U.S. patent application number 16/495364 was filed with the patent office on 2020-05-14 for measuring apparatus counterbalance.
This patent application is currently assigned to RENISHAW PLC. The applicant listed for this patent is RENISHAW PLC. Invention is credited to Christian BROWN, Hugo George DERRICK.
Application Number | 20200149859 16/495364 |
Document ID | / |
Family ID | 58606203 |
Filed Date | 2020-05-14 |
United States Patent
Application |
20200149859 |
Kind Code |
A1 |
BROWN; Christian ; et
al. |
May 14, 2020 |
MEASURING APPARATUS COUNTERBALANCE
Abstract
A positioning apparatus including a quill on which a probe
apparatus can be mounted, at least one motor for positioning the
quill in a substantially vertical dimension, and a pneumatic
counterbalance mechanism for the quill. The positioning apparatus
is configured, based on at least one factor relating to the quill,
to automatically effect a change in the pneumatic counterbalance
mechanism's pressure so as to thereby adapt the counterbalance
force on the quill provided by the pneumatic counterbalance
mechanism.
Inventors: |
BROWN; Christian;
(Wotton-under-Edge, GB) ; DERRICK; Hugo George;
(Stroud, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
RENISHAW PLC |
Wotton-under-Edge, Gloucestershire |
|
GB |
|
|
Assignee: |
RENISHAW PLC
Wotton-under-Edge, Gloucestershire
GB
|
Family ID: |
58606203 |
Appl. No.: |
16/495364 |
Filed: |
April 17, 2018 |
PCT Filed: |
April 17, 2018 |
PCT NO: |
PCT/GB2018/050994 |
371 Date: |
September 18, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01B 5/012 20130101;
G01B 5/008 20130101; G01B 5/0016 20130101; G01B 21/047 20130101;
G01B 21/045 20130101 |
International
Class: |
G01B 5/00 20060101
G01B005/00; G01B 5/012 20060101 G01B005/012; G01B 21/04 20060101
G01B021/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 19, 2017 |
EP |
17275051.5 |
Claims
1. A positioning apparatus comprising a quill on which a probe
apparatus can be mounted, at least one motor for positioning the
quill in a substantially vertical dimension, and a pneumatic
counterbalance mechanism for the quill, in which the positioning
apparatus is configured, based on at least one factor relating to
the quill, to automatically effect a change in the pneumatic
counterbalance mechanism's pressure so as to thereby adapt the
counterbalance force on the quill provided by the pneumatic
counterbalance mechanism.
2. A positioning apparatus as claimed in claim 1, in which the at
least one motor comprises a direct drive motor, optionally a linear
motor.
3. A positioning apparatus as claimed in claim 1, in which the at
least one factor relates to the actual or expected vertical
position of the quill.
4. A positioning apparatus as claimed in claim 1, further
comprising one or more position encoders for measuring the vertical
position of the quill, and in which the at least one factor
comprises the output from at least one of said one or more position
encoders.
5. A positioning apparatus as claimed in claim 1, in which the at
least one factor relates to the actual or expected power
requirement of the at least one motor.
6. A positioning apparatus as claimed in claim 1, in which the at
least one factor relates to the actual or expected direction of
travel of the quill.
7. A positioning apparatus as claimed in claim 6, configured to
adapt the pneumatic counterbalance mechanism's pressure so as to
assist the motor in moving the quill in the direction of
travel.
8. A positioning apparatus as claimed in claim 1, in which the at
least one factor relates to at least one module loaded or to be
loaded on the quill.
9. A positioning apparatus as claimed in claim 8, in which the at
least one factor relates to the weight of the at least one
module.
10. A positioning apparatus as claimed in claim 8, in which the at
least one factor is determined by assessing the effect the module
loaded on the quill has on the coordinate positioning
apparatus.
11. A positioning apparatus as claimed in claim 1, comprising a
pressure regulator which is configured to maintain the pneumatic
counterbalance mechanism's pressure at a set pressure, and in which
the apparatus is configured to alter the set pressure based on the
at least one factor.
12. A positioning apparatus as claimed in claim 1, in which the
change in the pneumatic counterbalance mechanism's pressure is
determined from a look-up table and/or function.
13. A positioning apparatus as claimed in claim 1, configured to
automatically adapt the pneumatic counterbalance mechanism's
pressure in response to an expected or measured change in the load
on the quill.
14. A positioning apparatus as claimed in claim 1, in which the
positioning apparatus comprises a Cartesian coordinate positioning
apparatus.
15. A method of operating a positioning apparatus comprising a
quill on which a probe apparatus can be mounted, at least one motor
for moving the quill in a substantially vertical dimension, a
pneumatic counterbalance mechanism for the quill, the method
comprising automatically effecting a change in the pneumatic
counterbalance mechanism's pressure so as to thereby adapt the
counterbalance force on the quill provided by the pneumatic
counterbalance mechanism, based on the quill's status.
16. A positioning apparatus, comprising: first and second members
relatively moveable in a substantially vertical degree of freedom,
in which an energy conduit is connected to at least one of the
first and second members, wherein the load, in the degree of
freedom of the first and second members, imparted by the energy
conduit on at least one of the members it is connected to varies
dependent on the relative position of the first and second members,
and further comprising a pneumatic counterbalance configured to
apply a load, in the degree of freedom of the first and second
members, that varies, dependent on the relative position of the
first and second members, inversely to the load applied by the
energy conduit, such variation in load being achieved by varying
the air pressure of the pneumatic counterbalance.
Description
[0001] This invention relates to a counterbalance for a positioning
apparatus such as a coordinate measuring machine (CMM). In
particular, the invention relates to a counterbalance for the quill
of a Cartesian coordinate positioning apparatus,
[0002] Positioning apparatus can comprise one or more moveable
members for positioning a tool and/or an object relative to each
other. For example, a CMM traditionally comprises a plurality of
moveable members, e.g. linearly moveable members arranged in
series. Generally, positioning apparatus are configured to
facilitate relative motion of a tool and/or object in at least two
or three mutually orthogonal dimensions, e.g. X, Y and Z. Such
positioning apparatus are commonly known as "Cartesian" positioning
apparatus (or Cartesian CMM). Typical Cartesian coordinate
positioning apparatus include Bridge, Portal, Cantilever,
Horizontal Arm, and Gantry type machines.
[0003] Often, the tool is mounted on a vertically moveable member.
This member is typically known as a "quill", but is also known as
z-ram or z-axis. As will be understood, the tool could be mounted
directly to the quill, or via another member, such as an
articulated head member which enables the tool to be repositioned
about one or more rotational axes.
