Apparatus, in particular an x-ray examination apparatus, with arrangement for collision protection

An arrangement for collision prevention is provided for an apparatus, in particular an x-ray examination apparatus, having components that can be moved by drive means. A collision is detected by way of detecting the speed of a relevant moving part and detecting the current and/or power supply to the drive means. Reference values for current and/or power supply at normal operation in dependence of the speed acquired by moving components are provided from a memory means and actually required current and/or power supplies are compared to said reference values. In addition, actual positions of components are detected and compared to computed expected positions of said components. A collision is detected when the required current and/or power supply exceeds a relevant reference value and the detected actual position deviates from the corresponding calculated expected position. As a consequence of a collision being detected, the moving component involved in a collision is detached from the drive means so as to avoid damage or injury as a cause of the collision. Apart from x-ray examination apparatus, also industrial robots which operate in circumstances where person may approach the apparatus to within the reach of moveable components are preferably fitted with an arrangement for collision protection as described above.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention pertains to an apparatus, comprising drive means for moving 
components of said apparatus and further comprising an arrangement for 
collision protection. 
2. Description of the Related Art 
An apparatus of said kind is described in the European Patent EP 0 087 198 
which corresponds substantially to U.S. Pat. No. 4,578,757. 
In the cited reference an x-ray examination apparatus is described that 
comprises an arrangement for collision protection based on calculation of 
distances between mutually moveable components or bodies and comparing 
said distances with safety distances. A collision is considered imminent 
in the known x-ray examination apparatus when a distance between 
components of the x-ray apparatus becomes smaller than a predetermined 
safety distance. Collision protection is achieved in the known x-ray 
examination apparatus in that movement of said x-ray examination apparatus 
is terminated when a relevant distance becomes smaller than the safety 
distance. The arrangement for collision protection as described in the 
cited reference aims at preventing collisions between components of the 
known x-ray examination apparatus. Therefore, a patient to be examined by 
way of a known x-ray apparatus is protected only from experiencing 
collision with a component of said x-ray examination apparatus when there 
are provided sufficiently large safety distances from a patient table that 
is a component of the x-ray apparatus. As a consequence, in the x-ray 
examination apparatus as described in the cited reference, required 
patient safety prohibits that the distance between a patient that is to be 
examined and components of the x-ray apparatus, in particular an x-ray 
image intensifier, can become arbitrarily small. Hence, spatial resolution 
of an x-ray image produced by the x-ray image intensifier is compromised 
by the requirement that an input screen of the x-ray image intensifier 
should be kept at least a safe distance away from the patient. 
It is inter alia an object of the invention to provide an apparatus, such 
as an x-ray examination apparatus or an industrial robot, comprising an 
arrangement for collision protection allowing arbitrarily close approach 
of components of said apparatus, mutually, or of any of such components 
with a patient that is to be examined, or a person being within a reach of 
a component of the apparatus. 
This is achieved in that such an apparatus, in accordance with the 
invention is characterized in that the arrangement for collision 
protection comprises power and/or current measuring means for determining 
(a) value(s) of power and/or current supplied to the drive means, and 
comparison means for comparing said determined value(s) of power and/or 
current supplied to drive means with (a) reference value(s) for said power 
and/or current supplied and for generating a first drive-disengaging 
signal for controlling disengaging a relevant component from the drive 
means. 
For the alternative motions of components of an apparatus in accordance 
with the invention, the power supply required by the drive means under 
normal circumstances can be measured and thus reference values for the 
required power supply are known. Should a collision occur of any component 
of the x-ray apparatus with another object, e.g. with another component of 
the x-ray apparatus or with a patient that is to be examined, then the 
motion of the colliding component meets additional resistance and 
therefore the power supply required by the drive means would increase 
beyond said reference value. Detection of the required power supply, and 
subsequently comparing with a relevant reference value provides for 
generating a first drive-disengaging signal for interrupting the motion of 
the colliding component, and thus preventing the collision to cause damage 
or injury. 
A preferred embodiment of an apparatus in accordance with the invention is 
characterized in that the arrangement for collision protection comprises 
current measuring means for measuring current supplied to the drive means, 
and current comparison means for comparing (a) measured value(s) of 
current supplied to drive means with (a) relevant reference value(s) for 
said current supplied and for generating a first drive-disengaging signal 
for controlling disengaging a relevant component from the drive means. 
