JPH1011128A - Off-line teaching method for robot for arc welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate teaching operation for a torch by making an operator move only a torch-shaped model over a look at a work on CAD and teach teaching points and torch angles. SOLUTION: An environment model operation part 3 inputs a torch model, a robot model, and a work model. A torch teaching data operation part 4 inputs torch angles at teaching points. An automatic generation part 5 for robot teaching data puts the torch teaching data and the torch one over the other so that the torch axis is common and also rotates the torch on its axis so that a torch- side fitting point is a predetermined position, and further calculates the angles of respective robot axes through inverse conversion from the position attitude at the torch-side fitting point. If a robot 11 does not reach the torch-side fitting point or causes interference, the torch is rotated on its axis by a specific angle and when there is no interference, the found angles of the respective axes are stored. Then data on defective parts are properly corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an off-line teaching method for an arc welding robot, which basically automatically generates teaching data of a robot using a computer-aided design system (CAD).

[0002]

2. Description of the Related Art As a teaching method of a robot, there is an off-line teaching method in which teaching data of a robot is created using CAD without using an actual robot.

Conventionally, as an off-line teaching method for an arc welding robot, for example, a robot model (hereinafter referred to as a torch) having a work model (hereinafter referred to as a work) and a torch model (hereinafter referred to as a torch) at a tip thereof is attached on a graphic display. (Hereinafter referred to as a robot). While the operator looks at the displayed model, interactively inputs and operates a command at the target instruction level, activates the robot, and checks the posture of the torch and the robot. However, robot teaching data of a plurality of teaching points is created one by one.

[0004]

The off-line teaching method for the arc welding robot requires interactive input of a command. Particularly, in the arc welding operation, the axis of the torch is appropriately aligned with the welding line. This method sets a so-called forward / backward angle of tilting, and has a problem that the number of man-hours for offline teaching the three-dimensional operation of the torch with respect to the work increases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to facilitate teaching work and to reduce the labor of an operator by automatically automatically generating teaching data of a robot. An object of the present invention is to provide an off-line teaching method for an arc welding robot.

[0006]

SUMMARY OF THE INVENTION An off-line teaching method for an arc welding robot according to the present invention comprises: (I) a torch model in which a torch side mounting point is shifted from a torch axis, a robot model having six degrees of freedom, and a three-dimensional workpiece. An environment model operation unit for inputting a model; (II) a torch teaching data operation unit for inputting and storing torch angles at a plurality of teaching points by moving a torch model by an operator; (III) following (a) And (i) the torch teaching data and the torch model are overlapped so that the torch axis is common, and the torch-side mounting point is at a predetermined position. The torch model is rotated about the torch axis as described above, and (b) the robot is determined based on the position and orientation of the torch-side mounting point, assuming the torch-side mounting point as the robot torch mounting reference point. The angle of the shaft is calculated by a known inverse conversion calculation, and (c) it is determined whether or not the angle of each axis of the robot has been obtained by the above calculation (= whether the reference point for mounting the torch of the robot reaches the mounting point on the torch side). , (D)
When the torch model does not reach (= when there is no solution of the above calculation), the torch model is rotated so as to increase by a predetermined angle around the torch axis, and the above (b) and (c) are repeated. If it does not reach even after one rotation around the axis, "not reach" is stored. (F) If it reaches, check the interference of the robot model. (G) If it does, increase the predetermined angle around the torch axis. After the torch model is rotated so as to perform (b) to (f), (h) When the torch model does not interfere even if it makes one rotation around the torch axis, “robot interference” is stored, and (i) ) When there is no interference, a robot teaching data correction unit is provided that stores the calculated angles of the robot axes. (IV) Calls automatically created robot teaching data and allows the operator to appropriately correct the data of the defective part. Specially To.

In the torch teaching data operation unit, the operator looks at the torch-like model and the work on the CAD,
A torch angle at a plurality of teaching points is input, and these states are stored in a computer as torch teaching data. That is, since only the torch-shaped model is moved with respect to the work to teach the teaching point and the torch angle, the teaching work of the torch is extremely easy, and it is necessary to teach at a plurality of points particularly during arc welding work. Because of this, the ease of teaching work is expanded.