[0004] In order to reduce the requirements on the motor, it is
known to provide a counterbalance mechanism for counterbalancing
the weight of the quill. An example of such a counterbalance
mechanism for a quill is described in U.S. Pat. Nos. 3,818,596 and
6,397,485. It is also known to provide pneumatic counterbalance
mechanisms, for example as described in DE4408912, US875594, U.S.
Pat. Nos. 4,389,781, 4,507,868, 4,799,316, 4,213,244 and
4,207,680.
[0005] The present invention relates to an improved pneumatic
counterbalance system for a quill of a positioning apparatus.
[0006] According to a first aspect of the invention there is
provided a positioning apparatus comprising a quill on which a
probe apparatus can be mounted, at least one motor for positioning
the quill in a substantially vertical dimension, and a pneumatic
counterbalance mechanism for the quill. The positioning apparatus
can be configured, on the basis of at least one factor relating to
the quill, to automatically effect (i.e. cause/bring about) a
change in the pneumatic counterbalance mechanism's pressure. Such a
change in the pneumatic counterbalance mechanism's pressure could
adapt the counterbalance force on the quill provided by the
pneumatic counterbalance mechanism. Accordingly, the positioning
apparatus of the present invention can be configured to
automatically effect/cause a change in the pneumatic counterbalance
mechanism's pressure so as to at least partially (and optionally
substantially) compensate for any assumed/expected or
actual/measured change quill circumstance, e.g. to compensate for
any assumed/expected or actual/measured change in load on the
quill, in the substantially vertical dimension.
[0007] The present invention has been found to improve the
performance of the positioning apparatus, for example its
metrological performance. In particular, automatically changing the
pneumatic counterbalance mechanism's pressure can reduce variation
in the power required of the motor for positioning (e.g. moving
and/or holding) the quill in the substantially vertical dimension.
This in turn can reduce variations in heat produced by the motor.
Reducing variations in heat produced by the motor can improve the
metrological performance of the positioning apparatus. As explained
in more detail, the present invention can be used to automatically
change the pneumatic counterbalance mechanism's pressure depending
on a variety quill factors/circumstances, including, for example,
the (expected/assumed or actual/measured) vertical position of the
quill, the (expected/assumed or actual/measured) direction of
travel of the quill in a vertical dimension, what module(s), such
as a probe, is or are to be mounted on the quill, the quill's motor
power requirement (e.g. expected/assumed or actual/measured),
and/or a particular operation performed by the apparatus/quill
(e.g. such as loading or unloading a probe to/from the quill). In
summary, the present invention can be used to automatically change
the pneumatic counterbalance mechanism's pressure depending on the
expected/assumed or actual/measured load, current or future, on the
quill.
[0008] As will be understood, the counterbalance mechanism can be
configured to partially counterbalance the load on the quill.
Optionally, the counterbalance mechanism can be configured to
substantially counterbalance the load on the quill. Either way,
preferably the apparatus is configured, based on the at least one
factor relating to the quill, to automatically cause a change in
the pneumatic pressure of the pneumatic counterbalance mechanism,
so as to adapt the counterbalance force on the quill, e.g. so as to
reduce (and for example to avoid substantial) variations in the
power required by the motor (i.e. reduce compared to what would
otherwise be required if the change in pressure is not made). For
instance, the invention can be used to reduce (and for example to
avoid substantial) variations in the power required by the motor to
hold the quill at different vertical positions, and/or to reduce
(and for example to avoid substantial) variations in the power
required by the motor to hold the quill at any given vertical
position but with different modules loaded thereon, and/or to
reduce (and for example to avoid substantial) variations in the
power required by the motor depending on whether the quill is being
moved either up or down.
[0009] As will be understood, the pneumatic counterbalance
mechanism could comprise a cylinder and associated piston.
Pressurised gas (e.g. gas above atmospheric pressure) could act on
the cylinder and/or piston in order to provide a counterbalance
force. The cylinder and/or piston may or may not be provided by the
quill (e.g. inside or on the quill). For example, the cylinder
and/or piston may be provided separately and attached to the quill,
e.g. via wire/cord, pulling system, rod or other linking
mechanism/means.
[0010] The positioning apparatus could comprise a counterbalance
controller. This could comprise a system. The positioning apparatus
(for example the counterbalance controller) could for example be
configured to monitor one or more aspects/factors/inputs regarding
the quill. The positioning apparatus (for example the
counterbalance controller) could be configured to automatically
control the counterbalancing effect of the counterbalance mechanism
on the quill based on said monitoring. The positioning apparatus
(for example the counterbalance controller) could be configured to
continuously monitor the aspect(s)/factor(s)/input(s) regarding the
quill and control/adapt the pneumatic pressure of the pneumatic
counterbalance mechanism instantaneously. Optionally the
positioning apparatus (for example the counterbalance controller)
is configured to control/adapt the pneumatic pressure of the
pneumatic counterbalance mechanism at intervals, e.g. regular
intervals and/or at predetermined instances (such as when changing
a probe). The positioning apparatus (for example the counterbalance
controller) could be configured to receive at least one input
regarding the quill (e.g. its status) and be configured to
automatically effect/cause said change in the pneumatic
counterbalance mechanism's pressure. The positioning apparatus (for
example the counterbalance controller) could be configured to
monitor (or respond to) the input continuously or could be
configured to monitor (or respond to) the input at intervals (e.g.
at regular intervals and/or at predetermined instances).
[0011] The positioning apparatus could comprise at least one energy
conduit connected/mounted to the quill. As will be understood, an
energy conduit can comprise one or more wires and/or pipes (e.g.
fluid lines), for supplying power, carrying signals and/or fluid to
and/or from various parts of the apparatus. An energy conduit can
comprise at least one wire and/or at least one pipe. An energy
conduit can comprise at least one group/bunch of wires and/or
pipes. The energy conduit could comprise a mix of wires and pipes.
The wires and/or pipes could be tied together, e.g. using cable
ties. An energy conduit can comprise a support track, e.g. for
supporting at least one cable and/or at least one pipe. The support
track could comprise an articulated support track. For example, an
articulated support track could comprise a chained arrangement of
pivotally connected links. Optionally, the support track could
comprise a band of material which bends with the relative movement
(e.g. comprise a continuous ribbon-like band of material).
[0012] The load/force in the substantially vertical dimension
imparted by an energy conduit on the quill could vary dependent on
the vertical position of the quill (e.g. due to the proportion of
the energy conduit's mass which the quill carries varying with
position). Accordingly, the positioning apparatus could be
configured to effect/cause a change in the pressure of the
pneumatic counterbalance mechanism so as to compensate for said
change in load imparted by the at least one energy conduit on the
quill.
