JPS60224597A - Method of measuring quantity of error of position of fittingof drawing pen in automatic drawing machine - Google Patents

Method of measuring quantity of error of position of fittingof drawing pen in automatic drawing machine

Info

Publication number
JPS60224597A
JPS60224597A JP8033084A JP8033084A JPS60224597A JP S60224597 A JPS60224597 A JP S60224597A JP 8033084 A JP8033084 A JP 8033084A JP 8033084 A JP8033084 A JP 8033084A JP S60224597 A JPS60224597 A JP S60224597A
Authority
JP
Japan
Prior art keywords
line
error
main scale
vernier
draw
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
JP8033084A
Other languages
Japanese (ja)
Other versions
JPH032077B2 (en
Inventor
千住 敦
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Dainippon Screen Manufacturing Co Ltd
Original Assignee
Dainippon Screen Manufacturing Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Dainippon Screen Manufacturing Co Ltd filed Critical Dainippon Screen Manufacturing Co Ltd
Priority to JP8033084A priority Critical patent/JPS60224597A/en
Priority to GB08509294A priority patent/GB2158256B/en
Priority to DE19853514537 priority patent/DE3514537A1/en
Publication of JPS60224597A publication Critical patent/JPS60224597A/en
Publication of JPH032077B2 publication Critical patent/JPH032077B2/ja
Granted legal-status Critical Current

Links

Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01BMEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B5/00Measuring arrangements characterised by the use of mechanical techniques
    • G01B5/14Measuring arrangements characterised by the use of mechanical techniques for measuring distance or clearance between spaced objects or spaced apertures
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01DMEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D9/00Recording measured values
    • G01D9/40Producing one or more recordings, each recording being produced by controlling either the recording element, e.g. stylus or the recording medium, e.g. paper roll, in accordance with two or more variables

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)

Abstract

(57)【要約】本公報は電子出願前の出願データであるた
め要約のデータは記録されません。
(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

【発明の詳細な説明】 (産業上の利用分野) 本発明は、複数の描画Rノを使用する自動製図機におけ
る描画ば/の取付位置誤差量測定方法に関する。
DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for measuring the amount of error in the mounting position of a drawing board in an automatic drawing machine that uses a plurality of drawing boards.

(従来技術) 従来、プロッタあるいは自動製図機と呼ばれている作図
装置は、描画ペンをヘッドに取付けX−Y方向に動かす
ことによって、紙上に、設計図、工業デザ゛イ/、1l
ll量図あるいは三次元の地形図等を描くことができる
ようになっている。
(Prior Art) Conventionally, a drawing device called a plotter or an automatic drawing machine prints blueprints, industrial designs, etc. on paper by attaching a drawing pen to a head and moving it in the X-Y direction.
It is now possible to draw quantitative maps or three-dimensional topographic maps.

この場合、多色の作図あるいは線の太さを選択して数種
に分けて描く場合には、第6図に示すように、予め用意
された複数本の描画ば7(a)(a’)のうち、所要の
描画ば/(a)を、最初にアーム(blをもって選択し
、ヘッド(d’r X −Yに動かして作図した後、次
に描画ばy(a’)を選択して同様に作図することとな
る。
In this case, if you want to draw in multiple colors or select the line thickness and draw in several types, as shown in FIG. ), first select the required drawing position (a) with the arm (bl), move the head (d'r X - Y), and then select the drawing position y(a'). The plot will be drawn in the same way.

しかしながら、このように描画ば/(a)(a’)を交
換し7て使用する際、個々の描画ば/の先端の位置、あ
るいけアーム(bl対する取付位置が僅かに異なるため
、ヘッドfclを例えばXIIIIIIVCついて同一
座標に設定しても、描画さt′1.た画線の中心位置け
、一方の位置をへノド中心(01からの距離Uとすれば
、他方の位置はI−sとなり、双方の描画パ/のズレ量
、すなわち、誤差量(slだけ狂うこととなる。
However, when replacing the drawing blades (a) and (a') in this way, the position of the tip of each drawing blade and the mounting position relative to the arm (bl) are slightly different, so the head fcl For example, even if you set the same coordinates for Therefore, the amount of deviation between both drawing parameters, that is, the amount of error (sl) is off.

