Application Note

    Development of a Personalized Electric Walking Assist Car Implementing Inverted Pendulum Control Technology

    Murata has jointly developed "KeePace™," a personalized electric walking assist car, with KOWA CO., LTD.(*Note) , a general welfare equipment manufacturer, based on the "stand-still" technology of MURATA BOY. Murata engineers' desire to "help people with their stand-still technology" manifested as an idea of a personalized electric walking assist car and materialized as "KeePace™" through collaboration with KOWA CO., LTD. We hope this technology will aid senior citizens and people with walking problems to become as mobile as possible in the wake of the aging society.

    What Is "Inverted Pendulum Control?"

    Murata developed a bicycle-riding robot, MURATA BOY and a unicycle-riding robot, MURATA GIRL (Fig. 1) for the purpose of promoting its technologies, and uses them to demonstrate the potential of Murata products.

    The most remarkable feature of MURATA BOY and MURATA GIRL is their ability to stand still when they come to a stop, realized by "inverted pendulum control." Inverted pendulum control is best described by the action you take when balancing a long stick on the palm of your hand. If you keep your hand still, the stick would simply fall down. If you want to keep the stick in balance, you would move your hand to counter the stick's falling motion.

    With MURATA BOY and MURATA GIRL, a built-in gyro sensor detects the angular velocity (slanting angle) in the left-right direction, and keeps balance by spinning the disc in the chest area to counter the slanting angle (MURATA GIRL compensates the front-back slanting angle with the wheel as well) .

    Fig. 1 "MURATA BOY" and "MURATA GIRL"

    Fig. 1 "MURATA BOY" and "MURATA GIRL"

    Current Status and Challenges for Personalized Electric Walking Assist Cars

    Desire of the MURATA BOY development team to "take the stand-still technology (inverted pendulum control) beyond technological promotion to help people," manifested in many application ideas.

    One field that seemed the most promising was walking assist equipment exemplified by "silver cars" and "walkers" (Fig. 2)*1 created to support senior citizens and the walking impaired. Approximately 600,000 of such units were produced in Japan (2011) . As the aging population grows in Japan, approximately 1.3 million units per year are expected to be in demand by the year 2025 (Fig. 3).

    Walking assist equipment are also in high demand overseas, especially in Europe where people are strongly interested in assistive technologies. The idea proposed by MURATA BOY development team was carefully examined and polished up by the "MIRAI initiative"*2, Murata's initiative to create new businesses through cross-organizational interaction, gave birth to the "personalized electric walking assist car" project. This led to a collaboration with KOWA CO., LTD., the general welfare equipment manufacturer commanding over a 50% share of the domestic "silver car" market, to create "KeePace™" (Fig. 4).

    The unit was named "KeePace™" because it gives walking support that "keeps pace" with the operator's walking speed.

    Fig. 2 A "Silver Car (on the Left)" and a "Walker (on the Right) "

    Fig. 2 A "Silver Car (on the Left) " and a "Walker (on the Right) "

    Fig. 3 Market Forecast for Walking Assist Equipment (in Japan)

    Fig. 3 Market Forecast for Walking Assist Equipment (in Japan)

    図4: 電動歩行アシストカー "KeePace™"

    Fig. 4 Personalized Electric Walking Assist Car, "KeePace™"

    *Note

    KOWA CO., LTD:

    A general welfare equipment manufacturer located in Sakai City, Osaka Prefecture. Its capital is ¥106,295,075 and the consolidated number of employees is 461, as of March 2012. In addition to silver cars and walkers, they manufacture and sell walking canes and bath goods, toilet goods and so on.

    Glossary

    *1 Difference between "silver cars" and "walkers":

    Silver cars are used by people who can walk on their own for carrying shopping items or belongings. Walkers are used by people who have difficulty walking, and used for training or stabilizing the body by resting against the unit while walking.

    *2 MIRAI:

    MIRAI is an acronym for "Murata Innovative Research Activity Initiatives," Murata's own activities to create new businesses through cross-organizational interaction.

    Characteristics of the Personalized Electric Walking Assist Car, "KeePace™

    KeePace™'s dimensions are 40cm W x 25cm D x 85cm H (orange model)/95cm H (black model) with approximately 10kg in weight. Its strong points are "fall prevention," "slope operations" and "compact maneuvering."