Because the drive means is operated at a fixed, or at least at a known, 
voltage, power supplied to the drive means is conveniently determined by 
measuring current supplied to the drive means. For the alternative motions 
of components of the apparatus in accordance with the invention, the 
current supply required by the drive means under normal circumstances can 
be measured and thus reference values for the required power supply can be 
determined and thus reference values for the required current supply are 
provided. Should a collision occur of any component of the apparatus with 
another object e.g. with another component of the apparatus, or in case of 
an x-ray examination apparatus with a patient that is to be examined, then 
the motion of the colliding component meets additional resistance and 
therefore the current supplied to the drive means would increase beyond 
said reference value. Measurement of the current supplied, and 
subsequently comparing with a relevant reference value provides for 
generating a first drive-disengaging signal for interrupting the motion of 
the colliding component, and thus preventing the collision to cause damage 
or injury. 
A further preferred embodiment of an apparatus in accordance with the 
invention is characterized in that the arrangement for collision 
protection comprises a memory means for storing said reference value(s). 
Reference values for current and/or power supply to drive means of the 
apparatus being fixed, a particularly simple way of supplying said 
reference values to the comparison means is to provide a memory means in 
which reference values can be stored and from which said reference values 
are supplied to the comparison means. Notably, when current supply to the 
drive means is compared with a relevant current reference value, the 
comparison means is formed by a current comparator. 
A further preferred embodiment of an apparatus in accordance with the 
invention is characterized in that the arrangement for collision 
protection comprises position detection means for detecting a position of 
a component of the apparatus, and also comprises computing means for 
calculating an expected position of said component, and further comprises 
position comparison means for determining a difference between said 
detected position and said expected position and for generating a second 
drive-disengaging signal for controlling disengaging a relevant component 
from the drive means. 
By comparing the actual position of a component of the apparatus to the 
expected position of said component, it is accurately determined if the 
motion of said component has been obstructed. Collision protection is 
achieved in that a disengaging signal is generated when the actual 
position deviates from the expected position in excess of a predetermined 
threshold value and when also the current and/or power supplied to the 
drive means exceeds a relevant reference value. 
A further preferred embodiment of an apparatus in accordance with the 
invention is characterized in that the arrangement for collision 
protection comprises a signal processing means whereto the first and 
second drive-disengaging signals are supplied and said signal processing 
means being arranged generate a third drive-disengaging signal for 
controlling disengaging a relevant component from the drive means, in 
dependence of the first and second drive-disengaging signals. 
A further refined way of detecting obstruction of a component of the 
apparatus consists of combinedly comparing current and/or power supply to 
the drive means to a reference value and comparing the detected position 
of said component to a corresponding expected position. Employing both 
current and/or power comparison and position comparison, which yield a 
first drive-disengaging signal and a second drive-disengaging signal, 
respectively, leads to reliable detection of obstruction, and hence a 
collision being imminent. If both first and second drive-disengaging 
signals indicate a collision being imminent, then a third drive 
disengaging signal is supplied for disengaging the drive means. 
A further preferred embodiment of an apparatus in accordance with the 
invention, also comprising a brake, is characterized in that the 
arrangement for collision protection comprises brake-engaging means, and a 
signal processing means arranged to receive relevant drive-disengaging 
signal(s) and for supplying a brake-engaging signal to said brake engaging 
means for engaging said brake, after a predetermined period of time after 
receipt of said drive-disengaging signal(s). 
Components of an apparatus which is balanced, are moveable without 
substantial effort. When a component of an apparatus in accordance with 
the invention and which is also balanced, is undesiredly obstructed by 
another component of the apparatus, or with a person within the reach of a 
component of the apparatus, or with a patient to be examined in the case 
where the apparatus is an x-ray examination apparatus, a component 
involved in obstruction is disengaged from the drive means by the 
arrangement for collision protection and by the recoil following the 
obstruction, the component involved in obstruction moves in a direction 
opposite to its direction of motion prior to the obstruction. After a 
predetermined period of time after generating the disengaging signal for 
disengaging a component involved in obstruction from the drive means, a 
brake-engaging signal is generated for engaging a brake, so as to stop a 
relevant components of the (x-ray examination) apparatus in such a 
position that neither a patient of another component is obstructed. 
A further preferred embodiment of an apparatus in accordance with the 
invention is characterized in that the arrangement for collision 
protection comprises a speed detection means for detecting a speed of a 
moving component and supplying a selection signal to the memory means, for 
selecting a reference value in correspondence with a detected speed. 