このような誤差を補正するためには、補正用の制御デー
タを、ヘッドを動かすCADシステム等に附加する必要
があるが、この誤差量(slけ通常微小であって、例え
ば、描画する線側の数分の1程度となり、その正確な測
定は困難であった。
In order to correct such errors, it is necessary to add control data for correction to the CAD system that moves the head, but this error amount (sl) is usually minute and, for example, on the line side to be drawn. It was difficult to accurately measure it.

従来、この誤差量の測定方法としては、ヘッドを同一位
置において、描画R]を交換り、なから描画し、それぞ
れの描画はンによる線のズレ紮目視するか、あるいは顕
微鏡全使用するかして、例えば第7図に示すように、目
盛telがついたルーば(「)によって計測していた。
Conventionally, methods for measuring this amount of error include placing the head in the same position, changing the drawing R, drawing from scratch, and visually observing the deviation of the line due to each drawing, or using a full microscope. For example, as shown in FIG. 7, measurements were made using a louver (") with a scale tel.

この場合、誤差量全針るため[は、例えば2本の線(g
Hhlのそれぞれの線の中心から中心捷での距離を計る
必要があるが、この距離は微小であるため、正確な測定
が困難であった。
In this case, since the error amount is all needles, [ is, for example, two lines (g
It is necessary to measure the distance from the center of each line of Hhl to the center point, but this distance is so small that accurate measurement has been difficult.

また、測定には長年の経験が必要であり、調整のための
時間を要する欠点があった。
In addition, the measurement requires many years of experience and has the drawback of requiring time for adjustment.

(本発明の目的及び構成) 本発明の目的は、計測法における主尺と副尺の関係、バ
ーニヤ目盛の原理を、自動製図機における描画にノの取
付位置誤差量測定方法に適用−することによって、誤差
量測定全容易にしかも正確に行なうことを可能にしよう
とするものであり、その特徴は、基準とし、て選んだ描
画ば/で、基準線から所定の間隔紮n目盛で等分した主
尺線を引き、次いで、その他の描画ば/で、上記基準線
の位置 ・から上記主尺線に重ねて前記所定の間隔をn
+1目盛で等分[、た副尺線を引き、前記主尺線と副尺
線の一致する位置を前記基準線からの主尺線あるいは副
尺線の目盛で数えることによって、基準として選んだ描
画R/と、その他の描画ば/との相対誤差全検出する手
順とからなっている。
(Object and structure of the present invention) An object of the present invention is to apply the relationship between the main scale and vernier scale in the measurement method and the principle of the vernier scale to a method for measuring the amount of error in the installation position for drawing in an automatic drawing machine. The aim is to make it possible to easily and accurately measure the amount of error, and its feature is to use a drawing chosen as a reference line and divide it equally from the reference line at a predetermined interval on a scale. Draw the main scale line, and then use another drawing tool to overlap the main scale line from the position of the reference line and draw the predetermined interval n.
A vernier line was drawn equally divided by +1 scale, and the points where the main scale line and the vernier line coincided were selected as the reference by counting the scale of the main scale line or the vernier line from the reference line. It consists of a procedure for detecting all relative errors between the drawing R/ and other drawing B/.

(実施例) 以下、本発明ケ、第1図乃至第5図において、詳細に説
明するが、実施例に使用する自動製図機は、公知の構成
であるので、説明は簡単に行う。
(Example) The present invention will be described in detail below with reference to FIGS. 1 to 5, but since the automatic drawing machine used in the example has a known configuration, the description will be brief.