In the robot teaching data automatic creation section, the torch teaching data and the torch are overlapped so that the torch axis is common, and the torch side mounting point is set around the torch axis so that the torch mounting point is at a predetermined position. The torch is rotated.- The angle of each axis of the robot is calculated by a well-known inverse conversion operation based on the position and orientation of the torch-side mounting point, assuming the torch-side mounting point as the robot's torch mounting reference point. Check if the torch mounting reference point reaches the torch side mounting point, and check for robot interference. ・ If the robot does not reach or interfere, the torch is rotated a predetermined angle around the torch axis and the above check is performed again. When there is no interference, the angle of each axis of the robot obtained by the above calculation is stored.

If the robot having six degrees of freedom taken in on the CAD has, for example, the mechanism shown in FIG. 8, the angle between the third links, that is, the posture data predicts the posture of "Arm DOWN". The position and orientation of the torch attachment reference point at the free end of the robot (X, Y,
Z, L, M, N) and "Arm DOWN", the position and orientation (X, Y, Z, L, M, N) of the torch attachment reference point can be calculated by an inverse transformation operation of a conventionally known configuration. The posture of the robot is determined by being converted into angles (θ _{1 to} θ ₆ ) of each axis of the robot.

Therefore, the expected posture of the robot, that is, the posture data is input in advance, or the order of the operation based on the posture data is input, and the torch side mounting as the teaching data is performed in a specific robot. A well-known inverse transformation operation is performed based on the position and orientation of the point (X ₁₀ , Y ₁₀ , Z ₁₀ , L ₁₀ , M ₁₀ , N ₁₀ ).

Of course, when the answer cannot be obtained by the above-mentioned inverse conversion operation, it means that the robot cannot reach.

On the other hand, if the robot interferes even if the answer is obtained by the above-mentioned inverse transformation operation, or if the robot does not reach as described above, the torch is rotated by a predetermined angle around the torch axis.

In this case, since the torch-side attachment point is rotated by a predetermined angle around a torch axis on a plane orthogonal to the torch axis at a radius peculiar to the torch, the torch-side attachment point after rotation on CAD is used. Position and orientation (X ₁₁ , Y ₁₁ , Z
₁₁ , L ₁₁ , M ₁₁ , N ₁₁ ) are obtained by calculation and grasped as torch teaching data.

The position and orientation (X ₁₁ , Y
₁₁ , Z ₁₁ , L ₁₁ , M ₁₁ , N ₁₁ ), the inverse conversion operation is again performed as described above → check whether or not the robot reaches → the robot is checked for interference, and “the robot does not interfere” is obtained. Until the torch makes one rotation about the torch axis, the operation of “increase in the increment of the torch rotation angle about the torch axis → whether the robot reaches → whether the robot interferes” is repeated.

In the above description, if the torch does not reach even if it makes one rotation around the torch axis, or if the robot interferes, the fact is memorized. Position and orientation (X _1j , Y _1j ,
_{Z 1j, L 1j, M 1j} , the angle of the inverse transform operation robotic axes based on _{N 1j) (θ 1j ~θ 6j} ) is stored, the robot teaching data corresponding to a plurality of teaching states automatically generated Is done.

Of course, in the robot teaching data correcting section, the data of the defective portion of the robot teaching data is corrected as appropriate by the operator.

As described above, the operator operates the torch teaching data and corrects the robot teaching data. However, after the operation of the torch teaching data, the operator performs other operations until the robot teaching data is automatically created. Can be performed.

The robot teaching data corresponding to the torch teaching data is such that the torch teaching data and the torch are overlapped so that the torch axis is common, and the torch axis is set so that the torch side mounting point is at a predetermined position. The torch is automatically rotated around the torch, and in this state, the torch whose mounting point on the torch is displaced from the torch axis rotates a predetermined angle around the torch axis.
Since the calculation is repeated and automatically generated by the computer, the labor of the operator is reduced as compared with the conventional case where the operator creates the robot teaching data one by one.

