EP2702350A1

EP2702350A1 - Portable measuring machine with high-precision five-axis articulated arms

Info

Publication number: EP2702350A1
Application number: EP12717865.5A
Authority: EP
Inventors: Nicola TOMELLERI; Monica TOMELLERI
Original assignee: Tomelleri Engineering Srl
Current assignee: Tomelleri Engineering Srl
Priority date: 2011-04-29
Filing date: 2012-03-28
Publication date: 2014-03-05
Also published as: WO2012146989A1; ITVR20110085A1

Abstract

Described is an articulated arm measuring machine having five axes and able to reach a very high level of precision. The arms of the machine and the probe are balanced so the machine is safer and less subjected to the loads which the operator exerts to support it. The machine is designed for fixing to a movable tripod equipped with an adjustable extension, allowing parts to be measured on the machine.

Description

Portable measuring machine with high precision five axis articulated arms

Technical Field

This invention relates to a portable measuring machine with five axis articulated arms characterized by the high precision which can be reached and in that the second joint is balanced.

Background Art

The portable machines with articulated arms, which will also be indicated by the acronym AMM (Articulated Measuring Machine), have the merit of a great flexibility of use which allows, for example, a part to be measured without moving it, but by moving the measuring machine close to it. Moreover, they allow the measuring of a part in a short time, especially when they are not large series of measurements, since unlike CMMs (Coordinate Measuring Machines) they do not require programming of the movements, which are performed manually directly by the operator. The AMMs, compared with the CMMs, have the advantage of the lower cost, but they have the disadvantage of the lower precision.

The AMMs are mainly characterized, as will be illustrated below in Figure 1, by the fact that they have three joints, each of which is equipped with three axes, between which two connecting arms are interposed, whilst the third joint provides the two axes to the measuring probe for orienting it in the required direction.

The measuring probe may also consist of a Laser Head which allows the surfaces to be scanned, and in that case it may be equipped with a further rotary axis so that the machine is equipped overall with seven axes, but this invention does not regard that scanning device.

There are AMMs equipped with five axes, wherein it is the second axis to be equipped with a single joint, and that solution is mainly present in machines designed for measuring pipes which do not require high levels of measurement precision.

As already mentioned, a first drawback of the AMMs is that they are not very precise if compared with CMMs, even though in some cases it is sufficient for measuring medium-sized parts for which a high level of precision is not required, whilst it is always insufficient for measuring small-sized parts, when the tolerances have very small values of around a few thousandths of a millimetre.

For example, the current AMMs are not able to precisely measure the diameter of a 50 H6 hole since the precision which may be reached by the machine is, in the best cases, equal to the tolerance required for the diameter, whilst the precision of the measuring instrument is normally required to be greater than the precision required for the part.

Another drawback of the existing AMMs designed for measuring parts is that they have at least six axes, and that the balancing system in them supports the weight present up to the second joint, so the final joint together with the probe must be supported by the operator, and this always results in the risk of falling with the danger of collision. This lack of total balancing of the joints of the machine means that the operator cannot perform the measuring with the gentleness required for high precision measurements, and the operator must also move the arms to the vertical rest position between one measuring step and the next.

Another drawback of the existing AMMs designed for measuring parts is that they are not suitably prepared for being close to the part whilst it is still mounted on the machine, so in many cases the part must be removed from the machine with consequent time wasting.

Another drawback of the existing AMMs designed for measuring parts is that they do not allow an easy access to the measurement on the surfaces located on the other side of the machine. Disclosure of the Invention

This invention is proposed for overcoming the aforementioned drawbacks of the AMMs, for measuring small and medium-sized parts.

The main aim of this invention is to considerably increase the measurement precision.

Another aim of this invention is to balance the weight of the second joint and of the probe preventing the danger of falling and therefore allowing the precision measurements to be performed gently, and without the need for the operator to replace the arms in the vertical rest position between one measuring step and the next.

A further aim of this invention is to allow an easy access for measuring the part when it is mounted on the operating machine, adopting a tripod with special features and performance.

Yet another aim of this invention is to allow an easy access to the measurement on the surfaces located on the other side of the machine.

These and other aims, which will become more apparent in the description which follows, are achieved according to this invention with a portable articulated arm measuring machine characterized to have in succession,

a base with a vertical axis,

a first arm fixed to said vertical axis,

a first joint with two axes on the end position of said first arm,

a second arm fixed to said first joint,

a second joint on the end position of the second arm,

a probe fixed to said second joint.

