contains elements that can be

    Fig. 2 Software architecture ofthe cognitive system [17]

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    123

  • related to the different steps in the CP process. The a priori

    knowledge of the reasoning component consists of a set of

    42 production rules.

    4.1.1 Achievable model

    First, the achievable model for the cognitive system has to

    be defined as a desired goal, for all further actions depend

    on this model. The desired goal in terms of the product to

    be assembled is specified using a CAD software package.

    In our particular scenario, the desired goal is the buildup of

    an arbitrary structure of LEGO bricks, e.g. a pyramid of

    identical bricks. Since SOARs internal representation is

    solely symbolic, the desired goal has to be compiled within

    the presentation layer to meet formal requirements. Addi-

    tionally, the desired goal is not only compiled but enriched

    with meta-information. This meta-information can be seen

    as the key to our concept of cognitive automation. Besides

    information on position and rotation of each brick in the

    desired goal, information about the relations of each brick

    to its adjacent neighbors is included in the compiled

    desired goal. We call these relations neighborhood rela-

    tions. The neighborhood relations are solely symbolic. In

    other words, if two bricks are nearest neighbors, we only

    know about the fact and the direction of the neighboring

    relationship. We do not know about a possible overlap in

    Cartesian space. The achievable goal as used in SOAR

    contains position, rotation, color, type and the neighboring

    relations of each brick in the product to be assembled.

    4.1.2 Procedural model

    In the second step the knowledge about procedures to

    achieve the desired goal has to be considered. Based on the

    neighboring relationship of the achievable model and

    additional constraints, the buildup of the product is planned

    by elaboration rules. For example, a brick can only be

    positioned if it is on the ground or if all of its neighbors

    below have already been assembled.

    When using SOAR as a cognitive simulation model, one

    also has to consider the operational model for designing the

    procedural model according to SOARs execution cycle

    [22]. For all operations that should later be executed in the

    application phase of SOAR, procedures have to be pro-

    posed that fire in the proposal phase of the execution

    cycle. Rules that propose a motion are part of the proce-

    dural model but are strongly connected to rules that apply

    the motion.

    4.1.3 Operational model

    The operational model puts the generated plans of the

    procedural model into action. The basic fundamental

    movements of the MTM-1 system were used to control

    the movement of the robot on the linear track (see

    Fig. 1). These movements are encoded as production

    rules in the operational model. The motion operators are

    REACH, GRASP, MOVE (including TURN), POSITION

    and RELEASE (including APPLY PRESSURE). A par-

    ticular rule can only be applied if the corresponding

    motion operator was selected by the procedural model.

    The five motion operators are the only action primitives

    in this scenario that can manipulate the assembly.

    4.1.4 Environmental model

    In the fourth step of the CP-method all elements that are

    needed in the previous steps have to be mapped onto an

    environmental model that can be used by the CCU. In the

    developed scenario the gripper of the robot, the conveyer

    belt, the brick feeder, the working area and the buffer are

    modeled. These elements are transmitted to the cognitive

    simulation model during initialization along with the goal

    state.

    4.2 Integration into assembly cell

    Manufacturing systems like the experimental assembly

    cell require robust, real-time-capable control hardware.

    Although PC-based hardware and software is often used

    for human supervisory control and for high level con-

    trollers, embedded systems with real-time operating sys-

    tems prevail as machine controllers. In the assembly cell

    robot controllers supplied by the robot manufacturer are

    used to control the handling robots. A motion controller

    controls the conveyer belt as well as the track switches.

    Additionally, a PC-based controller is connected to a

    hand-like robot gripper with three fingers. Each controller

    is able to execute control programs to perform movements

    of the attached components and to interact with other

    controllers via field bus or internet protocols. Action

    primitives covering the basic features of the robots, con-

    veyor belts, track switches and grippers were imple-

    mented on the controllers to be remotely activated. These

    action primitives, as well as the input signals from the

    sensors, were made available to the reactive layer of the

    CCU.