第1図の(1)は、自動製図機の描画ば/全保持するた
めのヘッドで、フレーム(図示略)に支持されたX方向
の軸(21及びY方向の軸+31に対して、水平に移動
自在に支承され、かつ図示しない駆動装置によって、X
−Y方向に、図示しないコノピユータによる制御のもと
で、自動的に移動させられるようになっている。
(1) in Figure 1 is a head for holding the entire drawing area of an automatic drafting machine. X
It is configured to be automatically moved in the -Y direction under the control of an unillustrated controller.

ヘット用)は、水平なアーム(4)ヲ有し、このアーム
(4)の先端の二叉状の描画ば/受け(4a)Fi、描
画はン(MO) の軸部を垂直に保持し1、またこれを
離して、別の描画ば/と交換しつるように作動する。
The head) has a horizontal arm (4), and the forked drawing plate/receiver (4a) Fi at the tip of this arm (4) holds the shaft of the drawing plate (MO) vertically. 1. Release this again and replace it with another drawing board.

描画ハン(Mn)の他に、同形で、かっ色あるいは描画
される線幅の異なる描画はン(M+ )(M2 ) (
Mn )・・・が用意されており、これら描画にノ(M
o ) (PJ+ )(M、)・・・全交換して使用す
ることにより、用紙u上に、各色のあるいは太さの異な
る線を引くことができる。
In addition to drawing lines (Mn), drawing lines (M+) (M2) (
Mn )... are prepared, and these drawings can be performed using ノ(M
o) (PJ+) (M,)... By replacing all the lines and using them, it is possible to draw lines of each color or of different thickness on the paper u.

第2図及び第6図は、描画Rンの取付位置誤差tfAl
l定方法を示すものであり、最初に、基準となる1の描
画にノ(Mo)′f/もって、X座標の原点、(5) 
CM ORflXoK基準線(n、o)>引き、この基準線(
rto)から、所定の間隔(Llkn等分(この場合1
0等分)したピンチで、主尺線(R1)(R2)・・・
を引く。
Figures 2 and 6 show the mounting position error tfAl of the drawing R.
This shows the method for determining l, and first, by drawing 1 as a reference, the origin of the X coordinate, (5)
CM ORflXoK reference line (n, o) > draw, this reference line (
rto) to a predetermined interval (Llkn (in this case 1
0 equal division) in a pinch, main scale line (R1) (R2)...
pull.

次いで、測定すべき他の描画イン(MX) Thもって
、X座標原点、0RGXoの位置から、前記所定の間隔
(Ll′Itn±1等分(この場合11等分)したピン
チで、副尺線(Qカ)(Q、)(Q2)・・・ を引き
、前記主尺線(R1) (]R1)・・・とY方向に互
いに部分的に重なり会うか、もし、〈は重なり合わない
までも、Y方向のギャップが殆ど生じないようにする。
Next, with the other drawing in (MX) Th to be measured, from the X coordinate origin, 0RG (Qka) (Q, ) (Q2)... are drawn, and the main scale line (R1) (]R1)... partially overlaps each other in the Y direction, or if < does not overlap. Even in this case, almost no gap in the Y direction should be created.

この場合、主尺線と副尺線のピッチ差をPとする。In this case, the pitch difference between the main scale line and the vernier scale line is assumed to be P.

そして、前記主尺線(喝)(几、)(几2)・・・と副
尺線(Qo ) (Q+ ) (Q2)・・・とが一致
する位aを検出する。
Then, a position a where the main scale line (几)(几、)(几2)... matches the vernier scale line (Qo) (Q+) (Q2)... is detected.

第6図においては、主尺線(R4)と副尺線(Q4)と
が基準線(Ro)からm番目 (この場合4目盛)にお
いて一致するため、誤差量をΔxnとすれば、Δxn=
P(ピンチ差)xmとなる。また、測定すべき描画はノ
(MX)の原点座標ORflX nとすれば、ORn 
X n = OR,(I X 6+Δxnの関係となる
In Fig. 6, the main scale line (R4) and the vernier scale line (Q4) match at the mth scale (in this case, 4 scales) from the reference line (Ro), so if the error amount is Δxn, Δxn=
P (pinch difference) xm. Also, if the drawing to be measured is the origin coordinates of (MX) ORflXn, then ORn
The relationship is X n = OR, (I X 6 + Δxn).