As a result, it is possible to obtain an off-line teaching method for an arc welding robot that can easily perform a teaching operation and reduce the labor of an operator.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. 1 to FIG. 11, FIG.
1 shows a schematic configuration of an off-line teaching system for an arc welding robot according to an embodiment of the present invention. In FIG. 1, a terminal device 1 having a display, a keyboard, a mouse, and the like, a user interface unit 2, a torch whose torch-side attachment point is displaced from the torch axis, a robot having six degrees of freedom, and a three-dimensional work figure are input. Environmental model operation unit 3, torch teaching data operation unit 4, robot teaching data automatic creation unit 5, robot teaching data correction unit 6, robot controller interface unit 7
Thus, the offline teaching system 8 for the arc welding robot is configured.

A robot controller 9 is connected to the off-line teaching system 8.
The movement of the arc welding robot 11 having a degree of freedom is controlled.

That is, as shown in FIG. 2, the entire hardware configuration of the arc welding robot apparatus is an off-line mainly composed of a computer including an input device including a graphic display 101, a keyboard 102 and a mouse 103, and a storage device. In the teaching system 8,
The robot controller 9 and an arc welding robot 11 having six degrees of freedom are sequentially electrically connected.

A teaching method using the arc welding offline teaching system 8 having the above configuration will be described below.

In FIG. 3, in step S101, a torch model whose torch-side attachment point is shifted from the torch axis (hereinafter, referred to as torch) is input. For example, the torch 20 is being formed in the shape of as shown in FIG. 5, the torch side attachment point O _t are formed offset distance a _t from the torch axis. Specifically, a point Tb separated from the welding point Ta on the tip side of the welding torch by an interval b _{t in} the axial direction of the torch.
With the vertex at the vertex, the vertex angle 2 × 軸 (π /
2) the generatrix of the cone of-gamma _t}, the intersection between the circle of radius a _t about the axis of the torch is in the position of the torch side attaching point O _t.

Next, in step S102 in FIG.
A straight rod-shaped torch model 21 having a sharp tip is input.

Next, in steps S103 and S104 in FIG. 3, a robot model (hereinafter, referred to as a robot) and a three-dimensional work model (hereinafter, referred to as a work) are input.

Steps S101 to S10
4 constitutes an environment model operation unit.

Next, in step S105 in FIG.
The display shows a torch-like model, namely the torch 20
Alternatively, the torch angle at the teaching point is input while displaying the straight rod-shaped torch-shaped model 21 and the workpiece and viewing them.

Incidentally, in the arc welding operation, it is necessary to appropriately tilt the axis of the torch with respect to the welding point.
For this reason, as shown in FIG. 6, at the time of teaching, at the time of teaching, using the mouse of the terminal device, place the cursor on the tip of a torch-shaped model, for example, a straight rod-shaped torch-shaped model 21 and click on it. The cursor to the teaching point TP and click on it to make a straight rod-shaped torch model 2
1 is made to coincide with the teaching point TP.

Next, the terminal operation is performed with the teaching point TP as the tilt center, for example, so that the axis of the torch is tilted at an angle α from the X axis and at an angle β from the Y axis. That is, FIG.
As shown in FIG. 5, the operator views the torch-shaped model on the CAD, for example, the straight-bar-shaped torch-shaped model 21 and the work, and appropriately operates the terminal, and the first to N-th teaching points TP. Torch angles at _{1 to} TP _n are input.

After performing the teaching operation at a plurality of points as described above, in step S106 in FIG. 3, N sets of torch teaching data are stored.

Steps S105 and S1
06 constitutes a torch teaching data operation unit.

Next, automatic creation of robot teaching data will be described. In FIG. 4, steps S201 through S2
In 03, the torch, robot and work are taken in,
Displayed on the display. In step S204,
N sets of torch teaching data are captured. The robot is displayed on the CAD at a predetermined position (= original position) apart from the work.

Next, in FIG. 4, in step S205, the torch teaching data and the torch 20 is polymerized as torch axis is common in the teaching point, a position where the torch side attaching point O _t-defined because Ji pre The torch is rotated about the torch axis. For example, pre Ji previously defined because the position of the torch side attaching point O _t at each teaching point farthest from the YZ plane about the torch axis. Therefore, the position and orientation of the torch side attachment point O _t at each teaching point is a computer on the uniquely already values.