    Fall prevention

    A user has a danger of tripping on a bump on the ground while operating existing walking assist equipment, losing control of the equipment and falling over and possibly suffering injury or bone fractures. As with MURATA BOY and MURATA GIRL, a built-in MEMS gyro sensor in "KeePace™," prevents the equipment from falling with the "inverted pendulum control." The control algorithm is described by the block diagram in Fig. 5. In this algorithm, we call the angle of the KeePace™'s center of gravity with respect to the vertical direction an inclination angle, and its angular velocity is called inclination angular velocity.

    Fig. 5 Block Diagram of Inverted Pendulum Control for 'KeePace™'

    Fig. 5 Block Diagram of Inverted Pendulum Control for "KeePace™"

    Step1
    The gyro sensor detects the inclination angular velocity. The inclination angle calculator calculates the inclination angle simultaneously.
    Step2
    Inclinometer and target angle generator calculates the target inclination angle.
    Step3
    Angular loop controller compensates for the difference of the angles between the target inclination angle and the angle calculated in Step 1.
    Step4
    Output from the angular loop controller in Step 3 becomes the target inclination angular velocity, and its difference from the inclination angular velocity in Step 1 is compensated for by the angular velocity loop controller.
    Step5
    Output from the angular velocity loop controller in Step 4 is given to the spindle motor as a torque command.
    Fig. 6 Operating Principle

    Fig. 6 Operating Principle

    By performing the algorithm above in 1 millisecond, nearly perfect vertical balance may be maintained. This control is performed independently for both the right and left wheels of KeePace™. This inverted pendulum control realizes natural interface by lightly pushing the handle forward to go forward, and pulling the handle to go backward, without having to operate switches and levers (Fig. 6) .

    Slope operations

    KeePace™, equipped with Murata Electronics Oy's inclinometer, realizes safe and easy operation while traveling on a slope. This inclinometer is characterized by

    • high anti-shock property (>20,000G) ,
    • offset temperature characteristics: approximately 0.5º and
    • low noise level, high resolution (0.0025º)

    due to the proprietary MEMS technology by Murata Electronics Oy.

    Main applications for the inclinometer are, construction equipment, medical equipment and measurement systems for airplanes. For example, when KeePace™ comes to an incline, the inclinometer detects the inclination angle and leans the unit forward. This lessens the load and easily lets the operator go forward. The unit leans backward on a decline, braking the forward motion. This way, KeePace™ realizes safe operation while keeping pace with the operator's walking speed (Fig. 7) .

    Fig. 7 Operating Principle on Slopes

    Fig. 7 Operating Principle on Slopes

    Compact maneuvering

    Independent two-wheel mechanism made very compact maneuvering possible. Its turning circle is less than 1/3 that of silver cars and walkers (Fig. 8) . A compact body with less than half the depth of conventional walking assist equipment is realized by optimal designing of control components and the driving mechanism.

    Silver car and walker users have been having a difficult time maneuvering in small quarters and store aisles. Users being conscious of the equipment taking up much space in elevators and cash register lines feel quite stressful. KeePace™ should contribute to solving these problems.

    Fig. 8 Turning Circle for 'KeePace™'

    Fig. 8 Turning Circle for "KeePace™"

    Final Remark

    "KeePace™," a personalized electric walking assist car, was given a runner up award in the Smart Key Technologies Category of the "CEATEC (Combined Exhibition of Advanced Technologies) AWARD 2012" (Fig. 9) .

    We were surprised by the positive review given by the judging committee, "With the ageing of the population, this technology is very practical and has great social significance." As we look around, we find many care robots "giving support to the disabled" or "easing the load off the caregivers", but we don't find many robots like KeePace™ to "keep people from becoming disabled." As our society becomes aged, we expect KeePace™ to keep people from being bed-bound or dependent on wheelchairs, and prolong the period of independent mobility.

    Meanwhile, we face a load of problems for the actual usage of the unit. Our immediate challenge is to ensure "safety" and "reliability." The unit must be made lighter so that senior citizens and walking-impaired individuals can handle it with ease. We will continue to work on its development, so that we can put the "stand still" technology of MURATA BOY to practical use while clearing hurdles one by one.

    Fig. 9 CEATEC AWARD 2012 Award Ceremony

    Fig. 9 CEATEC AWARD 2012 Award Ceremony
    Photo on the left: Murata Manufacturing Co., Ltd. commercialization staff member
    On the right: KOWA CO., LTD. Director: Development Division General Manager

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