    The assembly process requires the incoming LEGO

    bricks to be identified and grasped before they can be

    assembled in the working area. A computer vision system

    with one camera is therefore used to detect the shape and

    orientation of the bricks. The information it gathers is used

    to track the bricks and to grasp one brick in real-time from

    the moving conveyer belt. The real-time coupling between

    the vision system and the robot is coordinated by the

    reactive layer.

    Prod. Eng. Res. Devel. (2011) 5:423431 427

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  • The reactive layer connects the TAS to the high-level

    cognitive functions introduced. However, the reactive layer

    must also provide capabilities for real-time reaction to

    safetycritical events. In order to be able to ensure mini-

    mum response time, conventional compiled software

    code is used. This poses no restriction on higher cognitive

    functions since the rule-based behavior is determined by

    the layers above the reactive layer. Actuator commands

    received from the super-ordinate coordination layer are

    either interpreted by and executed within the reactive layer

    or passed to the TAS, where the robots, the motion con-

    trollers or PC-based gripper controllers execute them.

    Sensor readings from the TAS are also either passed on to

    the coordination layer or processed within the reactive layer.

    For instance, video streams from the camera are usually too

    complex to be interpreted by SOAR at a symbolic level. In

    this case the video streams are processed in the reactive

    layer and only the extracted image information about the

    bricks size and shape are transmitted to higher layers.

    5 System evaluation

    5.1 Reasoning component

    In the following, only simulation results regarding the

    reasoning component of the CCU are presented due to space

    limitations. The depending variables in the simulation study

    are the processing time and the number of required pick and

    place operations (termed MTM-1 cycles).

    To evaluate the effect of the independent variables

    on the dependent variables, we carried out independent

    simulation runs for workpieces assembled from identical

    bricks. The independent variables are (1) size of the

    product to be assembled (six levels: four to 24 bricks in

    steps of four), (2) number of bricks provided at the queue

    (seven levels: one, four to 24 in steps of four) and feeding

    regime (two levels: deterministic supply of needed bricks

    and random supply including unneeded bricks). For each

    combination of the levels of the independent variables 100

    simulation runs were calculated. Self-developed simulation

    software was used. The runs were scheduled for parallel

    processing on the high-end Compute Cluster in the Center

    for Computing and Communication at RWTH Aachen

    University.

    The simulation results show that the desired target state

    was assembled correctly by the CCU in all 8,400 runs.

    Assembly errors or deadlocks did not occur. Regarding the

    number of required MTM-1 cycles for a workpiece of a

    given size and a queue of a given length, all simulated

    sequences conform to expected number of cycles. This is

    shown in Fig. 3 for both feeding regimes.

    The corresponding results for processing time are shown

    in Fig. 4. The simulation results unambiguously show a

    disproportional increase in processing time with increasing

    part size and queue length for deterministic part feed.

    Conversely, a stochastic part feed surprisingly leads to a

    decrease in processing time over the queue length. This

    counter-intuitive result can be explained by the way SOAR

    processes production rules: Each needed brick in the queue

    is matched to all possible positions within the target state.

    Positive matches lead to proposals that have to be com-

    pared. Hence, for deterministic part feed the amount of

    comparisons increases disproportionally due to the known

    exponential worst-case runtime behavior of SOARs

    embedded RETE algorithm.

    5.2 Design for humanmachine compatibility

    In order to be able to use the full potential of cognitive

    automation, one ultimately has to expand the focus from a

    traditional humanmachine system to joint cognitive

    Fig. 3 Required MTM-1 cyclesof the reasoning component of

    the CCU as a function of part

    size and number of bricks

    available at the queue (leftdeterministic brick feed; rightstochastic brick feed)

    428 Prod. Eng. Res. Devel. (2011) 5:423431

    123

  • systems [23, 24]. In these systems both the human operator

    and the cognitive technical system cooperate safely and

    effectively at different levels of cognitive control to

    achieve a maximum of humanmachine compatibility.