Next, in FIG. 4, in step S206, the torch side attachment point O _t in the teaching point TP by regarded as torch attachment reference point O ₆ of the robot, the torch side attachment point O
_{Based on} the position and orientation (X, Y, Z, L, M, N) of _t , the angles θ _{1 to} θ ₆ of the respective axes of the robot are obtained by a known inverse conversion operation. Incidentally, theta ₁ and theta _{1 *} is the rotation angle of the first joint of the robot, theta ₆ and theta _{6 *} is the rotation angle of the sixth joint of the robot. Further, the robot has, for example, the mechanism shown in FIG.
WN "is input in advance.

[0036] Now, when the torch side attachment point of the first teaching point TP ₁ was O _t10, as described above, the position and orientation of the torch side attachment point _{O t10 (X 10, Y 10} , Z 10, L 10,
M _10, N ₁₀₎ is a computer on the uniquely already value, the torch side attachment point O _t10 and regarded as a torch attachment reference point O ₆ of the robot, the position and orientation of the torch side attachment point O _t10 (X
₁₀ , Y ₁₀ , Z ₁₀ , L ₁₀ , M ₁₀ , N ₁₀ ), and calculates the angles (θ _{110 to} θ ₆₁₀ ) of each axis of the robot by an inverse conversion operation.

There are a case where an answer is obtained and a case where an answer is not obtained for the inverse conversion operation. Therefore, in FIG. 4, in step S207, it is determined whether or not the angle (θ _{110 to} θ ₆₁₀ ) of each axis of the robot is obtained by the above calculation. That is, if no answer is obtained by the inverse transform operation, there when the torch attachment reference point O ₆ of the robot does not reach the torch side attachment point O _t10, in this case, not the robot moves, CAD having original It remains displayed at the location.

If the angles (θ _{110 to} θ ₆₁₀ ) of the axes of the robot are obtained by the above-described inverse conversion operation, it is determined in step S208 in FIG. 4 whether or not the robot interferes. That is, when the angle of each axis of the robot by the inverse transform operation (θ ₁₁₀ ~θ ₆₁₀₎ has been determined, said angle robot on CAD (θ ₁₁₀ ~θ ₆₁₀₎
And the torch mounting reference point _O610 and the torch side mounting point _Ot10 are displayed overlapping, and the presence or absence of interference between the robot supporting the torch in this position and the workpiece is determined by a computer. Checked automatically.

In the above judgment, if the torch mounting reference point O ₆ of the robot does not reach the torch side mounting point _{Ot 10} (= the robot does not reach) and if “the robot interferes”, FIG. In step S211, the torch is rotated so as to increase a predetermined angle around the torch axis. That is, while the robot remains displayed at the original position on the CAD, only the torch is rotated at a predetermined angle Δθ around the torch axis, for example, 30 degrees clockwise.

[0040] In this case, as shown in FIGS. 9 and 10, the torch side attachment point O _t10 is on a plane perpendicular to the axis of the torch, by a predetermined angle Δθ rotation radius a _t about the axis of the torch Therefore, i.e., the apex Tb, cone angle as the rotation about the axis of the torch (π / 2) for the upper cone-gamma _t at radius a _t is a predetermined angle Δθ rotation, torch side attachment point after rotation on CAD the position and orientation of the _{O t11 (X 11, Y 11} , Z 11, L 11, M 11, N 11) is a computer on the uniquely already values.

As described above, in FIG.
After rotating the torch at a predetermined angle around the torch axis at 211, steps S206 to S206 are performed again.
208 is executed. FIG. 11 is a diagram showing the relationship between the robot and the torch before and after rotating the torch around the torch axis.

[0042] That is, in step S206, the torch side attachment point O _t11 and regarded as a torch attachment reference point O ₆ of the robot, the position and orientation (X ₁₁ of the torch side attachment point O _t11,
Based on Y ₁₁ , Z ₁₁ , L ₁₁ , M ₁₁ , N ₁₁ ), the angle (θ _{111 to} θ ₆₁₁ ) of each axis of the robot is calculated by an inverse conversion calculation. It is determined whether or not the axis angles (θ _{111 to} θ ₆₁₁ ) have been obtained. Thereafter, as described above, the presence or absence of robot interference is checked in step S208.

