ISO 18646-4:2021

INTERNATIONAL ISO
STANDARD 18646-4
First edition
2021-08
Robotics — Performance criteria
and related test methods for service
robots —
Part 4:
Lower-back support robots
Robotique — Critères de performance et méthodes d'essai
correspondantes pour robots de service —
Partie 4: Robots de soutien du bas du dos
Reference number
ISO 18646-4:2021(E)
©
ISO 2021

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ISO 18646-4:2021(E)

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© ISO 2021
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Published in Switzerland
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ISO 18646-4:2021(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Test conditions . 3
4.1 General . 3
4.2 Environmental conditions . 3
4.3 Operating conditions . 4
5 Test method for assistive torque index and lumbar compression reduction .4
5.1 Purpose . 4
5.2 Relevant characteristics . 4
5.2.1 General. 4
5.2.2 Assistive torque index (ATI). 4
5.2.3 Lumbar compression reduction (LCR) . 5
5.3 Test facility . 7
5.3.1 Test apparatus . 7
5.3.2 Reference movement and target trajectory . 8
5.4 Test procedure .10
5.5 Test result .11
6 Test method for rate of assistance .11
6.1 Purpose .11
6.2 Relevant characteristics .11
6.3 Test facility .12
6.4 Test procedure .15
6.5 Test result .18
Annex A (informative) Time range of ATI and LCR .19
Annex B (informative) Example of lower-back support robots .23
Annex C (informative) Example table of test results .25
Annex D (informative) Example implementation of a test apparatus .26
Bibliography .29
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ISO 18646-4:2021(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 299, Robotics.
A list of all parts in the ISO 18646 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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ISO 18646-4:2021(E)

Introduction
This document is intended to facilitate understanding of performance of lower-back support robots
(see Annex B). This document defines the important performance characteristics and describes how to
specify them and how to test them.
The characteristics for which test methods are given in this document are those considered to affect
robot performance significantly. The user of this document selects which performance characteristics
to test, in accordance with the specific requirements.
The performance criteria specified in this document are not intended to be interpreted as the
verification or validation of safety requirements. The verification and validation of safety requirements
are specified in other standards developed by ISO TC 299.
The International Organization for Standardization (ISO) draws attention to the fact that it is claimed
that compliance with this document may involve the use of patents concerning the test apparatuses of
the performance of wearable robots for lower-back support referred to throughout the document.
ISO takes no position concerning the evidence, validity and scope of these patent rights.
The holders of these patent rights have assured ISO that they are willing to negotiate licences under
reasonable and non-discriminatory terms and conditions with applicants throughout the world. In this
respect, the statements of the holders of these patent rights are registered with ISO. Information may
be obtained from the patent database available at www .iso .org/ patents.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights other than those in the patent database. ISO shall not be held responsible for identifying
any or all such patent rights.
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INTERNATIONAL STANDARD ISO 18646-4:2021(E)
Robotics — Performance criteria and related test methods
for service robots —
Part 4:
Lower-back support robots
1 Scope
This document describes methods of specifying and evaluating the performance of lower-back support
robots.
This document applies regardless of the purpose and application of lower-back support robots and
the driving methods (e.g. electric, hydraulic and pneumatic). This document does not apply to medical
robots, although the test methods specified in this document can be utilized for medical robots.
This document is not intended for the verification or validation of safety requirements.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 8373, Robots and robotic devices — Vocabulary
ISO 13482, Robots and robotic devices — Safety requirements for personal care robots
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 8373, ISO 13482 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
robot
programmed actuated mechanism with a degree of autonomy, moving within its environment, to
perform intended tasks
Note 1 to entry: A robot includes the control system and interface of the control system.
Note 2 to entry: The classification of robot into industrial robot or service robot is done according to its intended
application.
[SOURCE: ISO 8373:2012, 2.6, modified — The words “actuated mechanism programmable in two or
more axes” have been replaced with “programmed actuated mechanism”.]
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ISO 18646-4:2021(E)