[0013] As will be understood, the pneumatic counterbalance
mechanism could be considered to be an active compensatory member
e.g. which compensates at least partially for any (e.g. varying)
load on the quill (e.g. in the vertical dimension). For example,
the pneumatic counterbalance mechanism/compensatory member could be
part of a system (e.g. which can comprise the counterbalance
controller) which monitors at least one (e.g. system)
input/variable (e.g. load applied to the quill, position of the
quill, and/or direction of motion of the quill) and adapt/change
the load the pneumatic counterbalance mechanism/compensatory member
applies so as to at least partially counteract any change in load
applied (e.g. applied by an energy conduit). Accordingly, the
pneumatic counterbalance mechanism/compensatory member could be
part of a servo system, which controls the pneumatic counterbalance
mechanism/compensatory member in response to an input. The
positioning apparatus could be configured to (e.g. dynamically)
vary the counterbalance force provided by the pneumatic
counterbalance mechanism in response to at least one input/variable
(e.g. load applied on the quill, and/or position of the quill). For
example, the positioning apparatus could be configured to (e.g.
dynamically) vary the air pressure of the pneumatic counterbalance
mechanism in response to at least one factor/input/variable (e.g.
load applied on the quill, and/or position of the quill).
[0014] The positioning apparatus (e.g. the counterbalance
controller) can be configured to determine how to change the
pneumatic counterbalance mechanism's pressure.
[0015] As will be understood, the positioning apparatus (e.g. the
counterbalance controller) can comprise a device. As will be
understood, the device could comprise circuitry, such as any or a
combination of a processor, microprocessor, central processing
unit, field-programmable gate array (fpga), and memory/storage,
which is configured, based on at least one factor relating to the
quill, to automatically effect a change in the pneumatic
counterbalance mechanism's pressure. As will be understood, the
invention could be implemented at least partly in software, for
example running on such a device. That is, the positioning
apparatus could comprise software which is configured, based on at
least one factor relating to the quill, to automatically effect a
change in the pneumatic counterbalance mechanism's pressure.
[0016] The positioning apparatus could comprise a controller for
controlling the position of the quill. For example, the controller
could be configured to execute a computer program and control the
at least one motor in accordance with the computer program (e.g. by
controlling a motor power amplifier, optionally in conjuction with
quill position information, such as from a position encoder).
Optionally, the controller is configured to automatically effect
said change in the pneumatic counterbalance mechanism's pressure
based on said at least one factor relating to the quill. For
example, optionally, the controller comprises the aforementioned
counterbalance controller.
[0017] The at least one motor could comprise a direct drive motor.
Optionally the at least one motor comprises a linear motor. It has
been found that the invention is particularly useful in overcoming
metrology problems caused by heating of direct drive motors, and in
particular linear motors. Optionally, the linear motor comprises an
elongate linear stator and an armature. Optionally, the armature is
mounted to the quill.
[0018] The at least one factor (e.g. aspect/input) can relate to
the actual or expected vertical position of the quill. The expected
position could be a position that the quill is expected or assumed
to be at. Such an expected position could, for example, be derived
from a computer program (such as an inspection program or a
calibration program, for example) being used to control the
positioning apparatus (e.g. so as to inspect an artefact or
calibrate the positioning apparatus or a sensor mounted thereon).
The actual position of the quill could be the position the quill is
measured to be at. For example, the actual position could be
determined from one or more sensors, e.g. mounted on the
positioning apparatus. For example, a sensor could comprise an
accelerometer or a position encoder, e.g. a linear position
encoder. For example, the actual vertical position of the quill
could be determined via a readhead mounted on one part of the
positioning apparatus reading a scale mounted on another part of
the positioning apparatus. Optionally, the scale is mounted on the
quill. Accordingly, the apparatus could comprise one or more
position encoders for measuring the vertical position of the quill.
The at least one factor (e.g. aspect/input) can comprise the output
from at least one of said one or more position encoders.
[0019] As will be understood, the positioning apparatus (e.g. the
counterbalance controller) may or may not determine how to change
the pneumatic counterbalance mechanism's pressure based on the
current/present (e.g. instantaneous) position of the quill (which
could be expected/assumed or actual/measured). For example, it
could do so based on an expected (e.g. near) future position of the
quill. For example, it could predict or determine the future
position of the quill and based thereon change the counterbalance
mechanism's pressure (e.g. slightly) in advance.
[0020] The at least one factor (e.g. aspect/input) can relate to
the actual/measured or expected/assumed power requirement of the at
least one motor. Such an expected power requirement could, for
example, be derived from a computer program (such as an inspection
program or a calibration program, for example) being used to
control the positioning apparatus (e.g. so as to inspect an
artefact or calibrate the positioning apparatus or a sensor mounted
thereon). The actual power requirement could be determined, for
example from a motor power amplifier used to power the motor. The
at least one factor (e.g. aspect/input) can relate to the
current/present (e.g. instantaneous) power requirement of the at
least one motor. As will be understood, the positioning apparatus
(e.g. the counterbalance controller) may or may not determine how
to change the pneumatic counterbalance mechanism's pressure based
on the current/present (e.g. instantaneous) power requirement of
the at least one motor. For example, it could do so based on an
expected (e.g. near) future power requirement of the at least one
motor. For example, it could predict or determine the future power
requirement of the at least one motor and based thereon change the
counterbalance mechanism's pressure (e.g. slightly) in advance.
[0021] The at least one factor (e.g. aspect/input) can relate to
the actual or expected direction of travel of the quill. Such an
expected direction of travel could, for example, be derived from a
computer program (such as an inspection program or a calibration
program, for example) being used to control the positioning
apparatus (e.g. so as to inspect an artefact or calibrate the
positioning apparatus or a sensor mounted thereon). The actual
direction of travel could be determined, for example, from one or
more sensors, such as an accelerometer or position encoder, e.g. a
linear position encoder. As will be understood, the positioning
apparatus (e.g. the counterbalance controller) may or may not
determine how to change the pneumatic counterbalance mechanism's
pressure based on the current/present (e.g. instantaneous)
direction of travel. For example, it could do so based on an
expected (e.g. near) future direction of travel. For example, it
could predict or determine the direction of travel and based
thereon change the counterbalance mechanism's pressure (e.g.
slightly) in advance.