In the above determination, when the robot does not reach or when the robot interferes, step S211 in FIG. 4 is executed, that is, the torch is rotated so as to further increase by a predetermined angle around the torch axis.
Steps S206 to S208 in FIG. 4 are repeatedly executed.

In the above, when the robot does not reach,
In step S209 in FIG. 4, it is determined whether or not the torch has made one rotation around the torch axis.
Then, if the torch does not reach even after making one rotation around the torch axis, "not reach" is stored.

Further, when the robot interferes, it is determined in step S210 in FIG. 4 whether or not the torch has made one rotation around the torch axis. In step S213, even if the torch has made one rotation around the torch axis, it does. At that time, “robot interference” is stored.

On the other hand, if the robot does not interfere with the robot even if the robot is displayed on the CAD so that the angle of each axis of the robot (θ _{1j to} θ _6j ) obtained by the above-mentioned inverse conversion operation, the robot shown in FIG. In step S214, the angles (θ _{1j to} θ _6j ) of each axis of the robot are stored.

[0047] As described above, steps S205 to step S214 in FIG. 4 the first against the teaching point TP ₁
Is executed, and one of “the robot does not reach”, “the robot interference”, or “the angle of each axis of the robot (θ _{1j to} θ _6j )” is stored.

Further, the second to Nth teaching points TP _{2 to} TP
Steps S205 to S214 in FIG. 4 are executed for each of P _n , and any one of “robot does not reach”, “robot interference”, or “angle of each robot axis (θ _{1j to} θ _6j )” Is stored.

As described above, step S2 in FIG.
From 01 to S214, an automatic creation unit of robot teaching data is configured, and robot teaching data corresponding to a plurality of teaching states is automatically created.

In the robot teaching data correcting section, the data of the defective portion in the automatically generated robot teaching data is corrected as appropriate by the operator. The work of correcting the data of the defective portion is optional and not specified.

[0051] However, if the robot teaching data K th teaching point TP _k is bad data, for example, attach the torch to the tip of the robot on the CAD, the terminal operation, the teaching point TP the weld point of the torch tip _By matching _k , the torch angle and the position of the torch-side attachment point can be set to an appropriate state in which the robot does not interfere. Of course, when the defective robot teaching data is corrected, it is preferable to replace the corresponding data in the torch teaching data with the corrected data.

The robot teaching data corrected as described above is transferred to the robot controller 9, and the offline teaching is completed. Of course, it is also possible to store the corrected robot teaching data in the offline teaching system 8 to complete the offline teaching, and to transfer the robot teaching data to the robot controller 9 when necessary.

Since the robot teaching data is for operating the actual robot, the robot teaching data corresponds to at least the angle data of each axis of the robot corresponding to each teaching point.

As described above, a straight rod-shaped torch-shaped model 21 with a sharp tip is used as a torch-shaped model at the time of teaching.
If you use, the screen is easy to see for easy display on CAD,
The operator's nerves can be concentrated on setting the position and angle of the tip of the model 21.

Notwithstanding the above, the torch 20 can be used as a torch-like model at the time of teaching.

According to the off-line teaching method of the arc welding robot according to the present invention, since the operator moves only the torch-like model while teaching the work on the CAD, and teaches the teaching point and the torch angle, The teaching work of the torch is extremely easy, and especially at the time of the arc welding work, it is necessary to teach at a plurality of points, so that the teaching work becomes easier.

The robot teaching data corresponding to the torch teaching data is such that the torch teaching data and the torch are overlapped so that the torch axis is common, and the torch axis is rotated around the torch axis so that the torch side attachment point is at a predetermined position. The torch is automatically rotated in this state, and in this state, the torch with the torch side attachment point deviated from the torch axis is rotated by a predetermined angle around the torch axis → The operation is repeated by the computer and automatically generated. The labor of the worker is reduced as compared with the related art in which one is created one by one.

After operating the torch teaching data, the operator
Other operations can be performed until the robot teaching data is automatically created.

As a result of the above, as a result, it is possible to obtain an off-line teaching method for an arc welding robot that can easily perform a teaching operation and reduce the labor of an operator.