3.2
wearable robot
robot that supplements or augments personal capabilities while attached to a human during use
Note 1 to entry: Wearable robots are referred to as restraint-type physical assistant robots in ISO 13482:2014.
3.3
lower-back support robot
wearable robot to reduce the load in the lower back of the user by its assistive force or torque
3.4
user
person who wears a wearable robot on his/her body and directly receives its assistive force or torque
3.5
restraint part
part of the wearable robot binding a corresponding attached body part of the user to transmit an
assistive force or torque
3.6
assistive torque
output torque of the wearable robot to assist a user to perform required tasks
3.7
attached body part
part of the user’s body on which the restraint part of the wearable robot is attached
3.8
input method
interface allowing the user to control the assistive force or torque of the wearable robot by an
appropriate input signal
3.8.1
biological input
input method where biological signals that are in correlation to the force or torque the user exerts at
his/her body part intended for assistance are used as the input
Note 1 to entry: Biological signals include bioelectrical signals such as myoelectric signals.
3.8.2
kinematic input
input method where movement and/or posture of the user’s body parts intended for assistance are
used as the input
Note 1 to entry: Biological input and kinematic input are mutually exclusive.
3.8.3
command input
any input method other than biological input or kinematic input
Note 1 to entry: Command input includes the use of commanding devices, breath switches or voice input.
Note 2 to entry: Command input includes the use of biological signals that are not in correlation to the force or
torque the user exerts at the body part intended for assistance.
Note 3 to entry: Command input includes movement and/or posture of the user’s body parts not intended for
assistance.
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ISO 18646-4:2021(E)

3.9
assistive torque index
ATI
measure of how much the output torque of the user is reduced when the user performs a specific
movement during a specific time range using the lower-back support robot
Note 1 to entry: ATI is an absolute quantity with respect to the average torque during the specific time period of
a specific test motion profile. It can be helpful for the relative comparison between robots.
3.10
lumbar compression reduction
LCR
measure of how much the compressive force on the user’s lumbar disks is reduced when the user
performs a specific movement during a specific time range using the lower-back support robot
3.11
normal operating conditions
range of environmental conditions and other parameters which can influence robot performance (such
as electrical supply instability, electromagnetic fields) within which the performance of the robot
specified by the manufacturer is valid
Note 1 to entry: Environmental conditions include, for example, temperature and humidity.
[SOURCE: ISO 8373:2012, 6.1]
3.12
rate of assistance
measure of the reduced torque by a lower-back support robot integrated over the time period of a
specific test motion profile
Note 1 to entry: Rate of assistance is a normalized quantity with respect to the integrated torque over the time
period of a specific test motion profile. It can be helpful for the relative comparison for different test motion
profiles within the robot.
4 Test conditions
4.1 General
The lower-back support robot shall be completely assembled, sufficiently charged and operational. All
self-diagnostic tests shall be satisfactorily completed. It should also be ensured that the robot operates
in a safe manner throughout the test.
The tests shall be preceded by the preparations for operation as specified by the manufacturer,
including calibration of any relevant sensors that effect on the test results.
All conditions specified in Clause 4 should be satisfied for the tests described in this document, unless it
is stated otherwise in the specific clauses.
Each test described in Clause 5 and Clause 6 of this document have different test configurations which
require separate test apparatuses and test procedures.
4.2 Environmental conditions
The following environmental conditions shall be maintained during all tests.
— Ambient temperature: 10 °C to 30 °C
— Relative humidity: 0 % to 80 %
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ISO 18646-4:2021(E)

If the environmental conditions specified by the manufacturer are outside the given conditions, then
this shall be declared in the test results.
4.3 Operating conditions
All performance shall be measured under normal operating conditions. When the performance is
measured under conditions outside the normal operating conditions, these conditions shall be specified
along with the test results.
5 Test method for assistive torque index and lumbar compression reduction
5.1 Purpose
This clause describes the method of specifying and evaluating the performance of lower-back support
robots.
NOTE Theoretical backgrounds and validation experiments are provided in Reference [6] which provides a
rationale of focusing only on bending torques and compression forces. At the current stage of the market, there
are only the products that are intended to assist sagittal movement. To keep the test apparatus and test method
simple, the limitation of the test method is considered acceptable to measure a representative performance of
the robots.
5.2 Relevant characteristics
5.2.1 General
Two performance indices are introduced for this test method: Assistive torque index (ATI) and Lumbar
compression reduction (LCR).
By the assistive torque of the robot, the user’s extension force of hip joints and that of the trunk will
be reduced, and then the compressive force on lumbar disks will be reduced. Ideally, the lumbar
compression can be derived from the extension torque of hip joints and the posture of the trunk.
The extension torque can be reduced by the assistive torque of the robot. For the robot with such
characteristics, the lumbar compression does not need to be measured because it can be inferred from
the assistive torque and the posture of trunk.
For some robots for which lumbar compression could be increased because of the robot’s mechanical
structure, mass and mass distribution above the lumbar joint and/or actuation method (e.g. artificial
muscles on user’s back skin), lumbar compression should be measured together with assistive torque.
NOTE According to Reference [1], compressive force on lumbar disks can be the major cause of back injury
and, therefore, often used as an index to estimate the risk of back injury. Based on this background, LCR is
introduced as a performance indication of the robot.
5.2.2 Assistive torque index (ATI)
Lower Lower Hold
The Assistive Torque Index (ATI) consists of 5 representative values, ATI , ATI , ATI ,
1 000 200 1 000
Raise Raise
ATI and ATI , which are calculated by the following formulae with t and t specified in
1 000 200 1 2
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ISO 18646-4:2021(E)