[0022] Accordingly, in accordance with the above embodiments, the
positioning apparatus could be configured to change the pneumatic
counterbalance mechanism's pressure based on a (expected) future
quill load/status. For example, it could predict or determine the
future quill load/status and based thereon cause a change the
counterbalance mechanism's pressure (e.g. slightly) in advance.
[0023] The positioning apparatus (e.g. the counterbalance
controller) could be configured to adapt the pneumatic
counterbalance mechanism's pressure so as to assist the motor in
moving the quill in the direction of travel.
[0024] The at least one factor (e.g. aspect/input) can relate to at
least one module, such as a probe, loaded or to be loaded on the
quill. The at least one factor (e.g. aspect/input) can relate to
the weight (or mass) of the at least one module loaded or to be
loaded on the quill. The at least one factor (e.g. aspect/input)
relating to the at least one module could, for example, be a
predetermined factor (e.g. aspect/input) associated with the module
loaded or to be loaded on the quill. For example, the at least one
factor (e.g. aspect/input) could be a module identifier. In such a
case, the unique module identifier could be used to look up the
weight of the module for example. Optionally, the predetermined
factor (e.g. aspect/input) associated with the module loaded or to
be loaded on the quill could comprise a value (e.g. the weight of
the probe) or setting which can be used to determine how to control
the pneumatic counterbalance mechanism's pressure.
[0025] Optionally, the at least one factor (e.g. aspect/input) can
be determined by the assessing the effect the module loaded on the
quill has on the positioning apparatus. Optionally, the at least
one factor (e.g. aspect/input) can be determined by controlling the
apparatus (e.g. the quill) in a predetermined manner and monitoring
how the apparatus (e.g. the quill) behaves. For example, the at
least one factor (e.g. aspect/input) could be determined by
determining the motor power required to hold the quill in a
stationary vertical position. For example, this can comprise moving
the quill with a given force, and measuring its acceleration.
Alternatively, this can comprise moving the quill up and/or down
and determining the power requirement for such motion.
[0026] The positioning apparatus (e.g. the counterbalance
controller) could be configured such that the pneumatic
counterbalance mechanism's pressure is set to be maintained at a
given (e.g. set/target) pressure. For example, the positioning
apparatus (e.g. the pneumatic counterbalance mechanism) can
comprise a pressure regulator which is configured to maintain the
pneumatic counterbalance mechanism's pressure at a set pressure.
The positioning apparatus (e.g. the counterbalance controller)
could be configured to alter the set pressure based on the at least
one factor (e.g. aspect/input). As will be understood, another term
for a pressure regulator is an air regulator or gas regulator. As
will also be understood, the pressure regulator could be a digital
regulator.
[0027] Optionally, the change in the pneumatic counterbalance
mechanism's pressure is determined from a look-up table and/or
function. For example, the positioning apparatus (e.g. the
counterbalance controller) could be configured to refer to a
look-up table and/or function to determine the change in the
pneumatic counterbalance mechanism's pressure. For example, the
apparatus (e.g. the counterbalance controller) could be configured
to refer to a look-up table and/or function to determine at least
one parameter related to the pneumatic counterbalance mechanism's
pressure and/or counterbalance force to be applied based on at
least one factor relating to the quill (e.g. such as the
expected/assumed or actual/measured position of the quill). It
might be that the pneumatic counterbalance mechanism's pressure
and/or counterbalance force to be applied does not vary linearly
with the vertical position of the quill. Such a look-up table or
function could be machine specific. Such a look-up table or
function could be determined via a calibration routine. Such a
look-up table or function could be specific to the module loaded on
the quill.
[0028] Accordingly, as described, the positioning apparatus (e.g.
the counterbalance controller) could be configured to automatically
adapt the counterbalancing force of the counterbalance mechanism on
the quill in response to an assumed/expected or actual/measured
change in the load on the quill. This could be so as to at least
partially (and optionally substantially) compensate for any
assumed/expected or actual/measured change in load.
[0029] The positioning apparatus could comprise a Cartesian
coordinate positioning apparatus. The positioning apparatus could
be a coordinate positioning apparatus, for example a coordinate
measuring machine (CMM), for example a Cartesian CMM.
[0030] According to a second aspect of the invention there is
provided a method of operating a positioning apparatus comprising a
quill on which a probe apparatus can be mounted, at least one motor
for moving the quill in a substantially vertical dimension, a
pneumatic counterbalance mechanism for the quill, the method
comprising automatically effecting a change in the pneumatic
counterbalance mechanism's pressure so as to thereby adapt the
counterbalance force on the quill provided by the pneumatic
counterbalance mechanism, based on the quill's status.
[0031] This application also describes positioning apparatus,
comprising: first and second members relatively moveable in a
substantially vertical degree of freedom (e.g. for effecting
relative movement of an inspection device and a workpiece in said
vertical degree of freedom). A (first) energy conduit is
connected/mounted to at least one of the first and second members.
The load/force (in the degree of freedom of the first and second
members) imparted by the (first) energy conduit on at least one of
the members it is connected/mounted to could vary dependent on the
relative position of the first and second members. There can also
be provided a compensatory member (e.g. a pneumatic counterbalance
mechanism) configured to apply a load/force (in the degree of
freedom of the first and second members) that varies dependent on
the relative position of the first and second members inversely to
the load applied by the (first) energy conduit, so as to at least
partially counteract the change in load applied by the (first)
energy conduit on said at least one of the members.
[0032] As will be understood, the compensatory member could
comprise an active system. For example, the compensatory member
could be part of a system which monitors at least one (e.g. system)
input/variable (e.g. load applied the first and/or second member,
and/or position of the first and/or second member) and adapt/change
the load the compensatory member applies so as to at least
partially counteract any change in load applied by the energy
conduit. Accordingly, the compensatory member could be part of a
servo system, which controls the compensatory member in response to
an input. The compensatory member could comprise a counterbalance
mechanism for the member (e.g. the quill) to which the energy
conduit is connected/mounted, for instance a pneumatic
counterbalance. The apparatus could be configured to (e.g.
dynamically) vary the counterbalance force provided by the
counterbalance in response to at least one input/variable (e.g.
load applied on the first and/or second member, and/or position of
the first and/or second member). For example, the apparatus could
be configured to (e.g. dynamically) vary the air pressure of the
pneumatic counterbalance in response to at least one input/variable
(e.g. load applied on the first and/or second member, and/or
position of the first and/or second member).
[0033] The compensatory member could be configured such that the
load it applies (in the degree of freedom of the first and second
members) varies substantially equally and oppositely to the
variation in load applied by the (first) energy conduit.