    Engineering methods like the presented CP method

    [3, 14] primarily aim at technical design of cognitive sys-

    tems. When developing joint cognitive systems that have to

    conform to operator expectations, it is important to acquire

    additional knowledge about the rules and heuristics

    humans use in manual assembly.

    To do so, two independent experimental trials with a

    total of 36 subjects were carried out. Based on the data

    three fundamental assembly heuristics could be identified

    and validated [25]: (1) humans begin an assembly at edge

    positions of the working area; (2) humans prefer to build in

    the vicinity of neighboring objects; (3) humans prefer to

    assemble in layers.

    To develop a humanoid mode for cognitively auto-

    mated assembly systems similar to the horse-metaphor

    for automated vehicles [26], the identified assembly

    heuristics where formulated as production rules. When the

    reasoning component is enriched with these rules, a sig-

    nificant increase in the predictability of the robot when

    assembling the products can be achieved [19]. In other

    words, if the knowledge base is extended by the rules and

    heuristics humans use, the system can be better anticipated

    by the human operator because it is compatible with his/her

    mental model of the assembly process. Hence, an increase

    in predictability leads to more intuitive human-robot

    cooperation and therefore increases safety significantly.

    6 Summary and outlook

    Especially in highly automated manufacturing systems that

    are aiming at producing products in almost any variety in

    product space, an increase in conventional automation will

    not necessarily lead to a significant increase in productiv-

    ity. Therefore, novel concepts towards proactive, agile and

    versatile manufacturing systems have to be developed.

    Cognitive automation is a promising approach to improve

    proactive system behavior and agility. In cognitively

    automated systems, the experienced machine operator

    plays a key architectural role as a competent solver of

    complex planning and diagnosis problems. Moreover, he/

    she is supported by cognitive simulation models which can

    quickly, efficiently and reliably solve algorithmic problems

    on a rule-based level of cognitive control and take over dull

    and dangerous tasks.

    A very interesting finding is that the system is especially

    efficient for stochastic part feed with a large variety in

    product space. The CCU is therefore able not only to

    reduce planning effort with autonomous assembly planning

    but also to reduce preparatory work in logistics.

    To be able to accomplish complex assembly tasks

    without impairing the CCU with calculations that cannot be

    solved in polynomial time, future investigations will focus

    on a hybrid approach [27] where the predefined planning

    problem is solved prior to the assembly by generating a

    state graph [28] that describes all possible assembly

    sequences for the intended product. This graph can also be

    updated during assembly. The reasoning component within

    SOAR uses this state graph to adapt the plan to the actual

    state of the assembly and part supply.

    To assist the human operator within this novel auto-

    mation concept, additional laboratory studies of a self-

    developed augmented vision system for error detection in

    assembled parts were carried out [29]. However, the aug-

    mented vision system has to be extended by a real-time

    decision-support function based on SOAR.

    In order to validate the introduced concepts and proto-

    types, future investigations also have to focus on real

    Fig. 4 Processing time in [s] ofthe reasoning component of the

    CCU as a function of part size

    and number of bricks available

    at the queue (left deterministicbrick feed; right stochastic brickfeed)

    Prod. Eng. Res. Devel. (2011) 5:423431 429

    123

  • industrial products. As stated before, many industrially

    processed components allow only a few procedural varia-

    tions. Hence, cognitive automation can be like breaking a

    butterfly on a wheel. Therefore, as a first step, a modular

    model of an engine was developed (see Fig. 5). The model

    allows for arbitrary sequences of the assembly process but

    provides sufficient complexity to demonstrate the flexibil-

    ity and effectiveness of cognitive automation.

    Acknowledgments The authors would like to thank the GermanResearch Foundation (DFG) for its kind support of the research on

    cognitive automation within the Cluster of Excellence IntegrativeProduction Technology for High-Wage Countries.

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