Table 1. The superscript and the subscript of ATI indicate a phase of reference movement and a time
duration in milliseconds, respectively.
t
2
1
ref
ATI = ψτ ()tt, τ () dt
()
tt−
∫
21
tt−
21
t
1
where
 αβ−≥if α 0

ψ αβ, = ,
()

−−αβ if α < 0
()

ref
is the actual output torque of the hip joints of the test apparatus (see 5.3.1) during the
τ t
()
reference movements (without robot);
τ ()t is the actual output torque of the hip joints of the test apparatus (see 5.3.1) during the
reference movements (with robot).
NOTE 1 In general, the assistive torque of a robot interferes with the duration of the movement and the
necessary force or torque of the user. This is a source of instability of the test results. Therefore, this document
adopts a time average within a specific time range during the reference movements.
ref
NOTE 2 As the reference movements defined in 5.3.2 are antigravity movements, τ ()t is expected to be
always negative and the relationship ψ ()αβ, =−()αβ− always applies. However, this document defines ψ in
a more general form to make ψ positive when the necessary torque for the reference movement and the torque
of the robot are in the same direction. See Annex A.
NOTE 3 When ψ is positive, the torque of the robot in the antigravity direction (extension) can reduce the
necessary torque of the user to achieve the reference movements. Or, in some cases, the user has to output the
torque in the gravity direction (flexion) to resist the torque of the robot. Whenψ is negative, the torque of the
robot in the gravity direction (flexion) can increase the necessary torque of the user to achieve the reference
movements. See Annex A.
5.2.3 Lumbar compression reduction (LCR)
Lower Lower
The Lumbar Compression Reduction (LCR) consists of 5 representative values LCR , LCR ,
1 000 200
Hold Raise Raise
LCR , LCR and LCR , which are calculated by the following formulae with t and t
1 000 1 000 200 1 2
specified in Table 1. The superscript and the subscript of LCR indicate a phase of reference movement
and a time duration in milliseconds, respectively.
t
2
1
ref
LCR = ψ Ft() , Ft() dt
()
tt−
21 ∫
tt−
21
t
1
where
 αβ−≥if α 0

ψ ()αβ, = ,

−−()αβ if α < 0

refref ref
Ft()=φ Mt() +Ft() ,
()
yz
Ft()=φ Mt() +Ft() ,
()
yz
 γγ/,0050if ≥

φγ = ,
()

−<γγ/,01 if 0

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ISO 18646-4:2021(E)