Accordingly, the compensatory member could be configured such that
the net load applied by the (first) energy conduit and compensatory
member (in the degree of freedom of the first and second members)
is substantially constant for a range of relative positions; for
example, substantially constant across at least 75% of the range of
motion of the first and second members, optionally across at least
90% of the range of motion of the first and second members.
[0034] The first and second relatively moveable members could bear
against each other. In other words, the first and second relatively
moveable members could comprise respective parts of a bearing
arrangement which cooperate so as to facilitate relative movement
between them. The bearing arrangement could comprise an air bearing
and/or mechanical bearing arrangement, for example. For instance,
one of the first and second relatively moveable members could
comprise at least one air bearing pad and the other comprise an air
bearing surface.
[0035] Optionally, the first member is moveable in the
substantially vertical degree of freedom. Optionally, the second
member is fixed/immovable in the vertical degree of freedom (e.g.
relative to the rest of the apparatus).
[0036] The (first) energy conduit could be connected/mounted to the
first and second members, e.g. at/towards a first end to the first
member and at/towards a second end to the second member.
[0037] Accordingly, this application also describes a positioning
apparatus, comprising: first and second members relatively moveable
in a substantially vertical degree of freedom (e.g. for effecting
relative movement of an inspection device and a workpiece in said
vertical degree of freedom), in which a (first) energy conduit is
connected/mounted to at least one of the first and second members,
wherein the load/force (in the degree of freedom of the first and
second members) imparted by the (first) energy conduit on at least
one of the members it is connected/mounted to varies dependent on
the relative position of the first and second members, and further
comprising a pneumatic counterbalance configured to apply a
load/force (in the degree of freedom of the first and second
members) that varies dependent on the relative position of the
first and second members inversely to the load applied by the
(first) energy conduit, e.g. by varying the air pressure of the
pneumatic counterbalance in response to at least one input/variable
(e.g. load applied on the first and/or second member, and/or
position of the first and/or second member).
[0038] There can also be provided a compensatory member (e.g. a
pneumatic counterbalance mechanism) configured to apply a
load/force (in the degree of freedom of the first and second
members) that varies dependent on the relative position of the
first and second members inversely to the load applied by the
(first) energy conduit,
[0039] Embodiments of the invention will now be described, by way
of example only, with reference to the following drawings, in
which:
[0040] FIG. 1 is a schematic isometric view of the front of a
gantry-type CMM according to a first embodiment of the present
invention;
[0041] FIG. 2 is an enlarged view of the top of the quill of the
CMM of FIG. 1;
[0042] FIG. 3 schematically shows the quill of the CMM of FIG. 1 in
cross-section, and also the possible units involved in controlling
the quill's counterbalance mechanism;
[0043] FIG. 4 is an enlarged view of the top of the quill of the
CMM of FIG. 1 according to another embodiment of the invention;
and
[0044] FIG. 5a is a graph illustrating how the counterbalance
mechanism's pneumatic pressure might vary over time during a
downward quill motion in accordance with one aspect of the
invention and FIG. 5b is a graph illustrating how the
counterbalance mechanism's pneumatic pressure might vary over time
during the same downward quill motion in a system of the art.
[0045] An overview of an example embodiment of how the invention
can be implemented will be described below. In this case, the
invention is implemented as part of a CMM 100. FIG. 1 shows a CMM
100 with its protective housings/covers (e.g. "main" covers/"hard"
covers) removed so that the relevant components of the CMM 100 can
be seen. FIG. 2 shows an enlarged view of the top end of the quill
110 of CMM 100.
[0046] As shown, a tool, for example an inspection device such as a
probe 102 for inspecting a workpiece, can be mounted on the CMM
100. In the embodiment shown, the probe 102 is a contact probe, in
particular a contact analogue scanning probe, for measuring the
workpiece by a stylus of the probe contacting the workpiece.
However, as will be understood the CMM 100 could carry any sort of
inspection device, including touch-trigger probes, non-contact
(e.g. optical) probes, or another type of instrument if
desired.
[0047] In the embodiment shown, the CMM 100 is a gantry-style
Cartesian CMM and comprises a platform 105 on which an artefact to
be inspected can be placed, and a movement system which provides
for repeatable and accurate control of the position of the probe
102 relative to the platform 105 in three orthogonal degrees of
freedom X, Y and Z.
[0048] In particular, the movement system comprises a cross-beam
106, a carriage 108, and a quill 110. The cross-beam 106 extends
between first 112 and second 114 raised rail members and is
configured to move along the rails along a Y axis via a bearing
arrangement (in this embodiment an air bearing arrangement--not
shown), and powered by a motor, such as a linear motor (not shown).
The carriage 108 sits on and is carried by the cross-beam 106, and
is moveable along the cross-beam along an X axis via a bearing
arrangement (in this embodiment an air bearing arrangement--not
shown) and powered by a motor, such as a linear motor (not shown).
The quill 110 is held by the carriage 108, and is moveable relative
to the carriage 108 along a Z axis via a bearing arrangement
(again, in this embodiment via an air bearing arrangement--not
shown), and powered by a motor, such as a linear motor. The stator
400 of the quill's linear motor is visible in FIGS. 1 and 2, but
the armature 402 (see FIG. 3) is not visible in FIGS. 1 and 2. As
will be understood, the stator 400 is fixed relative to the
carriage 108 (e.g. it can be anchored at a lower end to the
carriage 108 and at an upper end to a tower 194 which is mounted to
the carriage 108 so as to move therewith), and the armature 402 can
be fixed and mounted to the quill 110 so as to move therewith.
[0049] A pneumatic counterbalance mechanism for the quill is
provided for counterbalancing the weight of the quill 110 so as to
reduce the work required of the quill's motor. In particular, the
pneumatic counterbalance is configured to provide an opposing force
substantially equal to the weight of the quill 110 (and the
articulated head 116 and probe 102) such that substantially zero
force is required by the quill's motor to keep it at a stationary
position. The quill 110 is hollow and the pneumatic counterbalance
comprises a piston 300 within a counterbalance cylinder 302 located
inside the quill 110 (see FIG. 3). The piston 300 is anchored to a
tower 194 (in this case a carbon-fibre tube) via a cable 196. The
tower 194 is mounted to the carriage 108 so as to move therewith.
As described in more detail below, in accordance with the
invention, the apparatus is configured to adapt the pneumatic
counterbalance automatically in response to certain circumstances
so as to alter the counterbalance force provided.