In particular when the apparatus is an x-ray examination apparatus, in 
various stages of an examination procedure, components of the x-ray 
apparatus are moved with different speeds. The required current and/or 
power supply is dependent on the speed with which relevant components are 
moved. By the speed detection means selection signals are supplied to the 
memory means for selecting appropriate reference values for the current 
and/or power supply in correspondence with the speed of moving components 
of the x-ray apparatus. 
An apparatus comprising drive means for moving components of said apparatus 
and further comprising an arrangement for collision protection is 
characterized in that the arrangement for collision protection comprises 
means for determining actual values of differences between current and/or 
power supplies at consecutive instants to the drive means, and difference 
comparison means being arranged to compare (a) value(s) of (a) 
difference(s) between current and/or power supplied to drive means with 
(a) predetermined reference value(s) for said differences between current 
and/or power supplied and for generating a difference-excess signal for 
controlling disengaging a relevant component from the drive means. 
Should a collision occur of any component of the apparatus with another 
object e.g. with another component of the apparatus, or with a person 
within the reach of a component of the apparatus, or in the case where the 
apparatus is an x-ray examination apparatus, with a patient that is to be 
examined, then the motion of the colliding component meets additional 
resistance, and therefore the rate of increase of current and/or power 
supply required by the drive means would increase beyond said reference 
value. Detection of the rate of increase of required current and/or power 
supply, and subsequently comparing with a relevant reference value 
provides for generating a signal for interrupting the motion of the 
colliding component, and thus avoiding the collision to cause damage or 
injury. 
An industrial robot, e.g. for welding or for displacing parts, or an 
automatic manipulator, often comprises moveable components being driven by 
drive means. Such industrial robots are employed in circumstances where 
persons are within the reach of one or more of said moveable components. 
Therefore, providing an arrangement is called for to improve safety and to 
avoid malfunctioning of the industrial robot. Preferably, an industrial 
robot in accordance with the invention comprises an arrangement for 
collision protection comprising current and/or power measuring means for 
determining (a) value(s) of current and/or power supplied to the drive 
means, and comparison means for comparing said determined value(s) of 
current and/or power supplied to drive means with (a) reference value(s) 
and for generating a first drive-disengaging signal for controlling 
disengaging a relevant component from the drive means. 
An x-ray examination apparatus often comprises moveable parts which are 
driven by drive means. When performing a medical examination various parts 
of the apparatus often are positioned close to a patient that is being 
examined. For example an x-ray image intensifier is preferably placed 
almost in contact with the patient to obtain x-ray images with good 
spatial resolution. In order to achieve safety for the patient and to 
avoid damage to the x-ray apparatus owing to a collision of parts, an 
x-ray examination apparatus according to the invention comprises an 
arrangement for collision protection comprising current and/or power 
measuring means to determine (a) value(s) of current and/or power supplied 
to the drive means, and comparison means to compare said determined 
value(s) of current and/or power supplied to the drive means with (a) 
reference value(s), and to generate or a first drive-disengaging signal 
for controlling disengaging a relevant component from the drive means. 
The various functions which the arrangement for collision protection should 
execute in an apparatus in accordance with the invention, are preferably 
performed by a computer suitably programmed for performing said functions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows an x-ray examination apparatus comprising a C-shaped carrier 1 
mounted on a predominantly vertical support 2, by means of a sleeve 3 and 
a bearing 4, and supporting an x-ray source 5, and an x-ray detector 6. 
The components, e.g. the C-shaped carrier and the x-ray detector, of the 
x-ray examination apparatus can be moved by way of drive-means 9 
incorporated in the x-ray examination apparatus and brakes 10 are provided 
for maintaining positions of said components. In the embodiment depicted 
here the x-ray detector is an x-ray image intensifier. The x-ray 
examination apparatus is balanced in that a counterweight 7 is provided 
for compensating for a shift in a centre of gravity upon movement of the 
x-ray image intensifier along the central ray path 8 of the x-ray source 
of the C-shaped carrier with the x-ray source, the film holder, the frame 
and the x-ray source. The C-shaped carrier can be moved in the sleeve and 
the sleeve can be rotated around an axis A, so as to angulate the central 
ray path. Because the x-ray examination apparatus is balanced, as 
drive-means there are employed by low-power electric motors that require 
comparatively weak currents. 