The machine may be equipped with a system for balancing the weight of the second joint and of the probe, and it may also be fixed to a tripod to support it during movement equipped with an extensible adjustment part.

Brief Description of the Drawings

A preferred, non-limiting example of this invention is further illustrated below, with reference to the accompanying drawings, in which:

Figure 1 schematically shows an AMM equipped with three joints with two axes each.

Figure 2 schematically shows the AMM according to this invention with a vertical axis and two joints.

Figure 3 schematically shows a cross-section along the axis of the first arm of the AMM according to this invention showing the balancing system of the third joint.

Figure 4 schematically shows a cross-section at right angles to the axis of the first arm of the AMM according to this invention showing the balancing system of the third joint.

Figure 5 schematically shows the AMM according to this invention fixed to a tripod with an extensible adjustment part.

Figure 6 schematically shows the AMM according to this invention equipped with a balancing counterweight.

Detailed Description of the Preferred Embodiments of the Invention

Figure 1 shows an AMM of the type with three joints, with two axes for each joint. More specifically, the figure shows the base 10 of the machine fixed to the plane 11 , the first joint 1 with the two axes "a" and "b", the joint 2 with its two axes "c" and "d" and the joint 3 with its two axes "e" and "f '.

The joint 1 is supported by the base 10 and by the column 11, whilst the first arm 13 is interposed between the joint 1 and the joint 2 and the second arm 14 is interposed between the joint 2 and the joint 3. Lastly, the probe 15 is fixed to the joint 3.

Figure 2 shows an AMM made according to this invention, having an axis Al and two joints SI and S2. It consists of a base 20 fixed to the plane 11, which is integral with the column 21, which supports the axis Al consisting of the axis of vertical rotation "a" about which the first arm 22 is fixed and rotates according to said vertical axis. At the end of the first arm there is the first joint SI with two axes "c" and "d" to which the second arm, consisting of the two parts 24 and 25 integral with each other, is fixed and free to rotate according to said two axes "c" and "d".

At the end of the second arm there is the second joint S2 with two rotary axes "e" and "f ' to which the probe 26 is fixed and free to rotate according to said two axes "e" and "f ', which is therefore able to adopt the desired orientation.

The balancing device 23 which exerts a suitable torque on the second arm is applied to the arm 22 in such a way as to balance at least partly the torque due to its weight, that of the joint S2 and that of the probe.

Figure 3 schematically shows the balancing system present on the end of the first arm 22 and which allows the torque due to its weight, that of the joint S2 and that of the probe to be at least partly balanced.

The drawing shows a cross-section passing through axis "c". The spring 27 which is suitably pre-tensioned so as to exert the required balancing torque on the bushing 23 is applied on the structure of the arm 22. The bushing 23 is integral with the shaft 26, which has the degree of freedom for rotating about the axis "c", and therefore imparts the balancing torque to all the parts connected to it, comprising the second arm consisting of parts 24 and 25, the second joint S2 and the probe.

Figure 4 schematically shows the balancing system present on the end of the first arm with a view from IV. The bushing 23 is integral with the shaft 26 so as to to transmit to it the torque required for balancing all the subsequent parts connected to it and which load their weight on it.

For the purpose of maintaining the balancing function with different angles adopted by the axes "c" and "d", they may adopt angles between minimum and maximum values provided by stop positions prepared on the two axes. Thus, the axis "c" may adopt angles between the minimum value "cm" and the maximum value "cM", whilst the axis "d" may adopt angles between a minimum value "dm" and a maximum value "dM". Two aims are achieved with these two stop positions, on the one hand the balancing torque provided by the pre-tensioning of the spring is always sufficiently close to the torque exerted by the weight forces, and on the other hand the changes in the angles of the two axes is limited so as to allow the measurements to be performed within the planned range of work.

The pre-tensioning angle of the spring and the angles given to the two axes "c" and "d" are such as to achieve a good balancing condition which prevents the falling of the probe in all the conditions when it is released by the operator.

An alternative balancing solution is that of fixing a counterweight to the second arm, located on the other side of the axis "c" and in a position approximately opposite the centre of gravity of the second joint, which, however, could lead to obstruction problems.

The probe may be of the electronic or fixed type even if this second solution appears preferable. In the fixed probe the measurement ball is made integral, through the stylus which supports it, with axes "e" and "f of the second joint, and the measurement is enabled either by a measurement pick-up pushbutton or by using an automatic probe which enables the measurement when a predetermined force is exerted on the probe.