例えば、L=11JljI n=10 とし、n=01
111、(6) m = 4とすれば誤差量Jxn = 0.I X 4
 = 0.4朋となり、基準の描画ば/と、他の描画ば
/との相対誤差をめることができる。
For example, L=11JljI n=10 and n=01
111, (6) If m = 4, the error amount Jxn = 0. IX4
= 0.4, and the relative error between the standard drawing and other drawings can be calculated.

なお、上記実施例においては、主尺の目盛を、n、副尺
f n +1としたが、副尺の目盛k n −1として
もよい。
In the above embodiment, the scale of the main scale is n and the vernier scale f n +1, but the scale of the vernier scale may be k n -1.

第4図(Xl)〜(X6)は、描画はン(Ml)〜(M
a)の6本を使用した自動製図機において、本発明を適
用し、各描画はンのY軸における相対誤差、オフセット
量(Δd)全測定した場合の・ξター/を図示したもの
である。
FIG. 4 (Xl) to (X6) are drawing steps (Ml) to
The present invention is applied to an automatic drawing machine using the six drawers in a), and the relative error and offset amount (Δd) of each drawer on the Y axis are all measured. .

この実施例においては、基準2なる描画ば/(M4)の
主尺線(田を実線で示し、各描画ば/(M、)(M2)
(Ma)(M5)(Ma)の副尺線(Qlを破線で示し
である。
In this example, the main scale line (field) of the reference 2 drawing field /(M4) is shown as a solid line, and each drawing field /(M,)(M2)
The vernier line (Ql) of (Ma) (M5) (Ma) is shown by a broken line.

従って、前述したように、各主尺線(旬と副尺線xp フセソト量Δd−==m±御でめることができる。Therefore, as mentioned above, each main scale line (jun and vernier line xp The offset amount Δd−==m± can be determined.

第5図(Yl)〜(Y6)は、第4図における各描画ば
/のY軸における相対誤差、オフセット!(Δd)主尺
線(川を実線で示し、各描画はン(Ml)(M2)(M
a)でめることができる。
FIG. 5 (Yl) to (Y6) are the relative errors and offsets on the Y axis of each drawing field in FIG. (Δd) Main scale line (the river is shown as a solid line, each drawing is (Ml) (M2) (M
a) It can be done.

以上のようにし、で、基準となる描画’ /(M4 )
に対する各描画はノ(Ml)(M2)(Ma)(M5)
(Ma) のY軸及びY@におけるオフセット量(Δd
) 請求めたら、これら?、ヘッド(1)の制御プログ
ラムに、補正値として入力する。
Do the above and draw the reference '/(M4)
Each drawing for is (Ml) (M2) (Ma) (M5)
Offset amount (Δd
) If I can claim these? , is input as a correction value to the control program of the head (1).

補正後においては、製図作業の開始とともに、アーム(
4)がどの描画はン(Ml)〜(Ma)v選択しても、
基準となる原点(oanxo、or+nyo) と各描
画ば/の原点(ORflX、〜0Tit(IX、 、0
RGY、〜0RflY、)を合わせであるため、描画の
線は、ス゛しることなく一致する。
After correction, the arm (
4) No matter which drawing method (Ml) to (Ma)v is selected,
The reference origin (oanxo, or+nyo) and the origin of each drawing bar (ORflX, ~0Tit(IX, ,0
RGY, ~0RflY,), the drawn lines match without swiping.

(発明の効果) 本発明によれば、バーニヤ目盛の原理を応用し、基準と
して選んだ描画ば/と、その他の描画にノによる線引き
を、主尺線と副尺線の関係):なるように重ねて描くこ
とにより、ヘッドに対する各描画Rノの相対的な誤差量
を簡単に測定できる利点がある。
(Effects of the Invention) According to the present invention, by applying the principle of the vernier scale, the drawings selected as standards and the other drawings are drawn so that the relationship between the main scale line and the vernier scale line is as follows: There is an advantage that the relative error amount of each drawing R with respect to the head can be easily measured by overlapping the drawing.