An arrangement 50 for collision protection, provided to an x-ray 
examination apparatus in accordance with the invention will now be 
discussed. Current supplies required by drive-means incorporated in the 
x-ray apparatus, for moving different components of the x-ray examination 
apparatus are measured by current measuring-means 21, e.g. having the form 
of ammeters. Because the drive-means are operated, usually at a fixed 
voltage, or at least at a known voltage, the current measuring-means 
effectively act as determination means for determining power supplied to 
the drive-means. A reference value for a current supply required by the 
drive-means for normal operation, i.e. when no obstruction or collision is 
occurring, are available from a memory-means 22, e.g. having the form of a 
programmable read-only memory. By way of a comparison-means 23 a current 
supply required when displacing components of the x-ray examination 
apparatus is compared to a reference value. Should the current supply 
required exceed a corresponding reference value then a first 
drive-disengaging signal is provided to a signal processing means 43 
having the form of a logical unit. During motion of a component from a 
start position to a final position, the required current supply will vary. 
E.g. a higher current supply is required when a component is set in motion 
or when a centre of gravity of a component is moved oppositely the 
direction of gravity. Therefore, during the motion the required current is 
repeatedly compared to a relevant reference value which is supplied from 
the memory means 22. 
Actual positions of components of the x-ray examination apparatus are 
detected by position detection-means 40. By way of computation-means 41, 
being connected to a motion control-part 26, there are calculated expected 
positions of components of the x-ray examination apparatus. After a 
command has been supplied from the motion control-part 26 to the 
drive-means to displace components of the x-ray examination apparatus from 
a start position to a final position, repeatedly an actual position is 
detected by position detection-means 40 and an expected position is 
calculated by computation-means 41. An actual position and a corresponding 
expected position are compared by a position comparison-means 42. Should a 
difference, detected by the position comparison-means 42, between an 
actual position and a corresponding expected position exceed a 
predetermined value, then a second drive-disengaging signal is provided to 
the logical unit 43. 
Should a movement of a component be obstructed, then a difference between 
an actual position anti an expected position will exceed a predetermined 
threshold value and substantially simultaneously the required current for 
the drive-means will exceed a reference value. In such a situation, 
substantially simultaneously a first and an second drive-disengaging are 
supplied to the logical unit 43. Subsequently, by the logical unit 43 a 
deactivation signal is supplied the deactivation control-means 24 for 
deactivating the motion control-means, a third drive-disengaging signal is 
supplied to drive disengaging/engaging-means 25 for disengaging the 
drive-means and a time-delayed engaging signal is supplied to the brake 
disengaging/engaging-means 44 for engaging a brake. In its turn by the 
drive disengaging/engaging-means 25 a relevant component is disengaged 
from the drive-means and because the x-ray examination apparatus in 
accordance with the invention is balanced and can therefore be moved 
without substantial effort, the relevant component moves in reverse 
direction, by the recoil caused by the occurred obstruction. After some 
predetermined short period of time, (e.g. 1/2 second), the brake 
engaging/disengaging-means 44 that is activated by the time-delayed 
engaging signal and the brake is engaged, so that the relevant component 
is stopped in such a position that neither another component or a patient 
is obstructed. Furthermore, the obstruction not having evolved in a 
violent impact, damage or injury to a patient to be examined are avoided. 
Said deactivation signal is supplied to the motion control-part 26 being 
incorporated in a control desk 27. In addition the deactivation signal for 
deactivating the motion control-part 26, is supplied to the motion control 
part 26 of the control desk 27. As a consequence motion control-means 28 
e.g. a control button or joy-stick, mounted on the control desk is 
disengaged from motion control. After said control-means has been released 
by a person operating the x-ray apparatus, an activation signal is 
supplied to an activation control circuit-means 29. Subsequently, said 
activation control circuit-means re-activates the motion control part 26 
by way of an activation signal generated by the activation circuit-means 
29. After the cause of the obstruction has been removed, the examination 
procedure can be continued and motion of components of the x-ray apparatus 
can be performed by way of the control desk. 
In various stages of an examination procedure, components of the x-ray 
apparatus are moved with different speeds, or as an alternative, different 
speeds for moving components can be selected. The collision preventing 
arrangement is further refined by providing a speed detection-means 30. 
The required current supply is dependent on the speed with which relevant 
components are moved. By the speed detection-means 30 selection signals 
are supplied to the memory-means 22 for selecting appropriate reference 
values for the current supply in correspondence with the speed of moving 
components of the x-ray apparatus.