Figure 5 shows the AMM fixed to a tripod which is adjustable in height equipped with an adjustable lateral extension for allowing the machine to be moved close to the part when it is still in the machine.

The AMM of the invention 50 is fixed on a horizontal beam 57 which is free to rotate about a horizontal axis "h" relative to the other horizontal beam 56, which is in turn free to rotate about the axis "g" relative to the vertical sleeve 55. The vertical sleeve is adjustable in height being slidable inside the pipe 54, so as to allow the measuring machine, and in particular its probe 26, to be moved to the height of the part to be measured after having clamped the locking knobs 58.

The two beams 56 and 57 are free to rotate about the axes "g" and "h" so it is possible to move the AMM off centre by the desired quantity with the limit given by the length of the two beams.

During the measurement the tripod 51 is positioned on the three supporting struts 53 so that its has a stable position, whilst when moving from one position to another the three wheels 52 which detach the struts from the floor are lowered. During movement of the tripod the beam 57 must be folded above the beam 56 in such a way that the AMM is centred on the tripod thereby preventing the overbalancing from causing the tipping of the tripod.

Figure 6 shows the AMM in which the balancing of the second arm and of the second joint is achieved by means of the counterweights 62 and 63 fixed to the second arm by the rod 61.

The main aim of this invention to considerably increase the measuring precision is achieved thanks to the fact that the number of axes of the machine is equal to five instead of six, and that it is balanced thereby preventing the operator from exerting loads which deform the machine.

The aim of balancing the weight of the second joint and of the probe preventing the danger of falling and therefore allowing the precision measurements to be performed gently is achieved with this invention, also preventing the risk of falling.

The aim of allowing an easy access for measuring the part when it is mounted on the operating machine is achieved by adopting a tripod with the features described.

The another aim of facilitating access to the measurement on the surfaces located on the other side of the machine is achieved thanks to the particular shape of the second arm.

A particular embodiment of the machine according to this invention provides that the weight of the probe to be balanced with a small counterweight positioned symmetrically relative to the axis "f '.

A particular embodiment provides that the probe is made interchangeable with a device for fast coupling to the second joint.

A different solution relates to the type of probe, or a different shape of the second arm, or the adoption of a different system for balancing the second arm of the second joint and the probe.

An interesting solution may be that of providing the axis "d" with a rotation of

180° which allows the machine to adopt the symmetrical configuration for achieving a different condition for access to the measurement. In this case it is possible to have a system for balancing the second joint using a counterweight solution.

In a particular embodiment a laser head is fixed to the second joint instead of the probe.

Other embodiments of the AMM may be used, without thereby departing from the scope of this invention.

Claims

1. Portable articulated arm measuring machine characterized to have five axes and to have in succession:

a base in which there is a shaft free to rotate in a vertical axis, a first arm fixed to said shaft,

- a first joint with two axes on the end position of said first arm, a second arm fixed to said first joint,

a second joint with two axes on the end of said second arm, a measuring probe applied to said second joint.

2. Measuring machine as in the claim 1 characterized by having a balancing system that supports, even only partially, the weight of the second arm and of the probe.

3. Measuring machine as in the claims 1 and 2 characterized by having a balancing system that supports, even only partially, the weight of the probe.

4. Measuring machine as in the claims from 1 up to 3 characterized by the fact that the second arm is composed by more straight or curved parts, with the ending part that has a direction that differs not more than sixty degrees from the vertical when the axes of the first joint are in the mean position of the operational stroke.

5. Measuring machine as in the claims from 1 up to 4 characterized by the fact that the one of the two axes of the second joint is coaxial with said ending part of the second arm.

6. Measuring machine as in the claims from 1 up to 5 characterized by the fact that as a fixed probe with automatic measurement.

7. Measuring machine as in the claims from 1 up to 6 characterized by the fact that the axis c can rotate of about 180° giving the possibility of a another access to measurement.

8. Measuring machine as in the claims from 1 up to 6 characterized by the fact that it uses a tripod with an extensible adjustable part capable to support it during the measurement.

9. Measuring machine as in the claims 1 and 2 characterized by fact that to the balancing system is realized by means of one or more springs applied to the first arm.

10. Measuring machine as in the claims 1 and 2 characterized by fact that to the balancing system is realized by means of a counterweight fixed to the second arm.