従って、この測定値を基に、各描画はノの原点座標な基
準原点座標に合わせることができ、自動製図機において
、簡単かつ正確に、描画にツノオフセット量を調整でき
、描画ば/を自動的に交換しても、線ズレ、色ズレ等を
生じることはない。
Therefore, based on this measurement value, each drawing can be aligned with the reference origin coordinates of the horn, and automatic drafting machines can easily and accurately adjust the horn offset amount in the drawing, and the drawings can be automatically adjusted. Even if it is replaced, line misalignment, color misalignment, etc. will not occur.

【図面の簡単な説明】[Brief explanation of the drawing]

第1図は、本発明の実施に際して使用されろ描画R/用
ヘッドの概略正面図、 第2図及び第6図は、本発明の測定原理を説明するため
の線図、 第4図及び第5図は、本発明の一実施例を説明するため
の各種パターン2示す線図、 第6図は、従来の自動製図機を示す概略正面図、第7図
は、従来の誤差量測定方法を示す概略平面図である。 (1+ヘツド +21+31軸 (4)アーム (4a)描画ば/受け (Mo)〜(M、)描画ば/ 但)用紙(RJ(Ro 
) 〜(RIO)主尺線(QXQo)〜(Q+o)副尺
線(oanxo) x座標原点 (ORGYo)Y座標
原点(ORflX、 )〜(ORflXa )描画−!
:/X座標(ORGY、)〜(01%(’)Y、)描画
に/Y座標(卸)誤差量(オフセット量) (plピンチ差 第4図 −570− X −一÷
FIG. 1 is a schematic front view of a drawing head used in carrying out the present invention, FIGS. 2 and 6 are diagrams for explaining the measurement principle of the present invention, and FIGS. 5 is a diagram showing various patterns 2 for explaining an embodiment of the present invention, FIG. 6 is a schematic front view showing a conventional automatic drafting machine, and FIG. 7 is a diagram showing a conventional method for measuring the amount of error. FIG. (1+head +21+31 axis (4) arm (4a) drawing plate/receiver (Mo) ~ (M,) drawing plate/however) paper (RJ (Ro
) ~ (RIO) Main scale line (QXQo) ~ (Q+o) Vernier scale line (oanxo) x coordinate origin (ORGYo) Y coordinate origin (ORflX, ) ~ (ORflXa) Drawing -!
:/X coordinate (ORGY,) ~ (01% (') Y,) For drawing /Y coordinate (wholesale) error amount (offset amount) (PL pinch difference Fig. 4 - 570 - X - 1 ÷

Claims (1)

【特許請求の範囲】[Claims] 用紙に対して相対移動しつるヘッドに、複数の描画はン
を交換自在に取付ける自動製図機において、基準として
選んだ描画ば/で基準線から所定の間隔’?n目盛で等
分し、た主尺線を引き、次いで、その他の描画はノで、
上記基準線の位置から上記主尺線に部分的に重ねて前記
所定の間隔をn±1目盛で等分した副尺線を引き、前記
主尺線と副尺線の一致する位置?、前記基準線からの主
尺線あるいけ副尺線の目盛で数えることによって基準と
して選んだ描画はノと、その他の描画はンとの相対誤差
を検出することを特徴とする自動製図機における描画−
!:/の取付位置誤差量測定方法。
In an automatic drawing machine in which a plurality of drawing lines are replaceably attached to a crane head that moves relative to the paper, the drawing line selected as a reference is set at a predetermined distance from the reference line. Divide it into equal parts on the n scale, draw the main scale line, and then draw the other parts with no.
From the position of the reference line, draw a vernier line that partially overlaps the main scale line and equally divides the predetermined interval in n±1 scales, and find the position where the main scale line and the vernier line match? In an automatic drawing machine, the relative error between the drawing selected as a reference and other drawings is detected by counting the scales of the main scale line or the vertical vernier line from the reference line. Drawing-
! How to measure the mounting position error amount of :/.
JP8033084A 1984-04-23 1984-04-23 Method of measuring quantity of error of position of fittingof drawing pen in automatic drawing machine Granted JPS60224597A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
JP8033084A JPS60224597A (en) 1984-04-23 1984-04-23 Method of measuring quantity of error of position of fittingof drawing pen in automatic drawing machine
GB08509294A GB2158256B (en) 1984-04-23 1985-04-11 Coordinate plotter
DE19853514537 DE3514537A1 (en) 1984-04-23 1985-04-22 METHOD FOR MEASURING THE OFFSET OF THE ATTACHMENT POSITION OF A CHARACTER SPRING OF A COORDINATE PLOTTER