ref
is the actual lumbar compressive force of the test apparatus in z-axis direction during
Ft
()
z
the reference movements (without robot);
Ft()
is the actual lumbar compressive force of the test apparatus in z-axis direction during
z
the reference movements (with robot);
ref
is the actual lumbar bending moment of the test apparatus around y-axis during the
Mt()
y
reference movements (without robot);
Mt
() is the actual lumbar bending moment of the test apparatus around y-axis during the
y
reference movements (with robot).
The axes of the coordinate system are shown in Figure 1.
NOTE 1 In general, assistive torque of a robot interferes the duration of the movement and the compressive
force on the lumbar disks of the user. This is a source of instability of the test results. Therefore, this document
adopts a time average within a specific time range during the reference movements.
NOTE 2 A human would stiffen his/her muscles to resist the change of posture by the lumbar bending moment
around the y-axis. This tension of the muscles is known as a source of compressive force on lumbar disks. In
contrast, the trunk of the test apparatus does not have muscles and its mechanical structure does not allow any
change of posture. To compensate for this difference, the formula for LCR uses the corrected lumbar compressive
ref ref
force Ft() and Ft() under the assumption that Mt() and Mt() are all supported by virtual erector
y y
spinae muscles and virtual abdominal rectus muscles. This document adopts a 0,05 m moment arm from the L5/
S1 lumbar disk to the virtual erector spinae muscles and a 0,1 m moment arm to the virtual abdominal rectus
[4][5]
muscles .
NOTE 3 During the reference movement, the weight of the upper body of the test apparatus is expected to
always compress the fixed lumbar joint and ψ ()αβ, =−αβ always applies. However, this document defines
ψ in a more general form to be applicable to tensile forces and to be consistent with the formula for ATI.
NOTE 4 When ψ is positive, the lumbar stress of the user is expected to be reduced during the reference
movement. When ψ is negative, the lumbar stress of the user is expected to be increased during the reference
movement.
Table 1 — Time range to calculate ATI and LCR
Reference move-
b b a a
ATI LCR t t
1 2
ments
Lower Lower
c c
Lowering t −1 [s] t [s]
ATI LCR
d d
1 000 1 000
Lower Lower c c
Lowering t −02, [s] t [s]
ATI LCR
d d
200 200
t t
Hold Hold d d
Holding
ATI LCR −05, +05,
1 000 1 000 [s] [s]
2 2
a
t and t define a time range when the necessary torque of the user and the lumbar stress are the largest assuming
1 2
the beginning time of each reference movement is 0 (see Annex A). Because the angle trajectories of the reference movement
are increasing or decreasing monotonically, ATI and LCR can be considered as an average within a specific angle range.
However, because 1) assistive torque can generate varying angle trajectories; 2) it is difficult to define the relevant angle
ranges of the trunk, the hip joint and the knee joint simultaneously; and 3) the amount of data points for calculating the
average can vary, this document adopts a time average to define ATI and LCR.
Lower Hold Raise Lower Hold Raise
b
ATI and LCR with a 1 s average ( ATI , ATI , ATI , LCR , LCR and LCR ) can also be
1 000 1 000 1 000 1 000 1 000 1 000
considered as an indication whether the robot can output assistive torque and reduce the lumbar stress continuously. On
Lower Raise Lower Raise
the other hand, ATI and LCR with a 0,2 s average (ATI , ATI , LCR and LCR ) can be an indication of
200 200 200 200
how much the robot can reduce the peak of necessary torque and the compressive force on the lumbar disks responsively
(see Annex A). This is due to the fact that they only focus on a short time range. This document adopts a 0,2 s response time
[3][9]
for humans to reflect the reaction to sudden load on lumbar spinal cord .
c
t is the actual duration of the reference movement.
d
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ISO 18646-4:2021(E)

Table 1 (continued)
Reference move-
b b a a
t t
ATI LCR
1 2
ments
Raise Raise
Raising 0 s 1 s
ATI LCR
1 000 1 000
Raise Raise
Raising 0 s 0,2 s
ATI LCR
200 200
a
t and t define a time range when the necessary torque of the user and the lumbar stress are the largest assuming
1 2
the beginning time of each reference movement is 0 (see Annex A). Because the angle trajectories of the reference movement
are increasing or decreasing monotonically, ATI and LCR can be considered as an average within a specific angle range.
However, because 1) assistive torque can generate varying angle trajectories; 2) it is difficult to define the relevant angle
ranges of the trunk, the hip joint and the knee joint simultaneously; and 3) the amount of data points for calculating the
average can vary, this document adopts a time average to define ATI and LCR.
Lower Hold Raise Lower Hold Raise
b
ATI and LCR with a 1 s average ( ATI , ATI , ATI , LCR , LCR and LCR ) can also be
1 000 1 000 1 000 1 000 1 000 1 000
considered as an indication whether the robot can output assistive torque and reduce the lumbar stress continuously. On
Lower Raise Lower Raise
the other hand, ATI and LCR with a 0,2 s average (ATI , ATI , LCR and LCR ) can be an indication of
200 200 200 200
how much the robot can reduce the peak of necessary torque and the compressive force on the lumbar disks responsively
(see Annex A). This is due to the fact that they only focus on a short time range. This document adopts a 0,2 s response time
[3][9]
for humans to reflect the reaction to sudden load on lumbar spinal cord .
c
t is the actual duration of the reference movement.
d
5.3 Test facility
5.3.1 Test apparatus
A test facility shall include a test apparatus which has a linked and actuated mechanism simulating
a human user on which a robot is attached and tested. The robot is not included in the test facility.
The ratios of its dimensions and the distribution of its mass shall comply with Figure 1. In this figure,
the height and mass of a representative user specified by the manufacturer are set as 100 %. The
manufacturer may determine all other values not indicated in Figure 1. If the manufacturer determines
other values of ratio of height and mass are appropriate, they may be applied.
The compressive force to the lumbar z-axis and the bending moment around the lumbar y-axis are
measured at the f
...