[0050] As will be understood, motors, for example direct drive
motors such as linear motors, can be provided for effecting the
relative motion of the various members along their axis (of which
the stator 400 of the quill's linear motor is shown in FIGS. 1 and
2). Also, position encoders can be provided for reporting the
position of the cross-beam 106, carriage 108 and/or quill 110. The
scale 404 and readhead 406 of the quill's linear encoder are
visible in FIGS. 1 and 2. The linear motor and encoder arrangement
for driving and monitoring the position of the quill 110 is also
schematically shown and described in more detail below in
connection with FIG. 3.
[0051] In the particular example shown, an articulated head 116 is
provided on the lower free end of the quill 110 for carrying the
probe 102. In this case, the articulated head 116 comprises two
orthogonal rotational axes. Accordingly, in addition to the three
orthogonal linear degrees of freedom X, Y and Z, the probe 102 can
be moved about two orthogonal rotational axes (e.g. A and B axes).
A machine configured with such an articulated head is commonly
known as a 5-axis machine.
[0052] Articulated heads for tools and inspection devices are well
known, and for example described in WO2007/093789. As will be
understood, an articulated head need not necessarily be provided,
and for example the probe 102 could be mounted to the quill
assembly 110 via a fixed head which does not provide any rotational
degrees of freedom. Optionally, the probe itself can comprise an
articulated member so as to facilitate rotation about at least one
axis.
[0053] An energy conduit 502 is provided between the quill 110 and
the carriage 108. The energy conduit 502 comprises one or more
electrical wires and/or pipes for providing power, communications,
and/or gas, to and/or from the quill 110, the articulated probe
head 116, and the probe 102. For example, the pipe(s) could supply
gas for the quill's air bearings (not shown) and/or for the
pneumatic counterbalance. For the sake of clarity, most of the
wires and pipes are not shown in the Figures; only the pipe 420 for
supplying air to the inside of the quill 110 for the pneumatic
counterbalance mechanism is shown in FIGS. 2 and 3. In any case, in
this embodiment, in addition to the wires and pipes, the energy
conduit 502 comprises a support track 503 which flexes with
relative movement of the quill 110 and carriage 108. The support
track 503 is configured to keep the wires and pipes associated with
it tidy and to control how they flex with the relative movement of
the quill 110 and carriage 108. A first end of the support track
503 of the energy conduit 502 is connected to the carriage 108 (in
this case to the carriage's tower 194, via bracket 195), and a
second end of the support track 503 of the energy conduit 502 is
connected to the quill 110 (in this case via a bracket 198).
[0054] As is standard with measuring apparatus, a controller 118
can be provided which is in communication with the CMM's motors and
position encoders, the articulated head 116 (if present) and the
probe 102 so as to send and/or receive signals to and/or from them
so as to control the motion of the relatively moveable members as
well as receive feedback and measurement data. A computer 120, e.g.
a personal computer (which can be separate to or integrated with
the controller 118) can be provided which is in communication with
the controller 118. The computer 120 can provide a user-friendly
interface for an operator to, for example, program and initiate
measurement routines. Suitable computers and associated
control/programming software is widely available and well known.
Furthermore, a joystick 122 or other suitable input device can be
provided which enables an operator to manually control the motion
of the probe 102. Again, such joysticks are well known and widely
available.
[0055] A variety of tools/inspection devices could be stored in a
rack 450 located within the CMM's working volume. Furthermore, the
probe 102 mounted on the CMM 100 could be automatically changed
to/from the rack 450 in a known manner.
[0056] Referring now to FIG. 3, a cross-section of the CMM's quill
110 is schematically shown. As shown, a linear motor and encoder
apparatus are provided for effecting and monitoring movement of the
quill 110 along the z-axis relative to the carriage 108 (which is
not shown in FIG. 3). In particular, in this embodiment, the linear
motor comprises an elongate stator 400 fixed relative to the
carriage 108 (not shown) (in particular, the linear motor is fixed
at a bottom end to the carriage's box structure, and at a top end
to the carriage's tower 194--neither shown in FIG. 3) and an
armature 402 fixed to the quill 110. In this embodiment the encoder
comprises a scale 404 fixed to the quill 110 and a readhead 406
fixed to the carriage 108 for reading the scale. As will be
understood, the stator 400 and armature 402 could be mounted the
other way around (i.e. the armature could be mounted to the
carriage, and the stator to the quill), and likewise for the scale
404 and readhead 406.
[0057] FIG. 3 also schematically shows various parts of an example
controller 118. In particular, in this example, there is shown a
main processing unit (e.g. main processing board) 410, an encoder
interface 412, a motor power amplifier 414 and a counterbalance
controller 416. As will be understood, these various
units/interfaces/amplifiers could be provided as separate or as
combined components (e.g. on the same or different boards and/or
via the same or different processors/circuitry) and need not all be
provided in or by the controller 118 (e.g. the counterbalance
controller could be located separate from the controller 118. As
will also be understood, the circuitry for such
units/interfaces/amplifiers could comprise bespoke or generic
processor units, e.g. microprocessors, central processing units
(CPU), Field-Programmable Gate Arrays (FPGAs), or the like.
[0058] As also shown, a pressurised gas supply 418 such as a
pneumatic pump or, for example, a compressed gas supply is provided
which provides supply of pressurised gas (e.g. air) to the inside
of the quill 110, e.g. via pipe 420 (which is supported by the
support track of the energy conduit 502). The pressurised gas
inside the counterbalance cylinder 302 acts against the piston 300
and the inside walls of the counterbalance cylinder 302 so as to
provide an upwards force along the z-axis, thereby supporting at
least some (and preferably substantially all) of the weight of the
quill 110 and any components mounted thereon, such as the
articulated probe head 116 and the probe 102. The pressurised gas
supply 418 could be configured to try to maintain a set pressure
within the counterbalance cylinder 302, e.g. the apparatus, for
example the pressurised gas supply, could comprise a pressure
regulator, such as a digital pressure regulator.
[0059] According to an example embodiment, during normal use, the
controller 118 is configured to control the x, y and z axes of the
CMM 100, and for example the rotational positions of the
articulated head's 116 rotational axes. For example, this could be
in response to signals received from an input device, such as the
joystick 122 and/or computer 120. Optionally, the controller 118
(e.g. the main processing unit 410) could execute a program
comprising a predefined course of motion, and control the axes of
the CMM 100 and articulated head 116 accordingly. As shown in FIG.
3 in connection with the z-axis, the controller 118 can effect
movement of the z-axis by way of the main processing unit 410
instructing commands to the motor power amplifier 414 which in turn
powers the armature 402 so as to operate the linear motor. The
controller 118, by way of the main processing unit 410, readhead
406, encoder interface 412 and the motor power amplifier 414, can
operate to implement a servo loop, so as to ensure that the quill
110 is moving toward or at the desired position.