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP8033084A JPS60224597A (en) 1984-04-23 1984-04-23 Method of measuring quantity of error of position of fittingof drawing pen in automatic drawing machine

Publications (2)

Publication Number Publication Date
JPS60224597A true JPS60224597A (en) 1985-11-08
JPH032077B2 JPH032077B2 (en) 1991-01-14

Family

ID=13715239

Family Applications (1)

Application Number Title Priority Date Filing Date
JP8033084A Granted JPS60224597A (en) 1984-04-23 1984-04-23 Method of measuring quantity of error of position of fittingof drawing pen in automatic drawing machine

Country Status (3)

Country Link
JP (1) JPS60224597A (en)
DE (1) DE3514537A1 (en)
GB (1) GB2158256B (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0672095A (en) * 1992-08-06 1994-03-15 Iwatsu Electric Co Ltd Xy-plotter with multiple pens

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0672095A (en) * 1992-08-06 1994-03-15 Iwatsu Electric Co Ltd Xy-plotter with multiple pens

Also Published As

Publication number Publication date
GB2158256B (en) 1987-01-07
JPH032077B2 (en) 1991-01-14
GB8509294D0 (en) 1985-05-15
DE3514537A1 (en) 1985-10-24
DE3514537C2 (en) 1988-09-22
GB2158256A (en) 1985-11-06

Similar Documents

Publication Publication Date Title
EP0318557B1 (en) Workpiece inspection method
US4276699A (en) Method and test apparatus for testing the tooth flank profile of large diameter gears
CN107806825B (en) Three faces, five line lathe space geometry error measure discrimination method based on plane grating
JPH07102681B2 (en) Equipment for printing plate evaluation
JPH0565886B2 (en)
JPS60224597A (en) Method of measuring quantity of error of position of fittingof drawing pen in automatic drawing machine
CA2022089A1 (en) Moveable equipment for the verification of surfaces or in the process of correction
JPS6079209A (en) Automatic dimensions measuring system
DE102021004048A1 (en) RULE OR CONTROL METHOD OF A FORM MEASUREMENT APPARATUS
US4574483A (en) Measurement of degree of offset of attachment position of drafting pen in coordinate plotter
JPS59103140A (en) Pen exchange type recording method and apparatus
CN112731772B (en) Alignment method of double-table laser direct writing exposure machine
JPS63133700A (en) Method of correcting position of component insertion in electronic component automatic inserter
JPS6244463B2 (en)
JPS6239293Y2 (en)
JPH08108692A (en) Pen coaxiality correction device in plotter
JP2797954B2 (en) Magnifying glass device in pen plotter
JPS63133699A (en) Method of correcting position of component insertion in electronic component automatic inserter
DE10149828A1 (en) Electronic engraving machine correction system uses measured data to control carriage of machine
JPH0639284Y2 (en) Coordinate data generator
JPS6027200A (en) Automatic coordinates correcting device at electronic part mounting time
JP2591696B2 (en) How to measure flatness
JPH05272905A (en) Method of measuring coordinate measuring apparatus
JPS60500692A (en) Assembly of components on printed wiring board
CN113111432A (en) Data processing method and device based on model margin line and storage medium