[0060]

As is apparent from the above description, according to the off-line teaching method of the arc welding robot according to the present invention, at the time of teaching, the operator views only the torch-shaped model while looking at the work on the CAD. Since the teaching point and the torch angle are taught by being moved, the teaching operation of the torch is extremely easy. Particularly, in the arc welding operation, it is necessary to perform teaching at a plurality of points, so that the teaching operation becomes easier.

Further, the robot teaching data corresponding to the torch teaching data is such that the torch teaching data and the torch are overlapped so that the torch axis is common, and the torch-side mounting point is at a predetermined position. The torch is automatically rotated around the axis, and in this state, the torch whose mounting point on the torch side deviates from the torch axis is rotated by a predetermined angle around the torch axis. The labor of the operator is reduced as compared with the conventional case where the teaching data is created one by one.

Further, after the operation of the torch teaching data, the operator can perform other work until the robot teaching data is automatically created.

In short, as a result of the above, it is possible to obtain an off-line teaching method for an arc welding robot that can easily perform a teaching operation and can reduce the labor of an operator.

Further, according to the second aspect of the present invention, a straight rod-shaped torch model 21 having a sharp tip is used as a torch-shaped model at the time of teaching. The operator's nerves can be concentrated on the setting of the position and angle of the tip of the robot, so that the teaching operation can be easily performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of the present invention.

FIG. 2 is a conceptual configuration diagram of an entire robot apparatus for arc welding employing the method of the present invention.

FIG. 3 is a flowchart showing a torch teaching procedure in the teaching system shown in FIG. 1;

FIG. 4 is a flowchart showing a procedure for automatically creating robot teaching data in the teaching system shown in FIG. 1;

FIG. 5 is a front view showing an example of the torch used in FIG. 1;

FIG. 6 is a perspective view showing a teaching state of a torch-shaped model.

FIG. 7 is a perspective view showing a teaching state of a torch-shaped model with respect to a work;

FIG. 8 is an explanatory diagram of a robot having six degrees of freedom.

FIG. 9 is a front view for explaining a use state of the torch shown in FIG. 5;

FIG. 10 is a plan view of FIG. 9;

FIG. 11 is a front view showing the relationship between the rotation state of the torch and the robot.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Terminal device 3 Environment model operation part 4 Torch teaching data operation part 5 Robot teaching data automatic creation part 6 Robot teaching data correction part 8 Offline teaching system of arc welding robot 9 Robot controller 11 For arc welding with 6 degrees of freedom Robot _Ot Torch side mounting point O ₆ Robot torch mounting reference point

Claims (2)

[Claims] (1) an environment model operation unit for inputting a torch model whose torch-side mounting point deviates from the torch axis, a robot model having six degrees of freedom, and a three-dimensional work model; Teaching data operation unit for inputting and storing torch angles at a plurality of teaching points by moving a model in the shape of a torch; (III) an automatic creation unit for robot teaching data comprising the following (a) to (i); ) The torch teaching data and the torch model are overlapped so that the torch axis is common, and the torch model is rotated about the torch axis so that the torch mounting point is at a predetermined position. The mounting point is assumed to be a robot torch mounting reference point, and the angle of each axis of the robot is calculated by a well-known inverse conversion calculation based on the position and orientation of the torch side mounting point. Did Motoma' angle of bets each axis (= or torch attachment reference point of the robot reaches the torch side attachment point) to determine whether, (d)
When the torch model does not reach (= when there is no solution of the above calculation), the torch model is rotated so as to increase by a predetermined angle around the torch axis, and the above (b) and (c) are repeated. If it does not reach even after one rotation around the axis, "not reach" is stored. (F) If it reaches, check the interference of the robot model. (G) If it does, increase the predetermined angle around the torch axis. After the torch model is rotated so as to perform (b) to (f), (h) When the torch model does not interfere even if it makes one rotation around the torch axis, “robot interference” is stored, and (i) ) When there is no interference, a robot teaching data correction unit is provided that stores the calculated angles of the robot axes. (IV) Calls automatically created robot teaching data and allows the operator to appropriately correct the data of the defective part. Specially Line teaching method of arc welding robot of. 2. The offline teaching method for an arc welding robot according to claim 1, wherein the torch-like model in the torch teaching data operation unit is a straight rod-like torch-like model.