[0060] As briefly mentioned above, in accordance with the
invention, the apparatus is configured to adapt the pneumatic
counterbalance automatically in response to certain circumstances
so as to alter the counterbalance force it provides. This has been
found to be particularly beneficial to CMMs where a direct drive,
such as a linear motor, is used to control the z-axis position of
the quill 110. This is because the effect of the heat generated by
such motors on the metrological performance of the CMM can be more
pronounced due to direct drive, and in particular linear motors,
typically being mounted closer to the CMM's metrology structure.
Also, in contrast to other types of motors, such as ball-screw or
geared systems, which cannot be back-driven, it is often necessary
to power a direct drive/linear motor, to hold a given position
should the counterbalance mechanism not counterbalance the load on
the quill, thereby producing heat even when stationary. If the
power required to hold position is different for different
positions, then the amount of heat generated may be different for
different positions, thereby affecting metrology differently in
different positions. Accordingly, avoiding significant changes in
the power requirement of a direct drive/linear motor (and hence
avoiding significant changes heat generated by the motor) can be
more important to the metrological performance of the CMM compared
to belt driven, ball-screw, or geared DC motors.
[0061] Accordingly, in one embodiment, the apparatus is configured
to adapt the pneumatic counterbalance's pneumatic pressure
automatically depending on the z-axis position of the quill 110.
The mass, and hence weight, carried by the quill 110 can vary
depending on the z-axis position, for example due to the proportion
of the energy conduit 502 that is carried by the quill 110. For
example, in this embodiment, this could be due to the proportion of
the energy conduit 502 that is carried by the quill 110 being
greater in a relatively raised/higher position compared to which it
is in a relatively lowered position. Accordingly, the linear motor
will have to work harder just to hold position at a first
vertical/z-axis position compared to a second vertical/z-axis
position. This means that the linear motor will generate more heat
at the first vertical/z-axis position compared to when it is the
second vertical/z-axis position. Such variation in heat output can
adversely affect metrology. As will be understood, the first
vertical/z-axis position could be higher than the second
vertical/z-axis position, or the first vertical/z-axis position
could be lower than the second vertical/z-axis position.
[0062] It might also be that irrespective of the energy conduit 502
(e.g. even if the energy conduit 502 is substantially balanced by a
corresponding second energy conduit 504 as in FIG. 4), the power
requirement of the motor could vary depending on the z-axis
position, due to, for example, hysteresis in the energy conduit,
varying cable tension, etc. Accordingly, such variations could be
determined (e.g. mapped) during a calibration stage and
subsequently used by the counterbalance controller 416 to control
the pressurised gas supply 418 accordingly. For example, a function
or map could be determined during the calibration stage. Such a
function/map could be configured so as to try to ensure that
substantially the same motor power (which could be substantially
zero motor power) is required to hold the quill 110 at all z-axis
position, or at least for a significant proportion of the quill's
z-axis position (e.g. for at least 50%, preferably at least 75% of
the quill's z-axis travel range).
[0063] According to one aspect of the invention, the counterbalance
controller 416 receives an input from the encoder interface 412
which indicates the current z-axis position of the quill 110. The
counterbalance controller 416 can then use this input to determine
how to control the pressurised gas supply 418 so as to vary the
pressure of the gas within the counterbalance cylinder 302
accordingly. For example, based on the input from the encoder
interface 412, the counterbalance controller 416 can be configured
such that it controls the pressurised gas supply 418 to ensure a
relatively greater pressure inside the counterbalance cylinder 302
for relatively higher positions of the quill 110, and to control
the pressurised gas supply 418 to ensure a relatively lower
pressure inside the counterbalance cylinder 302 for relatively
lower positions of the quill 110, or vice versa. If the pressurised
gas supply 418 comprises a pressure regulator, the counterbalance
controller 416 could be configured to change the pressure which the
pressure regulator is set to try to maintain.
[0064] The counterbalance controller 416 could be configured to
control the pressurised gas supply 418 (e.g. via changing the
pressure a pressure regulator is set to achieve) so as to at least
reduce any variation in the linear motor power required for holding
a stationary position along the z-axis. If desired, the
counterbalance controller 416 could be configured to control the
pressurised gas supply 418 so as to ensure that the linear motor
power required for holding a stationary position is substantially
constant for a significant proportion of the z-axis. Either way,
this could be achieved, for example, by the counterbalance
controller 416 using the input from the encoder interface 412 to,
for example, look up in a pre-calibrated table, or determine via a
predetermined function, a particular setting (e.g. a particular gas
pressure), which is then used to automatically determine how to
control the pressurised gas supply 418.
[0065] As will be understood, in an alternative embodiment, the
counterbalance controller 416 could automatically determine how to
control the pressurised gas supply 418 based on an input from the
main processing unit 410 (or the motor power amplifier 414). The
input from the main processing unit could indicate the actual
and/or demanded position of the quill 110. This could be rather
than, or in addition to, an input of the position of the quill 110
from the encoder interface 412.
[0066] In another embodiment, the apparatus is configured to adapt
the pneumatic counterbalance automatically depending on what is
mounted on the end of the quill 110 (e.g. depending on the
tool/probe mounted on the quill 110). This could be so as to adjust
the pressure of the gas inside the counterbalance cylinder 302
automatically so as to adjust for any change in weight caused by
the change in probe loaded on the quill 110, and therefore avoid a
change in the work required of the linear motor (e.g. to ensure
that counterbalance continues to substantially counterbalance the
total weight of the quill and what it carries). This can be
particularly significant when an optical probe, such as a camera or
video probe is loaded on the quill 110, because such probes can
have relatively heavy imaging optics.
[0067] For example, when a new probe is mounted on the articulated
head 116 from the rack 450, the counterbalance controller 416 can
receive an input indicative of the change. For instance, the
counterbalance controller 416 could receive an input from the main
processing unit 410 which indicates what probe is now (or is about
to be) loaded on the quill 116. The counterbalance controller 416
could then use this input to look up in a preconfigured table, one
or more parameters related to the weight of the probe, and then
instruct the pressurised gas supply 418 to change the pressure of
the gas inside the counterbalance cylinder 302 accordingly. In an
alternative embodiment, the main processing unit 410 could provide
the counterbalance controller 416 one or more parameters related to
the weight of the probe (rather than the counterbalance controller
416 having to look it up).
[0068] In another alternative embodiment, in response to the
counterbalance controller 416 receiving an input which indicates
that a probe change has taken place, the counterbalance controller
416 could determine the effect of the module on the coordinate
positioning apparatus and thereby determine how to control the
pressurised gas supply 418 so as to change the pressure of the gas
inside the quill 110 accordingly adjust the pressure accordingly.
For example, the counterbalance controller 416 could initiate a
"weighing operation" to determine a parameter relative to the
weight of the probe loaded on the quill 110. For example, this
could comprise the main processing unit 410 controlling the quill's
z-axis position in a particular predetermined way (such as keeping
the quill 110 in a stationary position, moving the quill up and/or
down, and/or for accelerating the quill 110 over a known distance)
and determining from the motor power amplifier 414 what the power
requirement is for performing such control. The power requirement
(or one or more parameters indicative of the power requirement) can
be input to the counterbalance controller 416 (e.g. optionally via
the main processing unit 410) to determine a parameter related to
weight of the probe. As another example, the main processing unit
410 could control the motor power amplifier 414 to move the quill
110 with a particular force. The acceleration of the quill 110
could be measured. This would enable the mass/load of the quill (or
a parameter related thereto) to be determined. In any case, the
counterbalance controller 416 could then use the information from
any or a combination of such above described routines to determine
how to control the pressurised gas supply 418 so as to change the
pressure of the gas inside the counterbalance cylinder 302
accordingly.
[0069] The above described embodiment requires determining a
parameter related to the weight of the probe. Such a parameter
could be the weight of the probe (e.g. in a unit of weight, such as
grams). However, as will be understood, this need not necessarily
be the case. For example, a parameter which is dependent
on/indicative of the weight could be identified instead. For
example, rather than using a look-up table to determine the weight
of a probe loaded (or to be loaded) on the quill 110, the look-up
table could be used to determine what setting (e.g. what air
pressure) the pressurised gas supply 418 should be set to depending
on the probe loaded (or to be loaded) on the quill 110. As another
example, the "weighing operation" could merely determine a
particular setting (e.g. what air pressure) the pressurised gas
supply 418 should be set to, rather than actually determining the
weight (in a unit of weight) of the probe.
[0070] In another embodiment, the counterbalance controller 416
could be configured to automatically control the pressurised gas
supply 418 so as to adjust the pressure inside the counterbalance
cylinder 302 depending on the direction motion of the quill 110.
For instance, in the described embodiment when the quill 110 is
moving upward gas the pressure within the counterbalance cylinder
302 could be increased, and when the quill 110 is moving downward
the pressure within the counterbalance cylinder 302 could be
reduced, thereby assisting the linear motor. Accordingly, the
counterbalance controller 416 could receive an input from the
controller 410 indicating a direction in which the quill 110 is
moving, and the counterbalance controller 416 could control the
pressurised gas supply 418 so as to adjust the supply of
pressurised gas accordingly (e.g. by adjusting the pressure a
pressure regulator of the pressurised gas supply 418 is set to
maintain). For instance, if the counterbalance controller 416
receives an input from the controller 410 indicating that the quill
110 is moving, or is about to move, upwards, the counterbalance
controller 416 can control the pressurised gas supply 418 so as to
increase the pressure inside the counterbalance cylinder 302,
whereas if the counterbalance controller 416 receives an input from
the controller 410 indicating that the quill 110 is moving
downwards, the counterbalance controller 416 can control the
pressurised gas supply 418 so as to decrease the pressure inside
the counterbalance cylinder 302. As will be understood, rather than
waiting for the movement to occur before adjusting the pressure,
the counterbalance controller 416 could pre-empt a future motion by
adjusting the pressure shortly before the motion is due to
occur.
[0071] An example of how pressure within the counterbalance
cylinder 302 might vary over time when implementing this aspect of
the invention is illustrated in FIG. 5a. As shown, when the quill
110 is stationary at a notional axial position of Z=100, the
pressure is maintained at a first constant set (i.e. target)
pressure (e.g. 5 bar). However, when the quill is about to be moved
downwards, the counterbalance controller 416 (on the basis of an
input from the controller 410) can know in advance that such motion
is to take place and thereby control the pressurised gas supply 418
so as to decrease the set (i.e. target) pressure inside the
counterbalance cylinder 302 during such motion (e.g. 4.5 bar) so as
to assist the linear motor (e.g. to reduce the motor power
requirement, or to increase the travel speed for a given motor
power/current). On returning to a stationary position, the
counterbalance controller 416 (on the basis of an input from the
controller 410) can bring the pressurised gas supply 418 back up to
a level where it substantially counterbalances the total load on
the quill. As shown, in this case (and in accordance with the other
above described aspect of the invention), the counterbalance
controller 416 does not return the pressure back to the same set
(i.e. target) pressure, but instead to a slightly different set
(i.e. target) pressure (e.g. 4.9 bar) because the total load on the
quill is different at this different z-axis position (e.g. because
the quill 100 is carrying less of the energy track at this new
z-axis position). As also shown, during the motion there might be
some small fluctuation in the actual pressure within the
counterbalance cylinder 302 due to lag/hysteresis in the pressure
regulator which is trying to maintain the pressure at the new set
level of 4.5 bar.
[0072] The graph of FIG. 5a is to be contrasted with the graph of
FIG. 5b which illustrates the how pressure within the
counterbalance cylinder 302 might vary over time when using a known
pressure regulator which is configured to maintain a set (i.e.
target) pressure of a pneumatic counterbalance system. As shown, in
this case, the system is configured such that the at all times
(i.e. when stationary and during motion), the same pressure is
maintained within the counterbalance cylinder 302. As shown, there
might be some initial fluctuations during the motion due to
lag/hysteresis in the pressure regulator, but nominally the
pressure is the same, and in contrast to the present invention, as
illustrated in FIG. 5a, the system is configured such that the
pressure is maintained constant in all circumstances.
[0073] In the above described embodiments, the counterbalance
controller 416 is shown as having dedicated inputs from the various
other units/interfaces/amplifiers in the controller 118. However,
as will be understood, this need not necessarily be the case and
other configurations are possible. For example, the counterbalance
controller 416 could receive a single input from the main
processing unit 410 (e.g. which could relay signals from the
encoder interface 412 and/or amplifier 412). Optionally, the
counterbalance controller is provided by the main processor unit
410 (i.e. in which case the unit 416 as a separate entity need not
exist).
[0074] Optionally, the main processing unit 410 communicates with,
and controls, the pressurised gas supply 418 directly (this could
be the case when the unit 416 as a separate entity does or does not
exist).
* * * * *